The 1906 San Francisco earthquake a century later: Introduction to the special section

Abstract

The great 1906 San Francisco earthquake is perhaps the landmark event in the history of earthquake science. It began with a foreshock at 5:12 a.m. local time in the morning of 18 April 1906. Some 30 sec later, the main event initiated on the San Andreas fault, just off the San Francisco coast ( Lawson, 1908 ). Within 90 sec, nearly 480 km of the San Andreas fault ruptured (see Fig. 1 ), extending south to the northern end of the creeping section near San Juan Bautista and north to the terminus of the fault at the triple junction near Cape Mendocino ( Song et al. , 2008 ). As it ruptured, it generated powerful seismic waves over the entire rupture length and set in motion a chain of events that led to the destruction of most of San Francisco, the largest city of the western United States at the time. The earthquake occurred in the early days of instrumental seismology, which renders the data difficult to analyze, but our best estimate is that the moment magnitude was 7.9 ( Song et al. , 2008 ), about 26 times the size of the 1989 magnitude 6.9 Loma Prieta earthquake as measured by seismic moment ( Hanks and Krawinkler, 1991 ; Song et al. , 2008 ).