About that M>8 Earthquake Near Japan (Technical)

john's picture

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. 

For the purposes of this discussion, we will assume the global average for the Gutenberg-Richter b-value, b=1.  Then for every M>8, we would expect to see 1000 M>5 earthquakes, 100 M>6 earthquakes, and 10 M>7 earthquakes.  The actual data are a reasonable approximation to the expected numbers.  What seems to be missing is the M>8 event.

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