Magma ascent and the extent of the Pinatubo volcano conduit inferred from the 1991 pre-eruption seismicity


G.M. Besana*,+, M. Ando*, T.Ohkura#, J.A. Daligdig+ and R.S. Punongbayan+

*Research Center for Earthquake Prediction, Disaster Prevention Research Institute, Kyoto University, Kyoto, Japan 611-0011

+Philippine Institute of Volcanology and Seismology, Quezon City, Philippines 1104

#Integrated Human Studies, Faculty of Science, Kyoto University, Kyoto, Japan 606




The Pinatubo volcano magma migrates at the rate of 1-4km/day along a cylindrical conduit several days prior to its climactic eruption in June 15, 1991. These were inferred from the observed "A-type", "BH-type" and "BL-type" earthquakes in the volcano. The analysis were done after relocation and classification of events based on the Minakami classification scheme. Since "A-type" events are generally related to rock fracturing while "BH-type" and "BL-type" earthquakes to gaseous explosions along the conduit, the results for Pinatubo volcano indicate the state of the magma along the conduit and the velocity of the ascending magma 4-9 days prior to its climactic eruption. The results therefore emphasize the usefulness of the recognition and monitoring of these types of volcanic earthquakes and their viability as a tool for monitoring volcanic activity and possibly, even in forecasting an impending eruption.

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