Brawley Seismic Zone, Dextral Transcurrent and Rift Tectonics Connecting the San Andreas and Imperial Faults Across the Salton Trough, Southern California, USA

Egill Hauksson, Joann M. Stock, & Allen L. Husker

Submitted August 8, 2021, SCEC Contribution #11207, 2021 SCEC Annual Meeting Poster #186

We analyze 40 years of seismicity in the (BSZ) Brawley Seismic Zone to elucidate its current mode of crustal deformation. The 30 km long BSZ extends south-southeast across the Salton Trough, from the southernmost tip of the San Andreas fault (SAF) to the Imperial fault in the south, and accommodates transtensional plate motion and magma starved rifting along the Pacific North-America plate boundary at rates of up to 17 mm/yr.

The BSZ seismicity is characterized by linear seismicity distributions that often are accommodated simultaneously on conjugate faults. These sequences rarely reactivate previous seismicity alignments even when they may be located within 1 km distance. This seismicity consists mostly of short-duration earthquake sequences of up to 10 days duration, and consist of foreshocks, mainshock, and aftershocks.

The BSZ is complex with a 12 [deg] change in strike that is collocated with a 4-6 km right lateral offset and a volcanic zone at the south end of the Salton Sea, called Salton Buttes. These tectonic features reflect the rift tectonics of crustal thinning as well as recent volcanics at the south shore of the Salton Sea. Thus the BSZ consists of two zones, the 12 km long BSZ-north that extends from Bombay Beach in the north, to the south end of the Salton Sea, near the Salton Sea Geothermal areas. The 18 km long BSZ-south extends from the south shore of the Salton Sea to the Imperial fault in the south.

The state of stress as determined from focal mechanisms, shows that the conjugate strike-slip faulting is simultaneously accommodating crustal extension and thinning as well as the dominant dextral transcurrent Pacific North-America plate motion.

Key Words
seismicity, seismotectonics

Citation
Hauksson, E., Stock, J. M., & Husker, A. L. (2021, 08). Brawley Seismic Zone, Dextral Transcurrent and Rift Tectonics Connecting the San Andreas and Imperial Faults Across the Salton Trough, Southern California, USA. Poster Presentation at 2021 SCEC Annual Meeting.


Related Projects & Working Groups
Seismology