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Monitoring velocity change over 20 years at Parkfield
  • Kurama Okubo,
  • Brent G. Delbridge,
  • Marine Denolle
Kurama Okubo
National Research Institute for Earth Science and Disaster Resilience

Corresponding Author:[email protected]

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Brent G. Delbridge
Los Alamos National Laboratory
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Marine Denolle
University of Washington
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We monitored the time history of the velocity change (dv/v) from 2002 to 2022 to investigate temporal changes in the physical state near the Parkfield Region of the San Andreas Fault throughout the interseismic period. Following the coseismic decrease in dv/v caused due to the 2003 San Simeon and the 2004 Parkfield earthquakes, the dv/v heals logarithmically and shows a net long-term increase in which the current dv/v level is equivalent to, or exceeding, the value before the 2003 San Simeon earthquake. We investigated this long-term trend by fitting the model accounting for the environmental and coseismic effects to the channel-weighted dv/v time series. We confirmed with the metrics of AIC and BIC that the additional term of either a linear trend term, or a residual healing term for the case where the healing had not been completed before the San Simeon earthquake occurred, robustly improved the fit to the data. We eventually evaluated the sensitivity of the dv/v time history to the GNSS-derived strain field around the fault. The cumulative dilatational strain spatially averaged around the seismic stations shows a slight extension, which is opposite to what would be expected for an increase in dv/v. However, the cumulative rotated axial strain shows compression in a range near the maximum contractional horizontal strain (azimuth of N35°W to N45°E), suggesting that the closing of pre-existing microcracks aligned perpendicular to the axial contractional strains would be a candidate to cause the long-term increase observed in the multiple station pairs.
17 Oct 2023Submitted to ESS Open Archive
27 Oct 2023Published in ESS Open Archive