A data acquisition module acquires seismic data actually measured at a plurality of observation points; a pulse calculation module acquires information of a propagation environment where seismic waves propagate from a hypocenter of earthquake to each observation point, and applies time reversal processing on the seismic waves received at the observation points by considering the propagation environment to acquire time reversal pulses at each observation point; a line calculation module calculates a parametric line in a length direction of a fault from a distribution of azimuths of frequency spectra of the time reversal pulses acquired by the pulse calculation module; a head searching module searches a parametric head by analyzing the seismic waves received in the vicinity of the parametric line calculated by the line calculation module; and a monitoring module monitors developments of a crack in the fault by observing the parametric head searched by the head searching module.
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