Source dimensions and stress drops of small earthquakes near Parkfield, California
Source dimensions and stress drops of small earthquakes near Parkfield, California
Bulletin of the Seismological Society of America (February 1984) 74 (1): 27-40
Source dimensions and stress drops have been estimated from short-period velocity-transducer seismograms. Times from the initial onset to the first zero crossing, corrected for attenuation and instrument response, have been interpreted in terms of a circular source model in which rupture expands radially outward from a point until it stops abruptly at radius a. For each earthquake, duration magnitude M (sub D) gave an estimate of seismic moment M (sub 0) , and M (sub 0) and a together gave an estimate of static stress drop. All earthquakes occur on the San Andreas Fault at a depth range of about 8 to 13 km. Source radius systemically increases with magnitude from about 70 m for events near M (sub D) 1.4 to about 600 m for an event of M (sub D) 3.9 Static stress drop ranges from about 2 to 30 bars and is not strongly correlated with magnitude. Static stress drop does appear to be spatially dependent; the earthquakes with stress drops greater than 20 bars are concentrated in a small region close to the hypocenter of the magnitude 5 1/2 1966 Parkfield earthquake.--Modified journal abstract.