Implications of an earthquake super-swarm for the genesis of seismicity

by Ross S. Stein
U.S. Geological Survey

3-4pm
Friday October 25, 2002
Refreshments served at 2:45pm
Munk Conference Room
Cecil and Ida M. Green Institute of Geophysics and Planetary Physics
Scripps Institution of Oceanography
University of California, San Diego
http://mahi.ucsd.edu/seminar/

Abstract

During the summer of 2000, a burst of 7,000 M>3 shocks--including five
damaging M>6 shocks--occurred 75 miles south of Tokyo. This is the most
energetic swarm recorded since 1912. Whereas most earthquakes around
the globe are followed by aftershocks that become less frequent with
time, swarms are a sustained high rate of seismicity. Swarms are common
in volcanic areas, but also occur on tectonic faults such as the San
Andreas.  Why? We offer a new explanation for the occurrence of swarms,
attributing them to a sustained increase in the rate at which the crust
is stressed. We attribute mainshock-aftershock sequences to a sudden
but permanent increase in stress, rather than a change in stressing rate.