Poster #025, San Andreas Fault System (SAFS)
Detecting creep event propagation along the San Andreas Fault
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Poster Presentation
2020 SCEC Annual Meeting, Poster #025, SCEC Contribution #10519 VIEW PDF
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Here we seek to better constrain and understand creep events along the San Andreas by (1) identifying the events in the creepmeter record, (2) determining the along-strike length of creep events, and (3) examining the slip rate evolution during the creep event onsets.
To detect creep events, we use a cross-correlation approach. We pick a template creep event for each creepmeter which has a well-defined shape. Then we identify portions of the creep record that are similar to the template creep event. Finally, we check that these creep intervals have slip that is significantly larger than the instrumental noise. By isolating intervals with high similarity and significant slip, we successfully detect at least 99% of the creep events identified in a visual inspection.
Using identified creep events from neighbouring creepmeters XSJ, XHR and CWN, at the northern end of the creeping section, we estimate the length of creep events. Some creep events that are detected at both XHR and CWN, creepmeters located 4 km away from each other. These creep events, which represent at least 10-17% of the events at XHR, must have an along-strike length of at least 4 km. This along-strike length is a significant fraction of the along-depth extent of the seismogenic zone. It suggests that shallow creep events may play an important role in the creeping region’s slip dynamics.
Currently, we are now examining the shape of the onset of creep event. We are investigating how slip rate decays with time after the event begins: whether it decays as a power-law, as expected for velocity-strengthening friction, or as an exponential, as expected for distributed viscous shear.
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To detect creep events, we use a cross-correlation approach. We pick a template creep event for each creepmeter which has a well-defined shape. Then we identify portions of the creep record that are similar to the template creep event. Finally, we check that these creep intervals have slip that is significantly larger than the instrumental noise. By isolating intervals with high similarity and significant slip, we successfully detect at least 99% of the creep events identified in a visual inspection.
Using identified creep events from neighbouring creepmeters XSJ, XHR and CWN, at the northern end of the creeping section, we estimate the length of creep events. Some creep events that are detected at both XHR and CWN, creepmeters located 4 km away from each other. These creep events, which represent at least 10-17% of the events at XHR, must have an along-strike length of at least 4 km. This along-strike length is a significant fraction of the along-depth extent of the seismogenic zone. It suggests that shallow creep events may play an important role in the creeping region’s slip dynamics.
Currently, we are now examining the shape of the onset of creep event. We are investigating how slip rate decays with time after the event begins: whether it decays as a power-law, as expected for velocity-strengthening friction, or as an exponential, as expected for distributed viscous shear.
SHOW MORE
Citation: Gittins, D. B., & Hawthorne, J. C. (2020, 08). Detecting creep event propagation along the San Andreas Fault. Poster Presentation at 2020 SCEC Annual Meeting.
Keywords: creep, aseismic slip, creep events
