Lower Seismogenic Depth Model for Western U.S. Earthquakes

Yuehua Zeng, Mark D. Petersen, & Oliver S. Boyd

Published September 10, 2023, SCEC Contribution #13218, 2023 SCEC Annual Meeting Poster #201

We present a model of the lower seismogenic depth of earthquakes in the western United States (WUS) estimated using the hypocentral depths of events M>1, a crustal temperature model, and historical earthquake rupture depth models. Locations of earthquakes are from the Advanced National Seismic System (ANSS) Comprehensive Earthquake Catalog (ComCat) from 1980 to 2021 supplemented with seismicity in southern California for event hypocenters that were relocated by Hauksson et al. (2012) to obtain higher precision and better resolution in the model. We calculated the average depth of the deepest 10% of the merged catalog using an adaptive radius of 15 km or more. Along the San Andreas Fault, the deepest seismogenic depths are located at 23 km around the Cholame segment, whereas the shallowest depths are located at about 10 km along the Rodgers Creek and Maacama faults. For the WUS outside California, the depth generally varies between 10 and 25 km with an average around 14 km but could extend to 35 km along Cascadia subduction zone. We find good agreement between the small magnitude depths and rupture depths derived from coseismic slip of large earthquakes across the region. Our estimates are generally deeper than previous seismogenic depths determined for the Uniform California Earthquake Rupture Forecast version 3 (UCERF3) model based on work by Petersen et al. (1996) who used seismicity cross sections along major fault zones in California. Our new seismogenic depth distribution correlates closely with crustal temperature derived from WUS heat flow (Blackwell et al., 2011). This correlation allowed us to develop a map of the brittle¬–ductile transition that we use to replace seismogenic depths in the model east of the Intermountain West Seismic Belt where the seismicity rate is low. This updated depth model is useful for recalibrating the lower geologic fault rupture depths and constraining deformation and seismicity source models in updates of the U.S. Geological Survey National Seismic Hazard Model (NSHM).

Key Words
Lower seismogenic depth

Citation
Zeng, Y., Petersen, M. D., & Boyd, O. S. (2023, 09). Lower Seismogenic Depth Model for Western U.S. Earthquakes. Poster Presentation at 2023 SCEC Annual Meeting.

Related Projects & Working Groups
SCEC Community Models (CXM)