This evening (my time) there was an earthquake in Morocco. Magnitude 6.8, rather shallow, reverse or thrust (compressional) mechanism.

https://earthquake.usgs.gov/earthquakes/eventpage/us7000kufc/executive

This M 6.8 earthquake happened in the Atlas Mountains, a compressional system with south dipping reverse faults on the north and north dipping reverse faults on the south.

It is possible, if not probable, that this earthquake is related to one of these reverse faults. Based on the location, it seems possible that this earthquake is on a south dipping thrust fault (associated with the North Atlas fault system).

I used the USGS earthquake catalog and it appears that this is the largest magnitude earthquake to happen in Morocco (since we started recording earthquakes on seismometers).

Here is the sobering part of this earthquake. The USGS PAGER Alert provides an estimate for the number of casualties and economic impact. Read more about how these estimates are produced (and how to read this report) here.

UPDATE: (2023.09.10 Version 7)

• Version 1
• Version 4
• Version 7
• Version 14

UPDATE: (2023.09.11)

Fault Scaling Relations

Empirical fault scaling relations are ways that we can compare fault rupture sizes with earthquake magnitudes. One of the most used and well cited empirical fault scaling relations paper is Wells and Coppersmith, 1994.

• Wells and Coppersmith developed relations between earthquake magnitude/moment magnitude and surface rupture length, subsurface rupture length, and rupture area. They also consider the difference between mean and maximum displacement measures.
• The length of fault rupture is the distance that the fault slipped measured parallel to Earth’s surface. When we see fault lines mapped on a map, these lines are representative of the fault length.
• The width of fault rupture is the distance that the fault slipped measured down into the Earth. For a fault that dips straight down into the Earth (perpendicular to the Earth’s surface), the width of the fault rupture is the distance between the Earth’s surface and the depth where the fault slipped. For faults that dip at an angle (like along a subduction zone, or a reverse/thrust fault like the fault that caused this M 6.8 earthquake), the distance measured is measured along this non-perpendicular distance.
• The area of fault slip is basically the fault length times the fault width.

Here is the USGS fault slip model for the M 6.8 earthquake. The length of the fault slip figure is about 40 kilometers (km) and the width of the fault is about 45 km. The color represents the amount that the fault slipped (in meters) during the earthquake. So, the slip area does not fill this entire area. Most of the slip length is within ~30 km and width is within ~35km. The maximum slip is ~1.7 meters.




• There have been some updates to these scaling relations that attempt to improve these relations. However, Wells and Coppersmith still work pretty well (the updates are not really that much different).
• There remain certain types of earthquakes where we have small amounts of information to constrain these relations for those types of earthquakes (particularly large magnitude earthquakes, which are more rare than small and medium sized earthquakes). So, there is room for improvement.

Here is a plot from Wells and Coppersmith that shows the data relating magnitude with subsurface rupture length. We can see that there is a positive relation between magnitude and length (as the length is larger, so is the magnitude).




(a) Regression of subsurface rupture length on magnitude (M). Regression line shown for all-slip-type relationship. Short dashed line indicates 95% confidence interval. (b) Regression lines for strike-slip relationships. See
Table 2 for regression coefficients. Length of regression lines shows the range of data for each relation.

• Note that there is lots of variation, so these empirical relations (represented by the lines that are drawn to “fit” these data) have lots of range. So, these empirical relations are not perfect predictors (i.e., fault length does not perfectly predict magnitude).
• For example, a fault with subsurface rupture length of 10 km could have a magnitude that ranges between 5.25 and 6.25+. Remember, a M 6.25 releases about 32 times as much energy as a M 5.25. A M 6.25 earthquake is much larger than a M 5.25.

So, I used these scaling relations to calculate the magnitude for earthquakes of varying subsurface fault length. Here is a table from those calculations.




• The M 6.8 USGS earthquake slip model suggests that this earthquake fits well with these subsurface fault scaling relations from Wells and Coppersmith (1994).
• Well, as I was wrapping up for the day, I refreshed the USGS website for the earthquake and they had updated a bunch of the data (intensity, GIS data, and the slip data). So, the slip model shows a much smaller slip area. Though, if we look at the EMSC aftershock region, we may think that their first slip model was better. The aftershock region has a better fit for the scaling relations.

Below is my interpretive poster for this earthquake

• I plot the seismicity from the past month, with diameter representing magnitude (see legend). I include earthquake epicenters from 1922-2022 with magnitudes M ≥ 3.0 in one version.
• I plot the USGS fault plane solutions (moment tensors in blue and focal mechanisms in orange), possibly in addition to some relevant historic earthquakes.
• A review of the basic base map variations and data that I use for the interpretive posters can be found on the Earthquake Reports page. I have improved these posters over time and some of this background information applies to the older posters.
• Some basic fundamentals of earthquake geology and plate tectonics can be found on the Earthquake Plate Tectonic Fundamentals page.

I include some inset figures. Some of the same figures are located in different places on the larger scale map below.

• In the upper left corner is a map that shows the tectonic plates and seismicity for northwestern Africa.
• In the upper right corner is a map that shows the earthquake intensity using the modified Mercalli intensity scale. Earthquake intensity is a measure of how strongly the Earth shakes during an earthquake, so gets smaller the further away one is from the earthquake epicenter. The map colors represent a model of what the intensity may be.
• Below the intensity map is a plot that shows the same intensity (both modeled and reported) data as displayed on the map. Note how the intensity gets smaller with distance from the earthquake.
• In the lower left center are two maps showing the probability of earthquake triggered landslides and possibility of earthquake induced liquefaction. I will describe these phenomena below.
• In the lower right corner is a larger scale map showing the Atlas Mountains and the North and South Atlas faults.
• To the left of this large scale map is a map from Beauchamp et al., 1999. This map is for the Atlas Mtns to the east of where this earthquake happened. Note the tectonic folds associated with the underlying reverse faults.
• In the upper left is a map from TEixel et al. (1999) that includes cross section locations. Cross section C is displayed to the right. The location of this cross section is also shown on the main map with the green line.
• To the left of the intensity map is a map from Banault et al. (2023) that includes a yellow star where the M 6.8 earthquake occurred.

• Here is the map with a month’s seismicity plotted.




• This is an updated poster with COMET InSAR analytical results. I also figured out how to download the EMSC seismicity data (they changed their website, so had to learn something new. Here is where one may download data from their catalog.
• The USGS earthquake catalog (aka ComCat) is a global network, so a global catalog. The EMSC catalog relies, in places, on a more local network, so has more events in the catalog than in ComCat.
• However, ComCat usually has all the major events and spans a longer time period.
• SO, the 3 month seismicity I use here is from EMSC and the century dataset is based on the ComCat catalog.

Other Report Pages

• INGV: https://ingvterremoti.com/2023/09/12/terremoto-in-marocco-aggiornamento-del-12-settembre-2023/
• INGV: http://terremoti.ingv.it/en/finitesource_summary/36092321#SorgenteEstesa
• Dr. Judith Hubbard: https://earthquakeinsights.substack.com/p/deadly-m68-earthquake-hits-morocco
• Dr. Judith Hubbard re: InSar Explanation https://earthquakeinsights.substack.com/p/satellite-images-suggest-slip-on
• USGS: https://earthquake.usgs.gov/earthquakes/eventpage/us7000kufc/region-info
• EERI: https://www.eeri.org/about-eeri/news/18451-eeri-response-to-september-8-2023-m6-8-morocco-earthquake
• tEMBLOR: https://temblor.net/temblor/2023-morocco-quake-africa-europe-collision-15527/

Discussion about aftershocks

the following is a series of statements that i wrote to respond to someone who is in Morocco. i thought that perhaps others might find this useful.

aftershocks may last for weeks, possibly months. aftershocks typically decay at a rate that is dependent on the fault system. each fault system is slightly different.

Here is a short story about aftershocks in Northern California but this story is relevant to earthquakes elsewhere.

we don’t know the specific rate of decay for a fault system until we observe the aftershocks decay for that fault. some faults have few aftershocks and others have robust aftershock sequences (many events).

it is not satisfying to not know how long they will last, i understand.

e.g., there was an earthquake in central Washington USA in 1872 and some argue that this continues to have aftershocks.

so, they will last a while and nobody will know when they will stop.

but for people to feel safe to start living in their homes again, they need to get an expert, like an engineer, to evaluate the stability of their houses. only an expert, who is trained to inspect structures, can make these evaluations.

will there be other large earthquakes? this is something nobody can know.

follow advice for getting an engineer to check out one’s building(s) so that they can feel safe living in them; if the engineer decides that the structure is safe to withstand earthquakes, that is the best we can do.

the M6.8 changed the stresses in the crust adjacent to the earthquake. in some places, these stresses increased the chance for earthquakes on different (or the same) faults. in other places, they decreased the stress.

these changes in stress are modest but can trigger a new earthquake. but this depends on the state of stress of the other earthquake fault, something that we cannot yet know. so, we cannot know if the places where stress is increased will have a triggered/new earthquake.

the best we can do is to make sure that buildings are resistant to earthquake forces. this capability is reliant on engineers, building inspectors, competent building contractors, building codes, etc. AND that these people follow the rules (building codes).

the Feb 2023 Türkiye earthquakes destroyed buildings that were constructed under well designed building codes. but they were destroyed because people did not follow the code. lots of buildings were built before the codes existed and those did not perform well either.

so, when living in earthquake country, one simply needs to ensure that they are living/working in earthquake resistant buildings. they may find comfort to live outside these structures until they are inspected. this is the smart thing to do.

i don’t have the expertise to know if a building is designed to withstand earthquakes. i am not a structural engineer, an earthquake engineer. i know some and can follow the local building codes here where i live. and i sure could not offer advice remotely. one simply needs to seek local expertise. i wish i could offer more advice.

finally, people who have been traumatized by this earthquake and continue to be traumatized by these aftershocks are going through what everyone does when faced with these conditions. this is typical. maybe finding comfort with friends and family and neighbors will help (?).

i hope i have provided some constructive feedback to your questions/concerns.

hopefully this information can help those in Morocco cope with this extremely challenging natural hazard.

if nothing else, the survivors will be able to build back stronger and more earthquake resistant.

Shaking Intensity

• Here is a figure that shows a more detailed comparison between the modeled intensity and the reported intensity. Both data use the same color scale, the Modified Mercalli Intensity Scale (MMI). More about this can be found here. The colors and contours on the map are results from the USGS modeled intensity. The DYFI data are plotted as colored dots (color = MMI, diameter = number of reports).
• In the upper panel is the USGS Did You Feel It reports map, showing reports as colored dots using the MMI color scale. Underlain on this map are colored areas showing the USGS modeled estimate for shaking intensity (MMI scale).
• In the lower panel is a plot showing MMI intensity (vertical axis) relative to distance from the earthquake (horizontal axis). The models are represented by the green and orange lines. The DYFI data are plotted as light blue dots. The mean and median (different types of “average”) are plotted as orange and purple dots. Note how well the reports fit the green line (the model that represents how MMI works based on quakes in California).
• Below the lower plot is the USGS MMI Intensity scale, which lists the level of damage for each level of intensity, along with approximate measures of how strongly the ground shakes at these intensities, showing levels in acceleration (Peak Ground Acceleration, PGA) and velocity (Peak Ground Velocity, PGV).

Potential for Ground Failure

Luckily I updated this page because I noticed that the interpretive figure below was incorrect (it was for a different earthquake).

• Below are a series of maps that show the potential for landslides and liquefaction. These are all USGS data products.
  There are many different ways in which a landslide can be triggered. The first order relations behind slope failure (landslides) is that the “resisting” forces that are preventing slope failure (e.g. the strength of the bedrock or soil) are overcome by the “driving” forces that are pushing this land downwards (e.g. gravity). The ratio of resisting forces to driving forces is called the Factor of Safety (FOS). We can write this ratio like this:

  FOS = Resisting Force / Driving Force

• When FOS > 1, the slope is stable and when FOS < 1, the slope fails and we get a landslide. The illustration below shows these relations. Note how the slope angle α can take part in this ratio (the steeper the slope, the greater impact of the mass of the slope can contribute to driving forces). The real world is more complicated than the simplified illustration below.




• Landslide ground shaking can change the Factor of Safety in several ways that might increase the driving force or decrease the resisting force. Keefer (1984) studied a global data set of earthquake triggered landslides and found that larger earthquakes trigger larger and more numerous landslides across a larger area than do smaller earthquakes. Earthquakes can cause landslides because the seismic waves can cause the driving force to increase (the earthquake motions can “push” the land downwards), leading to a landslide. In addition, ground shaking can change the strength of these earth materials (a form of resisting force) with a process called liquefaction.
• Sediment or soil strength is based upon the ability for sediment particles to push against each other without moving. This is a combination of friction and the forces exerted between these particles. This is loosely what we call the “angle of internal friction.” Liquefaction is a process by which pore pressure increases cause water to push out against the sediment particles so that they are no longer touching.
• An analogy that some may be familiar with relates to a visit to the beach. When one is walking on the wet sand near the shoreline, the sand may hold the weight of our body generally pretty well. However, if we stop and vibrate our feet back and forth, this causes pore pressure to increase and we sink into the sand as the sand liquefies. Or, at least our feet sink into the sand.
• Below is a diagram showing how an increase in pore pressure can push against the sediment particles so that they are not touching any more. This allows the particles to move around and this is why our feet sink in the sand in the analogy above. This is also what changes the strength of earth materials such that a landslide can be triggered.




• Below is a diagram based upon a publication designed to educate the public about landslides and the processes that trigger them (USGS, 2004). Additional background information about landslide types can be found in Highland et al. (2008). There was a variety of landslide types that can be observed surrounding the earthquake region. So, this illustration can help people when they observing the landscape response to the earthquake whether they are using aerial imagery, photos in newspaper or website articles, or videos on social media. Will you be able to locate a landslide scarp or the toe of a landslide? This figure shows a rotational landslide, one where the land rotates along a curvilinear failure surface.




• Below is the liquefaction susceptibility and landslide probability map (Jessee et al., 2017; Zhu et al., 2017). Please head over to that report for more information about the USGS Ground Failure products (landslides and liquefaction). Basically, earthquakes shake the ground and this ground shaking can cause landslides.
• I use the same color scheme that the USGS uses on their website. Note how the areas that are more likely to have experienced earthquake induced liquefaction are in the valleys. Learn more about how the USGS prepares these model results here.

Remote Sensing of Surface Deformation

• One way to learn about the processes that happen during an earthquake is to evaluate the “coseismic” (during earthquake) surface deformation from that earthquake.
• There are many ways to do this type of analysis. One may use classic surveys (using levels and tape measures) to measure the changes. One may use digital observations from satellites or airplanes, called remote sensing.
• One of the ways to do this remote sensing is with a method called interferometric synthetic aperture radar (InSAR).
• The techniques to apply InSAR methods are advanced and take years to master. I will not attempt to explain the full description of what InSAR is but below is a list of online resources where others do a great job at explaining InSAR:
• Explanation about InSAR from Dr. Judith Hubbard
• Wikipedia
• NASA
• United Nations
• USGS

Learning Resource: Sentinel-1 Synthetic Aperture Radar Interferometric Coherence Image Services StoryMap

This StoryMap tutorial enhances access to the Global Seasonal Sentinel-1 Interferometric Coherence and Backscatter dataset with image services. #SAR https://t.co/VjghtQiBUL pic.twitter.com/zMNLwuAdi3

— NASAEarthdata (@NASAEarthData) September 11, 2023

• Basically, there are satellites that pass over Earth over a regular schedule. These satellites have sensors (called platforms) that acquire a variety of data that span different parts of the electromagnetic spectrum.
• Many are familiar with the visible light part of the electromagnetic spectrum (recall the Pink Floyd album, The Dark Side of the Moon, which has an image of light going through a prism, showing the different colors of the visible spectrum.
• The different parts of the electromagnetic spectrum are described by the wavelength of the waves that these different types of radiation use to travel. The wavelength span for blue light is between 400 and 500 nanometers (nm). Green is 500 to 600 nm and red is 600 to 700 nm.
• Other bands have longer or shorter wavelengths. X-Rays have much shorter wavelengths and infrared radiation has longer wavelengths.
• Radar operates at long wavelengths (1-100 cm or 10,000,000-1,000,000,000 nm)
• InSAR analysis, generally, uses radar data collected at two different times to determine how the Earth’s surface moved between the radar acquisitions.
• There are some organizations that have programs that staff people to work on these InSAR analyses for events like earthquakes. NASA Jet Propulsion Laboratory (JPL) and the Centre for Observation and Modeling of Earthquakes, Volcanoes, and Tectonics (COMET) are two of these programs. They provide the results from their analyses online for anyone to download for free.
• Here is the COMET event page for this M6.8 Morocco Earthquake.
• This is a plot of the “unwrapped” InSAR results from the first Sentinel 1 (one of the radar satellites used for InSAR analysis) post-earthquake radar acquisition.
• Color represents how the surface moved towards or away from the Satellite between 30 August and 11 September 2023. This is an ascending track and once we get a descending track acquisition, we will be able to get a better idea of the coseismic deformation.
• This result helps us learn that the area in red generally went up and that the fault is dipping to the north (looking at the unwrapped data in the lower panel help with this interpretation).




• Here is the source of data that I used to plot the above figures.

Some Relevant Discussion and Figures

• Here is the tectonic map from the poster (Teizel et al., 2002).




(a) Location sketch map of the Atlas Mountains in the North African foreland. (b) Geological map of the central High Atlas, indicating the section lines of Figure 2. ATC, Ait Tamlil basement culmination; SC, Skoura basement culmination; MC, Mougueur basement culmination; FZ, Foum Zabel thrust.

• Here is the cross section from the poster (Teizel et al., 2002).




Serial geological cross sections through the High Atlas of Morocco (location in Figure 1b): (a) Midelt-Errachidia section, (b) Imilchil section, and (c) Demnat section. Segment x–x0 in 2c is adapted from Errarhaoui [1997].

• This part of the world was once a mid ocean spreading ridge (aka a rifted margin). This figure shows the tectonic plate boundary configurations from this time of Earth’s past.
• We will revisit this paper further down in the report where we see a geologic map and cross section in the region of this M 6.8 earthquake.




Plate reconstruction of the Central Atlantic to the Triassic-Jurassic boundary (200 Ma) (modified from Schettino and Turco, 2009). Rift zones are shown in dark grey. The square indicates the reconstructed position of the Marrakech High Atlas pf Morocco (MHA).

(Domènech et al., 2015)

• Here is the Babault et al. (2013) tectonic map.




Tectonic sketch map of the Moroccan High Atlas Mountains, indicating the lines of section of Figure 4a, b.

• Here are the Babault et al. (2013) cross sections.




Structural cross-sections across the High Atlas and the Eastern Cordillera of Colombia. (a, b) Sections across the eastern and central High Atlas (from Teixell et al. 2003). These sections are based on field data and were modified from the original according to gravity modelling by Ayarza et al. 2005 (see location in Fig. 1). Although largely eroded, the Cretaceous sediments probably formed a tabular body that covered the entire Atlas domain, representing post-rift conditions. (c) Simplified structural cross-section of the Eastern Cordillera of Colombia, approximately through the latitude of Bogota´ (see location in Fig. 2). This section was constructed on the basis of maps, seismic profiles and structural data provided by ICP-Ecopetrol. The deep structure of the Sabana de Bogota´ region is conjectural as it is poorly imaged in the seismic profiles. The lower–upper Cretaceous boundary is taken for the sake of convenience at the top of the Une and Hilo´ formations. MMVB, Middle Magdalena Valley basin; LLB, Llanos basin.

