The San Felipe Fault Zone (also known as the Agua Caliente or Murrieta Hot Springs Fault zone) is an active Quaternary fault zone made up of continuous right-lateral fault strands].Janecke, S. U., Dorsey, R. J., Forand, D., Steely, A. N., Kirby, S. M., Lutz, A. T., ... & Rittenour, T. M. (2011). High geologic slip rates since early Pleistocene initiation of the San Jacinto and San Felipe Fault zones in the San Andreas Fault system: Southern California, USA. It is a part of the

San Andreas Fault The San Andreas Fault is a continental Fault (geology)#Strike-slip faults, right-lateral strike-slip transform fault that extends roughly through the U.S. state of California. It forms part of the tectonics, tectonic boundary between the Paci ...

system and it is located in the western

Salton Trough The Salton Trough is an active tectonic pull-apart basin, or graben. It lies within the Imperial, Riverside, and San Diego counties of southeastern California and extends south of the Mexico–United States border into the state of Baja Califo ...

spanning three counties: Imperial, Riverside, and

San Diego San Diego ( , ) is a city on the Pacific coast of Southern California, adjacent to the Mexico–United States border. With a population of over 1.4 million, it is the List of United States cities by population, eighth-most populous city in t ...

county, California. It is hypothesized to have originated during the early

Pleistocene The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...

period.

Geography

The fault zone strikes WNW and consists of a central Easterly fault with adjacent strands extending out from the San Felipe

anticline In structural geology, an anticline is a type of Fold (geology), fold that is an arch-like shape and has its oldest Bed (geology), beds at its core, whereas a syncline is the inverse of an anticline. A typical anticline is convex curve, c ...

.Alexander N. Steely, Susanne U. Janecke, Rebecca J. Dorsey, Gary J. Axen; Early Pleistocene initiation of the San Felipe Fault zone, SW Salton Trough, during reorganization of the San Andreas Fault system. GSA Bulletin 2009;; 121 (5-6): 663–687. doi: https://doi.org/10.1130/B26239.1 The fault zone is part of the Earthquake Valley, within the Pacific Border Ranges and Basin and Range physiographic provinces. In total the faults run 170 kilometers long. The main San Felipe Fault extends from the Elsinore Fault to the San Jacinto Fault, South on the Yaqui and Pinyon ridge. The Fish Creek Mountains fault is the eastern extension that runs along the Fish Creek Mountains.

Origin

The San Felipe Fault zone is estimated to have originated 1.1-1.3 Ma. During its rise to the surface, the San Felipe Fault created the San Felipe-Borrego basin and the San Felipe anticline.

Movement

About half of the San Andreas Fault system's movement has been from the San Felipe fault zone. It has seen 5.8±2.8 km of right separation since its inception. Both the San Jacinto Fault zone and San Felipe fault zones reorganized in the middle to late Pleistocene era and accumulated 600 meters of sediment during uplift and folding.Kirby, S. M., Janecke, S. U., Dorsey, R. J., Housen, B. A., Langenheim, V. E., McDougall, K. A., & Steely, A. N. (2007). Pleistocene Brawley and Ocotillo formations: Evidence for initial strike-slip deformation along the San Felipe and San Jacinto fault zones, southern California. The Journal of Geology, 115(1), 43-62. These 600 meters of sediment make up the Sunset strand of the San Felipe Fault zone. The current deformation (started 0.5-0.6 Ma) is the shortening of the fault, which inverts and exhumes sediment accumulation. It is estimated to have between 4 and 12.4 kilometers of right slip.

References

{{reflist Wikipedia Student Program Salton Trough Active faults Seismic faults of California Geography of Imperial County, California Geography of Riverside County, California Geography of San Diego County, California