Patent ID: 7005993

Claim:
Apparatus for detecting earthquake generated P-waves comprising: means forming a housing adapted to be mounted to a supporting structure subject to movement by seismic forces; sensor means affixed to said housing and operative to generate electrical signals proportional to motion experienced by said support structure, said sensor means including multiple sensor elements each of which is responsive to motion in a direction normal to one of a corresponding plurality of mutually orthogonal intersecting planes and operative to generate an electrical signal commensurate therewith, each said sensor element including a thin-film, cantilevered piezo-electric sensor element having an unsupported distal extremity and a proximal extremity rigidly affixed to said housing; signal amplifying and filtering means responsive to said electrical signals and operative to amplify and pass signals having frequencies within the range of approximately 0.5 to 15 Hz; and signal processing means for sampling the passed signals and for performing an automatic real-time offset zeroing function by averaging the signals over successive periods of time greater than approximately 10 seconds, and for taking the ongoing mean of the averaged signals as the zero point, but causing the sum of the passed signals over any said period of time to drop to a “zero” value after a few seconds of no signal, and for determining that a P-wave has been detected if (a) the averaged signal over a particular one of said periods rises above a predetermined level, and/or (b) power spectral density integrated sum rises above a predetermined trigger value within a predetermined window of time during the particular period, and for generating an output signal commensurate therewith.