Earth Planets Space, Vol. 56 (No. 12), pp. 1347-1355, 2004
Satoshi Miura, Toshiya Sato, Akira Hasegawa, Yoko Suwa, Kenji Tachibana, and Satoshi Yui
Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
(Received May 31, 2004; Revised September 29, 2004; Accepted October 22, 2004)
A nationwide GPS array with more than 1,000 permanent stations operated by the Geographical Survey Institute of Japan, has provided many invaluable deformation data such as co- and post-seismic, volcanic, and ongoing secular deformations in the Japanese islands. Based on daily coordinate data of the GEONET stations together with results from a regional network operated by Tohoku University, we derived a map of the strain rate distribution in NE Japan showing that there exists a notable strain concentration zone of EW contraction along the Volcanic Front. The area demonstrates active seismicity including some disastrous earthquakes. Recent seismic tomography studies have revealed the existence of inclined seismic low-velocity zones (LVZ) at depths shallower than ~150 km in the mantle wedge sub-parallel to the subducted slab. The inclined LVZ reaches the Moho right beneath the Volcanic Front, indicating that the formation of the strain concentration zone is closely related to the rheological structure of the island-arc system.
Key words: Strain concentration zone, Volcanic front, Inland earthquakes, GPS.