In the middle of the night (my time) I got a notification from the EMSC earthquake notification service. I encourage everyone to download and use this app.
There was an intermediate depth magnitude M 7.5 earthquake in Peru. The tectonics in this region of the world are dominated by the convergent plate boundary, a subduction zone formed by the convergence of the oceanic Nazca and continental South America plates.
As the Nazca plate subducts, it dips below the South America plate at different dip angles. In this region of Peru, the dip angle is shallow and we term this flat-slab subduction.
This M 7.5 earthquake occurred in the downgoing Nazca plate, so was not a subduction zone megathrust event, but a “slab” event (for being in the Nazca slab).
I prepared a much more extensive report for a M 8.0 earthquake in a nearby location that happened on 26 May 2019. Read more about the tectonics of this region in that report here.
Was this M 7.5 an aftershock of the M 8.0? Probably not, based on the USGS M 8.0 slip model. However this M 7.5 could have been triggered by changes in static coulomb stress following the M 8.0.
I don’t always have the time to write a proper Earthquake Report. However, I prepare interpretive posters for these events.
Because of this, I present Earthquake Report Lite. (but it is more than just water, like the adult beverage that claims otherwise). I will try to describe the figures included in the poster, but sometimes I will simply post the poster here.
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 1921-2021 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.
- In the upper left corner is a large scale plate tectonic map showing the major plate boundary faults.
- In the lower left center is a map showing how the Nazca slab is configured in different locations (Ramos and Folguera, 2009).
- In the left center is a cross section showing seismicity in this region (Kirby et al., 1995). The source area for this plot is designated by a dashed yellow box on the map.
- In the upper right corner is a pair of maps that show the landslide probability (left) and the liquefaction susceptibility (right) for this M 7.5 earthquake. I spend more time describing these types of data here. Read more about these maps here.
- In the lower right corner I plot the USGS modeled intensity (Modified Mercalli Intensity scale, MMI) and the USGS “Did You Feel It?” observations (labeled in yellow). Above the map is a plot showing these same data plotted relative to distance from the earthquake. Read more about what these data sets are and what they represent in the report here.
I include some inset figures.
- 2010.02.27 M 8.8 Earthquake Review
- 2021.11.28 M 7.5 Peru
- 2019.08.01 M 6.8 Chile
- 2019.06.14 M 6.4 Chile
- 2019.05.26 M 8.0 Peru
- 2019.05.12 M 6.1 Panama
- 2019.03.01 M 7.0 Peru
- 2019.02.22 M 7.5 Ecuador
- 2019.01.20 M 6.7 Chile
- 2018.08.21 M 7.3 Venezuela
- 2018.08.24 M 7.1 Peru
- 2018.04.02 M 6.8 Bolivia
- 2018.01.14 M 7.1 Peru
- 2018.01.15 M 7.1 Peru Update #1
- 2017.06.30 M 6.0 Ecuador
- 2017.04.24 M 6.9 Chile
- 2017.04.23 M 5.9 Chile
- 2016.12.25 M 7.6 Chile
- 2016.11.24 M 7.0 El Salvador
- 2016.11.04 M 6.4 Maule, Chile
- 2016.04.16 M 7.8 Ecuador
- 2016.04.16 M 7.8 Ecuador Update #1
- 2015.11.29 M 5.9 Argentina
- 2015.11.11 M 6.9 Chile
- 2015.11.24 M 7.6 Peru
- 2015.11.26 M 7.6 Peru Update
- 2015.09.16 M 8.3 Chile
- 2014.04.01 M 8.2 Chile
- 2010.02.27 M 8.8 Chile
- 1960.05.22 M 9.5 Chile
Chile | South America
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Basic & General References
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