all right, another M 6.2 aftershock in Chile

While I was writing my post about the M 7.6 aftershock, we got a M 6.2 aftershock. A M 6.2, while still large, is much smaller than a M 7.6. Each step in earthquake magnitude (e.g. from M 5 to M 6) coincides with a energy release that is 33 times larger for the larger magnitude earthquake. In other words, a M 6.0 earthquake is 3,300 times more energetic than a M 5.0 earthquake. An M 7.0 would be about 1,089% larger than a M 5.0 earthquake, or 1,089,000 more energetic. This is the USGS web page for this M 6.2 earthquake.
Here is the map with the latest aftershock plotted as a red star.


This map shows the shaking intensity (using the Modified Mercalli Intensity scale). The shaking intensity is much smaller than the other earthquakes, but still very large. Larger than the recent M 5.1 earthquake in southern California. We can here rest assured that the people in coastal northern Chile are probably not sleeping well. Lets hope that the M 8.2 and all these aftershocks, do not trigger a much larger earthquake. The larger earthquake will happen eventually. So, perhaps it is better than it happens sooner than later. At the least, if it happens now, people are the most prepared for such an earthquake and tsunami as they ever would be. People typically are most aware of any given hazard right after they have experienced that hazard. Over time, people forget and become complacent. The people in this region are most assuredly all ready and aware of the existence of earthquakes and tsunami.


Also for comparison with the PAGER loss estimate pages from some of the other earthquakes, here is the PAGER page for this earthquake:

large magnitude aftershock in northern Chile

There have been many aftershocks in the region of the 4/1/14 M 8.2 subduction zone earthquake offshore Iquique, Chile. There was a swarm of earthquakes up to M 6.7 in the weeks prior to the current main shock, here is my page about those foreshocks. Then there have been many aftershocks. These aftershocks will be used, in part, to model and define the fault zone that the mainshock probably directly influenced (the slip patch). Earlier there was a M 6.2 aftershock near the coast. This M 6.2 earthquake, while much smaller in magnitude than the mainshock, was much closer in distance to the people who felt it. Tonight there was a magnitude M 7.6 aftershock near the coastline. While I was writing this, there was another M 6.2 aftershock. Here is the USGS page for that earthquake.
This earthquake swarm began a few weeks ago with a swarm that had earthquakes as large as magnitude M 6.7. These epicenters were in the region of a M 8.8 subduction zone earthquake in northern Chile that ruptured last in 1877, just south of the rupture zone from the 1868 M 8.8 earthquake. Since those two earthquakes, this region has not had a large magnitude earthquake. Given plate convergence there, people have used GPS to measure how much they think this part of the subduction zone is “ready to go” (aka moment deficit). I include some plots of this on the main page for the M 8.2 earthquake and more figures about “moment deficits” here. We might have expected a larger magnitude earthquake, but there are reasons to expect earthquakes of any range in magnitude (we have such a short record of earthquake history, it is nearly impossible to know very well about what we really would expect). In 2001 there was an earthquake pair (M 8.4 and 7.6) in Peru that were both within the possible slip patch for the 1868 earthquake. The pre-instrumental slip patches are not well constrained.

  • Here is my main page for the M 8.2 earthquake.
  • Here is my main page for the tsunami from the M 8.2 earthquake.
  • I placed some tsunami records on this page.

Here is a map with tonight’s M 7.6 aftershock. The YELLOW EPICENTER in the southeast part of the swarm is tonight’s aftershock.


This is the moment tensor from the USGS. What type of earthquake do you think this is? Scroll down for a refresher image to help you.

This map shows the shaking intensity using the Modified Mercalli Intensity Scale.


Compare that above map with this one, for the M 8.2 earthquake.


This is the record on the HSU Department of Geology (thanks to their facebook page) seismometer. The M 8.2 is the big record in the middle and the M 7.6 aftershock is the smaller earthquake on the right. Time goes from left to right.


Here is a plot that shows how the shaking intensity attenuates (goes down, tapers off) with distance. The further from the earthquake epicenter, the less ground shaking.


