Details of the abstract

Title of paper Magnetotelluric Images of Volcanic Zones in NE Japan Arc and
Co-seismic Deformations during the 2011 Tohoku M9 Earthquake
List of authors Masuda, S., Ogawa, Y. and Ichiki M.
Affiliation(s) Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Japan
Volcanic Fluid Research Center, Tokyo Institute of Technology, Japan
Research Center for Prediction of Earthquakes and Volcanic Eruptions, Tohoku University, Japan
Summary We have compiled wide-band magnetotelluric data collected at 590 sites over the last 30
years in NE-Japan. The period ranges are from 3ms to 2000s. Previous studies have
focused on specific volcanic or seismic zones and had restrictions such as twodimensional
modeling methodology or three-dimensional modeling with 20kmx20km scale
limitations. After compilating all the datasets, we have found strong current-channeling due
to the elongated distributions of thick sedimentary layers, which introduce high threedimensionality
data around them. We identified such strong channeling by the induced
electric field distribution and induction vectors for hypothetical event analyses using Hx
and Hy inducting fields. This nature of the dataset requires complete three-dimensional
modeling incorporating a large survey area with a 100 km x 100km scale.
We have used 410 sites in the central part of the survey area and inverted the resistivity
structure from the full impedances and induction vectors in 8 periods using WSINV3DMT
code. The most significant feature is the distribution of electrical conductors below 20 km
along the volcanic arc, which runs in the SSW-NNE directions with a 10 km width. Its
extension to the uppermost upper mantle depth shows resistivity of less than ten ohmm.
These conductors get shallower toward Quaternary volcanoes as plume-like conduits,
implying magmatic melt with potentially saline fluids in their upper part.
The distribution of those anomalous conductors at the volcanic zones has good spatial
correlations to the co-seismic crustal depressions of the M9 Tohoku earthquake in 2011
inferred by InSAR (Takada and Fukushima, 2013).
Session Keyword 4.0 Tectonics, Magmatism, Geodynamics
File upload 4.0_magnetotelluric_images_of_ogawa_01.pdf
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