• The following are some maps from Lanari et al. (2020).
• This is the main tectonic map.




Location of the study area and simplified geological map of the High Atlas and Anti‐Atlas Mountains. Africa Plate motion considering Eurasia fixed by Serpelloni et al. (2007). FWHA = far western High Atlas; WHA = western High Atlas; CHA = central High Atlas, AA = Anti‐Atlas; MA = Middle Atlas; SAF = South Atlas fault; JTF = Jebilet thrust front.

• This is a map that shows how complicated the faulting is in this region.




Simplified geological map of the study area with schematic logs. See Figure 1 for location. The black lines are the cross‐section traces. Data from Baudon et al. (2009), Domènech et al. (2016, 2015), and El Arabi et al. (2003).

• Here is a study about the geodetics of the western Mediterranean (Vernant et al., 2010). This study just barely reaches into the western Atlas Mountains, where the M 6.8 earthquake happened.
• Geodesy is the study of the deformation of the Earth’s surface. Geodesists may study interseismic (between earthquakes) deformation or coseismic (during earthquakes) deformation.
• These researchers used Global Positioning System (GPS, like in your smartphone) to measure the motion of locations in this area of study.
• This map shows the two profiles plotted in the next figure. Profile 1 is of interest.




(a) GPS site velocities with respect to Nubia and 95% confidence ellipses. Heavy dashed lines show locations of profiles shown in Fig. 3 with the widths of the profiles indicated by lighter dashed lines. Focal mechanism indicates the location of the February 2004 Al Hoceima earthquake. Base map as in Fig. 1. (b) GPS site velocities with respect to Eurasia and 95% confidence ellipses. Format as in (a).

• Profile 1 makes it into the western Atlas Mountains.
• On the left, note sites MARO and AZIL. Look at the profile normal plot (the vertical axis represents how much the sites are moving relative to the direction perpendicular to the profile, which is sort of the direction of convergence in the Atlas Mountains).
• The difference in convergence along the western part of profile 1 shows that there is very little interseismic deformation here. This supports the hypothesis that these faults are low slip rate faults.
• There does appear to be some amount of interseismic deformation parallel to the profile. This suggests that there is some amount of lateral strain accumulating on these faults. However, these profiles are not oriented in an optimal direction to study the faults in the Atlas Mountains (so my crude interpretations are moderately inaccurate; what do you think about these geodetic data?).




Profiles 1 and 2 (see Fig. 2a). (a and d) Component of velocities and 1-sigma uncertainties along the direction of plate motion (normal to profile). (b and e) Component of velocities and 1-sigma uncertainties normal to the direction of plate motion (i.e., parallel to profiles). The interseismic deformation predicted by elastic block models is shown for the three main hypothesized plate boundaries (Red = Klitgord and Schouten, 1986; Green = Bird, 2003; Blue = Gutscher, 2004, see Fig. 1 for geometry). The pink line is for a model with a central Rif block (see the figure for geometry). (c and f) Topography and interpretative cross-section along Profiles 1 and 2. CC = Continental crust, LM= lithospheric mantle, OC= ocean crust, LVA = low velocity, high attenuation seismic anomaly (Calvert et al., 2000a,b).

UPDATE: 11 Sept 2023

• Albert Griera tweeted a figure that is included in a reference (Domènech et al., 2015). I used a couple figures from that journal article in an interpretive illustration below.
• This Domènech et al. (2015) paper includes a cross section very close to the M 6.8 earthquake. At the top of this illustration is the map that shows the geology, faults, and the location for the cross section. Below is this cross section at two different time periods.
• I include the figure captions for the map and cross section in block quote below the illustration.




(a) Geologic map of the western and Marrakech High Atlas (modified from Hollard, 1985), showing location of the study area detailed in (b). (b) Geologic map of the Marrakech High Atlas showing the main structural elements. Squares correspond to areas described in detail in this paper.

Present-day cross section of the Marrakech High Atlas (see location in Fig. 2) and restoration to a state previous to the orogenic inversion in the Late Cretaceous.

Seismic Hazard and Seismic Risk

• These are the two maps that show seismic and seismic risk for the western Mediterranean, the GEM Seismic Hazard and the GEM Seismic Risk maps from Pagani et al. (2018) and Silva et al. (2018).

The GEM Seismic Hazard Map:







• The Global Earthquake Model (GEM) Global Seismic Hazard Map (version 2018.1) depicts the geographic distribution of the Peak Ground Acceleration (PGA) with a 10% probability of being exceeded in 50 years, computed for reference rock conditions (shear wave velocity, VS30, of 760-800 m/s). The map was created by collating maps computed using national and regional probabilistic seismic hazard models developed by various institutions and projects, and by GEM Foundation scientists. The OpenQuake engine, an open-source seismic hazard and risk calculation software developed principally by the GEM Foundation, was used to calculate the hazard values. A smoothing methodology was applied to homogenise hazard values along the model borders. The map is based on a database of hazard models described using the OpenQuake engine data format (NRML). Due to possible model limitations, regions portrayed with low hazard may still experience potentially damaging earthquakes.
• Here is a view of the GEM seismic hazard map for the western Mediterranean.




The GEM Seismic Risk Map:







• The Global Seismic Risk Map (v2018.1) presents the geographic distribution of average annual loss (USD) normalised by the average construction costs of the respective country (USD/m2) due to ground shaking in the residential, commercial and industrial building stock, considering contents, structural and non-structural components. The normalised metric allows a direct comparison of the risk between countries with widely different construction costs. It does not consider the effects of tsunamis, liquefaction, landslides, and fires following earthquakes. The loss estimates are from direct physical damage to buildings due to shaking, and thus damage to infrastructure or indirect losses due to business interruption are not included. The average annual losses are presented on a hexagonal grid, with a spacing of 0.30 x 0.34 decimal degrees (approximately 1,000 km² at the equator). The average annual losses were computed using the event-based calculator of the OpenQuake engine, an open-source software for seismic hazard and risk analysis developed by the GEM Foundation. The seismic hazard, exposure and vulnerability models employed in these calculations were provided by national institutions, or developed within the scope of regional programs or bilateral collaborations.
• Here is a view of the GEM seismic risk map for the western Mediterranean.




Africa

Earthquake Reports

• 2023.09.08 M 6.8 Morocco
• 2018.05.15 M 5.8 Madagascar
• 2018.03.08 M 5.6 Mozambique and Malawi
• 2017.04.03 M 6.5 Botswana
• 2016.9.10 M 5.7 Tanzania

Social Media

#EarthquakeReport for M6.8 #Earthquake in #Morroco

Looks like it will be quite damaging and may lead to a large number of casualties
Reported intensity MMI 7
Hopefully suffering is minimalhttps://t.co/mO3uGkOkeK pic.twitter.com/JEOnKz4kpc

— Jason "Jay" R. Patton (@patton_cascadia) September 8, 2023

#EarthquakeReport for M6.8 #Earthquake in #Morocco

high intensity (reported at least MMI 9)
associated with tectonics of the Atlas Mountains

read report here:https://t.co/D6VNcSBjWS pic.twitter.com/uzvloTTa9B

— Jason "Jay" R. Patton (@patton_cascadia) September 9, 2023

#EarthquakeReport for M6.8 #Earthquake in #Morocco

updated @USGS_Quakes intensity and ground failure data and earthquake slip estimate

read report here:https://t.co/D6VNcSBjWS pic.twitter.com/p6vukhjgVn

— Jason "Jay" R. Patton (@patton_cascadia) September 10, 2023

The recent M6.8 earthquake in Morocco is the largest ever recorded in the country – and news reports indicate that it was deadly.

What happened? Why? What can we expect next? Read more in our blog, Earthquake Insights. Find the link in my bio. pic.twitter.com/FQQBdhzgCs

— Dr. Judith Hubbard (@JudithGeology) September 9, 2023

Mw=6.9, MOROCCO (Depth: 24 km), 2023/09/08 22:11:01 UTC – Full details here: https://t.co/WoG8zWb5j2 pic.twitter.com/cdypxjgAjO

— Earthquakes (@geoscope_ipgp) September 8, 2023

Prelim. M6.8 in Morocco, about 50 miles southwest of Marrakesh. That's a sizeable population center. USGS estimates over 2 million people were exposed to "strong to very strong" shaking. Fatalities and building damages are sadly expected. #earthquake #morocco pic.twitter.com/V0DVrSho04

— Brian Olson (@mrbrianolson) September 8, 2023

Recent shallow 6.8 Mw (#Morocco 🇲🇦) Western High Atlas, oblique reverse faulting. pic.twitter.com/1T6IxJRyBW

— Abel Seism🌏Sánchez (@EQuake_Analysis) September 8, 2023

For sure the causative structure is related to Atlas, however, the preliminary focal mechanism suggests also a N122 trending structure, which may correspond to an oblique structure that is subtle but visible in the satellite imagery. Cannot find literature on this. pic.twitter.com/la7a8t1Ym5

— Dr. Paula M Figueiredo (@paleoquake.bsky.social) (@pm_figueiredo) September 9, 2023

Just half an hour ago, Mw6.8 #earthquake in Morocco, not far from Agadir.
Very shallow and very large for that area (the tragic Agadir 1960 EQ was just M5.9)
Felt over a very large area, including Portugal, Spain and Algeria.
Dangerous!https://t.co/cFfpsUSS9c pic.twitter.com/WLU5c686sT

— José R. Ribeiro (@JoseRodRibeiro) September 8, 2023

#Earthquake 76 km SW of #Marrakech (#Morocco) 29 min ago (local time 23:11:00). Updated map – Colored dots represent local shaking & damage level reported by eyewitnesses. Share your experience:
📱https://t.co/bKBgMenA4F
🌐https://t.co/lZLiJgtzeF pic.twitter.com/GYCSBv0zT6

— EMSC (@LastQuake) September 8, 2023

This is a raw seismogram of the Mw 6.8 High Atlas, Morocco Earthquake which hit about 4.5 hours ago. It is recorded on a seismograph located ~115km east, at Tiouine (where a dam was built in 2013 to provide water for Ouarzazate). The seismograph is recorded many tiny aftershocks pic.twitter.com/ybi1fayxO6

— Jamie Gurney 🇬🇧🇳🇿 (@UKEQ_Bulletin) September 9, 2023

M 6.8 – 56 km W of Oukaïmedene, Morocco https://t.co/Vy54y0q0vc pic.twitter.com/VHLPmgMWS3

— Wendy Bohon, PhD 🌏 (@DrWendyRocks) September 8, 2023

A complex plate boundary separates the African Plate from the Eurasian Plate, skirting the northern edges of Algeria & Morocco. Today's M6.8 was not in the middle of a tectonic plate, but neither was it immediately along an active plate boundary. pic.twitter.com/wZ82Z5sUn6

— Dr. Susan Hough 🦖 (@SeismoSue) September 8, 2023

3 looks at the M6.8 Morocco earthquake: data from a seismometer in Rabat, past earthquakes in the region, and local plate motion relative to Eurasia (pink scale arrow is 25 mm/yr).
Explore for yourself ⬇️https://t.co/yZeORNrlN6https://t.co/XKHNEprsTchttps://t.co/0P2wufC5ez pic.twitter.com/Igsjwp6OJ4

— EarthScope Consortium (@EarthScope_sci) September 9, 2023

WATCH: 6.8-magnitude earthquake hits Morocco, killing more than 300 people pic.twitter.com/sOHj2HRSMs

— BNO News (@BNONews) September 9, 2023

https://t.co/C5kuv1zn61

— Jason "Jay" R. Patton (@patton_cascadia) September 9, 2023

Reports of damage after 6.8-magnitude earthquake hits Morocco pic.twitter.com/tQqYsosW8x

— BNO News (@BNONews) September 8, 2023

Preliminary M7.0 #Earthquake
ID: #rs2023rspqys
31km/19miles from #OuladBerhil, in #Morocco
2023-09-08 22:10 UTC@raspishake network

Join the largest #CitizenScience #seismograph community ➡ https://t.co/Y5O0dgJqJF

EVENT ➡ https://t.co/TPA2YZeitu pic.twitter.com/9lj9vO1oPw

— Raspberry Shake Earthquake Channel (@raspishakEQ) September 8, 2023

Schweres Erdbeben mit Magnitude 6.9 im Zentrum von Marokko, etwa mittig zwischen Marrakech und Agadir. Spürbar bis weit nach Spanien und Portugal. Mit Abstand das stärkste Erdbeben in der Geschichte von Marokko (auf dem Festland). Viele Opfer zu befürchten. pic.twitter.com/A57vM45hcF

— Erdbebennews (@Erdbebennews) September 8, 2023

By reminding that SCENARIOS ARE NOT REAL DATA, that could also significantly differ, this is what (and when) we expect from #InSAR for the M 6.8 #moroccoearthquake, both planes
First Sentinel-1 data in 2 days
more here: https://t.co/70vbRGVzxm@antandre71 @maferp_13 @FraxInSAR pic.twitter.com/ei873ucSmd

— Simone Atzori (@SimoneAtzori73) September 9, 2023

Creo que aún no somos conscientes de que acabamos de sobrevivir al terremoto más grande de la historia de marruecos. Nosotros estamos aún en shock, pero bien. No se como describir lo que estamos viviendo #terremotomarruecos #terremoto #earthquake #Marrakech #terremotomarrakech pic.twitter.com/4Ac64w86NS

— Juan Bilbao (@joanbilbao93) September 9, 2023

Recent Earthquake Teachable Moment for the M6.8 earthquake in Morocco.

Teachable Moments presentations capture the opportunity to bring knowledge, insight, and critical thinking to the classroom following a newsworthy earthquake.

➡️ https://t.co/oZ08dRr8A8 pic.twitter.com/oU66f6sv7f

— EarthScope Consortium (@EarthScope_sci) September 9, 2023

רעידת אדמה עוצמתית במרוקו 🇲🇦, החזקה ביותר שתועדה שם! שרשור גיאולוגי מתגלגל. נתחיל במיקום- כמו שאפשר לראות במפה הטופוגרפית הזאת, הרעידה קרתה בשולי אזור הררי. אזור זה נקרא הרי האטלס הגבוהים (High atlas) והוא אחד ממספר תתי רכסים שמרכיבים את הרי האטלסhttps://t.co/P80eBHCY36

— Tom (@Karnafush) September 9, 2023

How did the ground shake in Morocco? The most immediate data can come from contributed felt reports, from which we estimate "intensities" that indicate the severity of shaking.
A 🧵https://t.co/VjwM1LiKwM
#earthquake #Morocco

— Dr. Susan Hough 🦖 (@SeismoSue) September 9, 2023

Hi everyone – we're looking to make our posts more accessible to impacted people.

Here is a link to our post via Google Translate; choose your preferred language: https://t.co/02gDh9ZBni

If you want to help generate more accurate versions in Arabic/Berber/French, DM me! https://t.co/Tr60gdbf8J

— Dr. Judith Hubbard (@JudithGeology) September 9, 2023

At least 1,000 people were killed and 1,200 injured after a 6.8-magnitude earthquake shook Morocco late Friday, the Interior Ministry said. The earthquake struck in the province of Al Haouz, about 43 miles south of Marrakesh, devastating buildings and sending panicked residents… pic.twitter.com/xrQxizRMBA

— The Washington Post (@washingtonpost) September 9, 2023

You can find images of destruction submitted to the EMSC here: https://t.co/T6ZCHSBhdh

If you live in the region and felt shaking, consider submitting your own description. This helps guide scientific analysis of the event and its impacts: https://t.co/PtinNqMLGu

— Dr. Judith Hubbard (@JudithGeology) September 9, 2023

https://t.co/xvnQ2DMePB

This is the story. The link of reactivation of the Atlas to the dragging I figured out this morning, so is not in this paper :)

— Douwe van Hinsbergen (@vanHinsbergen) September 9, 2023

Information on the M6.8 earthquake in Morocco, including video showing the seismic waves from that event as detected in North America.

My heart goes out to everyone impacted by this tragedy. pic.twitter.com/TkoQyKAqUS

— Wendy Bohon, PhD 🌏 (@DrWendyRocks) September 9, 2023

Powerful earthquake hits Morocco 😢 😢😢
Recorded across New England.@westportskyguys @jpulli @BCSchillerInst pic.twitter.com/1mdEqtPApD

— Alan Kafka (@Weston_Quakes) September 9, 2023

#Séisme au Maroc : « Sa survenue dans cette région n’est pas une surprise » mes explications dans @lemondefr https://t.co/hlCkOCMukY

— Robin Lacassin – @RobinLacassin@qoto.org (@RLacassin) September 9, 2023

6.8-magnitude-earthquake-triggered landslide has swept away the town of Adassil in the Moroccan Atlas. >7000 people live there. pic.twitter.com/iXQ773kEpz

— Δρ(García-Castellanos) (@danigeos) September 10, 2023

Sections showing responses on @raspishake citizen seismometers across the globe, to yesterday's deadly M6.8 earthquake in Morocco. On the 0-180° section, a response can be seen in Wellington, NZ. On the 0-95° section, filtered at 0.1-10Hz, there are PcP reflections from the core. pic.twitter.com/26hLx0yNVt

— Mark Vanstone (@wmvanstone) September 10, 2023

While earthquakes in western Morocco are rare and there have been no other M6+ quakes since 1900, many residences in the area are vulnerable to shaking and earthquake impacts can be severe. In 1960, the M5.8 Agadir earthquake killed 12,000-15,000 people in coastal Morocco.

— USGS Earthquakes (@USGS_Quakes) September 9, 2023

It's been a day and a half since the earthquake in Morocco, and we're starting to learn more.

Landslides caused damage and are complicating rescue efforts. Aftershocks hint at a possible fault geometry. Satellite images are pending.

Read more on our blog; link in my bio. https://t.co/Tr60gdbf8J pic.twitter.com/fjZr1nQM1m

— Dr. Judith Hubbard (@JudithGeology) September 10, 2023

The Tinmal Mosque, a historical structure dating back to the 12th century located in the High Atlas mountains of Morocco and renowned for its Almohad architecture, has been reduced to ruins in the aftermath of the devastating earthquake. pic.twitter.com/ijALCucM97

— Morocco World News (@MoroccoWNews) September 9, 2023

I tried to look at the correlation between the location of aftershocks (according to EMSC) and coulomb stress change using the @USGS_Quakes model. Not a good overlap, but informative. @JudithGeology Maybe some insights for your previous blog today. pic.twitter.com/iECjFlPZeR

— Achraf (@KoulaliAchraf) September 14, 2023

The comparison between observed and modeled data for track 154 (descending, left) and track 45 (ascending, right).

Previous model tweet: https://t.co/d52hngYRzV pic.twitter.com/uLYzKgEl81

— Simone Atzori (@SimoneAtzori73) September 16, 2023

How did the earthquake in Morocco change the shape of the High Atlas mountains – and how do we know? In our latest post, we explain InSAR, and what it can – and can't – tell us.

