Temperature Variations at the Base of the Seismogenic Zone throughout Southern California

Suerken C. Matsuyama, & Laurent G. Montesi

Published August 4, 2021, SCEC Contribution #11161, 2021 SCEC Annual Meeting Poster #110

Earthquakes activity stops at a depth of between 12 and 15 km on most continental fault strands, including in the San Andreas Fault System and the North Anatolian Fault. One possible explanation for this transition is that earthquakes are limited by a critical temperature that could represent the brittle-ductile transition or a transition from velocity weakening to velocity-strengthening frictional behavior. Previous studies have correlated the maximum depth of earthquake with surface heat flow to infer a critical temperature around 400°C. We take advantage here of the rich seismic dataset of Southern California and a recent community-derived temperature model of the region to reevaluate the concept of a critical temperature and examine possible variations with tectonic setting or lithology. To do so, we first determine the depth above which 95% of earthquakes occur within a 10 km radius of target locations distributed every 0.1° in southern California. For this purpose, we use the Southern California Seismic Network earthquake, separated in a two-year interval catalog from 2000 to 2020, and calculate the average value standard deviation of the 95 percentile earthquake depth over that time. Although some locations had very few earthquakes, seismicity is diffuse enough to reveal robust patterns. The temperature at the base of the seismogenic zone is then taken from the Southern California Earthquake Center’s Community Thermal Model (DOI: 10.5281/zenodo.4010834) using its online viewer and query tool. Our analysis indicates that seismicity is often limited to a temperature much smaller than expected, around 250°C, in regions of diffuse seismicity. This may be related to the lower strain rate experienced inside the lithotectonic blocks delineated by major faults. Higher temperatures are observed in the most active regions, consistent with the possible importance of strain rate. Earthquakes are surprisingly deep and therefore hot in the Salton Sea area and the southern end of the Great Valley. Thermal models may need to be revised in these regions. The apparent correlation with activity favors an explanation where the depth of earthquakes is controlled by the onset of ductile creep rather than a change in frictional properties.

Matsuyama, S. C., & Montesi, L. G. (2021, 08). Temperature Variations at the Base of the Seismogenic Zone throughout Southern California. Poster Presentation at 2021 SCEC Annual Meeting.

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Stress and Deformation Over Time (SDOT)