Dr. Donald Turcotte

University of California Davis, Department of Geology

Title: Statistical Physics of Earthquakes

Earthquake hypocenters are defined in a 5D space (x,y,z,t,m[magnitude]). The rupture zones of earthquakes range from less than a centimeter to hundreds of kilometers. Over this range the frequency-size statistics are fractal (power law). Earthquakes in a tectonically active region (i.e.California) behave as a statistical noise. There is a steady energy input due to the motion of the plate (North American relative to the Pacific in California). This energy is stored as elastic deformations and is lost in brittle ruptures (earthquakes). The system is nonlinear, very high order, and chaotic.

Earthquakes are always followed by aftershock sequences. These sequences obey universal scaling laws. The rate of aftershock occurrence decays inversely with time. The largest aftershock is generally 1.2 magnitude units less than the main shock. There is evidence for a systematic time delay before an equilibrium frequency-magnitude distribution of aftershocks is established. A numerical simulation of earthquake occurrences in California is described. The statistical distribution of earthquake waiting times is shown to satisfy a Weibull distribution to a good approximation. The current risk of a great earthquake in the San Francisco region is given. An earthquake forcasting algorithm based on a principal component analysis is described. The past successes of this forecast in California and the present forecasts will be given. There is increasing evidence that an earthquake rupture behaves like a critical point. It is possible to associate the status of the region prior to the rupture with nucleation in a metastable region.

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Refreshments 3:50 p.m., Entrance of Phy/Geo Bldg. (Outdoor breezeway area)

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