Aftershock Map for Bolinas M4.7
08/17/1999 18:06 PDT
The first figure below is a map, the second figure is a cross section. The map shows the epicenters and magnitudes of the Bolinas main shock (large magenta circle), two weeks of aftershocks (smaller magenta circles), and 10 years of background seismicity (blue circles). The red lines are mapped faults, and the colored background indicates elevation. The dashed brown lines contain the earthquakes whose hypocenters are plotted as a function of depth and distance across the strike of the fault in the cross-section. Because this earthquake occurred on a thrust fault, we chose a cross-section perpendicular to the strike of the fault. The dashed dark-blue line on the cross-section approximates the rupture extent of the earthquake, as inferred from the PGA rupture directivity and the M4.7 magnitude. The aftershock distribution agrees with the inferred northeast and downdip rupture in the earthquake, but the aftershocks are not aligned on the inferred fault plane.
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