New Zealand Journal of Geology and Geophysics abstracts
The precursory earthquake swarm and the inferred precursory quarm
F. F. EVISON
Institute of Geophysics, School of Earth Sciences
Victoria University of Wellington
P.O. Box 600
Wellington, New Zealand
D. A. RHOADES
Institute of Geological & Nuclear Sciences
P.O. Box 30 368
Lower Hutt, New Zealand
Abstract The earthquake swarm as a long-term precursor to
major earthquakes is being studied empirically by the method of hypothesis
formulation and testing. Results suggest that swarms occur as an early stage of
the seismogenic process for major earthquakes, but that the phenomenon is
limited to shallow subduction regions and other environments where high fluid
pressure provides a triggering mechanism for swarms. An inference from a
proposed seismogenic model is that, if swarms are not triggered, the same
precursory earthquakes should occur, though in a more protracted manner.
A cluster of four major earthquakes (ML6.7, 6.3, 6.0, 5.8) occurred
without precursory swarms in the area around Arthur's Pass, New Zealand, during
1992-95. This area is in the region of continental collision which lies between
the Hikurangi and Fiordland subduction regions. A prior cluster of seismicity
anomalies has now been identified which displays the same precursory relations
as have been established for swarms. These anomalies are termed quasi-swarms,
or quarms, and the swarm hypothesis is now being extended to include the
precursory quarm.
Keywords long-range earthquake forecasting; precursory swarm;
precursory quarm
New Zealand Journal of Geology and Geophysics, 1999, Vol. 42: 229-236
0028-8306/99/4202-0229 $7.00/0 (c) The Royal Society of New Zealand
1999
PDF file of entire paper: medium quality (733K); (scanned from paper original: notes about this process)
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