IGPP Seminar Series

Earthquakes, Past and Future

by David D. Jackson, Prof. of Geophysics
Dept. Earth and Space Sciences, UCLA

Abstract

Following the 1906 San Francisco Earthquake, H.F. Reid articulated the concept of “elastic rebound,” which has become the guiding principle to explain earthquake occurrence. Reid even made a prediction of sorts, suggesting a method for estimating the time of the next great San Francisco earthquake. His basic idea has since been made more explicit in the form of the characteristic earthquake hypothesis and the seismic gap model. These ideas too have been the bases of predictions of sorts, some even testable. Elastic rebound, characteristic earthquakes, and seismic gaps are essentially deterministic attempts to explain nature. But nature throws curveballs. For example, earthquakes spawn plentiful aftershocks, just where the main shock should have reduced the stress. In response, Ogata, Kagan, Knopoff, and many others have developed a much more stochastic approach, sometimes called the Epidemic Type Aftershock Sequence (ETAS) focusing on the interactions between earthquakes. After a century of increasingly more accurate data and sophisticated models, we are left with several outstanding questions: Does a large earthquake increase or decrease the probability of another one? Can earthquakes, or some features of them, be predicted? What is the relationship between faults and earthquakes? Where does stress fit into the picture? Are the deterministic and stochastic approaches compatible? Why do questions proliferate faster than answers? And of course, when will the next big one hit?
Tuesday, 13 March 2007
3853 Slichter Hall
Refreshments at 3:45 PM
Lecture at 4:00 PM