PATTERNS OF SEISMIC ACTIVITY PRECEDING LARGE EARTHQUAKES
SHAW BE, CARLSON JM, LANGER JS
JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH
97: (B1) 479-488 JAN 10 1992
Abstract:
We analyze the patterns of seismic activity which precede
large events in a mechanical model of a fault. The model generates a statistical
distribution of events similar to that observed for a single fault, with
a scaling region consistent with the Gutenberg-Richter law at small and
moderate magnitudes, and an excess of events at large magnitudes. We find
only slight variation in the scaling behavior during a long cycle. However,
we do observe systematic variations in space and time of the overall rate
of activity. In the model, the activity accelerates dramatically preceding
a large event and is usually a maximum in the neighborhood of the future
epicenter. These results we compared to California seismicity data, where
we find that activity patterns vary regionally. Looking at patterns of
activity in the San Francisco Bay Area since 1948, we find an increase
of activity on the Calaveras fault new San Jose beginning in the 1980s
which, if our model is relevant, would forecast a large earthquake in that
region. The 1989 Loma Prieta earthquake occurred on the San Andreas fault
within 30 km of the section of the Calaveras fault showing increased activity.