5-2. NETWORK-MT Project

 

NETWORK-MT is one of the major components of the Earthquake Prediction Program. This experiment aims to reveal the mean nation-wide distribution of electrical conductivity in the Earth.  Major experimental efforts focus on measuring electric field variations over 10-30 km distances using commercial telephone lines.  Scientists from eleven universities and institutions in Japan are collaborating in this project. Up-to-date observation sites are shown in Fig.1. Cumulative number of dipoles is getting more than 1000 and a regional feature of electromagnetic variation is revealed through this project as shown in Fig.2.

 

 

Fig.1 Cumulative plots of the sites in which NETWORK-MT observations were made since 1994 under the Earthquake Prediction Research program (in red circles). Green circles indicate the sites of continuous monitoring of the telluric voltage differences. Measurements in other areas were taken in 1989-1993 in other projects.

 

 

Fig.2 Spatial distribution of phase of Network-MT impedances in Kyushu district (left) and Hokkaido & Tohoku districts (right). Period is 64 minutes. Impedances, where electric field varies in the direction perpendicular to the strike of the Japan arc (i.e. EW in Kyushu and Tohoku districts, NS in Hokkaido district), are shown here. Magnetic field varies in the direction parallel to the strike of the Japan arc. Larger phase value indicates the existence of lower resistivity bodies in the deeper portion. Such high phase values are commonly detected in the backarc side of respective districts along the strike of the Japan arc.