Today's M8.9 Sendai Earthquake

Veiwers everywhere on the planet have once again witnessed the destructive power of mother earth.  As the waves recede, we will surely be witness to loss of hundreds, if not thousands of lives, and damages in excess of $100 billion.  Several things about this event are noteworthy from a risk/hazard perspective.

1.  On July 30, 2010, this author wrote a blog, which can be found on this web site, discussing the chance of earthquakes larger than magnitude 6.7, within 12 months of that date, for 4 cities in Japan.  These cities were Tokyo, Niigata, Osaka and Sendai.  Reference to those calculations shows that of the four cities, Sendai had the second-highest chance of a major earthquake within 150 miles of that city. The city with the highest chance was Tokyo.

2.  The USGS web site listing the world's largest earthquakes can be found at: http://earthquake.usgs.gov/earthquakes/world/10_largest_world.php  The occurrence of 5 earthquakes having magnitudes M>8.5 during the last 7 years is highly unusual.  While not leading to a definitive conclusion, these events may indicate the existence of strong space-time correlations.  These correlations may also be due to a coordinated shifting of the Pacific plate, the tectonic plate whose boundary is the ring of fire.  Correlations of this nature may imply that we are in a period of enhanced probability of large and great earthquakes around the ring of fire, including in California.

3.  Aftershocks of the Sendai earthquake have migrated steadily to the south, indicating an increased risk to Tokyo.  Initially, the major aftershocks were confined to the epicentral region near Sendai, but the steady southward march of the aftershocks is cause for alarm for Tokyo and surrounding regions.  Aftershock patterns are thought to indicate other regions that may be at risk from triggered activity.  For example, following the M9.1 December 26, 2004 Sumatra-Andaman earthquake, a second great earthquake occurred on March 28, 2005, with a magnitude of 8.6.  A similar pattern of one great earthquake closely followed in space and time by another great earthquake has been seen several times throughout history in the Nankai Trench off southwest Japan.