A high-frequency secondary event during the 2004 Parkfield earthquake

Citation:
Allmann, BP, Shearer PM.  2007.  A high-frequency secondary event during the 2004 Parkfield earthquake. Science. 318:1279-1283.

Date Published:

Nov

Keywords:

california, energy, envelope inversion, japan, models, oki, radiation, san-andreas fault, slip, stress drop

Abstract:

By using seismic records of the 2004 magnitude 6.0 Parkfield earthquake, we identified a burst of high-frequency seismic radiation that occurred about 13 kilometers northwest of the hypocenter and 5 seconds after rupture initiation. We imaged this event in three dimensions by using a waveform back-projection method, as well as by timing distinct arrivals visible on many of the seismograms. The high-frequency event is located near the south edge of a large slip patch seen in most seismic and geodetic inversions, indicating that slip may have grown abruptly at this point. The time history obtained from full-waveform back projection suggests a rupture velocity of 2.5 kilometers per second. Energy estimates for the subevent, together with long-period slip inversions, indicate a lower average stress drop for the northern part of the Parkfield earthquake compared with that for the region near its hypocenter, which is in agreement with stress-drop estimates obtained from small-magnitude aftershocks.

Notes:

n/a

Website

DOI:

10.1126/science.1146537