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Overpressured Underthrust Sediment in the Nankai Trough Forearc Inferred From Transdimensional Inversion of High‐Frequency Teleseismic Waveforms
Author(s) -
Akuhara Takeshi,
Tsuji Takeshi,
Tonegawa Takashi
Publication year - 2020
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2020gl088280
Subject(s) - forearc , geology , seismology , subduction , trough (economics) , inversion (geology) , accretionary wedge , sediment , geomorphology , tectonics , economics , macroeconomics
Active‐source seismic surveys have resolved the fine‐scale P ‐wave velocity ( V p ) of the subsurface structure in subduction forearcs. In contrast, the S ‐wave velocity ( V s ) structure is poorly resolved despite its usefulness in understanding rock properties. This study estimates V p and V s structures of the Nankai Trough forearc, by applying transdimensional inversion to high‐frequency teleseismic waveforms. As a result, a thin ( ∼ 1 km) low‐velocity zone (LVZ) is evident at ∼ 6 km depth beneath the sea level, which is located ~3 km seaward from the outer ridge. Based on its high V p / V s ratio ( ∼ 2.5) and comparison to an existing seismic reflection profile, we conclude that this LVZ reflects a high pore pressure zone at the upper portion of the underthrust sediment. We infer that this overpressured underthrust sediment hosts slow earthquake activities and that accompanied strain release helps impede coseismic rupture propagation further updip.