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Seismicity in the vicinity of the Farallon Escarpment
Author(s) -
Uhrhammer Robert
Publication year - 1977
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/gl004i010p00469
Subject(s) - escarpment , geology , seismology , induced seismicity , continental margin , san andreas fault , crust , continental crust , fault (geology) , geophysics , geomorphology , tectonics
On April 30, 1977, at 1903 UTC an earthquake (M L = 2.6) occurred in the vicinity of the Farallon Escarpment (37.7°N ‐ 123.3°W), approximately 25 km west of the Farallon Islands. This well located earthquake is of particular interest in that it establishes earthquake activity along the California continental margin as far as 65 km west of the San Andreas fault. The significance is that the active seismic zone west of the San Andreas fault extends up to the edge of the continental margin but not past it into the oceanic crust. The occurrence rate is very low with an inter‐occurrence time for earthquakes with M L ≥ 1.9, in a 3000 square kilometer area in the vicinity of the escarpment, of about two years. The first motions recorded at local seismographic stations are consistent with a right‐lateral strike‐slip mechanism orientated parallel to the strike of the San Andreas fault.