Artículos de revistas
THE EARTHQUAKE SWARM OF FEBRUARY 1981 IN MEXICO CITY
THE EARTHQUAKE SWARM OF FEBRUARY 1981 IN MEXICO CITY
Autor
Havskov, J.; Instituto de Ingeniería, UNAM, México 04510, D.F.
Institución
Resumen
Between February 4 and 15, 1981, a particularly well recorded earthquake widely felt in Mexico City. These events were rather large by local standard; magnitude estimates for the initial and a couple of later shocks are in the range of 3.0 to 3.4. Consequently the events were recorded as far as Oaxaca and Acapulco, Mex. Several portable seismographs from the Institute of Geophysics and Institute of Engineering were mobilized capturing many of the later events. In general our knowledge about the local seismicity in the Valley of Mexico is rather poor and imprecise due to small number of local stations and to a large extent unknown crustal structure. However no other local event has been recorded with such a large number of local distant stations, both digitally and analog, and this data set is definitely the best ever obtained for any event in Mexico City. In the present study only the 5 largest events, hereafter called 1 to 5, occurring between Feb. 4 and Feb. 9, 1981 will be analyzed, since they have the most complete data set. A study of all the events between Feb. 4 and Feb. 15 is under preparation at the Institute of Geophysics (R. Mota, personal communication). A comparison will also be made with the largest event of apparently a similar earthquake sequence, felt in the same region of Mexico City in February 1980. Entre el 4 y el 15 de febrero de 1981 ocurrió en la Cd. De México una serie de temblores particularmente bien registrados. Los 5 eventos mayores aquí analizados (2.7 ≤ ML ≤3.2) tuvieron hipocentros dentro de un volumen de 1 KM3, con localización media en 19.378° N – 99.196° W y una profundidad de 1.2 KM. Las localizaciones relativas de estos eventos mostraron una migración de 0.7 a 1.6 KM en un plano casi vertical. Se obtuvo una solución de plano de falla normal con el eje tensional en la dirección casi Este-Oeste, usando estaciones locales y regionales. El análisis espectral dio momentos sísmicos en el rango 0.5 – 2.0 x1020 dinas-cm y caídas de esfuerzo de 1 a 5 bares. Se obtuvieron parámetros similares para el venteo mayor ocurrido en una serie de temblores en la misma área en febrero de 1980. Parece ser probable que estos eventos ocurran como resultado de la acumulación de tensión regional; no obstante, el hundimiento del Valle de México podría posiblemente originar tensiones orientadas similares, las cuales, si no ocasionaran los sismos, los pudieran disparar.