The Puysegur Bank earthquake of 1979 October 12

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Abstract
An earthquake of local magnitude 6.4 and surface-wave magnitude of 7.4 (USGS) occurred on 1979 Oct 12d 10h 25m U.T. The epicentre was at 46°.67S, 165°.73E and a focal depth of 12 km was adopted. The epicentre was well constrained, but there was poor control of the focal depth in computed solutions. The maximum felt intensity was MM V, the isoseismal pattern being similar to that observed for events in the neighbouring Fiordland region. Damage claims numbered 198 and were mainly for structural damage rather than contents. The strike of one focal plane is 339° with a dip of 78°W. First motions suggest thrust faulting with an unknown strike-slip component. One foreshock and a sequence of 176 aftershocks were studied, a value for b of 1.1 ± 0.2 being determined for the latter. The aftershock area was 9500 km2 for events within 24 h of the main shock and 13 500 km2 for all events. The maximum dimension (for 90% of events) was 130 km. The lowfrequency nature of this event, characterised by the type of damage, felt effects, and large excitation of surface waves, is similar to that of tsunamigenerating earthquakes located near the Japan Trench.

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