Seismic velocity structure around the Hyuganada region, Southwest Japan, derived from seismic tomography using land and OBS data and its implications for interplate coupling and vertical crustal uplift

M. Tahara, K. Uehira, H. Shimizu, M. Nakada, T. Yamada, K. Mochizuki, M. Shinohara, M. Nishino, R. Hino, H. Yakiwara, H. Miyamachi, K. Umakoshi, M. Goda, N. Matsuwo, T. Kanazawa

研究成果: Contribution to journalArticle査読

27 被引用数 (Scopus)

抄録

The Hyuganada region, a forearc region of Southwest Japan, is characterized by several interesting geological and geophysical features, i.e., significant aseismic crustal uplift of ∼120 m during the past ∼120 thousand years at the Miyazaki Plain, negative free-air gravity anomalies with the maximum magnitude of -130 mgal, and relatively less cohesive interplate coupling compared with that for off the Shikoku and Kii Peninsula. In order to examine the causes of these observations, we determined a detailed three-dimensional seismic velocity structure based on the seismic data observed by ocean bottom seismometers (OBS) and land stations. P- and S-wave tomographic velocity structures clearly indicate the subducting slab and also the zones of high Poisson's ratio at 25-35 km depth along the coastline of the northeastern part of the Hyuganada. The region with high Poisson's ratio may correspond to the serpentinized mantle wedge as suggested for other mantle wedges, and appears to be coincident with the zone for observed aseismic slips such as the slow-slip and after-slip events. Also, the detection may be related to a relatively weak interplate coupling in the Hyuganada region. The tomographic structures also indicate low velocity zones with a horizontal scale comparable to the Kyushu-Palau Ridge in and around the subducting slab. If we assume that the low velocity zones correspond to the subducted Kyushu-Palau Ridge, then the predicted gravity anomaly due to the density contrast between the low velocity zones and the surrounding region can explain about 60% of the gravity anomaly in the Hyuganada region. The buoyancy is probably an important factor for the crustal uplift observed in the Miyazaki Plain, the steep bending of the subducting slab and the normal fault-type earthquakes around the Hyuganada region.

本文言語英語
ページ(範囲)19-33
ページ数15
ジャーナルPhysics of the Earth and Planetary Interiors
167
1-2
DOI
出版ステータス出版済み - 3 2008

All Science Journal Classification (ASJC) codes

  • 天文学と天体物理学
  • 地球物理学
  • 物理学および天文学(その他)
  • 宇宙惑星科学

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