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What New Madrid Shows About Intracontinental Earthquakes

UTIG Seminars

What New Madrid Shows About Intracontinental Earthquakes

Seth Stein
Department of Earth and Planetary Sciences
Northwestern University

When: Friday, February 24, 2012, 10:30 a.m. to 11:30 a.m.
Join us for coffee beginning at 10:00 a.m.
Where: Seminar Conference Room, 10100 Burnet Road, Bldg 196-ROC, Austin, Texas 78758
Host: Sean Gulick, UTIG

Click for a Live Broadcast.

image from Seth's talk

Intracontinental seismic zones have traditionally been treated like slowly deforming plate boundaries. We expect steady deformation focused in narrow zones, such that the past rates and locations shown by geology and the earthquake record would be consistent with present and future deformation and seismicity. However, GPS studies in the New Madrid seismic zone show no detectable motion, inconsistent with steady recurrence of large earthquakes and indicating that the recent cluster of large events may be ending. Data from China, Europe, and Australia reveal a similar picture: Earthquakes migrate between faults, which remain inactive for long periods and then have pulses of activity. This time- and space-variable behavior arises because in mid-continents tectonic loading is slow and stress is strongly influenced by mechanical interaction among a network of widespread faults. Slow loading also causes aftershock sequences to continue for hundreds of years, much longer than at plate boundaries. As a result, conventional seismic hazard assessment, which assumes steady behavior over 500-2500 years, can overestimate risks in regions of recent large earthquakes and underestimate them elsewhere. This issue is important for developing cost-effective mitigation strategies.