Studies of the Georesistivity Structure in the Central Part of the Northeastern Japan Arc

Abstract

Wideband magnetotelluric measurements were conducted along three traverses in the central Tohoku district of the northeastern Japan arc. These data provide independent constraints for understanding seismo-tectonics and geology where the Pacific plate subducts beneath the Eurasian plate. Smooth twodimensional models of the data acquired along the three transects were obtained using the Generalized Rapid Relaxation Inversion algorithm. Modeling suggest that the area can be reasonably treated as twodimensional with the structural direction being north-south in agreement with the strikes of geological units. The three 2-D models correlate well with the regional geological morphology in the central part of the Tohoku district which is divided by three high altitude regions. The resistivity profiles indicate two clear conductive anomalies in the Central Basin Range and in the Kitakami, Abukuma river regions that show considerable variability in each of the three 2-D models. Boundaries of conductive bodies correlate well with mapped faults, including those of pre-Tertiary age. The northernmost cross section is more complex possibly because of the presence of Quaternary volcanoes and an active geothermal source area in the vicinity.

2-D georesistivity structure in the central part of the northeastern Japan arc

“…We used the impedance tensors fully corrected for the three-dimensional galvanic distortion effects including static shift effects in order to refine previous 2-D models (discussed in Fujinawa et al, 1997). The subsurface 3-D effects are found to be generally small with the result of a slight difference between the present model and the previously reported one.…”

Local Galvanic Distortions in the Central Part of North-Eastern Japan (Part 1)

“…1). Many geological and geophysical studies have been conducted in this district (see Fujinawa et al, 1997, hereafter cited as F). Ogawa (1987a) carried out two-dimensional resistivity modeling based on a regional broadband magnetotelluric survey following earlier studies by Honkura (1974), Ogawa etal.…”

“…Site gain factors, one of the GBD distortion parameters, are not dealt with here. Static shift corrections are made using TEM data (Fujinawa et al, 1997) to complete the evaluation of galvanic distortion effects.…”

Conductivity distribution and seismicity in the northeastern Japan Arc

“…The final TM mode 2-D models along the three long tra- Fujinawa et al, 1997). Miocene and Quaternary volcanic fronts are shown with several tectonic lines.…”

“…Magnetotelluric observation data are briefly described here (see Fujinawa et al, 1997Fujinawa et al, , 1999. Broadband magnetotelluric data were acquired along six traverses (A, B, C, D, Copy right c The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences.…”