The earthquake swarm of february 1981 in Mexico City
Main Article Content
Abstract
Between February 4 and 15, 1981, a particularly well recorded earthquake swarm occurred in Mexico City. The 5 largest events analyzed here (2.7 <ML<3.2) had hypocenters within a volume of 1 km3 with mean location at 19.3780N-99.1960W, and a depth of 1.2 km. Relative locations of these events showed a migration from 0.7 to 1.6 km on a nearly vertical plane. A normal fault plane solution with the tensional axis almost east-west was obtained using local and regional stations. Spectral analysis gave seismic moments in the range 0.5 - 2.0 x 1020 dyne-cm and rather low stress drops (1 to 5 bars). Similar parameters were obtained for the largest event occurring in a swarm in the same area in February 1980. It seems most likely that these events occur as a result of accumulating regional tension; however, the sinking of the Valley of Mexico could possibly produce similar oriented tensions, which, if not causing the earthquakes, might trigger them.
Article Details
This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.
References
ASTIZ, L., 1980. Sismicidad en Acambay, Estado de México. El temblor del 22 de febrero de 1979. Thesis, Facultad de Ingeniería, UNAM, México.
BRUNE, J. N., 1970. Tectonic stress and the spectra of seismic shear waves from earthquakes. Journ. Geophys. Res., 78, 4997-5009. DOI: https://doi.org/10.1029/JB075i026p04997
HANKS, T. C. and M. WYSS, 1972. The use of body wave spectra in the determination of seismic source parameters. Bull. Seism. Soc. Am., 62, 569-590. DOI: https://doi.org/10.1785/BSSA0620020561
HANKS, T. C. and H. KANAMORI, 1979. A moment magnitude scale. Journ. Geophys. Res., 84, 2348-2350. DOI: https://doi.org/10.1029/JB084iB05p02348
HAVSKOV, J. and S. K. SINGH, 1978. Shallow crustal structure below Mexico City, Geofísica Internacional, 17, 223-229. DOI: https://doi.org/10.22201/igeof.00167169p.1978.17.2.935
JIMENEZ, Z. and L. PONCE, 1978. Focal mechanism of six large earthquakes in Northern Oaxaca, México, for the period 1928-1973. Geofísica Internacional, 17, 379-386. DOI: https://doi.org/10.22201/igeof.00167169p.1978.17.3.1059
KOVACH, R. C., 1974. Source mechanisms for Wilmington oil field, California, subsidence earthquakes. Bull. Seism. Soc. Am., 64, 699-715. DOI: https://doi.org/10.1785/BSSA0643-10699
LEE, W. A. K. and J. C. LARHR, 1978. HYPO-71 (revised 1978): A program for determining hypocenter, magnitude and first motion pattern of local earthquakes. U. S. Geological Survey, open file report 75-311.
MOLNAR, P. and L. R. SYKES, 1969. Tectonics of the Caribbean and Middle American regions from local mechanisms and seismicity. Bull. Geol. Soc. Am., 80, 1639-1684. DOI: https://doi.org/10.1130/0016-7606(1969)80[1639:TOTCAM]2.0.CO;2
REAL, C. R. and T. TENG, 1973. Local Richter magnitude and total signal duration in Southern California. Bull. Seism. Soc. Am., 63, 1809-1827. DOI: https://doi.org/10.1785/BSSA0630051809
SINGH, S. K. and M. WYSS, 1976. Source parameters of the Orizaba earthquake of August 28, 1973. Geofísica Internacional, 16, 165-184. DOI: https://doi.org/10.22201/igeof.00167169p.1976.16.3.1119
SINGH, S. K. and J. HAVSKOV, 1980. On moment-magnitude scale, Bull. Seism. Soc. Am., 70, 379-383. DOI: https://doi.org/10.1785/BSSA0700010379
TALWANI, P., 1976. Earthquakes associated with the Clark Hill Reservoir. South Carolina, a case of induced seismicity. Engineering Geology, 10, 239-253. DOI: https://doi.org/10.1016/0013-7952(76)90024-7
WADE, L. R., A. J. B. MOLL and L. R. CABELLO, 1975. Boletín de Mecánica de Suelos, No. 2, published by Secretaría de Recursos Hidráulicos, Comisión de Aguas del Valle de México.