10:45 〜 12:15
[PEM09-P24] Numerical modeling of the geoelectric field at Kakioka reflecting the conductivity estimated from the P-wave velocity
キーワード：地電位、電気伝導度、地震波速度
The geoelectric field is known to show local features reflecting local geologies. For instance, the eastward component of the geoelectric field at Kakioka has a few times larger amplitude than the northward component there, while the northward component is larger than the eastward one at Memambetsu.
In this study, we attempt to model the geomagnetic field at Kakioka by using a conductivity distribution inferred from the seismic P-wave velocity at the Kanto region. Although information of the conductivity distribution at Kanto is limited because of urban noise, a fine distribution of the seismic velocity is available. The conductivity and the P-wave velocity are both related to the porosity, therefore, it is theoretically possible that the conductivity can be estimated from the P-wave velocity via the porosity, However, the relationship between the conductivity and the P-wave velocity depends on conditions of rocks and several conversion formulae are proposed. We tested three formulae based on Corcione et al. (2007). All estimated conductivity distributions show the granite around Tsukuba mountain area including Kakioka has 100 – 1000 times larger conductivities than surrounding sediments. Forward modeling of the geoelectric field induced by the geomagnetic variations in the air suggests that this conductivity contrast and the geometry of Tsukuba mountains result in an larger amplitude of the eastward component of the geoelectric field at Kakioka.
In this study, we attempt to model the geomagnetic field at Kakioka by using a conductivity distribution inferred from the seismic P-wave velocity at the Kanto region. Although information of the conductivity distribution at Kanto is limited because of urban noise, a fine distribution of the seismic velocity is available. The conductivity and the P-wave velocity are both related to the porosity, therefore, it is theoretically possible that the conductivity can be estimated from the P-wave velocity via the porosity, However, the relationship between the conductivity and the P-wave velocity depends on conditions of rocks and several conversion formulae are proposed. We tested three formulae based on Corcione et al. (2007). All estimated conductivity distributions show the granite around Tsukuba mountain area including Kakioka has 100 – 1000 times larger conductivities than surrounding sediments. Forward modeling of the geoelectric field induced by the geomagnetic variations in the air suggests that this conductivity contrast and the geometry of Tsukuba mountains result in an larger amplitude of the eastward component of the geoelectric field at Kakioka.