Well, we just had a Mw 6.7 earthquake along the coast of New Britain. This region has been active lately… Here is the USGS web page for this earthquake.
Here is a map showing the epicenter with Modified Mercalli Intensity contours.
Here is the moment tensor.
Based upon the PAGER alert, there is low likelihood of a large number of casualties. This was a rather deep earthquake and may contribute to this…
I have added one more polygon data set to the three main data sets that include records of historic earthquake slip patches. The three data sets now include Bilham (2004), Bettinelli et al (2006), and Berryman et al. (2009). I left the Rajendran and Rajendran (2011) data set off of this map because it is a point data set and the locations do not lie within the polygons from the other studies. While this may not be evidence alone, but the city locations plotted in the Rajendran article are also plotted incorrectly.
I have taken a couple products and combined them in google earth to help us learn about the impact of the Nepal 2015.04.25 Mw 7.8 earthquake. Here is the link to the USGS web page for this earthquake. I provide links to the different pages where I have summarized the record of historic and prehistoric earthquakes in this region, along with other background information about the regional tectonics.
First, here is a map that shows an estimate of the ground displacement based upon a model of the crust and an inversion of the USGS earthquake fault slip model. This surface displacement comes from GEO GATEWAY (you can download the kmz file too!). I have plotted the moment tensors for the three largest earthquakes. These are graphical ways of depicting the possible motion of the earthquake along two possible fault planes. These are calculated based upon seismologic observations. While focal mechanisms and moment tensors are determined differently, their graphical representation is similar. Find out more about focal mechanisms here and moment tensors here.
Second, here is a map that shows the modeled ground shaking intensity, using the Modified Mercalli Intensity Scale. These model results also utilize the USGS earthquake fault slip model.
Here is the USGS slip model. Go to their web site for more information. Basically, they create a fault plane and split it up into fault elements. Then one assigns a slip amount (e.g. in meters) and direction (i.e. rake) for the earthquake. Then, one “slips” (in computer space) the fault. The model sends out simulated seismic waves. Then one compares the simulated wave forms with the observed wave forms to see how well the slip model fits the observations. The slip model is modified to optimize the fit between the observed and simulated wave forms.
Here is the earthquake fault slip model overlain upon the map with some earthquake epicenters plotted as well.
Well, data continue to come in.
Below I plot the USGS Peak Ground Acceleration model results overlain upon the local map that I have been using to compare the current swarm of seismic activity with historic and prehistoric earthquake slip areas. This is a model based upon an earthquake slip model and Ground Motion Prediction Equations (GMPE). GMPE are empirical relations between earthquakes and recorded seismologic observations from those earthquakes, largely controlled by distance to the fault, ray path (direction and material properties), and site effects (the local geology).
When seismic waves propagate through sediment, the magnitude of the ground motions increases in comparison to when seismic waves propagate through bedrock. We can see this by looking at the PGA pattern as the 0.2-0.4 g region spans the mountains and the flatlands. Look at the how the 0.2-0.4 g region is wider (in the east-west direction) in the south (e.g. west of Rajbiraj and east of Bhairawa).
Here is the USGS Modified Mercalli Intensity Scale (MMI) map for this earthquake (based upon a model using the same earthquake slip inversion that was used to estimate PGA plotted in my map above). MMI is a measure of shaking intensity (like PGA, but based upon a subjective scale comprised of observations from people). We can also see how the flat lands shake more strongly than the mountains.
Here I present the USGS Did You Feel It map. This is more comprehensive than the one that I shared earlier as more people have reported their observations. I find it amazing that there are so many observations so close to the epicenter.
This is the latest attenuation plot that matches the above map. We can see how the ground shaking intensity attenuates (or diminishes) with distance from the earthquake hypocenter. The data from the USGS DYFI online reporting form are plotted as green dots and binned as brown dots (with +- 1 standard deviation error bars). Two GMPE models are plotted in orange and green. Note how the observations generally align with these two curves, but neither fully explains the variation.
Finally, here are two cross-section plots of geodetic motion (horizontal and vertical), denudation (lowering of the ground surface due to erosion), and seismicity (plotted with fault structures). Thanks to Grandin et al. (2012). Note the plot on the right, which passes through the region of today’s seismic activity. Today’s hypocenters would plot in the region of seismicity shown as a blue curve in the lowest panel.
I have updated a couple of these maps and include a figure from a recent presentation given by Roger Bilham at AGU (2011). Here was my original and first updated posts about this earthquake and here is my first compilation post.
Here is the regional map. I have added epicenter locations from Rajendran and Rajendran (2011). These, in some cases, do not coincide with the slip patches published by others. The Rajendran epicenter locations are probably the ones that may be incorrect. I compared where they placed the locations of cities and I found those to be largely incorrect.
Note how the region that has not ruptured since 1505 is immediately adjacent to the 2015 earthquake activity. Faults in this region possibly are experiencing an increase in stress following the earthquake. I will have to take a looksie at some analogous models (or run my own).
