Inverting temporal velocity changes at SAFOD from cross-well active source seismic data using a Markov Chain Monte Carlo approach
Abstract
Monitoring of in-situ, stress-induced, seismic velocity change provides an increasingly important contribution to the study of the earthquake nucleation process. Continuous Active-Source Seismic Monitoring (CASSM) with borehole sources and sensors has proven to be a very effective tool to monitor seismic velocity and to identify its temporal variations at depth. Since June 2017, we have been operating a crosswell CASSM field experiment at the San Andreas Fault Observatory at Depth (SAFOD) where a previous CASSM experiment identified the two seismic velocity reductions approximately 10 and 2 hours before micro-earthquakes.
The ultimate goal of our experiment is to continuously monitor tectonic stress for the San Andreas Fault near seismogenic depth. Our active-source experiment makes use of two boreholes drilled at the SAFOD project site. A piezoelectric source and a three-component accelerometer have been installed in the SAFOD pilot and main holes, respectively, at about 1 km depth. A seismic pulse is generated by the piezoelectric source four times per second, and waveforms are recorded with a 48 kHz sample rate, with recordings summed for 1 to 10 minutes to capture seismic velocity changes at a high-temporal resolution. To obtain robust temporal changes in delay time from the repeated active source recordings, we employed a Markov Chain Monte Carlo approach to avoid uncertainties introduced in the selection of reference trace. We have identified a velocity reduction at the SAFOD site right after the 6 July 2019 M 7.1 Ridgecrest earthquake and other changes, which we will investigate and report in our presentation.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMS062.0017N
- Keywords:
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- 7299 General or miscellaneous;
- SEISMOLOGY