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To further investigate the data underlying the forecast, we defined a polygon of (lat,long) pairs around the main islands of Japan.  These (lat,long) pairs are given by: (34.3,128.2), (38.0,136.8), (45.6,141.0), (42.9,147.7), (32.0,145.5), (27.5,131.5).  These were entered into the ANSS User Interface.  We found the following for the earthquakes occurring from just after the M9.1 event on 3/11/2011 through 12/29/2012 (Note that there is no data in the catalog from 12/30/2012 through today, 1/28/2013): 911 events with M>5;   94 events  with M>6; and 6 events with M>7. 

Unfortunately it is very possible, at least according to the calculations on this web site.  We can use the earthquake viewer, found under the "Tools tab", to define a selection polygon in the Japan region (Figure 1 below).  A relatively recent addition to the viewer tool then computes the numerical probability for events M>5, M>6, M>7, and M>8 for time periods 1 month from now, 1 year from now, and 3 years from now, occurring within the defined region.  Figure 1 below shows that the probability for an M>8 earthquake is very high.

In the December 29, 2012 blog we saw that earthquake probabilities have changed dramatically in the region devastated by the March 11, 2011 earthquake and tsunami off the Tohoku coast of Japan.  It is therefore interesting to see that the chance of a M>6.5 earthquake during the next year seems to be increasing in the area of Tokyo and Chiba, Japan, even over a period as short as 2 weeks.  The screenshots below document this change. 

The figure below shows the time-dependent changes in spatial forecast contours associated with the M7.7 Prince Rupert, Canada (10/27/2012) - M7.5 Craig, Alaska (1/5/2013) earthquake sequence.  The Prince Rupert earthquake was an oblique-thrust (compressional) event, whereas the Craig earthquake was a right lateral strike (horizontal) slip event. Of concern, the forecast contours representing chance of an earthquake correspond to a higher probability down towards the southeast, nearer to Vancouver and Seattle.

An M7.5 earthquake has just occurred off southern Alaska at 8:58:16 1/5/2013 UTC (11:58:16 pm 1/4/2013 local time), just at the NW tip of the area identified in the previous blog as having undergone a rapid change in the last several days. Hypocenter depth was 9.9 km, and a tsunami warning has been issued.  More as the story develops. A screenshot from the earthquake viewer is shown below.  The mechanism for this event was right lateral strike slip (horizontal slip) so a great tsunami is probably unlikely.

As readers of this blog know, I've been following locations of several large earthquakes to document time-dependent changes in local spatial forecast contours.  Two weeks ago, we looked at the Prince Rupert, Canada area, site of the M7.7 earthquake that occurred near the Queen Charlotte Islands fault zone on 10/27/2012, causing a minor 1 meter tsunami in regions as far away as Hawaii.  Forecast probabilities for future M>6.5 events over the next year and within 50 km seem to be adjusting and changing rapidly at the moment. 

Following the M7.3 earthquake on December 7, 2012, a series of obvious changes in spatial forecast contours are occurring off the Tohoku coast of Japan.  In the near vicinity of the M7.3 event and the M9 March 11, 2011 earthquake, it appears that the probability of an event having magnitude M>6.5 has declined.  However, in adjacent regions, spatial probabilities have evidently increased.  Of particular note is the area southeast from Tokyo, where probabilties seem to be intensifying.

The M7.7 Prince Rupert, Canada earthquake occurred near the Queen Charlotte Islands fault zone on 10/27/2012, causing a minor 1 meter tsunami in regions as far away as Hawaii.  It was a somewhat unusual event, in that it was an oblique thrust-faulting or compressional earthquake.  Previous blogs documented the change in spatial forecast contours as the probabilities in the area evolved.  Below we continue to see changes in spatial probabilities, with the are north west of the epicenter seeing increases in probability.

The earthquake occurred about 263 km SW of Avalon, California (red star) with few aftershocks.  It was a normal faulting (tensional) event, not the usual strike slip event we expect in California earthquakes.  It also occurred in what we consider to be a region at low probability for a M>6.5 event as shown by the image below.  While one can never say for certain that a given event is/is not a foreshock of a larger event, the fact that it occurred in a such a low probability region would argue against viewing this event as a direct precursor to a larger event.  

On December 10, 2012, a magnitude M7.1 earthquake occurred at 16:53:09 UTC (December 11, 01:53:09 local time) in the Banda Sea, in the area where the Australian tectonic plate, the Eurasian plate, and the Philippine Sea plate converge.  As large earthquakes go, this one was not particularly significant because it occurred at a depth of about 160 km (100 miles) in a part of the plate undergoing the process of subduction.  Probably few felt it, and because of the depth, it produced no tsunami.