Introduction We live next to this fault It’s active It has a history of major earthquakes We had better know something about it
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
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
Complexity in detail
Note that foundations matter
Pallett Creek Work of T. Sieh, ~1987 Ph.D., California Tech.
Detailed map of sag-pond sediments across fault
Key to understanding Carefully relating ages to offset of pond sediments
Summation of findings Covers 1700 years Median frequency = one per 132 years Range 50 – 500 years
Features 1857 (before reliable, common seismometers and reproducible results) Magnitude ~8.0 Offset near epicenter ~ 9 m
Dostları ilə paylaş: |