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A fluid‐rich layer along the Nankai trough megathrust fault off the Kii Peninsula inferred from receiver function inversion
Author(s) -
Akuhara Takeshi,
Mochizuki Kimihiro,
Kawakatsu Hitoshi,
Takeuchi Nozomu
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 - 10.1002/2017jb013965
Subject(s) - geology , receiver function , seismology , inversion (geology) , submarine pipeline , subduction , explosive material , seismometer , peninsula , fault (geology) , waveform , petrology , tectonics , geotechnical engineering , lithosphere , chemistry , organic chemistry , history , physics , archaeology , quantum mechanics , voltage
Investigation of fluid distribution along megathrust faults is an important issue, since the fluid affects frictional properties and thus slip behavior on faults. Scattered teleseismic phases, or receiver functions (RFs), have made significant contributions to understanding the fluid content of subducting plates beneath the onshore regions but have been rarely applied in offshore settings. In this study, we conducted receiver function inversion analysis to investigate detailed seismic properties near the megathrust fault using ocean bottom seismometers deployed off the Kii Peninsula, southwest Japan. RFs were calculated at high frequencies (up to 4 Hz), removing the effect of water reverberations from vertical component records. Our inversion was performed in two steps: first, we modeled sediment layer by a simple stacking method and then solved for deeper structure by a waveform inversion. The results indicate the presence of a thin low‐velocity zone (LVZ) of a thickness of 0.2–1.2 km with a S wave velocity of 0.7–2.4 km/s along the plate interface. We interpret this LVZ as thin fluid‐rich sediment layer between the overriding and subducting plates that acts as a pathway of fluid migration.