A Computer Program for Locating Earthquakes Both Locally and Globally

INTRODUCTION Since the original version of HYPOCENTER was published (Lienert et al. , 1986), it has been used primarily to locate earthquakes using data collected by small networks of seismometers (e.g., Ambos et al. , 1985). In its original form it suffered from many of the same limitations as its predecessors (HYPO71, HYPOINVERSE, etc.). It could not use azimuth data, was unable to force the calculation of specific phases ( Pn, Pg , etc.) and was limited to locating events at station distances of less than about 500 km, due to a “flat earth” velocity model and coordinate system. The increasing use of portable three-component seismometers has made it possible to determine the azimuth of a given event in addition to the arrival times of both primary and secondary phases. In principle, this allows single-station locations to be obtained, provided that the location software can use azimuth data. Global location capability is useful in...

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