Volcano-seismic networks in the Taupo Volcanic Zone : description and evaluation of the autolocation system

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Hurst, A.W.; Scott, B.J. 1997 Volcano-seismic networks in the Taupo Volcanic Zone : description and evaluation of the autolocation system. Lower Hutt: Institute of Geological & Nuclear Sciences. Institute of Geological & Nuclear Sciences science report 97/20 36 p.

Abstract: This report describes the Autolocation system currently operated by the Institute of Geological & Nuclear Sciences (GNS) on its volcano-seismic networks. Each of these systems used the estimated P-arrival times (''picks'') made by an EARSS seismic recorder, processed by two earthquake location programs. The results of the Autolocation system for the combined networks which were operated in the Taupo Volcanic Zone (TVZ) have been analysed for the period from 13 November 1993 until 31 January 1995. The results indicate firstly that many earthquakes (especially those with magnitudes less than 3.0) which were subsequently located by the Seismological Observatory did not produce 3 EARSS picks. Secondly, a substantial number of shallow TVZ earthquakes were mislocated, and thirdly, a substantial number of the shallow TVZ earthquakes reported by the autolocation system were subsequently located outside the region, or found not to be earthquakes at all. Two newer location programs, HYPOCENTER and HYPOELLIPSE were tested with the same data, to see if they performed better than HYPO71. They each showed a slight improvement, but it was apparent that significant improvements would require more seismometers and better sites, and preferably also improved routines for picking P-arrival times. (auth)