New estimates of the magnitudes and locations for the strongest earthquakes in 1906-1907 Socorro, New Mexico, earthquake swarm

Rossi-Forel (RF) intensities reported by Reid (1911) for the three strongest earthquakes in the 1906–1907 Socorro earthquake swarm are used to estimate magnitudes, locations, and fault parameters. RF intensities have been converted to Modified Mercalli (MM) intensities using the relationships by Richter (1958) and then to peak ground accelerations (PGAs) using empirical equations established by Wald et al. (1999). Final estimates of magnitudes were obtained from the distribution of PGAs versus distances beyond 50 km (31 mi) using the attenuation relationship of Spudich et al. (1999). The procedure yielded local magnitudes of 5.57 (12 July 1906), 5.76 (16 July 1906), and 6.18 (15 November 1906). Further analysis revealed that these earthquakes had to occur very near Socorro, most likely on the Socorro Canyon fault, a major Quaternary fault of the Rio Grande rift (Machette and Chamberlin 1997a, b; Phillips et al. 2003). Rupture parameters based on the estimated magnitudes (Wells and Coppersmith 1994) indicate that only the 15 November 1906 earthquake would have had a chance to rupture the surface, but the displacement would probably be too small to detect.