Read more on our blog; the link is in my bio (and in the image below). pic.twitter.com/AkXQ5KxMB2

— Dr. Judith Hubbard (@JudithGeology) September 21, 2023

References:

Basic & General References

• Frisch, W., Meschede, M., Blakey, R., 2011. Plate Tectonics, Springer-Verlag, London, 213 pp.
• Hayes, G., 2018, Slab2 – A Comprehensive Subduction Zone Geometry Model: U.S. Geological Survey data release, https://doi.org/10.5066/F7PV6JNV.
• Holt, W. E., C. Kreemer, A. J. Haines, L. Estey, C. Meertens, G. Blewitt, and D. Lavallee (2005), Project helps constrain continental dynamics and seismic hazards, Eos Trans. AGU, 86(41), 383–387, , https://doi.org/10.1029/2005EO410002. /li>
• Jessee, M.A.N., Hamburger, M. W., Allstadt, K., Wald, D. J., Robeson, S. M., Tanyas, H., et al. (2018). A global empirical model for near-real-time assessment of seismically induced landslides. Journal of Geophysical Research: Earth Surface, 123, 1835–1859. https://doi.org/10.1029/2017JF004494
• Kreemer, C., J. Haines, W. Holt, G. Blewitt, and D. Lavallee (2000), On the determination of a global strain rate model, Geophys. J. Int., 52(10), 765–770.
• Kreemer, C., W. E. Holt, and A. J. Haines (2003), An integrated global model of present-day plate motions and plate boundary deformation, Geophys. J. Int., 154(1), 8–34, , https://doi.org/10.1046/j.1365-246X.2003.01917.x.
• Kreemer, C., G. Blewitt, E.C. Klein, 2014. A geodetic plate motion and Global Strain Rate Model in Geochemistry, Geophysics, Geosystems, v. 15, p. 3849-3889, https://doi.org/10.1002/2014GC005407.
• Meyer, B., Saltus, R., Chulliat, a., 2017. EMAG2: Earth Magnetic Anomaly Grid (2-arc-minute resolution) Version 3. National Centers for Environmental Information, NOAA. Model. https://doi.org/10.7289/V5H70CVX
• Müller, R.D., Sdrolias, M., Gaina, C. and Roest, W.R., 2008, Age spreading rates and spreading asymmetry of the world’s ocean crust in Geochemistry, Geophysics, Geosystems, 9, Q04006, https://doi.org/10.1029/2007GC001743
• Pagani,M. , J. Garcia-Pelaez, R. Gee, K. Johnson, V. Poggi, R. Styron, G. Weatherill, M. Simionato, D. Viganò, L. Danciu, D. Monelli (2018). Global Earthquake Model (GEM) Seismic Hazard Map (version 2018.1 – December 2018), DOI: 10.13117/GEM-GLOBAL-SEISMIC-HAZARD-MAP-2018.1
• Silva, V ., D Amo-Oduro, A Calderon, J Dabbeek, V Despotaki, L Martins, A Rao, M Simionato, D Viganò, C Yepes, A Acevedo, N Horspool, H Crowley, K Jaiswal, M Journeay, M Pittore, 2018. Global Earthquake Model (GEM) Seismic Risk Map (version 2018.1). https://doi.org/10.13117/GEM-GLOBAL-SEISMIC-RISK-MAP-2018.1
• Storchak, D. A., D. Di Giacomo, I. Bondár, E. R. Engdahl, J. Harris, W. H. K. Lee, A. Villaseñor, and P. Bormann (2013), Public release of the ISC-GEM global instrumental earthquake catalogue (1900–2009), Seismol. Res. Lett., 84(5), 810–815, doi:10.1785/0220130034.
• Zhu, J., Baise, L. G., Thompson, E. M., 2017, An Updated Geospatial Liquefaction Model for Global Application, Bulletin of the Seismological Society of America, 107, p 1365-1385, https://doi.org/0.1785/0120160198

Specific References

• Arboleya, M.L., Teoxe;. A., Charroud, M., Julivert, M., 2004. A structural transect through the High and Middle Atlas of Morocco in Journal of African Earth Sciences, v. 39, p. 319-327, https://doi.org/10.1016/j.jafrearsci.2004.07.036
• Beauchamp, W., Allmendinger, R.W., Barazangi, M., Demnati, A., El Alji, M., and Dahmani, M., 1999. Inversion tectonics and the evolution of the High Atlas Mountains, Morocco, based on a geological-geophysical transect in Tectonics, v. 18, no. 2, p. 163-184, https://doi.org/10.1029/1998TC900015
• Domènech, M., Teixell, A., Babault, J., and Arbolya, M-L., 2015. The inverted Triassic rift of the Marrakech High Atlas: A reappraisal of basin geometries and faulting histories in Tectonophysics, v. 663, p. 177-191, https://doi.org/10.1016/j.tecto.2015.03.017
• Domènech, M., Teixell, A., and Stockli, D.F., 2016. Magnitude of rift-related burial and orogenic contraction in the Marrakech High Atlas revealed by zircon(U-Th)/He thermochronology and thermal modeling in Tectonics, v. 35, p. 2609–2635, https://doi.org/10.1002/2016TC004283
• Jiménez‐Munt, I., M. Fernàndez, J. Vergés, D. Garcia‐Castellanos, J. Fullea, M. Pérez‐Gussinyé, and J. C. Afonso(2011), Decoupled crust‐mantle accommodation of Africa‐Eurasia convergence in the NW Moroccan margin,J. Geophys. Res.,116, B08403, https://doi.org/10.1029/2010JB008105
• Babault, J., Teixell, A., Struth, L., Van Den Driessche, J., Arboleya, ML., Tesón, and E., 2013. “Shortening, structural relief and drainage evolution in inverted rifts: insights from the Atlas Mountains, the Eastern Cordillera of Colombia and the Pyrenees”, Thick-Skin-Dominated Orogens: From Initial Inversion to Full Accretion, in Nemcˇok, M., Mora, A. & Cosgrove, J. W. (eds) Thick-Skin-Dominated Orogens: From Initial Inversion to Full Accretion. Geological Society, London, Special Publications, 377, http://dx.doi.org/10.1144/SP377.14
• Lanari, R., Faccenna, C., Fellin, M. G., Essaifi, A., Nahid, A., Medina, F., & Youbi, N. (2020). Tectonic evolution of the western High Atlas of Morocco: Oblique convergence, reactivation, and transpression. Tectonics, 39, e2019TC005563. https://doi.org/10.1029/2019TC005563
• Teixell, A., Arboleya, M., Julivert, M., and Charroud, M., 2003. Tectonic shortening and topography in the central High Atlas (Morocco) in Tectonics, v. 22, no. 5, 1051, https://doi.org/10.1029/2002TC001460
• Vernant et al., 2010. Geodetic constraints on active tectonics of the Western Mediterranean: Implications for the kinematics and dynamics of the Nubia-Eurasia plate boundary zone in Journal of Geodynamics, v. 49, no 3-4, p. 123-129, https://doi.org/10.1016/j.jog.2009.10.007

Return to the Earthquake Reports page.

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I am catching up with this today as I have been busy with other things.

I am still behind on those things, but wanted to get this put together since I am currently working on a project that includes tsunami sources in this region.

There was a magnitude M 7.7 earthquake on 19 May 2023 offshore of New Caledonia.

https://earthquake.usgs.gov/earthquakes/eventpage/at00ruvxj7/executive

This earthquake happened in the Australia plate, west of the deep sea trench.

The deep sea trench owes its existence to the plate boundary fault system there, a convergent plate boundary where plates move towards each other. The plate boundary here is formed by the subduction of the Australia plate beneath the North Fiji Basin.

The largest earthquakes that happen on Earth happen on these subduction zone faults.

At first I thought that this was an interface earthquake along the megathrust subduction zone fault. These are called interface events because they happen along the fault interface between the two plates. They are also called interplate earthquakes.

However, the location showed this to be west of the subduction zone. Also, as the earthquake mechanisms (e.g., focal mechanism or moment tensor) were calculated and posted online, it was clear that this was not a megathrust earthquake.

Here is an illustration that shows a cross section of a subduction zone. I show hypothetical locations for different types of earthquakes. I include earthquake mechanisms (as they would be viewed from map view) for these different types of earthquakes.

Here is a legend for these different mechanisms. We can see what the mechanisms look like from map view (from looking down onto Earth from outer space or from flying in an airplane) and what they look like from the side.

The mechanism for the M 7.7 Loyalty Isles earthquake is an extensional (normal) type of an earthquake that happened in the slab of the Australia plate.

Typically, the extension in these slab events is perpendicular to the plate boundary fault because that is the direction that the plate is pulling down (slab pull) due to gravity or that is the orientation of bending of the plate that causes this extension.

There are also records of tsunami and seismic waves on water level sensors in this region. A tsunami was observed on the Ouinne (New Caledonia) tide gage.

Here are the tide gage data from https://webcritech.jrc.ec.europa.eu/SeaLevelsDb/Home.

This M 7.7 earthquake is having lots of aftershocks and the largest was a M 7.1.

https://earthquake.usgs.gov/earthquakes/eventpage/us6000kdce/executive

Not only did the M 7.7 generate a tsunami but so did the M 7.1 earthquake. The plot below shows both earthquake times relative to the tsunami produced by those events.

These tsunami were recorded on other gages as well but this was the best record I saw.

My initial tweet called this normal faulting event a tensional earthquake. Dr. Harold Tobin provided an excellent overview of the difference between tension and extension.

In the Earth, all 3 principal stresses are (nearly) always compressional or inward-directed. A tensional stress state is a rare condition indeed. If the biggest principal stress is vertical, then high-angle (but not vertical!) extensional normal faults are the result. pic.twitter.com/cvYar2f010

— Harold Tobin (@Harold_Tobin) May 20, 2023

Below is my interpretive poster for this earthquake

• I plot the seismicity from the past month, with diameter representing magnitude (see legend). I include earthquake epicenters from 1923-2023 with magnitudes M ≥ 7.5 in one version.
• I plot the USGS fault plane solutions (moment tensors in blue and focal mechanisms in orange), possibly in addition to some relevant historic earthquakes.
• A review of the basic base map variations and data that I use for the interpretive posters can be found on the Earthquake Reports page. I have improved these posters over time and some of this background information applies to the older posters.
• Some basic fundamentals of earthquake geology and plate tectonics can be found on the Earthquake Plate Tectonic Fundamentals page.

I include some inset figures. Some of the same figures are located in different places on the larger scale map below.

• In the lower center is a tectonic map from Patriat et al. (2019). I place a yellow star in the general location of this M 7.7 earthquake.
• In the upper left corner shows the tectonic plates and seismicity from the past century for events with magnitudes larger than M 7.5.
• Below this map is a figure from the USGS that shows their estimate of how much the fault slipped during this M 7.7 earthquake. Dark red shows where the fault may have slipped as much as 3 meters.
• In the lower right corner is a map that shows the earthquake intensity using the modified Mercalli intensity scale. Earthquake intensity is a measure of how strongly the Earth shakes during an earthquake, so gets smaller the further away one is from the earthquake epicenter. The map colors represent a model of what the intensity may be. The USGS has a system called “Did You Feel It?” (DYFI) where people enter their observations from the earthquake and the USGS calculates what the intensity was for that person. The transparent colors with yellow labels show what people actually felt in those different locations.
• in the lower left is the tide gage plot from Ouinne, New Caledonia (location shown on the map).
• In the upper right is a map that shows earthquakes and their aftershock sequences for three events in the past 3 years. There is some overlap, but mostly, these three sequences have aftershocks in different areas. The 2021 and 2022 earthquakes are probably (?) subduction zone earthquakes based on their mechanisms. it sure seems like these two events may have changed the stresses in the Australia plate (i.e., they may have triggered the 2023 earthquake).
1. 2021 M 7.7 (green)
2. 2022 M 7.0 (blue)
3. 2023 M 7.7 (orange)
• Here is the map with a month’s seismicity plotted.

Other Report Pages

Want to read more about this quake and its tectonic setting? Read my new blog article about it – and the other weird earthquakes in the area, with all kinds of interactions between quakes in the outer rise and on the megathrust.

Find the link in my bio! pic.twitter.com/NpBRDv40BU

— Dr. Judith Hubbard (@JudithGeology) May 20, 2023

Some Relevant Discussion and Figures

The U.S. Geological Survey (USGS) has a spectacular web page that helps us learn about the plate tectonics (seismotectonics) of the eastern margin of the Australia plate. Check out their webpage here.

• Here is the plate tectonic map from Patriat et al. (2019).




A) Simplified present-day geodynamic map of the New Hebrides and Matthew-Hunter subduction systems (modern trenches shown in black). Inferred location of the New Hebrides subduction and its termination as a STEP fault before 2 Ma shown in light grey. Inset map shows the regional bathymetry. B) Schematic evolution of the North Fiji Basin when the system shifted from a STEP fault to subduction initiation at 2 Ma (after Patriat et al., 2015). LR, Loyalty Ridge; NC, New Caledonia.

• This is the plate tectonic map from de Alteriis et al. (1993) that shows the major fault systems in the region.




Location map of North Fiji Basin ridge; box indicates full multibeam covered area of Figure 2. Heavy lines denote north-south, N15°, and N160° main segments of ridge axis; dashed lines are pseudofaults indicating double propagation. F. Z.— fracture zone.

• Here is a figure from Schellart et al. (2002) that shows their model of tectonic development of the North Fiji Basin. Schellart et al. (2002) include a long list of references for the tectonics in this region here. Below I include the text from the original figure caption in blockquote.




Tectonic reconstruction of the New Hebrides – Tonga region (modified and interpreted from Auzende et al. [1988], Pelletier et al. [1993], Hathway [1993] and Schellart et al.(2002a)) at (a) ~ 13 Ma, (b) ~ 9 Ma, (c) 5 Ma and (d) Present. The Indo-Australian plate is fixed. DER = d’Entrcasteaux Ridge, HFZ = Hunter Fracture Zone, NHT = New Hebrides Trench, TT = Tonga Trench, WTP = West Torres Plateau. Arrows indicate direction of arc migration. During opening of the North Fiji Basin, the New Hebrides block has rotated some 40-50° clockwise [Musgrave and Firth 1999], while the Fiji Plateau has rotated some 70-115° anticlockwise [Malahoff et al. 1982]. During opening of the Lau Basin, the Tonga Ridge has rotated ~ 20° clockwise [Sager et al. 1994]. (Click for enlargement)

• This is the plate tectonic history map from Begg and Gray (1993) that shows how they interpret the Fiji Plateau to have formed.




Tectonic setting (Figures 1a–1c) and tectonic reconstructions (Figures 1d and 1e) of the Outer Melanesian region (adapted from Hathway [1993]; reprinted with permission from the Geological Society of London).

(a) Map of the Fiji platform and north end of the Lau Ridge showing the major islands in the Fiji area, the major early Pliocene volcanoes of Viti Levu, the major seafloor fracture zones, and part of the spreading center of the Fiji Basin (adapted from Gill and Whelan [1989]). Shoshonitic volcanoes, including the Tavua Volcano (T), are shown by squares and calc-alkaline volcanoes by circles.

(b) Tectonic features of the northeastern segment of the plate boundary between the Australian and Pacific plates showing the Outer Melanesian Arc of the southwest Pacific, trenches and ridge systems, and oceanic plateaus (adapted from Kroenke [1984]). Fiji, as part of the Fiji Platform, consists of a series of islands at the north end of the Lau Ridge, with the North Fiji Basin formed as part of a spreading center.

(c) Present plate configuration.

(d) Reconstruction at 5.5 Ma.

(e) Reconstruction at 10 Ma. In Figures 1a–1e the Australian plate is fixed and the east-west convergence rate between plates was assumed to be 9–10 cm yr-1. Shading represents submarine depths <2000 m.

Abbreviations are as follows: VT, Vitiaz trench; VAT, Vanuatu trench; LR, Lau Ridge; LB, Lau Basin; TR, Tonga Ridge; FFZ, Fiji Fracture Zone; LL, Lomaiviti lineament; V-BL, Vatulele-Beqa lineament. Long dashes denote southern margin of the Melanesian Border Plateau (MBP). The open square (Figures 1b and 1c) denotes the location of the Tavua Volcano.

• Here are figures from Richards et al. (2011) with their figure captions below in blockquote.
• The main tectonic map




bathymetry, and major tectonic element map of the study area. The Tonga and Vanuatu subduction systems are shown together with the locations of earthquake epicenters discussed herein. Earthquakes between 0 and 70 km depth have been removed for clarity. Remaining earthquakes are color-coded according to depth. Earthquakes located at 500–650 km depth beneath the North Fiji Basin are also shown. Plate motions for Vanuatu are from the U.S. Geological Survey, and for Tonga from Beavan et al. (2002) (see text for details). Dashed line indicates location of cross section shown in Figure 3. NFB—North Fiji Basin; HFZ—Hunter Fracture Zone.

• Here is the map showing the current configuration of the slabs in the region.




Map showing distribution of slab segments beneath the Tonga-Vanuatu region. West-dipping Pacifi c slab is shown in gray; northeast-dipping Australian slab is shown in red. Three detached segments of Australian slab lie below the North Fiji Basin (NFB). HFZ—Hunter Fracture Zone. Contour interval is 100 km. Detached segments of Australian plate form sub-horizontal sheets located at ~600 km depth. White dashed line shows outline of the subducted slab fragments when reconstructed from 660 km depth to the surface. When all subducted components are brought to the surface, the geometry closely approximates that of the North Fiji Basin.

• This is the cross section showing the megathrust fault configuration based on seismic tomography and seismicity.




Previous interpretation of combined P-wave tomography and seismicity from van der Hilst (1995). Earthquake hypocenters are shown in blue. The previous interpretation of slab structure is contained within the black dashed lines. Solid red lines mark the surface of the Pacifi c slab (1), the still attached subducting Australian slab (2a), and the detached segment of the Australian plate (2b). UM—upper mantle;
TZ—transition zone; LM—lower mantle.

• Here is their time step interpretation of the slabs that resulted in the second figure above.




Simplified plate tectonic reconstruction showing the progressive geometric evolution of the Vanuatu and Tonga subduction systems in plan view and in cross section. Initiation of the Vanuatu subduction system begins by 10 Ma. Initial detachment of the basal part of the Australian slab begins at ca. 5–4 Ma and then sinking and collision between the detached segment and the Pacifi c slab occur by 3–4 Ma. Initial opening of the Lau backarc also occurred at this time. Between 3 Ma and the present, both slabs have been sinking progressively to their current position. VT—Vitiaz trench; dER—d’Entrecasteaux Ridge.

• Here is a map from the USGS report (Benz et al., 2011). Read more about this map on the USGS website. Earthquakes are plotted with color related to depth and circle diameter related to magnitude. Today’s M 6.8 earthquake occurred south of cross section G-G’.




• This is the legend.




• Here is a cross section showing the seismicity along swatch profile G-G’.




• Craig et al. (2014) evaluated the historic record of seismicity for subduction zones globally. In particular, the evaluated the relations between upper and lower plate stresses and earthquake types (cogent for the southern New Hebrides trench). Below is a figure from their paper for this part of the world. I include their figure caption below in blockquote.




Outer-rise seismicity along the New Hebrides arc. (a) Seismicity and focal mechanisms. Seismicity at the southern end of the arc is dominated by two major outer-rise normal faulting events, and MW 7.6 on 1995 May 16 and an MW 7.1 on 2004 January 3. Earthquakes are included from Chapple & Forsyth (1979); Chinn & Isacks (1983); Liu & McNally (1993). (b) Time versus latitude plot.

• Here is a summary figure from Craig et al. (2014) that shows different stress configurations possibly existing along subduction zones.




Schematic diagram for the factors influencing the depth of the transition from horizontal extension to horizontal compression beneath the outer rise. Slab pull, the interaction of the descending slab with the 660 km discontinuity (or increasing drag from the surround mantle), and variations in the interface stress influence both the bending moment and the in-plane stress. Increases in the angle of slab dip increases the dominance of the bending moment relative to the in-plane stress, and hence moves the depth of transition towards the middle of the mechanical plate from either an shallower or a deeper position. A decrease in slab dip enhances the influence of the in-plane stress, and hence moves the transition further from the middle of the mechanical plate, either deeper for an extensional in-plane stress, or shallower for a compressional in-plane stress. Increased plate age of the incoming plate leads to increases in the magnitude of ridge push and intraplate thermal contraction, increasing the in-plane compressional stress in the plate prior to bending. Dynamic topography of the oceanic plate seawards of the trench can result in either in-plane extension or compression prior to the application of the bending stresses.

