HR: 16:30h
AN: V14B-03    [Abstracts]
TI: Source Process of Volcanic Tremor Inferred From Waveform Inversion
AU: * Garcia-Aristizabal, A
EM: agarcia@igepn.edu.ec
AF: Instituto Geofisico, Escuela Politecnica Nacional, Quito, 2759 Ecuador
AU: Kumagai, H
EM: kumagai@bosai.go.jp
AF: National Research Institute for Earth Science and Disaster Prevention, 3-1 Tennodai, Tsukuba 305-0006, Tsukuba, 0006 Japan
AU: Nakano, M
EM: nakano@sharaku.nuac.nagoya-u.ac.jp
AF: School of Environmental Studies, Nagoya University, Nagoya 464-8601, Nagoya, 8601 Japan
AB: Guagua Pichincha located 12 Km west of Quito, Ecuador, is an active volcano in the Pichincha volcanic complex. Beginning on August 7 1998, Guagua Pichincha activity was characterized by phreatic eruptions, dome growth and collapse, and pyroclastic flows, accompanying volcano-tectonic earthquakes, tremor, and long-period events. In January 2003, after a two-year-long quiescent period, we observed tremor showing harmonic oscillations with a dominant spectral peak at around 2 Hz, which occurred periodically showing well-constrained tremor episodes with active periods of 11 minutes and repose periods of 30 minutes. This type of tremor sequence continued for a few months, and has intermittently occurred until the present. We performed waveform inversions of the tremor to quantify the source process. Since it was recorded only by three seismic stations (three-component seismometers at two stations and a vertical-component seismometer at one station) which are not enough for an accurate description of a moment tensor for the source of tremor, we performed waveform inversions assuming the moment tensors for both horizontal and vertical cracks, and a vertical pipe, which are possible geometries for the source of tremor. We obtained a vertical crack with the strike direction of N80§E in the northern rim of a dome at a depth nearly 200 m below the caldera floor as the best-fit solution for our inversions. The tremor may be interpreted as the resonance of a vertical crack-like conduit excited during repetitive releases of hot gases which are originating from the contact of hydrothermal water with magma inside the dome.
UR: http://www.igepn.edu.ec
DE: 8419 Eruption monitoring (7280)
DE: 9360 South America
DE: 7280 Volcano seismology (8419)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting