29 Cenozoic Tectonics in Asia and North America: Linking Processes Across Scales

This session invites research integrating geologic, geomorphic, and paleoclimate data to advance understanding on orogenesis, seismic hazards, and global change.

Tuesday, 19 May 2026
1:30 PM - 4:30 PM
Alvarado A

Evidence for Large Late-Pleistocene Multi-Segment Earthquakes on Blind Thrust Faults in the South-Central San Joaquin Fold-and-Thrust Belt, California

Paper number: 29-7
Program: Technical Sessions
Time: 3:50 PM – 4:10 PM

Authors

Abstract

The active South-Central San Joaquin fold-and-thrust belt lies east of the Parkfield segment of the San Andreas Fault and adjacent to Interstate I-5 and the California Aqueduct. From August 2024 to February 2025, this fold-and-thrust belt has produced a series of earthquakes Mw 3.3 to 4.3. These events occurred within the vicinity of several large earthquakes in the 1980’s (Mw 5.5 New Idria, Mw 6.3 Coalinga, and Mw 6.1 Avenal (North Dome). Recently, an internally consistent fault model has revealed the presence of large upper and lower regional detachments, linked by ramp segments, along the length of this 110 km-long fold-and-thrust belt. In the context of this fault model, the 1980s and 2024-2025 earthquake sequences were largely constrained to the ramps of the fault systems, indicating limited seismicity of the detachments present in this fold-and-thrust belt. This recent earthqaukes and the notable lack of activity on the lower detachment have, in part, motivated our efforts to better understand the history of earthquake activity on this active, blind fault system. We leverage a range of datasets (2D seismic reflection, CalGEM well, and groundwater well data) in conjunction with this fault model to constrain co-seismic folding events from the Pliocene to the late Pleistocene. In particular, we focus on the axial surfaces that define the transition between the active ramps that generated the 1980s and 2024-2025 earthquake sequences and the upper and lower detachments. Across the length of this fold-and-thrust belt, we find evidence of folding throughout the Pliocene and Pleistocene, indicating that these detachments, in addition to the ramps, were seismically active through the late Pleistocene. Should the ramps and detachments rupture together in the future, we calculate that this system has the potential to rupture Mmax 8.1 earthquakes. Additionally, we identify that activity is not just limited to the Kettleman and Lost Hills system but is also present in basinward faults.

Geological Society of America Abstracts with Programs. Vol. 58, No. 4

doi: 10.1130/abs/2026RM-410603

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