Extending the southernmost San Jacinto Fault: evidence for repeat Holocene motion along the Wienert Strand

Katherine M. Scharer, Thomas K. Rockwell, & Paula M. Figueiredo

Submitted September 7, 2025, SCEC Contribution #14659, 2025 SCEC Annual Meeting Poster #TBD

The 1987 M6.6 Superstition Hills earthquake ruptured 27 km of the Superstition Hills Fault and 4 km of the Wienert Fault. A southern continuation of the Wienert Fault is indicated by seismicity lineaments and geodetic studies, but geologic evidence of the fault trace is sparse in the heavily modified agriculture of the Imperial Valley. A sag pond visible in 1937 air photos suggests that faulting has been active since the deposition of the youngest Lake Cahuilla sediments, 300 years ago. We targeted the sag pond using cone penetration testing (CPT) soundings to map the subsurface and characterize the Holocene activity of faulting. The 175 m long transect with CPT soundings reaching depths of ~18 m demonstrated vertical separation of units within a ~15 m wide fault zone. A sandy layer near the base of the soundings is offset over 3 m, whereas a sandy layer in the upper 5 m is offset only 0.7 m, indicating episodic motion across the fault zone and repeated inundation by Lake Cahuilla sediments. A pending IRSL date on a sandy layer from 3.5 m depth will provide age context for this sequence. This study provides clear evidence the Wienert Fault is Holocene active to within 6 km of the town of El Centro and suggests it is a linkage between the Imperial Fault and the San Jacinto Fault. Outcomes of this project will contribute toward characterizing seismic hazard in the Imperial Valley.

Key Words
fault map, Imperial fault

Citation
Scharer, K. M., Rockwell, T. K., & Figueiredo, P. M. (2025, 09). Extending the southernmost San Jacinto Fault: evidence for repeat Holocene motion along the Wienert Strand. Poster Presentation at 2025 SCEC Annual Meeting.

Related Projects & Working Groups
Community Earth Models (CEM)