New Zealand Journal of Geology and Geophysics abstracts

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Geographical distributions of prospective foreshock probabilities in New Zealand

Alistair Merrifield

School of Mathematics and Computing Sciences
Victoria University of Wellington
P.O. Box 600
Wellington, New Zealand*

Martha K. Savage

Institute of Geophysics
Victoria University of Wellington

David Vere-Jones

School of Mathematics and Computing Sciences
Victoria University of Wellington

*Present address: School of Mathematics and Statistics F07, University of Sydney,
NSW 2006, Australia. Email: alistair@maths.usyd.edu.au

Abstract  The prospective foreshock occurrence rate is calculated as the sample conditional probability of a larger earthquake following a potential foreshock of certain magnitude. A non-aftershock event is considered a foreshock if it is followed by a larger magnitude event within the next 5 days and within a radius of 30 km from the epicentre of the original earthquake. An evaluation of foreshock probabilities is carried out on a regional basis over New Zealand, and the probabilities are presented in the form of an overlay map. The Taupo Volcanic Zone features as an area of larger probability in these maps. As the magnitude difference between the foreshock and mainshock increases, the foreshock probability in this area decreases. This is attributed to swarm-like events in the area. Foreshock probability maps are shown for a variety of foreshock magnitude bins.

Keywords  foreshocks; seismicity; foreshock probabilities; New Zealand; Taupo Volcanic Zone

G02039; Received 7 August 2002; accepted 3 December 2003; online publication date 20 May 2004
New Zealand Journal of Geology & Geophysics, 2004, Vol. 47: 327–339
0028–8306/04/4702–0327 © The Royal Society of New Zealand 2004

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