From Coalinga to the Tehachapi Mountains: Recent activity and earthquake potential of blind fault systems in the Southern San Joaquin Valley

Robert M. Welch, Chris Anthonissen, Andreas Plesch, Lluis Salo-Salgado, James F. Dolan, & John H. Shaw

Submitted September 7, 2025, SCEC Contribution #14505, 2025 SCEC Annual Meeting Poster #TBD

Since August 2024, the Southern San Joaquin Valley has experienced a series of small to moderate magnitude earthquakes on faults within the CFM, as well as systems that are not yet represented in the model. In particular, blind faults in two regions have experienced this heightened seismicity: the Kettleman–Lost Hills fold-and-thrust belt and structures within the Maricopa sub-basin (north of the Tehachapi Mountains).

Along the Kettleman-Lost Hills fold-and-thrust belt, a series of earthquakes occurred on the lower segment of the ramp that generates Kettleman North Dome anticline in the vicinity of the 1983 M 6.1 earthquake on this system. In the Maricopa sub-basin, a recent M 5.2 earthquake ruptured a fault not yet modeled in the CFM or represented in the U.S.G.S. Qfaults database. This recent activity has motivated, in part, our efforts to examine the complete extent and 3D geometry of these faults in relation to other known seismic hazards (e.g.., the San Andreas and White Wolf faults). Using a diverse set of datasets (seismic reflection, CalGEM well, and relocated seismicity data), we define the fault geometry and kinematics of these two fault systems and explore their implications for regional seismic hazards.

In this work, we extend our previous findings in the Kettleman-Lost Hills by constraining the regional geometry of this fold-and-thrust belt to the SAF. We find that the active ramps link to lower detachments across the length of this fold and thrust belt, resulting in a large fault area that may have the potential to rupture in Mmax 8.1 earthquakes. In the Maricopa sub-basin, we find that there is a complex series of faults, previously unrecognized to be active in the Holocene, that generated the August 2024 M 5.2 earthquake. Of note, we find that both north- and south-dipping faults may have been activated during this event. These faults are a part of a larger regional fault network that could produce far larger earthquakes.

Key Words
Faulting, Active Folding, Thrust Faults, Fault-Related Folding, Detachments, Central Valley

Citation
Welch, R. M., Anthonissen, C., Plesch, A., Salo-Salgado, L., Dolan, J. F., & Shaw, J. H. (2025, 09). From Coalinga to the Tehachapi Mountains: Recent activity and earthquake potential of blind fault systems in the Southern San Joaquin Valley. Poster Presentation at 2025 SCEC Annual Meeting.

Related Projects & Working Groups
Earthquake Geology