Magnetotelluric measurements at Kusatsu-shirane Volcano

*Sabri Bulent Tank[1] ,Yasuo Ogawa [1],Yoshimori Honkura [1]
Masaki Matsushima [1],Jun-ichi Hirabayashi [1]
Michiko Ohwada [1],Kazushige Nakamura [1]
Takashi Suzuki [1]
Tokyo Institute of Technology[1]

We collected wide-band magnetotelluric data at the Kusatsu-shirane Volcano. On the northeastern side of the summit crater Yugama, N-type earthquakes and decrease of total magnetic force were observed. These are thought to be resulting from volcanic fluid movements. However the geophysical structure is not known to fully understand the phenomena. Magnetotelluric method was chosen since resistivity is sensitive to fluids. We covered an area of 2 km x 2 km around the summit. We had 2 magnetotelluric and 22 telluric-only stations. Preliminary results show that upper layer (several hundred meters thick) of 10 to 100 ohmm, underlain by a conductor (<1 ohmm). Resistive basement is only sensed by one mode where the electric field is in north - south direction. This may suggest that resistive basement is dipping towards east.