Ground-based measurement of the seismo-electromagnetic signals

An earthquake is one of the most serious natural disasters leading to the death toll exceeding two million in the last century. As we see from the recent super earthquake near Japan triggered the complex disaster such as catastrophic huge Tsunami and damage to the nuclear power plant. Despite the incomplete understanding of the origin of earthquakes, short time warning must be an urgent issue of human beings. Recently new approach to study the seismic activities by using electromagnetic phenomena reported both by ground-based and satellite measurement has emerged in addition to the traditional seismological investigation since 1990s. This is we call it `Seismo-electromagnetics´, and is a study of short-term process of the earthquake sequence. One of the key advantages of the seismo-electromagnetic phenomena is their precursory nature. In this paper we introduce various ground-based radio physical measurements to study seismo-electromagnetic signals and review the major results of both case and statistical studies for last 10 years from different frequency ranges such as VLF, LF, HF transmitters to identify the ionospheric perturbations, and ULF emissions in relation with seismic activities. Updated results from VLF transmitter signals concerning super earthquake (Off the Pacific coast of Tohoku EQ) will be presented together with our statistical study on the basis of long-term observations.