Here is an figure from Bilham, 2011. Note the southern terminus of the epicenters in the map below and compare this with the three proposed slip models in this cross section. Then, compare the magnitude estimates between these three different possibilities. It appears that Bilham et al. (2011) were quite cogent on their magnitude estimate.
Here is a local scaled map that shows the epicenters, the closest historic patches, and the city of Katmandu.
I have digitized some compilations of earthquake slip regions from a few papers and summarize these on the map below. The two main references are Bilham (blue; 2004) and Bettinelli et al. (orange; 2006). There are a couple of earthquakes that are differently plotted in these two publications (e.g. 1934 and 1950). This earthquake of 2015 appears to coincide with the region that slipped in 1833 and the western portion of the region that slipped in 1934. Here is my original page for this earthquake. Here is an post that I updated later in the day.
Here is a map from Bilham and Hough that shows the entire history for this convergent margin. This is more of a schematic view of these earthquake locations.
This is a space-time diagram for earthquakes along the Himalayan front (from Bilham and Wallace, 2005)
There have been trenches that led to the interpretation of the 1100 A.D. prehistoric earthquake. Here is the map from Lave et al. (2005) which shows the estimated MMI contours (ground shaking contours).
This map shows the area of the fault that seems to have slipped, with a fault length of approximately 150 km.
Here is the Global Earthquake Model map and space-time diagram (Berryman et al., 2014).
This is a cross section from the GEM report (Berryman et al., 2014). This shows Elevation, coupling coefficient, seismicity rate, temperature on the main Himalayan Thrust (MHT) HFT from Ader et al. (2012).
This shows today’s seismicity at a more local scale. The top map uses aerial imagery and the bottom map is overlain upon SRTM (Space Shuttle Topography Mission) data.
This is from a security camera and gives us an idea about the local duration of ground motions. Historic Slip patches are as in the above maps.
Here is an updated map that shows the aftershocks following the devastating earthquake in Nepal. I have tentatively plotted the locations (epicenters) of some historic earthquakes in this region. Today’s earthquake ranks among the largest and approaches the size and devastation of the 1505 earthquake, that some consider the most devastating known earthquake in the region. Here is the post I made early this morning. After class (running late), I will post more material on the historic earthquakes in this region and some links to the human stories.
Here is the PAGER. The pager last night was not yet available. This is an estimate of the casualties to people and their belongings (roads, bldgs, etc. ). This is based upon the overlay analysis of two things. First there is a database that includes information abt the spatial distribution of the population and their infrastructure. Second, there is a numerical simulation of the ground shaking intensity. Just like how risk is the overlap of hazard with population, this estimate is the overlay of theses two analyses. Note the likelihood of an extremely large number of casualties. This is quite a devastating disaster.
We just had a large earthquake in Nepal! The moment tensor shows that this is a thrust/reverse (originally it was solved as a strike slip) earthquake. I will need to do a little more investigating about this tomorrow. (I am running short on sleep and have an early flight in the morning). Here is the USGS website for this Mw 7.9 earthquake. This is still plotting as a shallow earthquake. Originally it was listed as a 7.5. This is a large earthquake, shallow, and compressional. There will possibly be many injured and many casualties from this earthquake. :-(
Here is the map that I quickly put together. I have placed the moment tensor on the map. I have posted various tutorials about moment tensors on other earthquake posts, so will leave that out on this map.
This map shows the MMI contours with MMI VIII in nearest the epicenter.
Here is the USGS intensity map. The map uses the Modified Mercalli Intensity scale, which is largely based upon the qualitative observations by people just like you and me. The map below is generated using a numerical model to estimate the amount of ground motions from an earthquake given some assumptions about the crust nearby the earthquake (or, rather, the crust for the earthquakes used in the empirical relations used to create the model). These estimates are not direct observations, so the “Did You Feel It” map is better for people to learn about what the real ground motions, or shaking intensity, was for this earthquake.
Here is the current DYFI map, which should be updated over the next day as more people submit their observations to the web site.
This is a measure of how well the model used to create the intensity map above matches the DYFI map.
This sure looks like an earthquake on the Transform Plate Boundary fault system known as the Mendocino fault. I have plotted the moment tensor for this earthquake. The shaking intensity contours are plotted. Here is the USGS web page for this Mw 5.5 earthquake.
Well, we just had a swarm of earthquakes with magnitudes near Taiwan. The USGS web pages for these earthquakes are here: M = 6.0, 6.1, and 6.4. This is a complicated tectonic region and there are many different and differing interpretations. Taiwan is at a location where a westward vergent subduction zone (Manila trench) comes from the South and an eastward vergent subduction zone comes from the north (Ryukyu trench). I am getting ready to head to class and then to Pasadena for a Seismological Society of America meeting, so I cannot fully describe the complexity right now. I will try to follow up later.
Here is a map that shows the three earthquake epicenters as they relate to these plate boundary faults.
Here is an oblique view of the plate configuration in this region. This is from Chang (2001).
Here is a great interpretation showing how the Island of Taiwan is being uplifted and exhumed. This is from Lin (2002).
Needless to say, this is an excellent map showing the complicated faulting of this region. This is from Theunissen et al. (2012).
