Properties of triggered seismicity, modeling using the ETAS model 
and application for earthquake prediction

Agnes Helmstetter
UCLA


Abstract:
Observations of seismicity catalogs suggest that all earthquakes,
whatever their magnitude, can trigger other earthquakes, with a rate
that increases exponentially with the mainshock magnitude, and decays
with time according to Omori's law. The magnitude of triggered
earthquakes obeys the Gutenberg-Richter distribution, with the same
b-value as other earthquakes, independently of the size of the
triggering earthquake. The simplest model of seismicity, based on
these empirical laws, is the Epidemic Type Aftershock Sequence model
(ETAS).
We show that this simple model reproduces many properties of real
seismicity, such as the variability of the aftershocks decay law,
Bath's law, the acceleration of the seismic activity before large
earthquakes, the diffusion of aftershocks, the migration of
foreshocks, and the modification of the magnitude distribution before
large earthquakes.  This model provides a way to quantify the
importance of secondary aftershocks. We have also developed a
forecasting method based on this model, applied to Southern-California.