Joint Study of the 1952 Kern County Earthquake

Date: 4/26/2019

Time: 06:00 PM

Room: Grand Ballroom

Our understanding of earthquakes that occurred earlier than the WWSSN era is generally limited by the lack of quality observations. The 1952 Kern County earthquake, the second largest earthquake to occur in California in the 1900s, is no exception. Despite decades of research, significant discrepancies exist among seismic and geodetic interpretations for this event. Here, combining reported geodetic observations with a collection of previously unused, local seismic records, we conduct a series of finite fault inversions to constrain a slip model that is consistent with both datasets. Our results reveal that the 1952 Kern County earthquake had a complex rupture evolution. The rupture initiated on a low-angle fault with dominate strike-slip motion (strike=54°/ dip=36°/ rake=15°) then triggered an abnormally energetic rupture on a high-angle fault plane (strike=51°/ dip=75°), 1.5 s later. In the next three seconds, over 10 m slip accumulated on a 6 km by 6 km fault patch, near the hypocenter, with a cumulative seismic moment of 2.65 × 10¹⁹ N m (Mw 6.9). The average static stress drop of this subevent is ~50 MPa. The P wave excited by this powerful subevent saturated seismic records as far as Berkeley (430 km away). The rupture continuously propagated along strike at a slow speed of ~1.5 km/s and initiated another subevent 8 to 28 km away from the hypocenter, where the majority of moment release occurred. The total rupture has a duration ~20 seconds. Our estimate for the cumulative seismic moment is 1.37 × 10²⁰ N m (Mw 7.4), most of which occurred within a 33 km section in the southwest portion of White Wolf fault (assumed to be 60 km long). The weighted, average rake-angle over the entire fault is 53°, falling between previous results based on individual seismic or geodetic data. We note that all three large Southern California earthquakes with significant thrust components (1954 Kern County, 1971 San Fernando, 1994 Northridge) share the same initiation pattern — a small nucleation phase followed by the failure of a patch with an abnormally high stress drop.

Presenting Author: Scott J. Condon

Authors