Conductivity distribution and seismicity in the northeastern Japan Arc

Abstract

Wideband magnetotelluric (MT) observation data were obtained from 91 sites along six transects in the central part of the Japan Arc. Here, a quasi-3D georesistivity distribution, in addition to other geophysical and geological parameters, is used to better understand seismicity in the region. We found that high seismicity in the Central Mountain Range is due to relatively poor fluid saturation caused by volcanism. The high conductive fracture zone in the west of the Central Basin without big earthquakes is characterized by a low Poisson ratio. It is suggested that strains cannot be accumulated in those regions. The Miyagi-ken-hokubu region with a frequent occurrence of large earthquakes, is conductive-high Poisson ratio-high V p suggesting that the zone is relatively fluid-rich and brittle.

Joint inversion for Vp, Vs, and Vp/Vs at SAFOD, Parkfield, California

“…Many studies have shown significant correlations between electrical resistivity and seismic velocity structure, both theoretical [ Schmeling , 1986; L. MacGregor, personal communication, 2007] and empirical at a variety of scales (borehole logs [ Herwanger , 2001], cross‐hole tomography [ Herwanger et al , 2004; Saunders et al , 2005], local crustal models [ Eberhart‐Phillips et al , 1995], and crustal transects [ Fujinawa et al , 2002]). Unsworth et al [1997, 2000] and Unsworth and Bedrosian [2004] have developed a high‐resolution image of the resistivity structure near SAFOD using continuous MT profiling (Figure 7).…”

“…MacGregor, personal communication, 2007] and empirical at a variety of scales (borehole logs [Herwanger, 2001], cross-hole tomography Figure 7. Across-fault cross sections of the geology [Bradbury et al, 2007], Vp, Vp/Vs, Qp [Bennington et al, 2008], and resistivity [Herwanger et al, 2004;Saunders et al, 2005], local crustal models , and crustal transects [Fujinawa et al, 2002]). Unsworth et al [1997Unsworth et al [ , 2000 and Unsworth and Bedrosian [2004] have developed a high-resolution image of the resistivity structure near SAFOD using continuous MT profiling (Figure 7).…”

Electrical Resistivity Structure and Helium Isotopes around Naruko Volcano, Northeastern Japan and Its Implication for the Distribution of Crustal Magma

“…The inclusion of even a small amount of connected melt or fluids beneath a volcano can greatly decrease the bulk resistivity of the rock mass. Although recent MT studies have investigated the two-dimensional (2D) electrical resistivity structure in several locations in northeastern Japan (e.g., [12][13][14]), the crustal magma distribution related to seismological regimes beneath Naruko volcano has not been clearly imaged yet.…”