2:30 PM - 2:45 PM
[SVC26-16] 3-D resistivity structure under the Kikai submarine caldera volcano.
Keywords:magnetotelluric survey, Kikai caldera submarine volcano, resistivity structure, magma supply system
This study aims to better understand the magma supply system leading to giant caldera eruptions. To understand the current status of the magma supply system, we estimate the resistivity structure of the subsurface in the volcanic sea area. Our target is the Kikai submarine caldera volcano, located in the southern part of Kagoshima Prefecture. This volcano has lava dome inside its caldera rim, and it is proposed that this dome has been fed with magma even after the latest giant caldera eruptions at 7.3 ka (Tatsumi et al., 2018).
We conducted ocean-bottom MT observations by Ocean Bottom ElectroMagnetometers (OBEMs) at 32 points to image a sub-seafloor 3-D resistivity structure under the Kikai caldera volcano.
We estimated the MT response function using BIRRP (Chave and Thomson, 2004). In the MT response function, the two main features were found: yx of apparent resistivities tend to be larger than xy of ones; yx of MT responses' uncertainty tend to be smaller than yx of ones. Since the observation points were at shallow sea area, the MT data were affected by tilt and temperature changes caused by ocean currents.
A 3-D resistivity model was estimated using the MT inversion code ModEM+FS. This code is based on ModEM (Egbert and Kelbert, 2012; Kelbert et al., 2014) and can handle the undulating bathymetry by applying the FS method (Baba and Seama, 2002) to sea layers. By testing the estimation accuracy using actual observed MT data, it has been verified that conductive anomaly can be restored within the appropriate horizontal range by ModEM+FS.
We inverted only quality MT responses, and check the reliability of each anomaly in estimated model. In addition to that, we inverted same data using other MT inversion code FEMTIC (Usui 2015; Usui et al. 2017), and compare the estimated models. The results show that the estimated model has two reliable conductive anomalies. One conductive anomaly (C1) is located under the lava dome at depth ~1-5 km. The other one (C2) is connecting to C1 and extending to the deep north. We will report the interpretation of each areas and comparison with previous studies.
We conducted ocean-bottom MT observations by Ocean Bottom ElectroMagnetometers (OBEMs) at 32 points to image a sub-seafloor 3-D resistivity structure under the Kikai caldera volcano.
We estimated the MT response function using BIRRP (Chave and Thomson, 2004). In the MT response function, the two main features were found: yx of apparent resistivities tend to be larger than xy of ones; yx of MT responses' uncertainty tend to be smaller than yx of ones. Since the observation points were at shallow sea area, the MT data were affected by tilt and temperature changes caused by ocean currents.
A 3-D resistivity model was estimated using the MT inversion code ModEM+FS. This code is based on ModEM (Egbert and Kelbert, 2012; Kelbert et al., 2014) and can handle the undulating bathymetry by applying the FS method (Baba and Seama, 2002) to sea layers. By testing the estimation accuracy using actual observed MT data, it has been verified that conductive anomaly can be restored within the appropriate horizontal range by ModEM+FS.
We inverted only quality MT responses, and check the reliability of each anomaly in estimated model. In addition to that, we inverted same data using other MT inversion code FEMTIC (Usui 2015; Usui et al. 2017), and compare the estimated models. The results show that the estimated model has two reliable conductive anomalies. One conductive anomaly (C1) is located under the lava dome at depth ~1-5 km. The other one (C2) is connecting to C1 and extending to the deep north. We will report the interpretation of each areas and comparison with previous studies.