New Zealand Journal of Geology and Geophysics abstracts

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The precursory earthquake swarm in New Zealand: hypothesis tests

F. F. EVISON

Institute of Geophysics
Victoria University of Wellington
P.O. Box 600
Wellington, New Zealand

D. A. RHOADES

New Zealand Institute for Industrial Research and Development
P.O. Box 31 310
Lower Hutt, New Zealand

Abstract Tests have been carried out on the simple precursory swarm hypothesis, which proposes a one-to-one relation between swarms and mainshock events, and tests are in progress on the generalised hypothesis, which allows for clustering.
The performance of the simple hypothesis relative to the usual stationary Poisson model was favourable for several years after the start of the tests in 1977, then deteriorated, and fell to the proposed rejection level with the occurrence of the Doubtful Sound earthquake of 1989 May 31, M 6.1.
During the tests on the simple hypothesis, the database changed substantially with the adoption of a revised magnitude scale by the New Zealand Seismological Observatory. This resulted in additional swarms appearing in the past catalogue, and also in swarm clusters being recognised as far back as 1968-72, including a cluster precursory to the 1989 Doubtful Sound earthquake. These changes gave further grounds for rejecting the simple hypothesis.
Accordingly, the generalised hypothesis, which has been under test in Japan since 1983, was formulated for New Zealand conditions, and tests were started in July 1991.

Keywords earthquake prediction; earthquake precursors; precursory earthquake swarm; hypothesis testing

Received 28 September 1992; published 13 April 1993
New Zealand Journal of Geology & Geophysics, 1991, Vol. 36: 51—60
0028Ð8306/06/3601—0051 ©The Royal Society of New Zealand 1991

PDF file of entire paper: medium quality (887K); (scanned from paper original: notes about this process). Digitisation of this article from the printed journal was kindly facilitated by the Geological Society of New Zealand

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