• DOI:10.1126/science.1146537
• Corpus ID: 6612865

A High-Frequency Secondary Event During the 2004 Parkfield Earthquake

@article{Allmann2007AHS,
  title={A High-Frequency Secondary Event During the 2004 Parkfield Earthquake},
  author={Bettina P. Allmann and Peter M. Shearer},
  journal={Science},
  year={2007},
  volume={318},
  pages={1279 - 1283}
}

• B. Allmann, P. Shearer
• Published 23 November 2007
• Geology
• Science

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.