2:15 PM - 2:30 PM
[SEM16-03] Continuous Magnetotelluric Measurements at Kusatsu-Shirane Volcano
Keywords:MT, monitoring, volcano
We recorded continuous magnetotelluric (MT) data from the Yugama crater at the top of Kusatsu-Shiranesan (Mt. Kusatsu-Shiranesan), and investigated its temporal variation. MT can be used to monitor phreatomagmatic eruptions by detecting the distribution of fluids and clay minerals characteristic of volcanic hydrothermal systems. We analyzed two data sets: (1) the continuous data from May 14, 2021 to October 23, 2021 at Yugama, the simultaneous data at a station about 400m from Yugama for comparison, and (2) the annual repeat campaign data from 2007 to 2021. First, we analyzed the continuous observation data of 2021 by day and focused on the time series of impedance, apparent resistivity, and phase in order to see the variation of resistivity structure. As a result, we found temporal variations in apparent resistivity and phase on the order of one month, but there was a possibility that these variations included variations in the resistivity structure in very shallow areas near the observation points. In order to eliminate it, we performed a phase-tensor analysis and found a pronounced variation at a period of 0.31s. In order to investigate the spatial extent of this variation, we also analyzed the simultaneous records at a point 400m south of the Yugama station. It was suggested that the resistivity fluctuation around Yugama extends over 500 meters. Next, we analyzed the data from Yugama, which has been observed repeatedly every year since 2007, and found that the phase tensor at period 0.031s has been decreasing every year since 2014, when Kusatsu-Shirane volcano became active. In this study, we were able to find temporal variations in the resistivity structure, but it is necessary to study how to reinterpret these variations into the structure in the future.