• Here is an animation that shows the seismicity for this region from 1960 – 2016 for earthquakes with magnitudes greater than or equal to 7.0.
• I include some figures mentioned in my report from 2016.04.28 for a sequence of earthquakes in the same region as today’s earthquake (albeit shallower hypocentral depths), in addition to a plot from Cleveland et al. (2014). In the upper right corner, Cleveland et al. (2014) on the left plot a map showing earthquake epicenters for the time period listed below the plot on the right. On the right is a plot of earthquakes (diameter = magnitude) of earthquakes with latitude on the vertical axis and time on the horizontal axis. Cleveland et al (2014) discuss these short periods of seismicity that span a certain range of fault length along the New Hebrides Trench in this area. Above is a screen shot image and below is the video. To see more about the tectonics in the Vanuatu region, head over to a report from January 2023.




• Here is a link to the embedded video below (6 MB mp4)
• Here is a great overview map from Schellart et al. (2006).
• There is a cross section in subsequent figures and the location of this section is shown on the map on the left.




(a) Topography and bathymetry of the Southwest Pacific region (from Smith and Sandwell (1997)) and (b) regional tectonic setting of (a). Cfz, Cook fracture zone; ChRfsz, Chatham Rise fossil subduction zone; d’ER, d’Entrecasteaux Ridge; EP, East Papua; ER, Efate Re-entrant; LPl, Louisiade Plateau; LoR, Loyalty Ridge; LTr, Louisiade Trough; MaB, Manus Basin; MeR, Melish Rise; NB, New Britain; NBT, New Britain Trench; NCfsz, New Caledonia fossil subduction zone; Nd’EB, North d’Entrecasteaux Basin; NHT, New Hebrides Trench; NLoB, North Loyalty Basin; NST, North Solomon Trough; QT, Queensland Trough; ReB, Reinga Basin, ReR, Reinga Ridge; SCB, Santa Cruz Basin; SCT, San Cristobal Trench; SER, South Efate Re-entrant; SLoB, South Loyalty Basin; SoS, Solomon Sea; SReT, South Rennell Trough; TaB, Taranaki Basin; TKR, Three Kings Ridge; ToT, Townsville Trough; TrT, Trobriand Trough; VMfz, Vening Meinesz fracture zone;WoB,Woodlark Basin; WTP,West Torres Plateau. 1, normal fault; 2, strike-slip fault; 3, subduction zone; 4, spreading ridge (double line) and transform faults (single lines); 5, land; 6–8, sea, with 6, continental or arc crust; 7, oceanic plateau; and 8, basin/ocean floor. Structures in light grey indicate that they are inactive. Thick continuous east–west line at latitude 20° S in panel (a) shows location of cross-section plotted in Fig. 4h. Thick dashed line in panel (a) shows location of cross-section plotted in Fig. 5.

• Below is a series of cross sections (location on above map) through time.
• The panels start at 85 million years ago (Ma) and proceed to the present time (panel H).






East–west cross-sections illustrating the evolution of the Southwest Pacific region since the Cretaceous in an Australia-fixed reference frame. For location of final cross-section in Fig. 4h see Fig. 1. White arrows indicate convergence between Pacific plate and Australia. Black arrows illustrate the sinking kinematics of a slab. Diagrams illustrate that subduction of Pacific lithosphere from the Late Cretaceous to Paleocene and subduction of backarc lithosphere (e.g. South Loyalty slab) results primarily from slab rollback (i.e. negligible convergence between overriding and subducting plate), leading to a simple slab geometry with draping of the slab over the upper–lower mantle discontinuity. subduction of the Pacific plate from the Eocene to Present results from both slab rollback and convergence, leading to a more complex slab geometry with slab draping (due to rollback) and folding (due to convergence). Slab kinematics was inspired by subduction models from Guillou-Frottier et al. (1995), Griffiths et al. (1995), Funiciello et al. (2003) and Schellart (2004a, 2005).

• Here is a reconstruction that Schellart et al. (2006) prepared for the past 10 Ma.




Reconstruction of the clockwise rotation of the New Hebrides arc during opening of the North Fiji backarc Basin, resulting in collision of the arc with the d’Entrecasteaux Ridge and formation of the Efate re-entrant during initial collision. Location of the initial collision site provides an estimate of the eastward continuation of the d’Entrecasteaux Ridge, and therefore an estimate of the east–west width of the South Loyalty Basin (∼750km). Location of the rotation pole is indicated by the black dot and the curved arrow. Numbers indicate approximate amount of rotation of the New Hebrides arc since opening of the North Fiji Basin at ∼12–11Ma. Australia is fixed. Hfz, Hunter fracture zone; LB, Lau Basin; NFB, North Fiji Basin; NHT, New Hebrides Trench; SCT, San Cristobal Trench.

• Here is an interesting paper where van de Lagemaat et al. (2018) work out the tectonic history of the region between New Zealand, Australia, and the Loyalty Islands.
• They prepare a tectonic model to reconstruct the tectonic history and compare their model with seismic tomography models.




Topography and bathymetry (left) and tectonic map (right) of the SW Pacific. Tectonic map is based on our model (see Table 3 and the supporting information): continents in green, submerged continental fragments and volcanic arcs in gray. Present-day plate boundaries in red, former plate boundaries in dark gray. Pink and yellow stars are locations of New Caledonia and Northland ophiolites, respectively. (Former) plate names in dark blue. SW Pacific assemblage consists of multiple smaller plates. BT = Bellona Trough; DEB = D’Entrecasteaux Basin; DEZ = D’Entrecasteaux Zone; FAB = Fairway- Aotea Basin; HT = Havre Trough; KAP = Kupe Abyssal Plain; MAP = Minerva Abyssal Plain = NB, Norfolk Basin; NCB = New Caledonia Basin; NFB = North Fiji Basin; NLB = North Loyalty Basin; LB = Lau Basin; SFB = South Fiji Basin; SLB = South Loyalty Basin; WB = Woodlark Basin; NHT = New Hebdrides Trench; Cfz = Cook fracture zone; Hfz = Hunter fracture zone; VMfz = Vening Meinesz fracture zone; Tr = Trench.

• Here we see some tomographic cross sections from van de Lagemaat et al. (2018). The colder/denser crust is shown in blue (an oversimplification). We can identify the subducted plates as the blue regions that have a downward going shape.




W-E tomographic cross sections of the Tonga-Kermadec slab at the northern (left) and southern (right) ends of the trench, based on the UU-P07 tomographic model (Amaru, 2007). In the north, a significant portion of the slab is flat lying before it continues into the upper mantle, whereas in the south the slab penetrates straight into the upper mantle.

• This is a summary of their plate tectonic reconstruction.




Paleogeographic snapshots of the kinematic reconstruction at selected time slices in an Australia fixed frame. 83 Ma: Start of the reconstruction; 60 Ma: start of New Caledonia subduction; 45 Ma: oldest possible, and frequently mentioned, age of Tonga-Kermadec subduction zone; 30 Ma: end of New Caledonia subduction, youngest possible age of Tonga-Kermadec subduction zone initiation and start of Norfolk and South Fiji Basin back-arc spreading; and 15 Ma: end of Norfolk and South Fiji Basin back-arc spreading.

• Here is a great figure from here, the New Caledonian Seismologic Network. This shows how geologists have recorded uplift rates along dip (“perpendicular” to the subduction zone fault). On the left is a map and on the right is a vertical profile showing how these rates of uplift change east-west. This is the upwards flexure related to the outer rise, which causes extension in the upper part of the downgoing/subducting plate.




The subduction of the Australian plate under the Vanuatu arc is also accompanied by vertical movements of the lithosphere. Thus, the altitudes recorded by GPS at the level of the Quaternary reef formations that cover the Loyalty Islands (Ouvéa altitude: 46 m, Lifou: 104 m and Maré 138 m) indicate that the Loyalty Islands accompany a bulge of the Australian plate. just before his subduction. Coral reefs that have “recorded” the high historical levels of the sea serve as a reference marker for geologists who map areas in uprising or vertical depression (called uplift and subsidence). Thus, the various studies have shown that the Loyalty Islands, the Isle of Pines but alsothe south of Grande Terre (Yaté region) rise at speeds between 1.2 and 2.5 millimeters per decade.

New Britain | Solomon | Bougainville | New Hebrides | Tonga | Kermadec Earthquake Reports

General Overview

Earthquake Reports

• 2023.05.19 M 7.7 Loyalty Islands
• 2023.04.24 M 7.1 Kermadec
• 2023.04.02 M 7.0 Papua New Guinea
• 2023.03.16 M 7.0 Kermadec
• 2023.01.08 M 7.0 Vanuatu Islands
• 2022.11.22 M 7.0 Solomon Isles
• 2022.11.11 M 7.3 Tonga
• 2022.09.10 M 7.6 Papua New Guinea
• 2021.03.04 M 8.1 Kermadec
• 2021.02.10 M 7.7 Loyalty Islands
• 2019.06.15 M 7.2 Kermadec
• 2019.05.14 M 7.5 New Ireland
• 2019.05.06 M 7.2 Papua New Guinea
• 2018.12.05 M 7.5 New Caledonia
• 2018.10.10 M 7.0 New Britain, PNG
• 2018.09.09 M 6.9 Kermadec
• 2018.08.29 M 7.1 Loyalty Islands
• 2018.08.18 M 8.2 Fiji
• 2018.03.26 M 6.9 New Britain
• 2018.03.26 M 6.6 New Britain
• 2018.03.08 M 6.8 New Ireland
• 2018.02.25 M 7.5 Papua New Guinea
• 2018.02.26 M 7.5 Papua New Guinea Update #1
• 2017.11.19 M 7.0 Loyalty Islands Update #1
• 2017.11.07 M 6.5 Papua New Guinea
• 2017.11.04 M 6.8 Tonga
• 2017.10.31 M 6.8 Loyalty Islands
• 2017.08.27 M 6.4 N. Bismarck plate
• 2017.05.09 M 6.8 Vanuatu
• 2017.03.19 M 6.0 Solomon Islands
• 2017.03.05 M 6.5 New Britain
• 2017.01.22 M 7.9 Bougainville
• 2017.01.03 M 6.9 Fiji
• 2016.12.17 M 7.9 Bougainville
• 2016.12.08 M 7.8 Solomons
• 2016.10.17 M 6.9 New Britain
• 2016.10.15 M 6.4 South Bismarck Sea
• 2016.09.14 M 6.0 Solomon Islands
• 2016.08.31 M 6.7 New Britain
• 2016.08.12 M 7.2 New Hebrides Update #2
• 2016.08.12 M 7.2 New Hebrides Update #1
• 2016.08.12 M 7.2 New Hebrides
• 2016.04.06 M 6.9 Vanuatu Update #1
• 2016.04.03 M 6.9 Vanuatu
• 2015.03.30 M 7.5 New Britain (Update #5)
• 2015.03.30 M 7.5 New Britain (Update #4)
• 2015.03.29 M 7.5 New Britain (Update #3)
• 2015.03.29 M 7.5 New Britain (Update #2)
• 2015.03.29 M 7.5 New Britain (Update #1)
• 2015.03.29 M 7.5 New Britain
• 2015.11.18 M 6.8 Solomon Islands
• 2015.05.24 M 6.8, 6.8, 6.9 Santa Cruz Islands
• 2015.05.05 M 7.5 New Britain

Social Media

#EarthquakeReport for M7.7 #Earthquake offshore of #NewCaledonia #LoyaltyIslands

Looks like maybe outer rise tensional event

No tsunami threat in coast of USA
Possible tsunami in Vanuatu Fiji New Caledonia

Read abt regional tectonics in earlier reporthttps://t.co/Ocv4yZXEAn pic.twitter.com/H5v4B78Ypp

— Jason "Jay" R. Patton (@patton_cascadia) May 19, 2023

#EarthquakeReport for M7.7 #Earthquake offshore of #NewCaledonia

Felt intensity MMI2
Tensional mechanism supports interpretation of outer rise event in Australia plate

Similar event in 2017:https://t.co/2w0qDMoGy0https://t.co/7fid7EahHX pic.twitter.com/3J4ZITrcI6

— Jason "Jay" R. Patton (@patton_cascadia) May 19, 2023

#EarthquakeReport for M7.7 #Earthquake offshore of #NewCaledonia

check out the @USGS_Quakes website about the eastern margin of the Australia plate:https://t.co/yB8OayIAsy

analogue M7.7 event in 1995 shown on 2017 poster:https://t.co/KFiR3Z6NVghttps://t.co/Ocv4yZXEAn pic.twitter.com/ZvEYKULXdD

— Jason "Jay" R. Patton (@patton_cascadia) May 19, 2023

#EarthquakeReport #TsunamiReport for M7.7 #Earthquake and #Tsunami offshore of #NewCaledonia

initial waves arriving at Maré (New Caledonia, Loyalty Islands)https://t.co/9kPJP1Lyrdhttps://t.co/Ocv4yZXEAn pic.twitter.com/ctbW4cnj4L

— Jason "Jay" R. Patton (@patton_cascadia) May 19, 2023

#EarthquakeReport #TsunamiReport for M7.7 #Earthquake offshore of #NewCaledonia #LoyaltyIslands

head to https://t.co/wM2UgCJSGQ for tsunami information

message #4 shows the following https://t.co/sXS7cA9ixDhttps://t.co/Ocv4yZXEAn pic.twitter.com/h6clNtT2jB

— Jason "Jay" R. Patton (@patton_cascadia) May 19, 2023

#EarthquakeReport #TsunamiReport for M7.7 #Earthquake #Tsunami offshore of #NewCaledonia

tsunami observations

numbers in the table are actually the tsunami amplitude, the water surface elevation measured above the ambient water level

5th PTWC reporthttps://t.co/NBnD0OQir8 pic.twitter.com/cG7PYPv9Aj

— Jason "Jay" R. Patton (@patton_cascadia) May 19, 2023

#EarthquakeReport for M7.7 #Earthquake offshore of #NewCaledonia #LoyaltyIslands

the @USGS_Quakes fault slip model shows fault dipping to the south with slip up to about 3metershttps://t.co/oV1IvPqAbp pic.twitter.com/rgoitvjkvQ

— Jason "Jay" R. Patton (@patton_cascadia) May 19, 2023

#EarthquakeReport #TsunamiReport for M7.7 #Earthquake #Tsunami offshore of #NewCaledonia #LoyaltyIslands

Maré (New Caledonia, Loyalty Islands) tide gage shows continued oscillation

max wave height (peak to trough) about 38.6 cmhttps://t.co/vv78U0QFonhttps://t.co/Ocv4yZXEAn pic.twitter.com/pmHxWbiLHK

— Jason "Jay" R. Patton (@patton_cascadia) May 19, 2023

#EarthquakeReport #TsunamiReport for M7.7 #Earthquake #Tsunami offshore of #NewCaledonia #LoyaltyIslands

for official tsunami information: https://t.co/rEduVDLBBc

these wave heights are what we call tsunami amplitudes: height of water above ambient levelhttps://t.co/xIGgD9MeFr pic.twitter.com/uD6CztlvtK

— Jason "Jay" R. Patton (@patton_cascadia) May 19, 2023

#EarthquakeReport #TsunamiReport for M7.1 #Earthquake offshore #LoyaltyIslands

Aftershock also tensional outer rise event in Australia plate

Original and ongoing threadhttps://t.co/sDW4ZAzE4jhttps://t.co/ugD9uKip91 pic.twitter.com/pTkeI8YY34

— Jason "Jay" R. Patton (@patton_cascadia) May 20, 2023

A M 7.7 earthquake just now in the ocean off the east coast of Australia. At the moment, Vanuatu, Fiji, and New Caldonia are cautioned for possible tsunami. #earthquake pic.twitter.com/YMTsCxG8RE

— Brian Olson (@mrbrianolson) May 19, 2023

Tsunami Info Stmt: M7.7 Loyalty Islands Region 1957PDT May 18: Tsunami NOT expected; CA,OR,WA,BC,and AK

#NTWC

— NWS Tsunami Alerts (@NWS_NTWC) May 19, 2023

The waveforms of the M7.7 SE of Loyalty Islands and ~400 km E of New Caledonia, arriving at our seismic network in southeast Australia ~5 min later. pic.twitter.com/Zfi9NS4Q7F

— Dr. Dee Ninis (@DeeNinis) May 19, 2023

Mw=7.7, SOUTHEAST OF LOYALTY ISLANDS (Depth: 12 km), 2023/05/19 02:57:06 UTC – Full details here: https://t.co/53ZfsFdYoe pic.twitter.com/lmwQfhgyOC

— Earthquakes (@geoscope_ipgp) May 19, 2023

Waves from the M7.7 earthquake southeast of the Loyalty Islands shown on a seismic station in Fiji. https://t.co/Tir0KZELXN pic.twitter.com/XO9Sflv6Ol

— EarthScope Consortium (@EarthScope_sci) May 19, 2023

JMA also warning of “sea level changes” along entire south / east coast of Japan from Okinawa to Hokkaido in response to the M7.8 #earthquake in the S Pacific #tsunami pic.twitter.com/5KqZPNu7Af

— James Reynolds (@EarthUncutTV) May 19, 2023

Australia on #Tsunami Watch after magnitude 7.6 #earthquake near Southeast of Loyalty Islands. Potential threat for #LordHoweIsland. Latest info here: https://t.co/Tynv3ZQpEq. pic.twitter.com/RlP5ntbfKS

— Bureau of Meteorology, Australia (@BOM_au) May 19, 2023

#EarthquakeReport #TsunamiReport for M7.7 #Earthquake #Tsunami offshore of #NewCaledonia #LoyaltyIsles@EU_Commission World Sea Level wave height observed at Mare tide gage (measured from peak to trough) is now up to 38.4cmhttps://t.co/vv78U0QFonhttps://t.co/Ocv4yZXEAn pic.twitter.com/LKCwFbWQbq

— Jason "Jay" R. Patton (@patton_cascadia) May 19, 2023

The M7.7 earthquake southeast of the Loyalty Islands occurred in a highly seismically active region. The direction of subduction changes in this region, and the Australian Plate subducts beneath the Pacific Plate across the New Hebrides Trench. pic.twitter.com/bXI7ZobSwf

— EarthScope Consortium (@EarthScope_sci) May 19, 2023

A prelim M7.7 earthquake has occurred in the Loyalty Islands region at 2:57pm FJT, southwest of Fiji. According to PTWC there is a “potential tsunami threat” to Fiji. Follow advice from local authorities as the situation is assessed. Recorded on my @raspishake. pic.twitter.com/L2srDZ86Cr

— Fiji Earthquakes & Weather (@FijiEarthquakes) May 19, 2023

NO tsunami threat to Hawai'i is expected from the 7.7 magnitude earthquake detected at 4:57 p.m. HST southeast of the Loyalty Islands. There MAY be tsunami waves affecting coasts within about 600 miles of the epicenter, possibly including Vanuatu, Fiji and New Caledonia. pic.twitter.com/Nr7EK6xWSe

— Hawaii EMA (@Hawaii_EMA) May 19, 2023

#EarthquakeReport #TsunamiReport for M7.7 #Earthquake #Tsunami offshore of #NewCaledonia #LoyaltyIslands

largest wave so far at Lenakel, Tanna, Vanuatu, but the tide gage seems to be malfunctioning at times
about 45.5 cm wave height (peak to trough)https://t.co/2yp00Srpua pic.twitter.com/yexJnYLVhO

— Jason "Jay" R. Patton (@patton_cascadia) May 19, 2023

#Earthquake (#séisme) confirmed by seismic data.⚠Preliminary info: M7.7 || 347 km SE of #Tadine (New Caledonia) || 9 min ago (local time 13:57:07). Follow the thread for the updates👇 pic.twitter.com/ASriuls86Q

— EMSC (@LastQuake) May 19, 2023

This map shows affected areas. Strong currents and surges can injure and drown people. People in or near the sea in these areas should move out of the water, off beaches and shore areas and away from harbours, marinas, rivers and estuaries. More info at https://t.co/ccVFYR8001 pic.twitter.com/klTgDFHh4C

— National Emergency Management Agency (@NZcivildefence) May 19, 2023

Two hours ago, Mw7.7 #earthquake located southeast of New Caledonia, felt in Nouméa (Mainland) and in the Loyalty islands.https://t.co/rBNyghV7WM
The biggest earthquake this year since the M7.8 of Feb. 6 in Türkiye. pic.twitter.com/dFju1n6MCx

— José R. Ribeiro (@JoseRodRibeiro) May 19, 2023

ird2023jtocoa Southeast of Loyalty Islands mb 6.9 2023/05/19 02:57:07 – Event has not yet been reviewed by a seismologist. For subsequent updates and details, please see https://t.co/ZNvz6pXLuu #earthquake #séisme #terremoto #지진 #地震 pic.twitter.com/dA59YhVLdI

— New Caledonia Seismic Observatory – RT quake alert (@NCseismicobserv) May 19, 2023

Section from today's 37.7 km deep M7.7 earthquake in the Loyalty Islands, recorded on the global @raspishake network. See: https://t.co/dlC4hZ9mNA. Uses @obspy and @matplotlib. pic.twitter.com/xnhU6tXQm9

— Mark Vanstone (@wmvanstone) May 19, 2023

#BREAKING: Tsunami warning for Fiji, Vanuatu and #NewCaledonia after 7.7 magnitude quake#earthquake
Stay Safe pic.twitter.com/x1NfIMSxFf

— kiran joshi (100% Follow Back) (@kiranjoshi235) May 19, 2023

M7.7 earthquake in the South Pacific about 6 hours ago. It was a relatively shallow, normal-mechanism earthquake (38 km depth). The quake seems to have only triggered a minor tsunami (most observations <0.2m, one 0.6 m). pic.twitter.com/8dMTRRQvrr

— Dr. Judith Hubbard (@JudithGeology) May 19, 2023

In the Earth, all 3 principal stresses are (nearly) always compressional or inward-directed. A tensional stress state is a rare condition indeed. If the biggest principal stress is vertical, then high-angle (but not vertical!) extensional normal faults are the result. pic.twitter.com/cvYar2f010

— Harold Tobin (@Harold_Tobin) May 20, 2023

The activity after the major M7.7 & M7.1 SE of #LoyaltyIslands #earthquakes as detected by the @raspishake network.

