Some aspects of the seismicity associated with the 1982 eruption of El Chichon Volcano, Chiapas, Mexico

We review the different phases of the seismicity related to the 1982 eruption of El Chichon Volcano, Chiapas, Mexico. The pre-eruption seismicity was already anomalous by late 1980, became significant by late 1981 and increased towards 28 March, 1982, when the first eruptive event occurred. A noticeable feature within the 7-day period of unrest is the occurrence of three earthquake swarms before the devastating explosions of 3 and 4 April 1982 (local time). The periodicity and appearance of the swarms, close to the time of maximum tidal strain, suggests a large overpressure in the magmatic system, and the triggering of the events by the earth tides. The post-eruption seismicity occurred mostly in a radius 5 km from the crater and a depth range 11 to 15 km suggesting that this region was a deeper reservoir of the erupted magma.