Another Great Earthquake off Sumatra: Magnitude 8.6

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A magnitude 8.6 earthquake struck west of the coast of Sumatra today at 10:46:43 UTC.  This event is the fourth event to strike the region since the M9.1 event of December 26, 2004.  It is also among the largest 17 earthquakes ever recorded. 

An important question that is being asked is, "How unusual is this?".  A variety of statistical studies have been carried out in the last year or so, with the general conclusion being that this kind of temporal correlation or clustering cannot be distinguished from random clustering.  The statistics are poor with so few events, so the studies have generally been carried out with earthquakes having magnitudes larger than M7.0.  However in the context of such large events, M7.0 would have to be considered to be a "small" event.  So then the question arises as to whether the statistics of such "small" events can be applied to these great earthquakes.

What we do know is that, of the 17 greatest earthquakes larger than M8.5 to have occurred since 1900, 7 of them occurred between 1950 and 1965, 3 of then occurred between 1922 and 1938, 6 of them occurred between 2004 and the present, with the last occurring in 1906, the year of the "smaller" San Francisco earthquake (M8).  (see the data at:  So my take on this evidence is that these great events may well be correlated in time, on a global scale. 

Which raises the question for the immediate future: what about other active seismic zones that have the capability of experiencing major earthquakes?  To answer this question, we computed our new NTW forecast in the Japan region recently.  It appears that the Izu-Bonin-Mariana trench north of the islands of Iwo-Jima and Chichi-Jima has "lit up" with increased probability of another large earthquake. 

We also found that the M9.1 great Tohoku, Japan earthquake of March 11, 2011 may have been "triggered" by a smaller M7.4 event 100 km east of Chichi-Jima on December 21, 2010.

We also found that there appears to be a large "plume" of probability along the entire IBM trench as of January, 2012, indicating heightened risk of a major or great earthquake along this region of the trench.  Should such an event occur, it could cause a tsunami that could strike southern Japan, Taiwan, Hong Kong, and other areas of southeast Asia.

Readers who have an interest in this topic can find a talk I recently gave at Chapman University in Orange County, CA, at:

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