Download - San Andreas Fault
San Andreas San Andreas FaultFault
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 boundary between N. American and Pacific plates
Motion is transform with the Pacific plate moving northward
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
C-14 dating of organic material Carefully relating ages to offset of pond
sediments
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
Note that this break extended to Pallett Creek