Sierra Nevada Fault

The Sierra Nevada Fault is a normal (vertical motion) seismic fault along the eastern edge of the Sierra Nevada mountain block in California. The Sierra Nevada frontal fault zone forms the eastern escarpment of the Sierra Nevada, extending ~600 km from just north of the Garlock Fault to the Cascade Range.^[1]

Tectonic activity

Activity on this fault has been found to be about 0.01-0.03 mm of uplift per year. This movement, combined with the movement of the adjacent Owens Valley and Lone Pine Faults is responsible for the continuing uplift of the Sierra Nevada Mountains.^[1] However, no large earthquake has occurred on the Sierra Nevada Fault in recorded history. The largest earthquake in its vicinity was on the adjacent Owens Valley Fault in 1872, known as the Lone Pine earthquake, which has been estimated as having had a 7.8 magnitude. Seismic activity of the Sierra Nevada Fault is most accurately understood by looking into its history.

History

Around 200 million years ago an ancient oceanic plate named the Farallon Plate began to subduct beneath the North American Plate. As the oceanic plate was subducted, it became completely overridden and the water was literally baked out of the rock preceding the occurrence of crustal melting. As the magma began to cool, a large mass of igneous rock was created that is now visible as the granite domes that make up the Sierra Nevada Batholith.^[2] A batholith is a large mass of igneous rock that forms deep below the surface, and they are thought to be the “roots” of subduction zone volcanoes.^[3] After the below-surface formation of granite occurred, physical processes such as uplift and erosion eventually exposed the abundant granite to the surface.

Mechanics and processes

There are several contributors to the uplift of the Sierra Nevada Batholith. As the North American and Pacific plates come into direct contact for the first time, shear forces have replaced compression as the North American plate begins interacting with the Pacific plate. On the other side of the Sierra Nevada Range Basin and Range Province is being pulled apart as the force of compression increases.^[4] It is the Farallon Plate subsidence that is thought to be the driving force behind the creation of the Sierra Nevada.

References

1. Le K., Lee J., Owen L.A. & Finkel R. (2007). "Late Quaternary Slip Rates along the Sierra Nevada Frontal Fault Zone, California: Slip Partitioning across the Western Margin of the Eastern California Shear Zone–Basin and Range Province" (PDF). Geological Society of America Bulletin 119 (1-2): 240–256. doi:10.1130/B25960.1.
2. Nahler, Nathan. "Creation of the Sierra Nevada Batholith." N.p., n.d. Web. 3 Dec. 2015.
3. "Building California by Plate Tectonics." Tusd.org. N.p., n.d. Web. 3 Dec. 2015.
4. Kurbatova, Elena. "Geology of the Sierra Nevada Mountain Range." Geology of the Sierra Nevada Mountain Range. N.p., n.d. Web. 03 Dec. 2015.