4. Darwin recorded uplift of 3 meters after the 1835 Chilean earthquake. That wa

Question

4. Darwin recorded uplift of 3 meters after the 1835 Chilean earthquake. That was a subduction zone megathrustquake, with a primarily vertical component to the elastic rebound. Along the San Andreas Fault movement is primarily horizontal. At a restraining bend such as that forming the San Gabriel Mountains in the Transverse Ranges (a left step along the right-lateral San Andreas Fault), assume a maximum uplift of 0.5 meters per earthquake. Given the number of earthquakes you calculated above, what would be the resulting maximum uplift of the San Gabriel Mountains? (Don't freak out! Expect a huge number. Yuge!) The resulting maximum uplift of the San Gabriel Mountains would be 1737.6m. 5. The highest elevation in the San Gabriel Mountains is 3,069 meters. Given your answer to (4) above, does this seem at least possible as the result of cumulative small uplifts due to recurring earthquakes along the San Andreas Fault? What might account for the difference between the maximum uplift you calculated and the actual elevation of these mountains?

Explanation / Answer

San Andreas fault of California begins at about 30 million years ago and it demarcates the boundary between two faults i.e. North American and Pacific Plate. Earlier, another plate subducts Farallon plate subducts beneath North American plate at a subduction zone. In the new configuration of plates i.e. North American and Pacific plates the plates slide past each other and forms a strike slip plate boundary. Rock offsets of about 150 m have been found across the sides of the fault. San Andreas fault extends from the San Berandino mountains and Mendocino coast to the Salton sea and is about 800 km long.

Parkfield a site in California has moderate eartquakes with magnitude of 6 every couple decades. The earthquakes which had previously struck the area in 1857,1881,1901,1922, 1931,1936.

Surface uplift= uplift of rock-exhumation

Surface uplift: Displacement of earth's surface wrt geoid

Uplift of rock: Displacement of rocks in comparison to the geoid

Exhumation: Displacement of rocks taking geoid as the reference.

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