The infographic shows their area distribution with daily & magnitude data. Events in the latest 24h are circled in white.#Python @matplotlib #CitizenScience pic.twitter.com/uePZm9g2R1

— Giuseppe Petricca (@gmrpetricca) May 20, 2023

2023-05-20 M6.5 SE #LoyaltyIslands #earthquake recorded in #Scotland & #Stornoway + historical seismicity & cross section.

3rd largest event after yesterday's M7.7, clear core waves.

Dist: 16125km
Travel Time: 17m 17s
Depth: 10km#Python @raspishake @matplotlib #CitizenScience pic.twitter.com/MNRoPVa3Rp

— Giuseppe Petricca (@gmrpetricca) May 20, 2023

A few days ago there was a M7.7 earthquake in the Pacific Ocean.
Hours later, a tweet ‘predicted’ that “a strong aftershock of M6 is possible”.
An aftershock of ~M6 did occur 👀
Was this some remarkable prediction?
(Spoiler: No!)
Let’s talk about the Gutenberg-Richter Law 🤓
🧵/5 pic.twitter.com/bVJBuxuQzN

— Dr. Dee Ninis (@DeeNinis) May 21, 2023

Mw=6.0, SOUTHEAST OF LOYALTY ISLANDS (Depth: 9 km), 2023/05/23 06:41:58 UTC – Full details here: https://t.co/OfX7rMC4ss pic.twitter.com/tN09r3ggHA

— Earthquakes (@geoscope_ipgp) May 23, 2023

Tsunamis can reach to great heights on land, but the waves themselves aren’t necessarily that tall. The featured tsunami animation from last week’s magnitude 7.7 Loyalty Island earthquake can be found at @geonet pic.twitter.com/lBX6zyule8

— Adam Pascale (@SeisLOLogist) May 26, 2023

References:

Basic & General References

• Frisch, W., Meschede, M., Blakey, R., 2011. Plate Tectonics, Springer-Verlag, London, 213 pp.
• Hayes, G., 2018, Slab2 – A Comprehensive Subduction Zone Geometry Model: U.S. Geological Survey data release, https://doi.org/10.5066/F7PV6JNV.
• Holt, W. E., C. Kreemer, A. J. Haines, L. Estey, C. Meertens, G. Blewitt, and D. Lavallee (2005), Project helps constrain continental dynamics and seismic hazards, Eos Trans. AGU, 86(41), 383–387, , https://doi.org/10.1029/2005EO410002. /li>
• Jessee, M.A.N., Hamburger, M. W., Allstadt, K., Wald, D. J., Robeson, S. M., Tanyas, H., et al. (2018). A global empirical model for near-real-time assessment of seismically induced landslides. Journal of Geophysical Research: Earth Surface, 123, 1835–1859. https://doi.org/10.1029/2017JF004494
• Kreemer, C., J. Haines, W. Holt, G. Blewitt, and D. Lavallee (2000), On the determination of a global strain rate model, Geophys. J. Int., 52(10), 765–770.
• Kreemer, C., W. E. Holt, and A. J. Haines (2003), An integrated global model of present-day plate motions and plate boundary deformation, Geophys. J. Int., 154(1), 8–34, , https://doi.org/10.1046/j.1365-246X.2003.01917.x.
• Kreemer, C., G. Blewitt, E.C. Klein, 2014. A geodetic plate motion and Global Strain Rate Model in Geochemistry, Geophysics, Geosystems, v. 15, p. 3849-3889, https://doi.org/10.1002/2014GC005407.
• Meyer, B., Saltus, R., Chulliat, a., 2017. EMAG2: Earth Magnetic Anomaly Grid (2-arc-minute resolution) Version 3. National Centers for Environmental Information, NOAA. Model. https://doi.org/10.7289/V5H70CVX
• Müller, R.D., Sdrolias, M., Gaina, C. and Roest, W.R., 2008, Age spreading rates and spreading asymmetry of the world’s ocean crust in Geochemistry, Geophysics, Geosystems, 9, Q04006, https://doi.org/10.1029/2007GC001743
• Pagani,M. , J. Garcia-Pelaez, R. Gee, K. Johnson, V. Poggi, R. Styron, G. Weatherill, M. Simionato, D. Viganò, L. Danciu, D. Monelli (2018). Global Earthquake Model (GEM) Seismic Hazard Map (version 2018.1 – December 2018), DOI: 10.13117/GEM-GLOBAL-SEISMIC-HAZARD-MAP-2018.1
• Silva, V ., D Amo-Oduro, A Calderon, J Dabbeek, V Despotaki, L Martins, A Rao, M Simionato, D Viganò, C Yepes, A Acevedo, N Horspool, H Crowley, K Jaiswal, M Journeay, M Pittore, 2018. Global Earthquake Model (GEM) Seismic Risk Map (version 2018.1). https://doi.org/10.13117/GEM-GLOBAL-SEISMIC-RISK-MAP-2018.1
• Zhu, J., Baise, L. G., Thompson, E. M., 2017, An Updated Geospatial Liquefaction Model for Global Application, Bulletin of the Seismological Society of America, 107, p 1365-1385, https://doi.org/0.1785/0120160198

Specific References

• Baillard, C., W. C. Crawford, V. Ballu, M. Régnier, B. Pelletier, and E. Garaebiti (2015), Seismicity and shallow slab geometry in the central Vanuatu subduction zone, J. Geophys. Res. Solid Earth,120,5606–5623, https://doi.org/10.1002/2014JB011853
• Begg, G. and Gray, D.R., 2002. Arc dynamics and tectonic history of Fiji based on stress and kinematic analysis of dikes and faults of the Tavua Volcano, Viti Levu Island, Fiji in Tectonics, v. 21, no. 4, DOI: 10.1029/2000TC001259
• Benz, H.M., Herman, Matthew, Tarr, A.C., Furlong, K.P., Hayes, G.P., Villaseñor, Antonio, Dart, R.L., and Rhea, Susan, 2011. Seismicity of the Earth 1900–2010 eastern margin of the Australia plate: U.S. Geological Survey Open-File Report 2010–1083-I, scale 1:8,000,000.
• Bergeot, N., M. N. Bouin, M. Diament, B. Pelletier, M. Re´gnier, S. Calmant, and V. Ballu (2009), Horizontal and vertical interseismic velocity fields in the Vanuatu subduction zone from GPS measurements: Evidence for a central Vanuatu locked zone, J. Geophys. Res., 114, B06405, https://doi.org/10.1029/2007JB005249
• Cleveland, K.M., Ammon, C.J., and Lay, T., 2014. Large earthquake processes in the northern Vanuatu subduction zone in Journal of Geophysical Research: Solid Earth, v. 119, p. 8866-8883, doi:10.1002/2014JB011289.
• Craig, T.J., Copley, A., and Jackson, J., 2014. A reassessment of outer-rise seismicity and its implications for the mechanics of oceanic lithosphere in Geophyscial Journal International, v. 1974, no. 1, p. 63-89, https://doi.org/10.1093/gji/ggu013
• de Alterris, G. et al., 1993. Propagating rifts in the North Fiji Basin southwest Pacific in Geology, v. 21, p. 583-586.
• Deng, C., Jenner, F. E., Wan, B., & Li, J.-L. (2022). The influence of ridge subduction on the geochemistry of Vanuatu arc magmas. Journal of Geophysical Research: Solid Earth, 127, e2021JB022833. https://doi.org/10.1029/2021JB022833
• Hayes, G. P., D. J. Wald, and R. L. Johnson, 2012. Slab1.0: A three-dimensional model of global subduction zone geometries, J. Geophys. Res., 117, B01302, doi:10.1029/2011JB008524.
• Patriat, M., Tervor, F., Danyushevsky, L., Callot, J., Jean, M.M., Hoernle, J., Hauff, F., Maas, R., Woodhead, J.D., and Feig, S.T., 2019. Subduction initiation terranes exposed at the front of a 2 Ma volcanically-active subduction zone in EPSL, v. 508, p. 30-40, https://doi.org/10.1016/j.epsl.2018.12.011
• Richards, S., Holm., R., Barber, G., 2011. When slabs collide: A tectonic assessment of deep earthquakes in the Tonga-Vanuatu region, Geology, v. 39, pp. 787-790.

Oceanic-Oceanic Subduction Zone Figure
Music Reference (in 1900-2016 seismicity video)

• Schellart, W., Lister, G. and Jessell, M. 2002. Analogue modelling of asymmetrical back-arc extension. In: (Ed.) Wouter Schellart, and Cees W. Passchier, Analogue modelling of large-scale tectonic processes, Journal of the Virtual Explorer, Electronic Edition, ISSN 1441-8142, volume 7, paper 3, doi:10.3809/jvirtex.2002.00046
• Schellart, W.P., Lister, G.S., and Toy, V.B., 2006. A Late Cretaceous and Cenozoic reconstruction of the Southwest Pacific region: Tectonics controlled by subduction and slab rollback processes in Earth Science Reviews, v. 76, p. 191-233, http://dx.doi.org/10.1016/j.earscirev.2006.01.002
• van de Lagemaat, S. H. A., van Hinsbergen, D. J. J., Boschman, L. M., Kamp, P. J. J., & Spakman, W. (2018). Southwest Pacific absolute plate kinematic reconstruction reveals major Cenozoic Tonga-Kermadec slab dragging. Tectonics, 37, 2647–2674. https://doi.org/10.1029/2017TC004901

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I am currently taking a break following an excellent Seismological Society of America Meeting in San Juan Puerto Rico.

I presented a couple posters and one talk on the results from our USGS Powell Center meeting where we developed a basic logic tree for probabilistic tsunami hazard assessment for the Cascadia subduction zone.

Last night (my time, in Arecibo) there was an earthquake along the subduction zone, a convergent plate boundary, that forms the Kermadec trench (a deep sea trench, much like the Mariana trench).

Initially, there was one M 7.3 earthquake. I received a text message from the National Tsunami Warning Center stating that there was no tsunami risk for California, Oregon, Washington, British Columbia, and Alaska.

https://earthquake.usgs.gov/earthquakes/eventpage/us6000k6mg/executive

Shortly after that, there were then two M7.3 earthquakes. One was located east of the trench (an earthquake within the Pacific plate, much like the March 2023 M 7.3 earthquake, which was also in a similar location). The other earthquake was located west of the trench and had a depth that suggested it was a megathrust subduction zone earthquake.

Because these earthquakes happened at nearly the same time and had the same magnitude, I suspected that they were actually the same earthquake but had been automatically located in two locations (possibly due to something about the seismic waves that complicated the automatic location algorithm). In a few minutes, this was all worked out and the two earthquake pages began to show the same information, a single M 7.3 that was a subduction zone interface earthquake (an earthquake that slipped the megathrust fault).

Within a few more minutes, the magnitude was revised to be M 7.1. This is a much smaller earthquake than a M 7.3 but still quite significant. People on Raoul Island, about 75 km from the epicenter, reported strong ground shaking (intensity MMI 8, though initially reported as MMI 9).

After a few tweets, I went over to the tide gage websites that I monitor when there are subduction zone earthquakes. I often look at the UNESCO Sea Level Monitoring Facility website first. There is a map and one may click on the dots that represent most of the tide gages around the globe.

This page provides basic information about water surface elevations. One may take a quick look to see if there are excursions in the sea level data, possibly related to tsunami.

Then, when I am ready to download some data so that I may plot these data I head over to the European Commission World Sea Levels website. This is also a map interface and it takes a little more effort to learn how to operate the website to obtain the data one likes. These data are in a better format than the UNESCO site since they provide the observations, the tide prediction, and the excursion (i.e., the tsunami with the tide data removed).

I prefer to prepare my own plots so that I can control their graphical composition, these organizations create plots automatically and they are not always the best looking; I download these data, open them in excel, plot, then place them in adobe illustrator so that I can annotate them.

OK, back to the earthquake.

There was a magnitude M8.1 subduction zone earthquake in this area on 4 March 2021. Here is my poster for that earthquake, where I show that several large earthquakes happened closely in space and in time. It was phenomenal that these 3 earthquakes also generated 3 tsunami that showed up on tide gages across the south Pacific.

Yesterday’s M 7.1 happened within the area of aftershocks from the M 8.1. So, I interpret this to be an aftershock of the M8.1. (Though I could easily be convinced that it was instead simply a triggered earthquake; it also followed the 15 March 2023 M 7.0 earthquake which was directly east of yesterday’s M 7.1.

The earlier M 8.1 and yesterday’s M 7.1 earthquakes were along the subduction zone, where the Pacific plate subducts beneath the Australia plate. This subduction zone is quite active with many analogical historical earthquakes of similar magnitude in this area and also further to the north and to the south.

We may recall the 15 January 2022 Hunga Tonga eruption that generated a large trans-Pacific tsunami. Here is my report on that event. Here is a web page that I put together for the California Geological Survey where I serve the public in the Seismic Hazards Program and Tsunami Unit (actually, I cannot share that page as it does not work outside of the USA, sadly; I will add a link once I am back home).

At the bottom of this report are a series of tweets that include some additional educational material. Check out the EarthScope Consortium tweets!

Below is my interpretive poster for this earthquake

• I plot the seismicity from the past month, with diameter representing magnitude (see legend). I include earthquake epicenters from 1923-2023 with magnitudes M ≥ 7.0 in one version.
• I plot the USGS fault plane solutions (moment tensors in blue and focal mechanisms in orange), possibly in addition to some relevant historic earthquakes.
• A review of the basic base map variations and data that I use for the interpretive posters can be found on the Earthquake Reports page. I have improved these posters over time and some of this background information applies to the older posters.
• Some basic fundamentals of earthquake geology and plate tectonics can be found on the Earthquake Plate Tectonic Fundamentals page.

I include some inset figures. Some of the same figures are located in different places on the larger scale map below.

• In the upper left corner is a map that shows the major plate tectonic boundaries.
• In the lower right corner is a map that shows the ground shaking from the earthquake, with color representing intensity using the Modified Mercalli Intensity (MMI) scale. The closer to the earthquake, the stronger the ground shaking. The colors on the map represent the USGS model of ground shaking. There is one location with a report from people who posted information on the USGS Did You Feel It? part of the website for this earthquake. There are things that affect the strength of ground shaking other than distance, which is why the reported intensities are different from the modeled intensities.
• In the upper right corner is a plot that includes the 2021 M 8.1 & M 7.4 and 2023 M 7.0 earthquakes. I include the aftershocks from about one week after the M 8.1 and outline these aftershocks to show how yesterday’s M 7.1 is within this area.
• To the left of the aftershock map I include the USGS earthquake fault slip model. The colors represent the amount of slip that this fault experienced during the earthquake. We can see that they think the fault slipped up to about 1.25 meters (about 4 feet).
• To the left are tide gage plots from the tide gages on Raoul Island (shown on map). Anthony Lomax and I debated on Twitter about whether these signals were tsunami or seismic waves. We concluded that these are most likely tsunami waves because of their arrival time (seismic waves would have arrived sooner), their duration (seismic waves would not have lasted as long in time), and their amplitude & wave heights (seismic waves would have been smaller in size). Twitter is such a helpful place to discuss our observations in real time! I learn so much from my colleagues. It really is such a wonderful community that we have developed over the years!
• In the lower right center is a map from Benz et al. (2011) that shows earthquakes with circles that represent magnitude (diameter) and depth (color). Deeper = blue & shallower = red. There is a cross section (cut into the earth) profile through this seismicity (the blue line J-J’). I plot the M 7.0 as a blue star.
• To the left of the map is cross section J-J’ that shows earthquake hypocenters (3-D locations) in the region of the M 7.0 earthquake.

• Here is the map with a month’s seismicity plotted.

Tsunami

• Here I present the tide gage data from this earthquake and tsunami.
• These two gages are located on opposite sides of Raoul Island. Can you tell which is on the north side and which is on the south side? Go to the tide gage websites I link to above to see if you are correct.
• The size of the wave is similar for both of these gages (about 20 cm wave height).
• In the legend, one may learn the difference between wave height and amplitude. Wave height is the vertical distance between the peak wave and the trough of the wave. The amplitude is the height of the wave peak above the ambient water surface (the ambient tide level).

Some Relevant Discussion and Figures

• Here is the map from Timm et al., 2013.




Bathymetric map of the Tonga–Kermadec arc system. Map showing the depth of the subducted slab beneath the Tonga–Kermadec arc system. Louisville seamount ages are after Koppers et al.49 ELSC, eastern Lau-spreading centre; DSDP, Deep Sea Drilling Programme; NHT, Northern Havre Trough; OT, Osbourn Trough; VFR, Valu Fa Ridge. Arrows mark total convergence rates.

• Here is the tectonic map from Ballance et al., 1999.




