One-dimensional resistivity modeling of NE Japan from stationary wide-band magnetotelluric data

Stationary magnetotelluric (MT) systems were set up at the Esashi station and the Mizusawa Geodetic Observatories of Geographical Survey Institute (GSI) in NE Japan. Since 1996, continuous 24 h resistivity and phase data have been acquired by the wide-band MT measurement devices. The data from the two sites were processed by the remote reference technique to minimize the effect of local noise. Data quality at the Mizusawa was sometimes poor, but use of the data as reference improved the MT data of the Esashi station. As a result, extremely stable apparent resistivity and phase curves were obtained from the Esashi station. The resistivity structure of NE Japan was estimated using two ways of 1-D modelling procedure by evaluating the stability of apparent resistivity and phase data. The modelling suggests the existence of anomalous layers which represent anisotropic or inhomogeneous crust and/or upper mantle structures of the NE Japan of fore-arc. These features may relate with Cretaceous tectonic events.