San Andreas Fault Introduction



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tarix21.06.2018
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San Andreas Fault


Introduction

  • We live next to this fault

  • It’s active

  • It has a history of major earthquakes

  • We had better know something about it

  • ..so that we can better prepare



Features-1

  • Not recognized (in total) until ~1940

  • Not recognized as a plate boundary until ~1970 – plate tectonic theory had to happen first!

  • Named after Lake San Andreas (SW of San Fransico) following the 1906 earthquake



Features-2



Plate features



Features-3

  • Active since 23.5 my BP; total = 315 km

  • Long-term rate = 1.3 cm/year

  • NOTE – there have been other strands and similar faults have occurred in the region since ~~60 my BP; ~~480 km offset of Baja California peninsula



Major California Earthquakes



Complexity in detail



Note that foundations matter



Response of different Earth foundations



Pallett Creek

  • Work of T. Sieh, ~1987

  • Ph.D., California Tech.



  • Pallett Creek



Detailed map of sag-pond sediments across fault



Key to understanding



Summation of findings

  • Covers 1700 years

  • Median frequency = one per 132 years

  • Range 50 – 500 years



Ft. Tejon earthquake



Features

  • 1857 (before reliable, common seismometers and reproducible results)

  • Magnitude ~8.0

  • Offset near epicenter ~ 9 m



  • Ft. Tejon



  • Rupture

  • and felt area





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