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Low‐velocity zones in the crust beneath Aso caldera, Kyushu, Japan, derived from receiver function analyses
Author(s) -
Abe Yuki,
Ohkura Takahiro,
Shibutani Takuo,
Hirahara Kazuro,
Yoshikawa Shin,
Inoue Hiroyuki
Publication year - 2017
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 - 10.1002/2016jb013686
Subject(s) - geology , caldera , receiver function , seismology , sill , volcano , crust , magma , earthquake swarm , geophysics , petrology , induced seismicity , tectonics , lithosphere
Aso volcano, in central Kyushu Island in southwest Japan, has a large caldera (18 × 25 km) that formed by the ejection of more than 600 km 3 of deposits 89 thousand years ago. We calculated receiver functions from teleseismic waveform data obtained from densely distributed stations in and around the caldera. We estimated the crustal S wave velocity structure from the receiver functions by using genetic algorithm inversion. We detected a low‐velocity zone ( Vs > 2.2 km/s) at a depth of 8–15 km beneath the eastern flank of the central cones. A sill‐like deformation source has been detected at a depth of 15.5 km by analyses of GPS data, and a swarm of low‐frequency earthquakes exists at depths of 15–25 km just beneath this low‐velocity zone. Magma may be newly generated and accumulated in this low‐velocity zone as a result of hot intrusions coming from beneath it. Except for the region beneath the eastern flank of the central cones, a second low‐velocity zone ( Vs > 1.9 km/s) extends in and around the caldera at a depth of 15–23 km, although phenomena representing intrusions have not been detected below it. From the estimated velocity structure, these low‐velocity zones are interpreted to contain a maximum of 15% melt or 30% water.