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Source process of long‐period seismic events at Taal volcano, Philippines: Vapor transportation and condensation in a shallow hydrothermal fissure
Author(s) -
Maeda Yuta,
Kumagai Hiroyuki,
Lacson Rudy,
Figueroa Melquiades S.,
Yamashina Tadashi
Publication year - 2013
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1002/jgrb.50205
Subject(s) - volcano , fissure , geology , waveform , seismology , magma , water vapor , earthquake swarm , hydrothermal circulation , condensation , mineralogy , meteorology , physics , induced seismicity , paleontology , quantum mechanics , voltage
We analyzed observations of a swarm of more than 40,000 long‐period (LP) seismic events at Taal volcano, Philippines, in 2010–2011. The event waveforms are strongly correlated to each other, consistent with a fixed source location, and begin with a dilatational first motion. They have a peak frequency around 0.8 Hz and a quality factor Q of 6. Waveform inversion of the events pointed to a tensile crack source dipping 30°–60° at a shallow (100–200 m) depth. A simulation using a fluid‐filled crack model indicated that the complex frequencies of the waveforms are explained by the fundamental longitudinal mode resonance of a vapor‐filled crack 188 m long. A satellite thermal infrared image acquired during the swarm period suggests that the LP events were not accompanied by surface gas releases. We considered a vapor transportation model in which vapor exsolved from magma and rose in a fissure extending to the LP source. This model yielded estimates that 10 5 –10 7 m 3 of magma was involved in the LP swarm and that the temperature of vapor in the LP source crack was around 600 K. We modeled a triggering mechanism of the crack resonance based on sudden condensation of vapor at the crack tip in a cold aquifer. This model explained observed characteristics of the events including the dilatational first motion, the total volumetric change, and the fixed source location.