Map of the Southwest Pacific Ocean showing the regional tectonic setting and location of the two dredged profiles. Depth contours in kilometres. The presently active arcs comprise New Zealand–Kermadec Ridge–Tonga Ridge, linked with Vanuatu by transforms associated with the North Fiji Basin. Colville Ridge–Lau Ridge is the remnant arc. Havre Trough–Lau Basin is the active backarc basin. Kermadec–Tonga Trench marks the site of subduction of Pacific lithosphere westward beneath Australian plate lithosphere. North and South Fiji Basins are marginal basins of late Neogene and probable Oligocene age, respectively. 5.4sK–Ar date of dredged basalt sample (Adams et al., 1994).

• Here is a great summary of the fault mechanisms for earthquakes along this plate boundary (Yu, 2013).




Large subduction-zone interplate earthquakes (large open gray stars) labeled with event date, Mw, GCMT focal mechanisms, and GPS velocity vectors (gray arrows and black triangles labeled with station name). GPS velocities are listed in Table 3. Black lines indicate the Tonga–Kermadec and Vanuatu trenches. Note that the 2009/09/29 Samoa–Tonga outer trench-slope event (Mw 8.1) triggered large interplate doublets (both of Mw 7.8; Lay et al., 2010). The Pacific plate subducts westward beneath the Australian plate along the Tonga–Kermadec trench, whereas the Australian plate subducts eastward beneath the Vanuatu arc and North Fiji basin. The opposite orientation between the Tonga–Kermadec and Vanuatu subduction systems is due to complex and broad back-arc extension in the Lau and North Fiji basins (Pelletier et al., 1998).




Regional map of moderate-sized (mb > 4:7) shallow-focus repeating earthquakes and background seismicity along the (a) Tonga–Kermadec and (b) Vanuatu (former New Hebrides) subduction zones. Shallow repeating earthquakes (black stars) and their available Global Centroid Moment Tensor (GCMT; Dziewoński et al., 1981; Ekström et al., 2003) are labeled with event date and doublet/cluster id where applicable. Colors of GCMT are used to distinguish nearby different repeaters. Source parameters for the clusters and doublets are listed in Tables 1 and 2. Background seismicity is shown as gray dots and large interplate earthquakes (moment magnitude, Mw > 7:3) since 1976 are shown as large open gray stars. Black lines indicate the trench (Bird, 2003) and slab contour at 50-km depth (Gudmundsson and Sambridge, 1998). Repeating earthquake clusters in the (a) T1 and T2 plate-interface regions in Tonga and (b) V3 plate-interface region in Vanuatu are used to study the fault-slip rate ( _d). A regional map of the Tonga–Kermadec–Vanuatu subduction zones is
shown in the inset figure, with the gray dotted box indicating the expanded region in the main figure.

• Here is a great visualization of the Kermadec Trench from Woods Hole.

Kermadec Trench from Woods Hole Oceanographic Inst. on Vimeo.

• Here is another map of the bathymetry in this region of the Kermadec trench. This was produced by Jack Cook at the Woods Hole Oceanographic Institution. The Lousiville Seamount Chain is clearly visible in this graphic.




• I put together an animation of seismicity from 1965 – 2015 Sept. 7. Here is a map that shows the entire seismicity for this period. I plot the slab contours for the subduction zone here. These were created by the USGS (Hayes et al., 2012).




• Here is the animation. Download the mp4 file here. This animation includes earthquakes with magnitudes greater than M 6.5 and this is the kml file that I used to make this animation.
• Here is the oblique view of the slab from Green (2003). Some of the following figures are for the Tonga subduction zone, the same plate boundary as Kermadec, with some slightly different attributes.




Earthquakes and subducted slabs beneath the Tonga–Fiji area. The subducting slab and detached slab are defined by the historic earthquakes in this region: the steeply dipping surface descending from the Tonga Trench marks the currently active subduction zone, and the surface lying mostly between 500 and 680 km, but rising to 300 km in the east, is a relict from an old subduction zone that descended from the fossil Vitiaz Trench. The locations of the mainshocks of the two Tongan earthquake sequences discussed by Tibi et al. are marked in yellow (2002 sequence) and orange (1986 series). Triggering mainshocks are denoted by stars; triggered mainshocks by circles. The 2002 sequence lies wholly in the currently subducting slab (and slightly extends the earthquake distribution in it),whereas the 1986 mainshock is in that slab but the triggered series is located in the detached slab,which apparently contains significant amounts of metastable olivine

• Here are figures from Richards et al. (2011) with their figure captions below in blockquote.
• The main tectonic map




bathymetry, and major tectonic element map of the study area. The Tonga and Vanuatu subduction systems are shown together with the locations of earthquake epicenters discussed herein. Earthquakes between 0 and 70 km depth have been removed for clarity. Remaining earthquakes are color-coded according to depth. Earthquakes located at 500–650 km depth beneath the North Fiji Basin are also shown. Plate motions for Vanuatu are from the U.S. Geological Survey, and for Tonga from Beavan et al. (2002) (see text for details). Dashed line indicates location of cross section shown in Figure 3. NFB—North Fiji Basin; HFZ—Hunter Fracture Zone.

• Here is the map showing the current configuration of the slabs in the region.




Map showing distribution of slab segments beneath the Tonga-Vanuatu region. West-dipping Pacifi c slab is shown in gray; northeast-dipping Australian slab is shown in red. Three detached segments of Australian slab lie below the North Fiji Basin (NFB). HFZ—Hunter Fracture Zone. Contour interval is 100 km. Detached segments of Australian plate form sub-horizontal sheets located at ~600 km depth. White dashed line shows outline of the subducted slab fragments when reconstructed from 660 km depth to the surface. When all subducted components are brought to the surface, the geometry closely approximates that of the North Fiji Basin.

• This is the cross section showing the megathrust fault configuration based on seismic tomography and seismicity.




Previous interpretation of combined P-wave tomography and seismicity from van der Hilst (1995). Earthquake hypocenters are shown in blue. The previous interpretation of slab structure is contained within the black dashed lines. Solid red lines mark the surface of the Pacifi c slab (1), the still attached subducting Australian slab (2a), and the detached segment of the Australian plate (2b). UM—upper mantle;
TZ—transition zone; LM—lower mantle.

• Here is their time step interpretation of the slabs that resulted in the second figure above.




Simplified plate tectonic reconstruction showing the progressive geometric evolution of the Vanuatu and Tonga subduction systems in plan view and in cross section. Initiation of the Vanuatu subduction system begins by 10 Ma. Initial detachment of the basal part of the Australian slab begins at ca. 5–4 Ma and then sinking and collision between the detached segment and the Pacifi c slab occur by 3–4 Ma. Initial opening of the Lau backarc also occurred at this time. Between 3 Ma and the present, both slabs have been sinking progressively to their current position. VT—Vitiaz trench; dER—d’Entrecasteaux Ridge.

New Britain | Solomon | Bougainville | New Hebrides | Tonga | Kermadec Earthquake Reports

General Overview

Earthquake Reports

• 2023.04.24 M 7.1 Kermadec
• 2023.04.02 M 7.0 Papua New Guinea
• 2023.03.16 M 7.0 Kermadec
• 2023.01.08 M 7.0 Vanuatu Islands
• 2022.11.22 M 7.0 Solomon Isles
• 2022.11.11 M 7.3 Tonga
• 2022.09.10 M 7.6 Papua New Guinea
• 2021.03.04 M 8.1 Kermadec
• 2021.02.10 M 7.7 Loyalty Islands
• 2019.06.15 M 7.2 Kermadec
• 2019.05.14 M 7.5 New Ireland
• 2019.05.06 M 7.2 Papua New Guinea
• 2018.12.05 M 7.5 New Caledonia
• 2018.10.10 M 7.0 New Britain, PNG
• 2018.09.09 M 6.9 Kermadec
• 2018.08.29 M 7.1 Loyalty Islands
• 2018.08.18 M 8.2 Fiji
• 2018.03.26 M 6.9 New Britain
• 2018.03.26 M 6.6 New Britain
• 2018.03.08 M 6.8 New Ireland
• 2018.02.25 M 7.5 Papua New Guinea
• 2018.02.26 M 7.5 Papua New Guinea Update #1
• 2017.11.19 M 7.0 Loyalty Islands Update #1
• 2017.11.07 M 6.5 Papua New Guinea
• 2017.11.04 M 6.8 Tonga
• 2017.10.31 M 6.8 Loyalty Islands
• 2017.08.27 M 6.4 N. Bismarck plate
• 2017.05.09 M 6.8 Vanuatu
• 2017.03.19 M 6.0 Solomon Islands
• 2017.03.05 M 6.5 New Britain
• 2017.01.22 M 7.9 Bougainville
• 2017.01.03 M 6.9 Fiji
• 2016.12.17 M 7.9 Bougainville
• 2016.12.08 M 7.8 Solomons
• 2016.10.17 M 6.9 New Britain
• 2016.10.15 M 6.4 South Bismarck Sea
• 2016.09.14 M 6.0 Solomon Islands
• 2016.08.31 M 6.7 New Britain
• 2016.08.12 M 7.2 New Hebrides Update #2
• 2016.08.12 M 7.2 New Hebrides Update #1
• 2016.08.12 M 7.2 New Hebrides
• 2016.04.06 M 6.9 Vanuatu Update #1
• 2016.04.03 M 6.9 Vanuatu
• 2015.03.30 M 7.5 New Britain (Update #5)
• 2015.03.30 M 7.5 New Britain (Update #4)
• 2015.03.29 M 7.5 New Britain (Update #3)
• 2015.03.29 M 7.5 New Britain (Update #2)
• 2015.03.29 M 7.5 New Britain (Update #1)
• 2015.03.29 M 7.5 New Britain
• 2015.11.18 M 6.8 Solomon Islands
• 2015.05.24 M 6.8, 6.8, 6.9 Santa Cruz Islands
• 2015.05.05 M 7.5 New Britain

Social Media

#EarthquakeReport for at least 1 M7.3 #Earthquake along Kermadec trench

One M7.3 appears to be megathrust subduction interface earthquake maybe M8.1 aftershock

No tsunami likely in CA, OR, WA, BC, AK

Read earlier report for 8.1 https://t.co/57SWSkASPuhttps://t.co/Q6yHAqbrdR pic.twitter.com/3Qt9mqEwsB

— Jason "Jay" R. Patton (@patton_cascadia) April 24, 2023

#EarthquakeReport for M7.1 #Earthquake along the Kermadec trench north of #NewZealand south of #Fiji

report and interpretive poster#Tsunami plots from Raoul Island

read about the regional tectonics:https://t.co/FMza1rzeti pic.twitter.com/qe4kgEGrPl

— Jason "Jay" R. Patton (@patton_cascadia) April 24, 2023

Tsunami Info Stmt: M7.3 Kermadec Islands Region 1742PDT Apr 23: Tsunami NOT expected; CA,OR,WA,BC,and AK

#NTWC

— NWS Tsunami Alerts (@NWS_NTWC) April 24, 2023

#Earthquake confirmed by seismic data.⚠Preliminary info: M7.0 || 977 km NE of #Kerikeri (New Zealand) || 12 min ago (local time 12:41:52). Follow the thread for the updates👇 pic.twitter.com/ewrGObyPwb

— EMSC (@LastQuake) April 24, 2023

Mw=7.1, KERMADEC ISLANDS, NEW ZEALAND (Depth: 45 km), 2023/04/24 00:41:54 UTC – Full details here: https://t.co/rFPxkijKBP pic.twitter.com/iSHp9EU849

— Earthquakes (@geoscope_ipgp) April 24, 2023

No #tsunami threat to Australia from magnitude 7.2 #earthquake near the Kermadec Islands Region. Latest Advice at https://t.co/YzmlhRlr4V pic.twitter.com/ZQ7k8CjcPS

— Bureau of Meteorology, Australia (@BOM_au) April 24, 2023

Waves from the M7.1 Kermadec Islands earthquake shown using Station Monitor.

Use Station Monitor to see how the ground moved near you: https://t.co/Tir0KZELXN pic.twitter.com/sH1ktj0Kv4

— EarthScope Consortium (@EarthScope_sci) April 24, 2023

Seismic waves from the M7.3 Kermadec Islands earthquake are rolling under me here on the east coast of the US. These waves are far too small for people to feel but not too small to be detected by seismometers. Data from @EarthScope_sci Station Monitor. pic.twitter.com/yE1RkcWLyo

— Wendy Bohon, PhD 🌏 (@DrWendyRocks) April 24, 2023

The Kermadec Islands region experiences a very high degree of seismicity Here, the Pacific Plate subducts beneath the Australian Plate, and earthquakes increase in depth from east to west. pic.twitter.com/hCkvUMBgPg

— EarthScope Consortium (@EarthScope_sci) April 24, 2023

Good point about duration, looks like duration of long period seismic waves is only 1-2 min at (clipped) nearby seismic station at Raoul pic.twitter.com/JevcnqZjC6

— Anthony Lomax 🇪🇺🌍🇺🇦 (@ALomaxNet) April 24, 2023

Mw 7.1 earthquake near Raoul Island today. Reverse faulting at 50 km depth. Small tsunami (~20 cm peak-to-trough) recorded at Raoul Island. The earthquake was well recorded across the New Zealand seismic network. pic.twitter.com/gJfahJ6KAK

— John Ristau 🇨🇦 🇳🇿 (@SinistralSeismo) April 24, 2023

Watch the waves from the M7.1 Kermadec Islands earthquake roll across seismic stations in North America. pic.twitter.com/iERRx9v6Q2

— EarthScope Consortium (@EarthScope_sci) April 24, 2023

Recent Earthquake Teachable Moment for the M7.1 Kermadec Islands earthquake.

Teachable Moments presentations capture the opportunity to bring knowledge, insight, and critical thinking to the classroom following a newsworthy earthquake.https://t.co/Ltmp5G5EBu pic.twitter.com/gzHYlaCCX9

— EarthScope Consortium (@EarthScope_sci) April 24, 2023

1/3 – 2023-04-24 M7.1 #Kermadec #earthquake recorded in #Scotland & #Stornoway + historical seismicity & cross section.

Core waves clearly detected by all stations in the region.

Dist.: 16868km
Travel Time: 17m 42s
Depth: 49km#Python @raspishake @matplotlib #CitizenScience pic.twitter.com/eZvZEg03OJ

— Giuseppe Petricca (@gmrpetricca) April 24, 2023

You can see the seismic action northeast of NZ, around the Kermadec Islands.

The brown (🟤) colouring indicates the strongest activity. https://t.co/97AgBb6gz8 pic.twitter.com/7GTHcViRmh

— NIWA Weather (@NiwaWeather) April 24, 2023

Section from a M7.1 earthquake in the Kermadec Islands, New Zealand at 2023-04-24 00:41:56UTC recorded on the global @raspishake network. See: https://t.co/75dBE7ppyG…. Uses @obspy & @matplotlib. PcP are reflections from the outer core, PKIKP pass through the inner core. pic.twitter.com/YgppoTV4xD

— Mark Vanstone (@wmvanstone) April 24, 2023

M7.1 earthquake from the Kermadec Islands, New Zealand at 2023-04-24 00:41:56UTC recorded 17 670 km away on the @raspishake and @BGSseismology networks in SW England and Brittany, France. See: https://t.co/75dBE7ppyG. Uses @obspy, @matplotlib & folium libraries. pic.twitter.com/wI3GUfIhnd

— Mark Vanstone (@wmvanstone) April 24, 2023

References:

Basic & General References

• Frisch, W., Meschede, M., Blakey, R., 2011. Plate Tectonics, Springer-Verlag, London, 213 pp.
• Hayes, G., 2018, Slab2 – A Comprehensive Subduction Zone Geometry Model: U.S. Geological Survey data release, https://doi.org/10.5066/F7PV6JNV.
• Holt, W. E., C. Kreemer, A. J. Haines, L. Estey, C. Meertens, G. Blewitt, and D. Lavallee (2005), Project helps constrain continental dynamics and seismic hazards, Eos Trans. AGU, 86(41), 383–387, , https://doi.org/10.1029/2005EO410002. /li>
• Jessee, M.A.N., Hamburger, M. W., Allstadt, K., Wald, D. J., Robeson, S. M., Tanyas, H., et al. (2018). A global empirical model for near-real-time assessment of seismically induced landslides. Journal of Geophysical Research: Earth Surface, 123, 1835–1859. https://doi.org/10.1029/2017JF004494
• Kreemer, C., J. Haines, W. Holt, G. Blewitt, and D. Lavallee (2000), On the determination of a global strain rate model, Geophys. J. Int., 52(10), 765–770.
• Kreemer, C., W. E. Holt, and A. J. Haines (2003), An integrated global model of present-day plate motions and plate boundary deformation, Geophys. J. Int., 154(1), 8–34, , https://doi.org/10.1046/j.1365-246X.2003.01917.x.
• Kreemer, C., G. Blewitt, E.C. Klein, 2014. A geodetic plate motion and Global Strain Rate Model in Geochemistry, Geophysics, Geosystems, v. 15, p. 3849-3889, https://doi.org/10.1002/2014GC005407.
• Meyer, B., Saltus, R., Chulliat, a., 2017. EMAG2: Earth Magnetic Anomaly Grid (2-arc-minute resolution) Version 3. National Centers for Environmental Information, NOAA. Model. https://doi.org/10.7289/V5H70CVX
• Müller, R.D., Sdrolias, M., Gaina, C. and Roest, W.R., 2008, Age spreading rates and spreading asymmetry of the world’s ocean crust in Geochemistry, Geophysics, Geosystems, 9, Q04006, https://doi.org/10.1029/2007GC001743
• Pagani,M. , J. Garcia-Pelaez, R. Gee, K. Johnson, V. Poggi, R. Styron, G. Weatherill, M. Simionato, D. Viganò, L. Danciu, D. Monelli (2018). Global Earthquake Model (GEM) Seismic Hazard Map (version 2018.1 – December 2018), DOI: 10.13117/GEM-GLOBAL-SEISMIC-HAZARD-MAP-2018.1
• Silva, V ., D Amo-Oduro, A Calderon, J Dabbeek, V Despotaki, L Martins, A Rao, M Simionato, D Viganò, C Yepes, A Acevedo, N Horspool, H Crowley, K Jaiswal, M Journeay, M Pittore, 2018. Global Earthquake Model (GEM) Seismic Risk Map (version 2018.1). https://doi.org/10.13117/GEM-GLOBAL-SEISMIC-RISK-MAP-2018.1
• Zhu, J., Baise, L. G., Thompson, E. M., 2017, An Updated Geospatial Liquefaction Model for Global Application, Bulletin of the Seismological Society of America, 107, p 1365-1385, https://doi.org/0.1785/0120160198

Specific References

• Richards, S., Holm, R., and Barber, G., 2011. Skip Nav Destination When slabs collide: A tectonic assessment of deep earthquakes in the Tonga-Vanuatu region in Geology, c. 39, no. 8, p. 787-790, https://doi.org/10.1130/G31937.1
• Timm, C., Bassett, D., Graham, I. et al. Louisville seamount subduction and its implication on mantle flow beneath the central Tonga–Kermadec arc. Nat Commun 4, 1720 (2013). https://doi.org/10.1038/ncomms2702

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This morning (my time) I received a notification from the National Tsunami Warning Center, the organization responsible for generating notifications for my locality (California).

There was a magnitude M 7.0 earthquake in Papua New Guinea.

https://earthquake.usgs.gov/earthquakes/eventpage/at00rsi26z/executive

This earthquake was almost intermediate depth (about 63 km), not on a tsunamigenic fault, and far inland (so likely no tsunami).

There was an event last September just to the east. Here is the earthquake report for that event.

The USGS includes many products on their earthquake pages. We can see from their ground failure products that this earthquake likely generated significant liquefaction. I show this on the interpretive poster and include a write up about ground failure generated by earthquakes below.

Something that influences the liquefaction and landslide modeling is the topography. The M 7.0 earthquake happened in an area that is mostly low lying Earth adjacent to the Sepik River system. The ground is probably highly saturated with water.

Also, there is little steep topography in the area, which probably contributes to the low chance for landslides in the USGS model for earthquake triggered landslides.

As always, we hope that there was not much suffering from this earthquake. The shaking intensity was high, so it must have been quite terrifying. The region does not have a high population density, so the USGS PAGER alert estimate reflects this. There were about 133,000 people who may have been exposed to intensity MMI 7 and 333,000 exposed to MMI 6.

Below is my interpretive poster for this earthquake

• I plot the seismicity from the past 3 months, with diameter representing magnitude (see legend). I include earthquake epicenters from 1923-2023 with magnitudes M ≥ 0.0 in one version.
• I plot the USGS fault plane solutions (moment tensors in blue and focal mechanisms in orange), possibly in addition to some relevant historic earthquakes.
• A review of the basic base map variations and data that I use for the interpretive posters can be found on the Earthquake Reports page. I have improved these posters over time and some of this background information applies to the older posters.
• Some basic fundamentals of earthquake geology and plate tectonics can be found on the Earthquake Plate Tectonic Fundamentals page.

I include some inset figures. Some of the same figures are located in different places on the larger scale map below.

• In the upper right corner is a map showing the plate tectonic boundaries (from the GEM) and seismicity from the past century (from the USGS).
• In the lower right corner is a map that shows the earthquake intensity using the modified Mercalli intensity scale. Earthquake intensity is a measure of how strongly the Earth shakes during an earthquake, so gets smaller the further away one is from the earthquake epicenter. The map colors represent a model of what the intensity may be. The USGS has a system called “Did You Feel It?” (DYFI) where people enter their observations from the earthquake and the USGS calculates what the intensity was for that person. The dots with yellow labels show what people actually felt in those different locations.
• In the upper left corner are two maps showing the probability of earthquake triggered landslides and possibility of earthquake induced liquefaction. I will describe these phenomena below.
• In the lower left center is a figure from Baldwin et al. (2012). This figure shows a series of cross sections along this convergent plate boundary from the Solomon Islands in the east to Papua New Guinea in the west. Cross section ‘D’ is the most representative for the earthquakes today. I present the map and this figure again below, with their original captions. Above the map is cross section D-D’ that shows the PFTB to the south of today’s earthquake. I placed the yellow star marking today’s M 7.0 below the cross section. The faults are actually quite complex, so this schematic illustration may not be a perfect representation of the faults here.
• In the bottom center is a profile showing the GPS velocities across the two main fault systems that profile A-A’ crosses (also shown on map). The M 7.0 is somewhere between these two fault systems (possibly along a fault that leads up to the Fold and Thrust Belt(?).

• Here is the map with 3 month’s seismicity plotted.

Shaking Intensity

• Here is a figure that shows a more detailed comparison between the modeled intensity and the reported intensity. Both data use the same color scale, the Modified Mercalli Intensity Scale (MMI). More about this can be found here. The colors and contours on the map are results from the USGS modeled intensity. The DYFI data are plotted as colored dots (color = MMI, diameter = number of reports).
• In the upper panel is the USGS Did You Feel It reports map, showing reports as colored dots using the MMI color scale. Underlain on this map are colored areas showing the USGS modeled estimate for shaking intensity (MMI scale).
• In the lower panel is a plot showing MMI intensity (vertical axis) relative to distance from the earthquake (horizontal axis). The models are represented by the green and orange lines. The DYFI data are plotted as light blue dots. The mean and median (different types of “average”) are plotted as orange and purple dots. Note how well the reports fit the green line (the model that represents how MMI works based on quakes in California).
• Below the lower plot is the USGS MMI Intensity scale, which lists the level of damage for each level of intensity, along with approximate measures of how strongly the ground shakes at these intensities, showing levels in acceleration (Peak Ground Acceleration, PGA) and velocity (Peak Ground Velocity, PGV).

Some Relevant Discussion and Figures

• Here is the Holm et al. (2016) figure.




Topography, bathymetry and regional tectonic setting of New Guinea and Solomon Islands. Arrows indicate rate and direction of plate motion of the Australian and Pacific plates (MORVEL, DeMets et al., 2010); Mamberamo thrust belt, Indonesia (MTB); North Fiji Basin (NFB)

• These maps from Holm et al. (2016) show the tectonic plate boundaries and plates/microplates.
• The lower panel includes symbology for the magmatic centers associated with the different arcs analyzed in their study.







Tectonic setting of Papua New Guinea and Solomon Islands. a) Regional plate boundaries and tectonic elements. Light grey shading illustrates bathymetry b2000mbelow sea level indicative of continental or arc crust, and oceanic plateaus; 1000mdepth contour is also shown. Adelbert Terrane (AT); Bismarck Sea fault (BSF); Bundi fault zone (BFZ); Feni Deep (FD); Finisterre Terrane (FT); Gazelle Peninsula (GP); Kia-Kaipito-Korigole fault zone (KKKF); Lagaip fault zone (LFZ); Mamberamo thrust belt (MTB); Manus Island (MI); New Britain (NB); New Ireland (NI); North Sepik arc (NSA); Ramu-Markham fault (RMF); Weitin Fault (WF);West Bismarck fault (WBF); Willaumez-Manus Rise (WMR). b) Magmatic arcs and volcanic centers related to this study.

• The this map and cross section pair shows the Holm et al. (2016) interpretation of the oceanic crust in this region in the current position.




a) Present day tectonic features of the Papua New Guinea and Solomon Islands region as shown in plate reconstructions. Sea floor magnetic anomalies are shown for the Caroline plate (Gaina and Müller, 2007), Solomon Sea plate (Gaina and Müller, 2007) and Coral Sea (Weissel and Watts, 1979). Outline of the reconstructed Solomon Sea slab (SSP) and Vanuatu slab (VS)models are as indicated. b) Cross-sections related to the present day tectonic setting. Section locations are as indicated. Bismarck Sea fault (BSF); Feni Deep (FD); Louisiade Plateau (LP); Manus Basin (MB); New Britain trench (NBT); North Bismarck microplate (NBP); North Solomon trench (NST); Ontong Java Plateau (OJP); Ramu-Markham fault (RMF); San Cristobal trench (SCT); Solomon Sea plate (SSP); South Bismarck microplate (SBP); Trobriand trough (TT); projected Vanuatu slab (VS); West Bismarck fault (WBF); West Torres Plateau (WTP); Woodlark Basin (WB).

• Koulali et al (2015) use GPS data to resolve the kinematics of the central-eastern Papua New Guinea region. The first figure below is a map that shows the GPS velocities in this region There are two cross section profiles labeled on the map (the M 7.0 earthquake happened to the east of A-A’). Note the complicated and detailed fault mapping (the balck lines). The convergence is generally perpendicular to the PFTB in the east and more oblique to the PFTB on the western portion of this map.




The GPS velocity field and 95 per cent confidence interval ellipses with respect to the Australian Plate. Red and blue vectors are the new calculated field and black vectors are from Wallace et al. (2004). The dashed rectangle shows the area of Fig. 3. The blue dashed lines correspond to the location of profiles shown in Fig. 4. Note that the velocity scales for the red and blue vectors are different (see the lower right corner for scales). The black velocities are plotted at the same scale as the red vectors.

• Here are the two profiles. The red and blue lines plot vertical land motion (VLM) rates in mm/yr and show strain accumulates across the region. Today’s earthquake happened in the region labeled ‘Highland FTB.’ The plot shows that ~5 mm/yr of strain accumulates in this fault system.




Profiles A–A& and B–B& from Fig. 2 showing model fit to GPS observations. Red symbols and lines are the GPS observed and modelled velocities, respectively, for the profile-normal component. Blue symbols and lines correspond to the profile-parallel component. The green and pink lines corresponds to the model using the Ramu-Markham fault geometry from Wallace et al. (2004), south of Lae. Grey profiles show the projected topography. The seismicity is from the ISC catalogue for events > Mw 3.5 (1960–2011).

• This is the Cloos et al. (2005) map from the poster.
• Something that came up this week during a tsunami workshop/meeting was about the activity for each plate boundary that has a potential to generate trans-Pacific tsunami impacting the U.S. and U.S. territories.
• Over long periods of time, the plate boundaries around the world change shape. At some times, the relative plate motion between plates is localized one fault system. At other times, the active plate boundary fault is along a different fault system.
• The map below includes information about the activity of the plate boundary faults. The active convergent zones are the New Britain subduction zone, the Ramu-Markham fault zone (RMFZ), the Seram subduction zone, part of the Papuan Fold and Thrust Belt, and parts of the New Guinea subduction zone. The strike-slip zones are the Bewani-Torricelli fault zone, the Mamberamo deformation zone, the Yapen fault zone, the Sorong fault zone, and the Tarera-Aiduna fault zone.
• This map shows evidence for several different paleo-plate boundaries. Imagine how each subduction zone once had a pair of plates and those plates are still there. Even while inactive, earthquakes can occur on these faults.




Tectonic map of New Guinea, adapted from Hamilton (1979), Cooper and Taylor (1987), Dow et al. (1988), and Sapiie et al. (1999). AFTB—Aure fold and thrust belt, FTB—fold-and-thrust belt, IOB—Irian Ophiolite Belt, TFB—thrust-and-fold belt, POB—Papuan Ophiolite Belt, BTFZ—Bewani-Torricelli fault zone, MDZ—Mamberamo deformation zone, YFZ—Yapen fault zone, SFZ—Sorong fault zone, WO—Weyland overthrust. Continental basement exposures are concentrated along the southern fl ank of the Central Range: BD—Baupo Dome, MA—Mapenduma anticline, DM—Digul monocline, IDI—Idenberg Inlier, MUA—Mueller anticline, KA—Kubor anticline, LFTB—Legguru fold-and-thrust belt, RMFZ—Ramu-Markham fault zone, TAFZ—Tarera-Aiduna fault zone. The Tasman line separates continental crust that is Paleozoic and younger to the east from Precambrian to the west.

• This is the Cloos et al. (2005) cross section, showing a different interpretation of the delaminated slab.




Lithospheric-scale cross section at 2 Ma. Plate motion is now focused along the Yapen fault zone in the center of the recently extinct arc. This probably occurred because this zone of weakness had a trend that could accommodate the imposed movements as the corner of the Caroline microplate ruptured, forming the Bismarck plate, and the corner of the Australian plate ruptured, forming the Solomon microplate. The collisional delamination-generated magmatic event ends in the highlands as the lower crustal magma chamber solidifies. Upwelled asthenosphere cools and transforms into lithospheric mantle. This drives a slow regional subsidence of the highlands that will continue for tens of millions of years or until other plate-tectonic movements are initiated. Deep erosion is still concentrated on the fl anks of the mountain belt. RMB—Ruffaer Metamorphic Belt, AUS—Australian plate, PAC—Pacific plate.

• Here is the tectonic map figure from Sappie and Cloos (2004). Their work was focused on western PNG, so their interpretations are more detailed there (and perhaps less relevant for us for these eastern PNG earthquakes).




Seismotectonic interpretation of New Guinea. Tectonic features: PTFB—Papuan thrust-and-fold belt; RMFZ—Ramu-Markham fault zone; BTFZ—Bewani-Torricelli fault zone; MTFB—Mamberamo thrust-and-fold belt; SFZ—Sorong fault zone; YFZ—Yapen fault zone; RFZ—Ransiki fault zone; TAFZ—Tarera-Aiduna fault zone; WT—Waipona Trough. After Sapiie et al. (1999).

• This is the two panel figure from Holm and Richards (2013) that shows how the New Britain trench megathrust splays into three thrust faults as this fault system heads onto PNG. They plot active thrust faults as black triangles (with the triangles on the hanging wall side of the fault) and inactive thrust faults as open triangles. So, either the NG trench subduction zone extends further east than is presented in earlier work or the Bundi Fault Zone is the fault associated with this deep seismicity.




Topography, bathymetry and major tectonic elements of the study area. (a) Major tectonic boundaries of Papua New Guinea and the western Solomon Islands; CP, Caroline plate; MB, Manus Basin; NBP, North Bismarck plate; NBT, New Britain trench; NGT, New Guinea trench; NST, North Solomon trench; PFTB, Papuan Fold and Thrust Belt; PT, Pocklington trough; RMF, Ramu-Markham Fault; SBP, South Bismarck plate; SCT, San Cristobal trench; SS, Solomon Sea plate; TT, Trobriand trough; WB,Woodlark Basin; WMT,West Melanesian trench. Study area is indicated by rectangle labelled Figure 1b; the other inset rectangle highlights location for subsequent figures. Present day GPS motions of plates are indicated relative to the Australian plate (from Tregoning et al. 1998, 1999; Tregoning 2002; Wallace et al. 2004). (b) Detailed topography, bathymetry and structural elements significant to the South Bismarck region (terms not in common use are referenced); AFB, Aure Fold Belt (Davies 2012); AT, Adelbert Terrane (e.g. Wallace et al. 2004); BFZ, Bundi Fault Zone (Abbott 1995); BSSL, Bismarck Sea Seismic Lineation; CG, Cape Gloucester; FT, Finisterre Terrane; GF, Gogol Fault (Abbott 1995); GP, Gazelle Peninsula; HP, Huon Peninsula; MB, Manus Basin; NB, New Britain; NI, New Ireland; OSF, Owen Stanley Fault; RMF, Ramu-Markham Fault; SS, Solomon Sea; WMR, Willaumez-Manus Rise (Johnson et al. 1979); WT, Wonga Thrust (Abbott et al. 1994); minor strike-slip faults are shown adjacent to Huon Peninsula (Abers & McCaffrey 1994) and in east New Britain, the Gazelle Peninsula (e.g. Madsen & Lindley 1994). Circles indicate centres of Quaternary volcanism of the Bismarck arc. Filled triangles indicate active thrusting or subduction, empty triangles indicate extinct or negligible thrusting or subduction.

• This map shows plate velocities and euler poles for different blocks. I include the figure caption below as a blockquote.




Tectonic maps of the New Guinea region. (a) Seismicity, volcanoes, and plate motion vectors. Plate motion vectors relative to the Australian plate are surface velocity models based on GPS data, fault slip rates, and earthquake focal mechanisms (UNAVCO, http://jules.unavco.org/Voyager/Earth). Earthquake data are sourced from the International Seismological Center EHB Bulletin (http://www.isc.ac.uk); data represent events from January 1994 through January 2009 with constrained focal depths. Background image is generated from http://www.geomapapp.org. Abbreviations: AB, Arafura Basin; AT, Aure Trough; AyT, Ayu Trough; BA, Banda arc; BSSL, Bismarck Sea seismic lineation; BH, Bird’s Head; BT, Banda Trench; BTFZ, Bewani-Torricelli fault zone; DD, Dayman Dome; DEI, D’Entrecasteaux Islands; FP, Fly Platform; GOP, Gulf of Papua; HP, Huon peninsula; LA, Louisiade Archipelago; LFZ, Lowlands fault zone; MaT, Manus Trench; ML, Mt. Lamington; MT, Mt. Trafalgar; MuT, Mussau Trough; MV, Mt. Victory; MTB, Mamberamo thrust belt; MVF, Managalase Plateau volcanic field; NBT, New Britain Trench; NBA, New Britain arc; NF, Nubara fault; NGT, New Guinea Trench; OJP, Ontong Java Plateau; OSF, Owen Stanley fault zone; PFTB, Papuan fold-and-thrust belt; PP, Papuan peninsula; PRi, Pocklington Rise; PT, Pocklington Trough; RMF, Ramu-Markham fault; SST, South Solomons Trench; SA, Solomon arc; SFZ, Sorong fault zone; ST, Seram Trench; TFZ, Tarera-Aiduna fault zone; TJ, AUS-WDKPAC triple junction; TL, Tasman line; TT, Trobriand Trough;WD, Weber Deep;WB, Woodlark Basin;WFTB, Western (Irian) fold-and-thrust belt; WR,Woodlark Rift; WRi, Woodlark Rise; WTB, Weyland thrust; YFZ, Yapen fault zone.White box indicates the location shown in Figure 3. (b) Map of plates, microplates, and tectonic blocks and elements of the New Guinea region. Tectonic elements modified after Hill & Hall (2003). Abbreviations: ADB, Adelbert block; AOB, April ultramafics; AUS, Australian plate; BHB, Bird’s Head block; CM, Cyclops Mountains; CWB, Cendrawasih block; CAR, Caroline microplate; EMD, Ertsberg Mining District; FA, Finisterre arc; IOB, Irian ophiolite belt; KBB, Kubor & Bena blocks (including Bena Bena terrane); LFTB, Lengguru fold-and-thrust belt; MA, Mapenduma anticline; MB, Mamberamo Basin block; MO, Marum ophiolite belt; MHS, Manus hotspot; NBS, North Bismarck plate; NGH, New Guinea highlands block; NNG, Northern New Guinea block; OKT, Ok Tedi mining district; PAC, Pacific plate; PIC, Porgera intrusive complex; PSP, Philippine Sea plate; PUB, Papuan Ultramafic Belt ophiolite; SB, Sepik Basin block; SDB, Sunda block; SBS, South Bismarck plate; SIB, Solomon Islands block; WP, Wandamen peninsula; WDK, Woodlark microplate; YQ, Yeleme quarries.

• This figure incorporates cross sections and map views of various parts of the regional tectonics (Baldwin et al., 2012). These deep earthquakes are nearest the cross section D (though are much deeper than these shallow cross sections). I include the figure caption below as a blockquote.




Oblique block diagram of New Guinea from the northeast with schematic cross sections showing the present-day plate tectonic setting. Digital elevation model was generated from http://www.geomapapp.org. Oceanic crust in tectonic cross sections is shown by thick black-and-white hatched lines, with arrows indicating active subduction; thick gray-and-white hatched lines indicate uncertain former subduction. Continental crust, transitional continental crust, and arc-related crust are shown without pattern. Representative geologic cross sections across parts of slices C and D are marked with transparent red ovals and within slices B and E are shown by dotted lines. (i ) Cross section of the Papuan peninsula and D’Entrecasteaux Islands modified from Little et al. (2011), showing the obducted ophiolite belt due to collision of the Australian (AUS) plate with an arc in the Paleogene, with later Pliocene extension and exhumation to form the D’Entrecasteaux Islands. (ii ) Cross section of the Papuan peninsula after Davies & Jaques (1984) shows the Papuan ophiolite thrust over metamorphic rocks of AUS margin affinity. (iii ) Across the Papuan mainland, the cross section after Crowhurst et al. (1996) shows the obducted Marum ophiolite and complex folding and thrusting due to collision of the Melanesian arc (the Adelbert, Finisterre, and Huon blocks) in the Late Miocene to recent. (iv) Across the Bird’s Head, the cross section after Bailly et al. (2009) illustrates deformation in the Lengguru fold-and-thrust belt as a result of Late Miocene–Early Pliocene northeast-southwest shortening, followed by Late Pliocene–Quaternary extension. Abbreviations as in Figure 2, in addition to NI, New Ireland; SI, Solomon Islands; SS, Solomon Sea; (U)HP, (ultra)high-pressure.

• Here is the relevant cross section from Baldwin et al. (2012).




Across the Papuan mainland, the cross section after Crowhurst et al. (1996) shows the obducted Marum ophiolite and complex folding and thrusting due to collision of the Melanesian arc (the Adelbert, Finisterre, and Huon blocks) in the Late Miocene to recent.