This is the attenuation distance relation plot for the M 8.2 earthquake (just like the one above for the M 7.6^^^)


These are measurements of the tsunami generated by this aftershock.


This is the USGS PAGER report that is the estimate of loss, for people and their belongings/infrastructure. From the USGS, “PAGER (Prompt Assessment of Global Earthquakes for Response) is an automated system that produces content concerning the impact of significant earthquakes around the world, informing emergency responders, government and aid agencies, and the media of the scope of the potential disaster.” Here is more information about PAGER.


One may compare this loss estimate with the PAGER page from the M 8.2. The M 8.2 had a slightly higher probability for fatality and economic loss. The M8.2 is an ORANGE ALERT and the M 7.6 was a YELLOW ALERT. Both earthquakes, based on seismic data and modeling, have a large region inside the MM VI contour. The M 8.2 has a larger MM VI region, but the aftershock was closer to land.


Here is a primer for the different types of earthquake faults and moment tensor/focal mechanisms:

Tsunamis in the region of the M 8.2 northern Chile earthquake

Today we had a M 8.2 subduction zone earthquake in northern Chile. I have placed some records of this tsunami here.
Here is the National Tsunami Warning Center tusnami travel time map for this tsunami.


Here is the National Tsunami Warning Center modeled water surface elevations for this tsunami from the National Tsunami


This is the animation of tsunami model estimates of water surface elevations for this tsunami (from noaa)

Here is a video about subduction zone earthquakes and tsunamis from the USGS:

This is the tsunami as recorded in Hawaii as posted by Lori Dengler.

Here are the measured wave heights so far:
OBSERVATIONS OF TSUNAMI ACTIVITY – UPDATED

HEIGHT – OBSERVED MAX TSUNAMI HEIGHT IS THE WATER LEVEL ABOVE THE
TIDE LEVEL AT THE TIME OF MEASUREMENT.
In a different format:

LAT – LATITUDE (N-NORTH, S-SOUTH)
LON – LONGITUDE (E-EAST, W-WEST)
TIME – TIME OF THE MEASUREMENT (Z IS UTC IS GREENWICH TIME)
AMPL – TSUNAMI AMPLITUDE MEASURED RELATIVE TO NORMAL SEA LEVEL.
IT IS …NOT… CREST-TO-TROUGH WAVE HEIGHT.
VALUES ARE GIVEN IN BOTH METERS(M) AND FEET(FT).
PER – PERIOD OF TIME IN MINUTES(MIN) FROM ONE WAVE TO THE NEXT.
NOTE – DART MEASUREMENTS ARE FROM THE DEEP OCEAN AND THEY
ARE GENERALLY MUCH SMALLER THAN WOULD BE COASTAL
MEASUREMENTS AT SIMILAR LOCATIONS.
In 2001, a magnitude M 8.4 subduction zone earthquake in Peru sent out a trans Pacific tsunami. Here is a study of tsunami simulations.
Here is a NOAA simulation of the 2001 Peru tsunami.

Here is the table of recorded gage heights in 2001. The tsunami heights above and the tide gage heights below are calculated differently.

There was a large earthquake magnitude M 8.0 in 2007 in Peru also.


Here are some forecast tsunami arrival times for today’s tsunami:
ESTIMATED INITIAL TSUNAMI WAVE ARRIVAL TIMES AT FORECAST POINTS WITHIN THE WARNING AND WATCH AREAS ARE GIVEN BELOW. ACTUAL ARRIVAL TIMES MAY DIFFER AND THE INITIAL WAVE MAY NOT BE THE LARGEST. A TSUNAMI IS A SERIES OF WAVES AND THE TIME BETWEEN SUCCESSIVE WAVES CAN BE FIVE MINUTES TO ONE HOUR.

Here are some actual measured arrival times.

