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 transform fault that extends roughly through California. It forms the tectonics, tectonic boundary between the Pacific Plate and the North American Plate, and its motion is Fault (geology)#Strike-slip fau ...

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, United States and extends south of the Mexico–United States border into the state of ...

spanning three counties:

Imperial Imperial is that which relates to an empire, emperor, or imperialism. Imperial or The Imperial may also refer to: Places United States * Imperial, California * Imperial, Missouri * Imperial, Nebraska * Imperial, Pennsylvania * Imperial, Texa ...

Riverside Riverside may refer to: Places Australia * Riverside, Tasmania, a suburb of Launceston, Tasmania Canada * Riverside (electoral district), in the Yukon * Riverside, Calgary, a neighbourhood in Alberta * Riverside, Manitoba, a former rural m ...

, and

San Diego San Diego ( , ; ) is a city on the Pacific Ocean coast of Southern California located immediately adjacent to the Mexico–United States border. With a 2020 population of 1,386,932, it is the List of United States cities by population, eigh ...

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

Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...

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 that is an arch-like shape and has its oldest beds at its core, whereas a syncline is the inverse of an anticline. A typical anticline is convex up in which the hinge or crest is the ...

.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 Earthquake Valley is a desert valley east of Julian, California, which contains parts of the Anza-Borrego Desert State Park. It is the location of the Shelter Valley Ranchos subdivision, which is also known as the unincorporated community of She ...

, 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 The San Jacinto Fault Zone (SJFZ) is a major strike-slip fault zone that runs through San Bernardino, Riverside, San Diego, and Imperial Counties in Southern California. The SJFZ is a component of the larger San Andreas transform system and i ...

, 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

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