Group B, Poster #064, Seismology

A new look into the 2004 M6 Parkfield Earthquake sequence using an updated earthquake catalog

Miguel Neves, Zhigang Peng, Guoqing Lin, & Junle Jiang
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Poster Presentation

2022 SCEC Annual Meeting, Poster #064, SCEC Contribution #12556 VIEW PDF
We present the Parkfield Matched filter Relocated (PKD-MR) earthquake catalog, a new high-resolution catalog for the 2004 Mw 6 Parkfield earthquake sequence in Central California, spanning from November 6, 2003, to March 28, 2005. The new catalog contains 13948 earthquakes, which is about 3 times the number of events listed in the Northern California Seismic Network catalog, detected using high-quality seismic data recorded by the borehole High-Resolution Seismic Network combined with matched filter detection. Events in the new catalog are relocated using cross-correlation derived differential travel-times with the XCORLOC package and magnitudes are estimated by computing the amplitude ratio... between the detections and templates with a principal component fit.

Analysis of seismicity rate changes before the 2004 mainshock does not show clear precursory signals, although we find a change in the seismic activity in the creeping section of the San Andreas Fault (about ~25 km NW of the mainshock epicenter) in the weeks prior to the mainshock. We also observe a decrease in the b-value parameter in the Gutenberg-Richter relationship based on the b-positive estimate (van der Elst, 2021) in the creeping section in the months prior to the mainshock. However, no clear changes in the b-value and seismicity rate are found in the Parkfield section where the 2004 mainshock ruptured.

Additionally, we use the new catalog to study interactions between tidal stresses and afterslip with seismicity during the 2004 earthquake sequence. We find that seismicity before the mainshock is modulated by fortnightly tides and by semi-diurnal tides modulate only during the falling fortnightly tide. In contrast we find a significant semi-diurnal modulation of aftershocks at all periods. Preliminary results combining our PKD-MR catalog with the observations of afterslip evolution by Jiang et al. (2021) and the afterslip-driven aftershock model of Perfettini et al. (2018), show that the observed up- and down-dip and along-strike expansion of early aftershocks are well explained by afterslip evolution.