Transcript San Andreas Fault

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 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