Estudio del enjambre de San Quintin, Baja California, México, ocurrido durante 1975

Abstract

Epicentral locations for the events of the San Quintin earthquake swarm are confined to a small area, with radius 8±1 km, and between 15 and 20 km deep. Without showing any well defined tendency of the epicenters or hypocenters during the observation time with portable seismic stations (ten months). No well-defined tendency is shown by either the epicenters or hypocenters during the ten months period of observation with portable seismometers. There is the suggestion of a fault along the coast from the site of the San Quintin earthquake swarm, to San Antonio del Mar. The trend of such a fault would be in the northwesterly direction, and this agrees with one of the strikes N 45 W, of the fault plane solution. Unfortunately, due to the submarine location of the seismic activity· it is not possible to check the trend of the suggested fault with a geological inspection. The seismic moment of the main event, local magnitude 5 .2, was calculated comparing the amplitudes of the synthetic and real seismograms. This seismic moment was 1.53 ± 2 x 1024 dynes-cm. The cumulative seismic moment of all the events recorded during 1975, with local magnitudes between 3 and 5.2, was 3.68 x 1024dynes-cm, which is equivalent to an event of magnitude 5.4. The average displacement as a function of the cumulative seismic moment was 5. 7 ± 1.4 cm/year. The stress drop of the main event was 2.2 ± 1.7 bars. The b value associated with this earthquake swarm was 1.06. In order to calculate the seismic moment of the 112 events recorded in Rio Hardy we use the empirical relationship between local magnitude and seismic moment given by log M0 = 1.64 ML+ 15.6, which is similar to that given by Brune and Wyss (1968).
doi: https://doi.org/10.22201/igeof.00167169p.1982.21.4.871