PURPOSE:To calculate the epicenter of an earthquake regardless of amplitude of initial shock by detecting seismic vibrations in vertical, east-west and south-north directions to calculate and compare exponental smoothing values of products of amplitude values between the first and second components and the first and third components. CONSTITUTION:A sensor 1 for detecting seismic vibrations detects seismic vibrations in three components corresponding to the vertical, east-west and south- noth directions and sends information to a control processor 4 continuously. First and second exponental smoothing calculating means 112 and 113 calculate an exponental average value of the product between the amplitude value of the vertical vibration and the amplitude value of the south-north vibration and the product between the amplitude value of the vertical vibration and the east-west vibration and an epicenter azimuth calculating means 116 determines the epicenter azimuth. A means 12 of calculating the ratio between the vertical and horizontal amplitudes calculates the ratio between the amplitudes of the vertical vibration and the horizontal vibration. A seismic wave detection means 13 detects the arrival of a seismic wave depending on the amplitude value of the vertical vibration to discriminate a P wave and an S wave from the epicenter azimuth and the ratio of vertical and horizontal amplitudes.
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