Seismicity Migration and a Surface Creep Event in 2021 on the Calaveras Fault

Litong Huang, Susan Y. Schwartz, & Emily E. Brodsky

Published September 11, 2022, SCEC Contribution #12379, 2022 SCEC Annual Meeting Poster #155 (PDF)

Most surface creep events are thought to extend no deeper than 1-5km, but what possible relationship exists between surface creep and deeper geological processes remains unclear. Bilham et al. (SCEC poster 2021) reported a creep event on the Calaveras fault from June to August 2021 with a surface slip of more than 20 mm accompanied by along-fault migration of seismicity. To provide more detail on the relationship between earthquakes, surface creep, and potential aseismic slip at seismogenic depth, we increased the local earthquake catalog by a factor of 4 and compared its spatiotemporal behavior to the surface creep. We were able to increase the number of earthquakes in the Northern California Earthquake Catalog through the combined application of earthquake detection techniques based on template matching (EQCorrscan) and AI-based automatic earthquake phase picking (EQTransformer). After manual inspection, detected earthquakes were preliminarily located using ANTELOPE dbloc2 software followed by double-difference relocation. The improved seismicity catalog indicates that earthquakes located at seismogenic depth (between ~4-10 km) indeed migrated along the fault in a southeast direction during the creep event, but details of this migration timing do not exactly correlate with the creepmeter data. Specifically, slip at the surface begins with a very small amplitude as seismicity migrates directly below the creepmeter and increases to its maximum value about 50 days after the seismicity has passed and deepened. This may reflect a slow vertical migration of the creep event or that creep manifests differently in the shallow and deeper depth ranges.

Citation
Huang, L., Schwartz, S. Y., & Brodsky, E. E. (2022, 09). Seismicity Migration and a Surface Creep Event in 2021 on the Calaveras Fault. Poster Presentation at 2022 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)