Abstract
The relation between the Pinatubo eruption of 1991 and the Philippine earthquake of 1990 is studied on the basis of strain changes calculated from a fault model of the Philippine earthquake. At Pinatubo volcano, which is located 100 km away from the earthquake fault, the volumetric strain change induced by the earthquake is about 10-6. This caused gradual squeeze up of magma to the surface and the Pinatubo volcano erupted eleven months after the earthquake. The volumetric change calculated by a fault model of the 1990 earthquake is, however, several orders of magnitude smaller than the total volume observed during the eruptions. The magma squeezing model alone cannot explain the whole volume of ejected magma. A possible interpretation is that the volumetric strain change could have squeezed up magma in the magma reservoir, resulting in lowering the density of magma and enhanced the magma to rise further more. Such a positive feedback process could have occurred after the Philippine earthquake of 1990. It is possible that the Philippine earthquake triggered the activity of Pinatubo volcano.
