New Zealand seismicity: Patterns revealed by the upgraded National Seismograph Network

Abstract The upgrade of the New Zealand National Seismograph Network in the late 1980s has enabled more accurate earthquake locations to be determined. The catalogue data for events occurring from January 1990 until the end of February 1993 show some new patterns that have not been identified in previous observation periods, and also confirm the persistence of some phenomena observed previously, such as the aseismic corridor through the Nelson region. The deep seismicity data show spatial patterns remarkably similar to those for higher magnitude events recognised by Reyners in 1989. The Hikurangi Benioff zone is marked by intense seismic activity at depths between 150 and 200 km beneath the Central Volcanic Region; it has a sharp discontinuity beneath northwest Nelson and it extends as far southwest as Westport. The Fiordland Benioff zone is distinctly more seismically active in its northern block, and activity is noticeably concentrated in a zone to the west of Lake Te Anau. Shallow earthquakes (depth <1...

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