Three-dimensional P-wave Velocity Structure of Tungurahua Volcano, Ecuador

HR: 0800h
AN: V11B-1427 [Abstracts]
TI: Three-dimensional P-wave Velocity Structure of Tungurahua Volcano, Ecuador
AU: * Molina, I
EM: imolina@igepn.edu.ec
AF: Instituto Geofisico, Escuela PolitＤnica Nacional, Avda Ladron de Guevara s/n y Patria. Edificio de Ing. Civil, 6 piso, Insituto Geof, Quito, PIC 17-01-2759 Ecuador
AU: Kumagai, H
EM: kumagai@bosai.go.jp
AF: National Research Institute for Earth Science and Disaster Prevention, 3-1 Tennodai, Tsukuba, Ibaraki 305-0006, Tsukuba, TSU 305-0006 Japan
AU: Le Pennec, J
EM: lepennec@ird.fr
AF: Institut de Recherche pour le DＷeloppement, Whymper 442 y Coruna, Quito, PIC 17-01-2759 Ecuador
AU: Hall, M
EM: mhall@igepn.edu.ec
AF: Instituto Geofisico, Escuela PolitＤnica Nacional, Avda Ladron de Guevara s/n y Patria. Edificio de Ing. Civil, 6 piso, Insituto Geof, Quito, PIC 17-01-2759 Ecuador
AB: Tungurahua Volcano in the Ecuadorian Andes is a large andesitic stratovolcano (5023 m) that has been erupting mildly since 1999. We studied the three-dimensional (3-D) P-wave velocity (Vp) structure beneath the volcano down to 5 km below sea level. We inverted 1708 P-wave first arrival times from 263 volcano-tectonic (VT) earthquakes recorded by 5 to 10 1 Hz vertical seismic stations on the volcano from August 1999 to May 2003. A non-linear inversion method was used to image the velocity structure, in which first-arrival times were calculated with a finite-difference method. The hypocenters in our model are tightly clustered and aligned roughly along a vertical structure at depths between sea level and the summit crater. A high-velocity zone exists above the central base of the volcano under the vertically aligned hypocenters, and may be interpreted as the source zone for recharge of the shallow magmatic system. High-velocity zones are also identified under the lower northeastern and southern flanks of the edifice. The northeast anomaly extends down to 1 km below sea level and possibly represents an old volcanic conduit. The southern high-velocity anomaly is underlain by a relatively low-velocity zone and its geometry suggests an old lateral dike system connected at depth to the central conduit. Except for these high-velocity zones in the central, northern, and southern flanks, the volcanic edifice is composed of low-velocity materials down to a depth of 2 km above sea level. These low velocities correlate with young unconsolidated deposits, and older highly fractured and/or altered volcanic materials.
DE: 1700 HISTORY OF GEOPHYSICS
DE: 1749 Volcanology, geochemistry, and petrology
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting