Aftershock Map for Piedmont M4.2
07/20/2007 4:42 PDT
The first figure below is a map, the second is a cross-section. The map shows the epicenters and magnitudes of the Piedmont main shock (large magenta circle), two weeks of aftershocks (smaller magenta circles), six months of subsequent seismicity (orange 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 along strike in the cross-section. The dashed ellipse approximates the rupture area of the earthquake, as inferred from the rupture directivity and the M4.2 magnitude. The larger dashed circle corresponds to the rupture area obtained by Hardebeck and Aron (written communication, 2010) through an analysis of the P-waves. We plot six months of subsequent seismicity because there was an acceleration of creep observed across the Hayward fault in Oakland and Piedmont for 12-100 days following this earthquake (Lienkaemper, written communication, 2010).
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