ALBERT

Description: The geoelectric field is known to show local features reflecting local geologies. For instance, the eastward component of the geoelectric field has a few times larger amplitude than the northward component at Kakioka, Japan, while the northward component is larger than the eastward one at Memambetsu, Japan. In this study, we attempt to model the geomagnetic field at Kakioka by using a conductivity distribution inferred from data sets of the seismic P-wave velocity at the Kanto region. Although information of the conductivity distribution at Kanto is limited because of urban noise, the fine profile 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 several formulae based on Corcione et al. (2007). All estimated conductivity distributions show the granite distributed around Tsukuba mountains including Kakioka has 100 – 1000 times larger conductivities than surrounding sediments. Forward modeling of the geoelectric field around Kakioka induced by the geomagnetic variations in the air suggests that this conductivity contrast results in an larger amplitude of the eastward component of the geoelectric field at Kakioka.