17:15 〜 18:30
[SEM12-P01] Characteristic features of the response functions estimated from a wide-band magnetotelluric (MT) data in the southern Tohoku area
キーワード：比抵抗構造、南東北、地磁気地電流法観測
Following the 2011 great Tohoku earthquake, intense shallow earthquakes were observed at the Iwaki area, which is the fore-arc side of the southern Tohoku, Japan. At the same time, high strain rate accumulation at the back-arc side which corresponds to the Niigata-Kobe Tectonic Zone (NKTZ) was observed before the Tohoku earthquake and continues to this day. In addition, prominent geothermal activities are distributed along the backbone range in the central part of the area. We are encouraged to study the mechanism of those crustal activities from the electrical conductivity structure. By combining the result with the seismic and geodetic data, the physical processes of those activities can be comprehensively understood.
We performed a four years wide-band MT campaign (2015-2018) that consists of 3 survey lines, which respectively contain about 15 stations, along an approximately NW-SE profile running across the southern Tohoku. We simultaneously recorded 5-channel EM data or 2-channel E data with the basic sampling rate of 32Hz (continuous measurement) and 1024Hz (4 hours mid-night). Two-component horizontal magnetic field data at Yamagata prefecture are also used as the remote reference (Gamble et al., 1979). In this presentation, we discuss the preliminary analysis of the 25 days data obtained in 2015 along one of the 3 lines.
The time series were processed using the BIRRP robust inversion code by Chave and Thomson (2004). We computed the MT impedance and the vertical-horizontal magnetic field response. The apparent resistivities of the middle station are very high for the entire period range while those of the neighboring stations are relatively low. The phases also confirmed this laterally alternating structure. The principal 2D strike directions estimated using the phase tensor (Caldwell et al., 2004) seemed period- and site-dependent as well as the normalized skew angle. The consistency between the induction arrows and phase tensors will be discussed in the presentation. In addition, we also estimated the inter-station horizontal magnetic field transfer function in which the spatial variation of the horizontal magnetic field among the stations is examined.
We performed a four years wide-band MT campaign (2015-2018) that consists of 3 survey lines, which respectively contain about 15 stations, along an approximately NW-SE profile running across the southern Tohoku. We simultaneously recorded 5-channel EM data or 2-channel E data with the basic sampling rate of 32Hz (continuous measurement) and 1024Hz (4 hours mid-night). Two-component horizontal magnetic field data at Yamagata prefecture are also used as the remote reference (Gamble et al., 1979). In this presentation, we discuss the preliminary analysis of the 25 days data obtained in 2015 along one of the 3 lines.
The time series were processed using the BIRRP robust inversion code by Chave and Thomson (2004). We computed the MT impedance and the vertical-horizontal magnetic field response. The apparent resistivities of the middle station are very high for the entire period range while those of the neighboring stations are relatively low. The phases also confirmed this laterally alternating structure. The principal 2D strike directions estimated using the phase tensor (Caldwell et al., 2004) seemed period- and site-dependent as well as the normalized skew angle. The consistency between the induction arrows and phase tensors will be discussed in the presentation. In addition, we also estimated the inter-station horizontal magnetic field transfer function in which the spatial variation of the horizontal magnetic field among the stations is examined.