Central California foreshocks of the great 1857 earthquake

摘要: Analysis of contemporary accounts indicates that several small to moderate central California earthquakes preceded the great 1857 earthquake by 1 9 hr. The earliest events apparently were felt only in San Francisco area or Sacramento and Sierran Foothills region. Two later much more widely foreshocks experienced within region bounded Francisco, Visalia, Fort Tejon, Santa Barbara. A comparison with areas intensity distributions modern known source magnitude these two shocks 5 ≦M ≲ 6 probably originated at some point an radius ≈60 km includes southeastern 100 historically creeping segment Andreas fault. northwestern terminus rupture is located along this segment. If location indicative epicenter main event, then several-hundred-kilometer main-event propagated principally a unilateral fashion toward southeast. This implies that, like many earthquakes, on fault characterized activity into quiet segment. There strong possibility foreshock represents Parkfield-Cholame sequence similar those 1901, 1922, 1934, 1966. To extent such premonitory characteristic failure fault, studies may be relevant prediction large southern California.