HR: 08:45h
AN: V31B-04    [PDF]
TI: Precursory Seismic Activity at Guagua Pichincha Volcano, Ecuador: Implications for the Magmatic System of an Arc Volcano
AU: * Villagomez, D R
EM: darwin@newberry.uoregon.edu
AF: University of Oregon, 1272 Geological Sciences, Eugene, OR 97405 United States
AU: * Villagomez, D R
EM: darwin@newberry.uoregon.edu
AF: Instituto Geofisico, Ladron de Guevara s/n, Quito, 17 Ecuador
AU: Ruiz, M
EM: ruiz_mario@hotmail.com
AF: University of Oregon, 1272 Geological Sciences, Eugene, OR 97405 United States
AU: Yepes, H
EM: geofisico@igepn.edu.ec
AF: University of Oregon, 1272 Geological Sciences, Eugene, OR 97405 United States
AU: Hall, M L
EM: geofisico@igepn.edu.ec
AF: University of Oregon, 1272 Geological Sciences, Eugene, OR 97405 United States
AB: Earthquake activity at volcanoes can offer insight into the nature of the transport and storage of magma beneath active volcanoes. Understanding the relation between volcano seismicity and the magmatic system is important in long and short-term forecasting of volcanic activity. Guagua Pichincha, a dacitic volcano located in the western cordillera of the Ecuadorian Andes, showed two years of progressive reactivation that culminated with a dome extrusion and several dome collapses and eruptions in 1999. During the reactivation period, the volcano was continuously monitored using a network of 13 seismic stations. Guagua Pichincha showed three main types of seismic precursors. First, persistent occurrence of long-period earthquakes located 2-10 km S of the volcano (3-15 km depth) preceding the eruption by at least 20 months. Second, swarms of tectonic high-frequency events beneath the city of Quito, 10-15 km NE of the volcano (12-20 km depth), preceding the onsets of volcanic activity by 2-3 months. And third, swarms of high-frequency and long-period events, occurring below the crater (1-4 km depth), days before and during the extrusion of the lava dome. These events suggest the existence of a magmatic reservoir beneath the crater at 4-5 km depth. The deeper long-period events S of the volcano are evidence of magma being transported from mid-crustal levels to this shallower magmatic reservoir. The earthquakes of the Quito swarm may be the result of changes in the local stress regime caused by these deep magma movements. Few days before the first eruption, a rupture event manifested as swarms of high-frequency earthquakes below the crater opened the magmatic reservoir. The swarms of long-period events that followed could indicate rising magma and its interaction with the hydrothermal system. This sequence of events shows that the movement of magma and magmatic fluids through the plumbing system of a volcano could be revealed by the different types of seismicity it generates. And more importantly, that volcano seismicity can constraint the nature and time scale of these processes.
DE: 7280 Volcano seismology (8419)
DE: 8419 Eruption monitoring (7280)
DE: 8434 Magma migration
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting