TY - JOUR
T1 - Overpressured Underthrust Sediment in the Nankai Trough Forearc Inferred From Transdimensional Inversion of High-Frequency Teleseismic Waveforms
AU - Akuhara, Takeshi
AU - Tsuji, Takeshi
AU - Tonegawa, Takashi
N1 - Funding Information:
We thank Rie Nakata (Kamei) for providing the velocity model. We also thank anonymous reviewers for their insightful comments. This study was supported by JSPS KAKENHI Grant JP16H06472, JP16H06475, JP19K14811, JP19K21892, and JP20H01997.
Publisher Copyright:
© 2020. The Authors.
PY - 2020/8/16
Y1 - 2020/8/16
N2 - Active-source seismic surveys have resolved the fine-scale P-wave velocity (Vp) of the subsurface structure in subduction forearcs. In contrast, the S-wave velocity (Vs) structure is poorly resolved despite its usefulness in understanding rock properties. This study estimates Vp and Vs 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 Vp/Vs 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.
AB - Active-source seismic surveys have resolved the fine-scale P-wave velocity (Vp) of the subsurface structure in subduction forearcs. In contrast, the S-wave velocity (Vs) structure is poorly resolved despite its usefulness in understanding rock properties. This study estimates Vp and Vs 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 Vp/Vs 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.
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U2 - 10.1029/2020GL088280
DO - 10.1029/2020GL088280
M3 - Article
AN - SCOPUS:85089374502
SN - 0094-8276
VL - 47
JO - Geophysical Research Letters
JF - Geophysical Research Letters
IS - 15
M1 - e2020GL088280
ER -