5:15 PM - 6:45 PM
[SEM12-P09] Time-series analysis of the MT data observed in the Izu-Oshima
Izu-Oshima is an active island volcano in Japan that erupts about every 35 years. The latest eruption occurred in 1986, and it is possible that it will erupt in the near future. Thus, it is important to understand the subsurface structure of Izu-Oshima. Previous studies have estimated the velocity structure using sea-shots (Morita et al., 2021; Watanabe et al., 2023), the source location of geodetic change using GPS data (Watanabe 2012), the depth of magma reservoir from petrological analysis of the ejecta (Aramaki and Fujii, 1988), and the shallow 2-D resistivity structure (Onizawa et al., 2009). Based on the above, the location of the expansion source and the magmatic system of the 1986 eruption are revealed. However, the location and size of the magma reservoir at Izu-Oshima is not revealed. Thus, the purpose of our study is to estimate the spatial distribution of the present magma reservoir.
Magnetotelluric (MT) surveys are effective tools for investigating the existence of magma within a volcano. In 2021-2022, Earthquake Research Institute, the University of Tokyo (ERI) and Japan Agency for Marine-Earth Science and Technology (JAMSTEC) conducted joint land and marine MT observations on Izu Oshima. The land data were obtained from a total of 11 points at Izu-Oshima for about 40 days, with sampling frequencies of 32 Hz and 1024 Hz. The marine data were obtained from a total of 10 points on the seafloor around Izu-Oshima for about one year, with sampling frequencies of 8 Hz and 0.1 Hz. In this study, we use these data to apply 3D inversion and aim to estimate the resistivity structure of Izu Oshima.
First, we performed a time-series analysis by using BIRRP (Bounded Influence Remote Reference Processing) (Chave and Thomson, 2004). BIRRP is a spectrum analysis program that converts electromagnetic field time series data into the frequency domain by fast fourier transform (FFT) and calculates the response function for each frequency. BIRRP is characterized by its ability to reduce the impact of outliers by using data from remote reference sites, and to provide robust estimation by weighting the data according to its quality.
In this study, we calculated response functions for sampling frequencies of 32 Hz and 1024 Hz with data from Okura Village, Yamagata Prefecture, as a remote reference site. By adjusting parameters of BIRRP while using a large number of data, response functions with small errors could be calculated at many observation points in the frequency range of 0.78×10-2 Hz to 384 Hz. Therefore, this presentation will primarily focus on time-series analysis and discuss frequency and spatial distribution of the MT response functions.
Acknowledgment:
This study was supported by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan, under its The Second Earthquake and Volcano Hazards Observation and Research Program (Earthquake and Volcano Hazard Reduction Research). Remote reference data were kindly offered by Geothermal Energy Research & Development Co., Ltd.
Magnetotelluric (MT) surveys are effective tools for investigating the existence of magma within a volcano. In 2021-2022, Earthquake Research Institute, the University of Tokyo (ERI) and Japan Agency for Marine-Earth Science and Technology (JAMSTEC) conducted joint land and marine MT observations on Izu Oshima. The land data were obtained from a total of 11 points at Izu-Oshima for about 40 days, with sampling frequencies of 32 Hz and 1024 Hz. The marine data were obtained from a total of 10 points on the seafloor around Izu-Oshima for about one year, with sampling frequencies of 8 Hz and 0.1 Hz. In this study, we use these data to apply 3D inversion and aim to estimate the resistivity structure of Izu Oshima.
First, we performed a time-series analysis by using BIRRP (Bounded Influence Remote Reference Processing) (Chave and Thomson, 2004). BIRRP is a spectrum analysis program that converts electromagnetic field time series data into the frequency domain by fast fourier transform (FFT) and calculates the response function for each frequency. BIRRP is characterized by its ability to reduce the impact of outliers by using data from remote reference sites, and to provide robust estimation by weighting the data according to its quality.
In this study, we calculated response functions for sampling frequencies of 32 Hz and 1024 Hz with data from Okura Village, Yamagata Prefecture, as a remote reference site. By adjusting parameters of BIRRP while using a large number of data, response functions with small errors could be calculated at many observation points in the frequency range of 0.78×10-2 Hz to 384 Hz. Therefore, this presentation will primarily focus on time-series analysis and discuss frequency and spatial distribution of the MT response functions.
Acknowledgment:
This study was supported by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan, under its The Second Earthquake and Volcano Hazards Observation and Research Program (Earthquake and Volcano Hazard Reduction Research). Remote reference data were kindly offered by Geothermal Energy Research & Development Co., Ltd.