• Here is map that shows the tectonics in and to the east of Papua New Guinea from Ott and Mann (2015).
• These authors use seismic reflection data and onshore geologic and GPS studies to look at the formation of the Aure-Moresby and Papuan fold and thrust belts.




Active tectonic setting of eastern Papua New Guinea showing the boundaries of the Woodlark microplate that includes previously proposed oceanic Solomon Sea plate, the Trobriand platform, and the Woodlark plate [Wallace et al., 2014]. The New Britain trench along the northern margin of the Woodlark plate is a rapidly subducting, 600 km long slab that generates a strong pull on the unsubducted Woodlark microplate [Weissel et al., 1982; Wallace et al., 2004, 2014]. Small circles around the Trobriand platform/Australia pole predict the described pattern of transpressional deformation along the Aure-Moresby fold-thrust belt and the formation of the adjacent, late Miocene to Recent Aure-Moresby foreland basin. Approximate location of the downdip limits of the subducted Solomon Sea slabs are shown by dashed lines and modified from Pegler et al. [1995], Woodhead et al. [2010], and Hayes et al. [2012]. Earthquake data are provided courtesy of the U.S. Geological Survey. Note that the tapering triangular shape of the extension in the Woodlark basin closely matches the size and shape of the thrusting observed in the Aure-Moresby fold-thrust belt and foreland basin.

Potential for Ground Failure

Luckily I updated this page because I noticed that the interpretive figure below was incorrect (it was for a different earthquake).

• Below are a series of maps that show the potential for landslides and liquefaction. These are all USGS data products.
  There are many different ways in which a landslide can be triggered. The first order relations behind slope failure (landslides) is that the “resisting” forces that are preventing slope failure (e.g. the strength of the bedrock or soil) are overcome by the “driving” forces that are pushing this land downwards (e.g. gravity). The ratio of resisting forces to driving forces is called the Factor of Safety (FOS). We can write this ratio like this:

  FOS = Resisting Force / Driving Force

• When FOS > 1, the slope is stable and when FOS < 1, the slope fails and we get a landslide. The illustration below shows these relations. Note how the slope angle α can take part in this ratio (the steeper the slope, the greater impact of the mass of the slope can contribute to driving forces). The real world is more complicated than the simplified illustration below.




• Landslide ground shaking can change the Factor of Safety in several ways that might increase the driving force or decrease the resisting force. Keefer (1984) studied a global data set of earthquake triggered landslides and found that larger earthquakes trigger larger and more numerous landslides across a larger area than do smaller earthquakes. Earthquakes can cause landslides because the seismic waves can cause the driving force to increase (the earthquake motions can “push” the land downwards), leading to a landslide. In addition, ground shaking can change the strength of these earth materials (a form of resisting force) with a process called liquefaction.
• Sediment or soil strength is based upon the ability for sediment particles to push against each other without moving. This is a combination of friction and the forces exerted between these particles. This is loosely what we call the “angle of internal friction.” Liquefaction is a process by which pore pressure increases cause water to push out against the sediment particles so that they are no longer touching.
• An analogy that some may be familiar with relates to a visit to the beach. When one is walking on the wet sand near the shoreline, the sand may hold the weight of our body generally pretty well. However, if we stop and vibrate our feet back and forth, this causes pore pressure to increase and we sink into the sand as the sand liquefies. Or, at least our feet sink into the sand.
• Below is a diagram showing how an increase in pore pressure can push against the sediment particles so that they are not touching any more. This allows the particles to move around and this is why our feet sink in the sand in the analogy above. This is also what changes the strength of earth materials such that a landslide can be triggered.




• Below is a diagram based upon a publication designed to educate the public about landslides and the processes that trigger them (USGS, 2004). Additional background information about landslide types can be found in Highland et al. (2008). There was a variety of landslide types that can be observed surrounding the earthquake region. So, this illustration can help people when they observing the landscape response to the earthquake whether they are using aerial imagery, photos in newspaper or website articles, or videos on social media. Will you be able to locate a landslide scarp or the toe of a landslide? This figure shows a rotational landslide, one where the land rotates along a curvilinear failure surface.




• Below is the liquefaction susceptibility and landslide probability map (Jessee et al., 2017; Zhu et al., 2017). Please head over to that report for more information about the USGS Ground Failure products (landslides and liquefaction). Basically, earthquakes shake the ground and this ground shaking can cause landslides.
• I use the same color scheme that the USGS uses on their website. Note how the areas that are more likely to have experienced earthquake induced liquefaction are in the valleys. Learn more about how the USGS prepares these model results here.

New Britain | Solomon | Bougainville | New Hebrides | Tonga | Kermadec Earthquake Reports

General Overview

Earthquake Reports

• 2023.04.02 M 7.0 Papua New Guinea
• 2023.03.16 M 7.0 Kermadec
• 2023.01.08 M 7.0 Vanuatu Islands
• 2022.11.22 M 7.0 Solomon Isles
• 2022.11.11 M 7.3 Tonga
• 2022.09.10 M 7.6 Papua New Guinea
• 2021.03.04 M 8.1 Kermadec
• 2021.02.10 M 7.7 Loyalty Islands
• 2019.06.15 M 7.2 Kermadec
• 2019.05.14 M 7.5 New Ireland
• 2019.05.06 M 7.2 Papua New Guinea
• 2018.12.05 M 7.5 New Caledonia
• 2018.10.10 M 7.0 New Britain, PNG
• 2018.09.09 M 6.9 Kermadec
• 2018.08.29 M 7.1 Loyalty Islands
• 2018.08.18 M 8.2 Fiji
• 2018.03.26 M 6.9 New Britain
• 2018.03.26 M 6.6 New Britain
• 2018.03.08 M 6.8 New Ireland
• 2018.02.25 M 7.5 Papua New Guinea
• 2018.02.26 M 7.5 Papua New Guinea Update #1
• 2017.11.19 M 7.0 Loyalty Islands Update #1
• 2017.11.07 M 6.5 Papua New Guinea
• 2017.11.04 M 6.8 Tonga
• 2017.10.31 M 6.8 Loyalty Islands
• 2017.08.27 M 6.4 N. Bismarck plate
• 2017.05.09 M 6.8 Vanuatu
• 2017.03.19 M 6.0 Solomon Islands
• 2017.03.05 M 6.5 New Britain
• 2017.01.22 M 7.9 Bougainville
• 2017.01.03 M 6.9 Fiji
• 2016.12.17 M 7.9 Bougainville
• 2016.12.08 M 7.8 Solomons
• 2016.10.17 M 6.9 New Britain
• 2016.10.15 M 6.4 South Bismarck Sea
• 2016.09.14 M 6.0 Solomon Islands
• 2016.08.31 M 6.7 New Britain
• 2016.08.12 M 7.2 New Hebrides Update #2
• 2016.08.12 M 7.2 New Hebrides Update #1
• 2016.08.12 M 7.2 New Hebrides
• 2016.04.06 M 6.9 Vanuatu Update #1
• 2016.04.03 M 6.9 Vanuatu
• 2015.03.30 M 7.5 New Britain (Update #5)
• 2015.03.30 M 7.5 New Britain (Update #4)
• 2015.03.29 M 7.5 New Britain (Update #3)
• 2015.03.29 M 7.5 New Britain (Update #2)
• 2015.03.29 M 7.5 New Britain (Update #1)
• 2015.03.29 M 7.5 New Britain
• 2015.11.18 M 6.8 Solomon Islands
• 2015.05.24 M 6.8, 6.8, 6.9 Santa Cruz Islands
• 2015.05.05 M 7.5 New Britain

Social Media

#EarthquakeReport for M7.0 #Earthquake #Gempa in #PapuaNewGuinea

Strike-slip oblique event in one of several potential plates

Learn more abt complicated plate configuration in 2022 reporthttps://t.co/Y11LG1L4kQhttps://t.co/YYoUD6Y4Re pic.twitter.com/YZDefxU6GA

— Jason "Jay" R. Patton (@patton_cascadia) April 2, 2023

#EarthquakeReport for M 7.0 #Gempa #Earthquake in #PapuaNewGuinea

high chance for earthquake induced liquefaction along the floodplain of the Sepik River

see updated poster & read the Earthquake Report for this earthquake: https://t.co/q6snAD90D4 pic.twitter.com/4FWiJLbVv7

— Jason "Jay" R. Patton (@patton_cascadia) April 2, 2023

Mw=7.2, NEW GUINEA, PAPUA NEW GUINEA (Depth: 38 km), 2023/04/02 18:04:10 UTC – Full details here: https://t.co/2fyPxMfrBX pic.twitter.com/mKPZRxWN8L

— Earthquakes (@geoscope_ipgp) April 2, 2023

Prelim M 7.0 earthquake in Papua New Guinea. Lots of liquefaction is expected over an extensive area. Not sure how that will affect destruction or fatalities. #earthquake pic.twitter.com/37nVo6uIQ9

— Brian Olson (@mrbrianolson) April 2, 2023

Seismic shaking from the M7.0 Papua New Guinea earthquake as seen on a seismometer 720 km away. Data from @EarthScope_sci Station Monitor app. https://t.co/ZIY1tPTyqg pic.twitter.com/OpfoTvs7mI

— Wendy Bohon, PhD 🌏 (@DrWendyRocks) April 2, 2023

Just 20 minutes ago, M7.1 #earthquake near Ambuti, Papua New Guinea, not far from the epicenter of the July 16 1980 Mw7.3 earthquake.
Depth was 73 km, but landslides are always to fear…https://t.co/faDg8iiavF pic.twitter.com/EcHpOip5aW

— José R. Ribeiro (@JoseRodRibeiro) April 2, 2023

2023-04-02 M7.0 #PNG #earthquake recorded in #Scotland & #Stornoway + historical seismicity & cross section.

In the middle of the shadow zone, core waves well seen by all stations.

Dist: 13459km
Travel Time: 15m 19s
Depth: 62km#Python @raspishake @matplotlib #CitizenScience pic.twitter.com/akbkiEZWNa

— Giuseppe Petricca (@gmrpetricca) April 2, 2023

A M7 earthquake occurred an hour ago in Papua New Guinea. Here, the Australian Plate is colliding with the Pacific Plate, and … it's complicated, and extremely seismic.

1/ https://t.co/RLgoh6GHBH pic.twitter.com/mUFTWnpSO8

— Dr. Judith Hubbard (@JudithGeology) April 2, 2023

Preliminary M7.3 #Earthquake
ID: #rs2023gmlahs
New Guinea, Papua New Guinea
2023-04-02 18:04 UTC@raspishake #QuakeView

– Learn more about us at https://t.co/ojzht2DDAL

– EVENT: https://t.co/mqZvq8Q35O pic.twitter.com/DawcKV0u0Q

— Raspberry Shake Earthquake Channel (@raspishakEQ) April 2, 2023

Major ~M7, intermediate depth, mostly lateral slip #earthquake in northern #PapuaNewGuinea along Australian-Pacific plates 10cm/y convergence zone. Moderate surface shaking with limited societal impact. Some landslide potential.#geohazards https://t.co/S1cErfcnTN pic.twitter.com/lyyb4Ddbop

— 🌎 Prof Ben van der Pluijm ⚒️ (@vdpluijm) April 2, 2023

62.6Km deep, M7 earthquake in Papua New Guinea at 2023-04-02 18:04:11UTC recorded on the @raspishake and @BGSseismology networks in SW England and Brittany 14116km away, in the core shadow zone. See: https://t.co/EBWY5YqTIc. Uses @obspy, @matplotlib & folium libraries. pic.twitter.com/VIqO6xMQZR

— Mark Vanstone (@wmvanstone) April 2, 2023

Section from today's 62.6km deep, M7 earthquake in Papua New Guinea at 2023-04-02 18:04:11UTC recorded on the @raspishake network, with very clear PKiKP responses and good coverage in the core shadow zone, 104 to 140°. See: https://t.co/EBWY5YqTIc…. Uses @obspy & @matplotlib. pic.twitter.com/QwyXt2aGfw

— Mark Vanstone (@wmvanstone) April 2, 2023

Watch the earthquake waves from the M7.0 in Papua New Guinea sweep across seismic stations in Europe. GMV from @EarthScope_sci

Sound on 🔊 for an explanation pic.twitter.com/N0HbgerTf5

— Wendy Bohon, PhD 🌏 (@DrWendyRocks) April 2, 2023

The M7.0 earthquake in Papua New Guinea today occurred in a region of high seismicity, with complex tectonics and microplates where the Pacific Plate converges rapidly with the Australian Plate. pic.twitter.com/q3Q5LbLQoe

— EarthScope Consortium (@EarthScope_sci) April 2, 2023

Video overview on the M7.0 Papua New Guinea earthquake pic.twitter.com/2FUZba9l4e

— EarthScope Consortium (@EarthScope_sci) April 3, 2023

References:

Basic & General References

• Frisch, W., Meschede, M., Blakey, R., 2011. Plate Tectonics, Springer-Verlag, London, 213 pp.
• Hayes, G., 2018, Slab2 – A Comprehensive Subduction Zone Geometry Model: U.S. Geological Survey data release, https://doi.org/10.5066/F7PV6JNV.
• Holt, W. E., C. Kreemer, A. J. Haines, L. Estey, C. Meertens, G. Blewitt, and D. Lavallee (2005), Project helps constrain continental dynamics and seismic hazards, Eos Trans. AGU, 86(41), 383–387, , https://doi.org/10.1029/2005EO410002. /li>
• Jessee, M.A.N., Hamburger, M. W., Allstadt, K., Wald, D. J., Robeson, S. M., Tanyas, H., et al. (2018). A global empirical model for near-real-time assessment of seismically induced landslides. Journal of Geophysical Research: Earth Surface, 123, 1835–1859. https://doi.org/10.1029/2017JF004494
• Kreemer, C., J. Haines, W. Holt, G. Blewitt, and D. Lavallee (2000), On the determination of a global strain rate model, Geophys. J. Int., 52(10), 765–770.
• Kreemer, C., W. E. Holt, and A. J. Haines (2003), An integrated global model of present-day plate motions and plate boundary deformation, Geophys. J. Int., 154(1), 8–34, , https://doi.org/10.1046/j.1365-246X.2003.01917.x.
• Kreemer, C., G. Blewitt, E.C. Klein, 2014. A geodetic plate motion and Global Strain Rate Model in Geochemistry, Geophysics, Geosystems, v. 15, p. 3849-3889, https://doi.org/10.1002/2014GC005407.
• Meyer, B., Saltus, R., Chulliat, a., 2017. EMAG2: Earth Magnetic Anomaly Grid (2-arc-minute resolution) Version 3. National Centers for Environmental Information, NOAA. Model. https://doi.org/10.7289/V5H70CVX
• Müller, R.D., Sdrolias, M., Gaina, C. and Roest, W.R., 2008, Age spreading rates and spreading asymmetry of the world’s ocean crust in Geochemistry, Geophysics, Geosystems, 9, Q04006, https://doi.org/10.1029/2007GC001743
• Pagani,M. , J. Garcia-Pelaez, R. Gee, K. Johnson, V. Poggi, R. Styron, G. Weatherill, M. Simionato, D. Viganò, L. Danciu, D. Monelli (2018). Global Earthquake Model (GEM) Seismic Hazard Map (version 2018.1 – December 2018), DOI: 10.13117/GEM-GLOBAL-SEISMIC-HAZARD-MAP-2018.1
• Silva, V ., D Amo-Oduro, A Calderon, J Dabbeek, V Despotaki, L Martins, A Rao, M Simionato, D Viganò, C Yepes, A Acevedo, N Horspool, H Crowley, K Jaiswal, M Journeay, M Pittore, 2018. Global Earthquake Model (GEM) Seismic Risk Map (version 2018.1). https://doi.org/10.13117/GEM-GLOBAL-SEISMIC-RISK-MAP-2018.1
• Zhu, J., Baise, L. G., Thompson, E. M., 2017, An Updated Geospatial Liquefaction Model for Global Application, Bulletin of the Seismological Society of America, 107, p 1365-1385, https://doi.org/0.1785/0120160198

Specific References

• Abers, G. and McCaffrey, R., 1988. Active Deformation in the New Guinea Fold-and-Thrust Belt: Seismological Evidence for Strike-Slip Faulting and Basement-Involved Thrusting in JGR, v. 93, no. B11, p. 13,332-13,354
• Baldwin, S.L., Monteleone, B.D., Webb, L.E., Fitzgerald, P.G., Grove, M., and Hill, E.J., 2004. Pliocene eclogite exhumation at plate tectonic rates in eastern Papua New Guinea in Nature, v. 431, p/ 263-267, doi:10.1038/nature02846.
• Baldwin, S.L., Fitzgerald, P.G., and Webb, L.E., 2012. Tectonics of the New Guinea Region, Annu. Rev. Earth Planet. Sci., v. 40, pp. 495-520.
• Cloos, M., Sapiie, B., Quarles van Ufford, A., Weiland, R.J., Warren, P.Q., and McMahon, T.P., 2005. Collisional delamination in New Guinea: The geotectonics of subducting slab breakoff: Geological Society of America Special Paper 400, 51 p., doi: 10.1130/2005.2400.
• Dow, D.B., 1977. A Geological Synthesis of Papua New Guinea, Bureau of Mineral Resources, Geology, and Geophysics, Bulltein 201, Australian Government Publishing Sevice, Canberra, 1977, 58 pp.

..

• Hamilton, W.B., 1979. Tectonics of the Indonesian Region, USGS Professional Paper 1078.
• Holm, R. and Richards, S.W., 2013. A re-evaluation of arc-continent collision and along-arc variation in the Bismarck Sea region, Papua New Guinea in Australian Journal of Earth Sciences, v. 60, p. 605-619.
• Holm, R.J., Richards, S.W., Rosenbaum, G., and Spandler, C., 2015. Disparate Tectonic Settings for Mineralisation in an Active Arc, Eastern Papua New Guinea and the Solomon Islands in proceedings from PACRIM 2015 Congress, Hong Kong ,18-21 March, 2015, pp. 7.
• Holm, R.J., Rosenbaum, G., Richards, S.W., 2016. Post 8 Ma reconstruction of Papua New Guinea and Solomon Islands: Microplate tectonics in a convergent plate boundary setting in Eartth Science Reviews, v. 156, p. 66-81.
• Johnson, R.W., 1976, Late Cainozoic volcanism and plate tectonics at the southern margin of the Bismarck Sea, Papua New Guinea, in Johnson, R.W., ed., 1976, Volcanism in Australia: Amsterdam, Elsevier, p. 101-116
• Koulali, A., tregoning, P., McClusky, S., Stanaway, R., Wallace, L., and Lister, G., 2015. New Insights into the present-day kinematics of the central and western Papua New Guinea from GPS in GJI, v. 202, p. 993-1004, doi: 10.1093/gji/ggv200
• Ott, B., and P. Mann (2015), Late Miocene to Recent formation of the Aure-Moresby fold-thrust belt and foreland basin as a consequence of Woodlark microplate rotation, Papua New Guinea, Geochem. Geophys. Geosyst., 16, 1988–2004, http://dx.doi.org/10.1002/2014GC005668
• Sapiie, B., and Cloos, M., 2004. Strike-slip faulting in the core of the Central Range of west New Guinea: Ertsberg Mining District, Indonesia in GSA Bulletin, v. 116; no. 3/4; p. 277–293
• Tregoning, P., McQueen, H., Lambeck, K., Jackson, R. Little, T., Saunders, S., and Rosa, R., 2000. Present-day crustal motion in Papua New Guinea, Earth Planets and Space, v. 52, pp. 727-730.

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