Blogging the American Geophysical Meeting - II

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Latest word is that more than 22,000 attendees are expected at this years' meeting.  I went to some interesting talks on the March 11, 2011 M9 Tohoku, Japan earthquake this morning.  It seems that there was evidence of slow ("aseismic") slip prior to the earthquake, according to Yoshihiro Ito and colleagues from Japan.  There were two events in the years preceeding the mainshock. Both events were seen on ocean bottom pressure transducers, and on-shore volumetric strainmeters.

The first was in November 2008, and was equivalent to a M6.8 slow slip event.  The second slow slip event occurred in February 2011, had a duration of more than 1 month, and had a magnitude equivalent to a M7.0 earthquake.  These events occurred in the area of the mainshock, and seems to indicate (according to the authors) that the rupture plane can slip both in slow events that generate no waves, and in rapid "normal" slipping earthquakes that generate the seismic waves, the tsunami, and the destruction. In fact, the slow-slip events may have played an important role in the initiation of the earthquake.

On another note, the photo below is taken at the AGU donor lounge where I am sitting. The fellow in the red scarf is my old friend and colleague Bob Phinney, Professor Emeritus of Geology at Princeton University.  

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