Fig. 1. Map of earthquake epicenters (1975-1984) relative to the trace
of the San Andreas fault (bold line) and the epicenters of the foreshock
(ML 5.1) and the main shock in 1966 (small and large stars,
respectively, near the center of the map). All epicenters were
calculated from a crustal velocity model designed specifically for the
Parkfield section of the San Andreas fault (55). Brackets along the
fault show the preparation zone and rupture zone of characteristic
Parkfield earthquakes. Epicenter clusters near the western edge (faint
line) of the San Joaquin Valley are aftershocks of the earthquakes at
Cantua Creek in 1975, at Avenal in 1976, at New Idria in 1982, and at
Coalinga in 1983. Epicenters for all earthquakes of ML 2.3 or
greater are shown, except the very many aftershocks (ML <
3) of the 1983 Coalinga earthquake, which cover the Coalinga area when
plotted.
