The focus of the 1906 California earthquake

Abstract

abstract The location of the 1906 California earthquake is reexamined using both the P and S recordings at teleseismic distances and the local observations. Analysis of the observed travel times using modern empirical tables rules out a focus of the principal shock south of the Santa Cruz Mountains or north of Point Arena. By inter-comparison with the measurements from the 1957 San Francisco earthquake, it is demonstrated that the lines of evidence are slightly more favorable to a principal focus near that of the 1957 California shock (37°40′N, 122°29′W) with t0 = 13h12m21s than to Reid's focus near Olema, although the latter is not precluded. There is no evidence from the travel times against the hypothesis that the first rupture was associated with the San Andreas fault and occurred within the crust. The analysis confirms that the rupture was of the (perhaps unusual) bilateral type. Calculations which confirm the contentious magnitude of 814 are set down.