Strain concentration zone along the volcanic front derived by GPS observations in NE Japan arc

Abstract

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.

Strain anomalies induced by the 2011 Tohoku Earthquake (M w 9.0) as observed by a dense GPS network in northeastern Japan

“…This pattern may raise the possibility of a difference in the deformability of the forearc (eastern part) and backarc (western part) of the crust. In the interseismic period, the strain rate field indicates a tendency for a relatively small contraction in the forearc region and a large contraction in the backarc region (Miura et al, 2004; Fig. 1).…”

“…The EE regions also appear at the eastern and western side of the ED region in the OBR. The former is considered to be a branch of the strain concentration zone along the OBR (Miura et al, 2004). These areas correspond to sedimentary basins (Sendai and Yamagata basins).…”

“…However, assuming that the lower crust beneath the strain concentration zone has already relaxed to some extent, as suggested in the hypothesis, the elastic strain accumulation over the crust thickness is smaller than that of the surrounding area. Therefore, the Miura et al, 2004). The effect of interplate coupling is eliminated from a predicted model (Suwa et al, 2006).…”

“…1). Contemporary global positioning system (GPS) measurements have revealed a strain concentration zone along the Ou-backbone range (OBR), which runs through the center of the Tohoku region (Miura et al, 2004;Fig. 1).…”

Deep structure of the Ou mountain range strain concentration zone and the focal area of the 2008 Iwate-Miyagi Nairiku earthquake, NE Japan—seismogenesis related with magma and crustal fluid

“…Deformation of the island arc crust due to this compressive stress can be observed from global positioning system (GPS) data. Figure 1 shows the east-west strain distribution obtained from GPS data acquired by the Geographic Survey Institute and Tohoku University between 1997 and 2001 (Miura et al, 2004). Blue indicates regions of compressive strain and red shows regions of tensile strain.…”