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Lecture 9 (September 25)

Lecture 9 (September 25) - • Wasatch mountains(horst are...

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Subduction megathrust EQs generate tsunamis 1700 Cascadia Tsunami felt in Japan (only one that didn’t have an EQ in Japan) There have been 13 turbidites had been deposited off coastal Washington and Oregon since the eruption of Mt. Mazama (EQs generated by Cascadia every 539 yrs) Basin and Range Province (in the Pacific-North America Plate Boundary) o A world-famous region of crustal extension and thinning. Extension occurs by displacements along normal faults that bound the many mountain ranges within the province and that define its western (Sierra Nevada) and eastern (Wasatch Front) boundaries (Nevada, Utah, some Arizona, southern Oregon, eastern California) o The unusually topography of Nevada, western Utah, eastern California, and southeastern Oregon is the direct result of stretching the earth’s crust The Western edge of the Basin and Range coincides with the Eastern California Shear Zone (ECSZ)—right lateral strike-slip Owens valley is part of the ECSZ and the western part of the Basin and Range
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Unformatted text preview: • Wasatch mountains (horst) are the eastern part of the Basin and Range, so Salt Lake City is on the hangingwall of the Wasatch fault • The Wasatch fault is the eastern part of the Pacific-North American Plate boundary o 95% of the motion occurs in California (70% San Andreas, 25% ECSZ) • Seismic risk in terms of people • San Andreas Fault, connecting the spreading ridges of the Gulf of California north to the Cascadia Subduction zone o Relatively straight from Cape Mendecino until the Big Bend of the SAF o It is the biggest fault in California, almost 1000 km long and stores up and releases energy must faster than any other fault in California (slip rate of 35mm/yr) (total relative motion rate b/n North America Plate and Pacific Plate is only 50mm/yr) Slip rate of 10mm/yr on ECSZ o Generates biggest and most frequent earthquakes 1906 San Francisco M w 7.9 • 400 km long rupture • 5-8 m of slip 1857 Fort Tejon M w 7.9...
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