GEO 6950 Reviews in Earth Science, Fall 2011 Topic 2 Tectonics of Western North America 11. San Andreas Fault System Carrie Welker and Alex Turner

Geography of the SAFS The entire system is a zone approximately 3000 km long. It is bounded in the north by the Mendocino trench – transform – transform triple junction off north western California. It is bounded in the south by the Rivera ridge – trench – transform triple junction near the mouth of the Gulf of California. A splay off the SAFS called the Eastern California shear zone is connected with the main fault system south of the big bend. It trends north along the eastern front of the Sierra Nevada, where it is known as the Walker Lane belt.

SAFS Physical and geological characteristics Right-lateral transform plate boundary between Pacific and North American tectonic plates. Pacific plate moving northwestward at mm yr -1 ~550 km of total displacement since formation Ma Both seismic and aseismic slip occur on locked and creeping segments of SAF San Andreas Fault Observatory at Depth (SAFOD) at Parkfield, CA Fault Core contains the weak smectite clay mineral saponite  aseismic slip? North American Plate Pacific Plate

Crust and Lithosphere Properties

SAFS Important Chronology Formation Ma the Pacific-North American plate boundary transitions from a subduction to a transform boundary (Farallon subduction to right-lateral strike-slip on SAF) Historical Earthquakes YearMagnitudeNameLocationFatalities/damage Fort Tejon EarthquakeCentral SAFS San Francisco EarthquakeNorth SAFS3000 / $524 million Long Beach EarthquakeSouthern SAFS115 / $40 million Loma Prieta EarthquakeNorth SAFS63 / $6 billion Northridge EarthquakeSouthern SAFS60 / ~$15 billion Easter EarthquakeSouthern SAFS (Baja CA) 2 / most damage in Mexico