Seismic activity related to the March‐April, 1982 eruptions of El Chichon Volcano, Chiapas, Mexico

Interesting seismic activity occurred before, during, and following the recent eruptions of El Chichon Volcano in southeastern Mexico. Several eruptions took place in late March and early April 1982, ejecting large amounts of andesitic ash and pumice. The first eruption was preceded by one month of intense shallow seismicity (h∼5km). Two days before the first eruption of March 29, the seismicity changed character and was most likely shallow (h∼2km). This shallow seismicity continued until the last and probably largest eruption on April 4, after which only deep seismicity was observed (h∼15km). The different nature of shallow events and deep events suggest that the former are directly related with the magma movements and ground water interactions while the latter are probably controlled by regional tectonic stresses, acting on the weakened region left by the eruption at those depths.