M 8.2 earthquake in northern Chile

Alright. Lets hope not many people are harmed as a result of this earthquake and likely large tsunami. We all know what to do. Drop, duck, cover, and hold on. Run to high ground. Stay there.
Check back here for updates throughout the night. I am posting information about the tsunami here.
Here is an earthquake that ruptures today in the region of a recent swarm of earthquakes in the northern Chile subduction zone. This is the USGS web page for this earthquake.
Here is the USGS web page for a large aftershock (M 6.2).
Here is a great animation from IRIS that shows the tectonics and seismology associated with this earthquake.


This is a great animation of the seismic waves travelling through the transportable array.


This is the early moment tensor (Mww), which shows a pure thrust/reverse slip.

Here is a map showing the region with earthquakes from the last 30 days. The largest dot is today’s great earthquake.


This map is zoomed into the region of the swarm and mainshock. The earthquakes that ruptured prior to the megathrust earthquake may be now considered generally foreshocks. The colored lines represent the depth of the subduction zone fault shown in km. The two main red depth contours are 20 and 40 km respectively.


Here is a map put together by the Belfast Telegraph.

This is a map that shows instrumental and historic earthquake rupture regions. This figure from Chlieh et al. (2011) shows the slip models (earthquake slip in meters) and earthquake slip regions for pre-seimologic (prior to seismometers) earthquakes in grey. The swarm of earthquakes from this March are in the northern region of the 1877 M 8.8 subduction zone earthquake.


Here is an estimate of ground shaking intensity, with contours offshore and the fault slip region plotted at 21:00 PST:


This is the seismograph from the HSU seismometer, thanks to HSU Department of Geology facebook page.


This map shows a large M 6.2 aftershock right near the coastline. Lets hope people are safe from all these earthquakes. There is also a M 5.5 further south.


Here is the USGS PAGER page. These plots are generated by overlaying shaking intensity with estimates of population and infrastructure. These overlays are “multiplied” to predict what number of fatalities and amount of economic losses might be (in a probabilistic way). These are just models, but do help international and national efforts that may need to be arisen. Most earthquakes that I have shown these PAGER plots for have had low exposure, but this M 8.2 earthquake has possibly affected up to or over 100 fatalities and up to a hundred to hundreds of millions of USD.


This is an interesting plot, showing the coupling ratio. 0 means that the fault is not locked, or is slipping aseismically. 1 means that the fault is completely locked. The darker the map, the higher their estimate of % locking. This is from Metois et al., 2013.


This is the fault slip model just generated by the USGS. The red star represents the hypocenter and the red squares represent regions of higher slip. Notice how the region of highest slip is not collocated with the hypocenter.


This is the source time function, which tells us how much energy is released over time. This is generated by integrating the energy amplitudes from the seismic waves generated by the earthquake. If we were to go coring in a month, we would possibly find a turbidite with two main pulses.
3

Fault Model in 3-D

Here are a couple maps that I put together to help me visualize a potential fault that may have ruptured in La Habra on 2014/03/29. This is a very quick, coarse, and precursory look. Others have better tools and will create better visualizations that may actually be quantitative. These maps are qualitative at best.
I took the USGS earthquake database (arguably, there are better ones) and plotted these epicenters. Then i created a raster surface based on an Inverse Distance Weighted relation, for the depths of these earthquakes. I did several different versions, each with varying levels of adherence to adjacent depth values. Below are two different realizations of the same fault surface.
This one uses a common elevation-topography color ramp (green is low elevation, brown mtns are topped in white for higher elevation).


Here is the moment tensor as a reminder.

This one uses a novel color ramp with multiple “maxima” in value (brightness, in the form of yellow hue). These act like contours, but are distributed across the surface (which reveals something about the slope of the surface, without an additional slope map. These yellow regions allow one to visually move across the surface to see how it changes orientation in a continuous, or discontinuous manner. An added bonus is this map could be framed as modern art (?). Though the modeled surface is pretty noisy from an analytical perspective.


There are many assumptions that could be evaluated to filter these input data better. But the big picture is interesting. It looks like this is a ne striking, nw dipping fault, though it is not planar.