Abstract: A casing pipe is inserted into a drilled hole reaching the inside of a confined aquifer in which groundwater is stored and flows or a position near the confined aquifer. A measuring device measures an electromagnetic field at the distal end of the casing pipe. An analyzing device analyzes data concerning the electromagnetic field measured by the measuring device to sense motion of ground pore water, thereby predicting rapid motion in the earth's crust, such as a volcanic eruption, an earthquake, a landslide and ground collapse. The casing pipe is an electrically conductive pipe having a non-magnetic screen portion formed at the distal end thereof so that recycling groundwater passes through the screen portion. The measuring device includes an electromagnetic field sensor placed in the screen portion and the conductive casing pipe as an electrode for measuring an electric potential relative to an electric potential at the earth's surface detected with a reference electrode.

Abstract: A seismic electromagnetic field signal is detected at each of observation stations installed at at least two places, and civil noise and atmospheric discharge noise are eliminated from the signal to obtain a low-frequency seismic electromagnetic field signal O.sub.s. A local characteristic signal C.sub.e and a refined local characteristic signal C.sub.f are obtained by processing the signal O.sub.s. The signals O.sub.s, C.sub.e and C.sub.f are transmitted to a central station. At the central station, a delay time T and a half-width H are obtained from the cross-correlation function between the observation stations, and further a regional characteristic signal C.sub.r is obtained from the seismic electromagnetic field signal O.sub.s. An earthquake source region distribution, an earthquake magnitude, and earthquake occurrence time are estimated on the basis of the signals obtained at the central station and the local characteristic signal C.sub.e and refined local characteristic signal C.sub.