Sismicidad y mecanismos focales en el Valle Mexicali-Imperial (1973-1985)

Abstract

Se reportan 90 hipocentros relocalizados en la zona sísmica Mexicali y 60 soluciones de mecanismo focal de sismos del Valle Mexicali-Imperial. La información proviene de estaciones ubicadas en ambos lados de la frontera internacional y se complementa con catálogos y otros resultados ya publicados. Los epicentros con magnitud menor de 5.0 se concentran principalmente en las zonas sísmicas Mexicali y Brawley. En los últimos 50 años se produjeron periodos de fuerte actividad en el Valle. El ultimo, ocurrido entre 1973 y 1981, tuvo sus enjambres y replicas de sismos con ML>6.0 ubicados principalmente en sectores no-traslapados de las zonas sísmicas. Los focos están mayoritariamente entre os 5 y 13 km de profundidad. Los cuatro últimos temblores con ML>6.0 ocurrieron en las fallas Cerro Prieto e Imperial, inmediatamente afuera de las zonas sísmicas. Los mecanismos focales de estos cuatro temblores son compatibles con un desplazamiento de rumbo lateral-derecho en dirección noreste. Este desplazamiento es predominante en el Valle, aunque las zonas sísmicas presentan mecanismos de rumbo, normales y, en menor medida, inversos. Un mismo nido sísmico puede originar mecanismos de diferente tipo, aun en un lapso de pocas horas. Globalmente, las características encontradas concuerdan con una tectónica dominada por el movimiento relativo entre las placas Pacifico y Norteamericana.

The Victoria, Mexico, Earthquake of June 9, 1980

“…average azimuthal range in these determinations is about 100°. A similar approach was reported by Frez and Gonzalez (1987). Arrival corrections consisted of: (a) Small, mostly negative corrections for stations situated over sediments in the Valley, as at BON (-0.05), CLI (-0.03), VER (-0.02),NVL (-0.01).…”

“…The main shock was located at the SE end of the aftershock region which is compatible with an unilateral rup- This location is at the SE end of the Mexicali Seismic Zone. Similarly, the Imperial Valley and El Centro earthquakes were at the north end of the Mexicali Seismic Zone (Imperial Fault) and the SE end of the Brawley Seismic Zone, respectively (Johnson, 1979;Frez and Gonzalez, 1987). Mtershocks of these main events were mostly located inside the Mexicali and Brawley seismic zones.…”

“…SS = Salton Sea; SJF= San Jacinto Fault; BSZ = Brawley Seismic Zone; MSZ = Mexicali Seismic Zone; SHF = Sand Hills Fault; LSF = Laguna Salada Fault; SaJF = Sierra Juarez Fault; CR =Colorado River; CG =California Gulf. The segmented lines enclose the seismic zones (BSZ and MSZ) based on seismic activity (Johnson, 1979;Frez and Gonzalez, 1987). California Seismological Network (SCSN), jointly operated by the U.S.Geological Survey (USGS) and the California Institute of Technology (Caltech), were not available for the events of June 1980 (Wald et al, 1994).…”

“…In addition, we tested the stability of our calculations by selecting subsets from our data set. Finally, we analyzed our results in the context of the known features of Mexicali Valley seismicity (Frez and Gonzalez, 1987;Frez and Gonzalez, 1990).…”

“…Both aftershock sequences are mostly confined to a zone between the Imperial and Cerro Prieto faults, where 139 several earthquake swarms occurred between 1973 and 1981; this is called the Mexicali Seismic Zone (Frez and Gonzalez, 1987; see also Figures 1 and 2). This seismic wne is linked to the opening of the Gulf of California by the Cerro Prieto and the Imperial faults; it has been interpreted as• a small spreading center (Lomnitz et al, 1970;Elders et al, 1972).…”