四国西部域での広帯域MT観測

Abstract

Recent geodetic observations detect recurrent slow slip events (SSE), which occurred beneath the Bungo Channel and southwest Shikoku Island, with interval of approximately 6 years (e.g. GSI, 2010). In order to reveal a three-dimensional resistivity structure around SSE region, we are carrying out wideband magnetotelluric (MT) surveys. We also plan to establish a permanent long-term MT monitoring network that aims to detect temporal changes of resistivity structure during SSE cycle. As of June, 2016, MT surveys were performed at 31 sites by using Phoenix wideband MT instruments. In the most of sites, high quality MT responses were obtained using the BIRRP code (Chave and Thomson, 2004) for the period range 0.01 to 10, 000 sec. The spatial distributions of the phase tensor ellipses and the induction vectors suggest that resistivity contrasts are located around SSEs.