Bulletin of the Seismological Society of America; October 1975; v. 65; no. 5;
p. 1097-1104
© 1975 Seismological Society of America
Microearthquake study of the Alpine fault zone near Haast, South Island, New Zealand
JOHN G. CALDWELL and
CLIFF FROHLICH
DEPARTMENT OF GEOLOGICAL SCIENCES CORNELL UNIVERSITY, ITHACA, NEW YORK 14853
Abstract
During 1973, a 32-day study of microearthquakes along a section of the Alpine fault near Haast, South Island, New Zealand provided data on 122 earthquakes with SP times generally less than 8 sec. Sixty of these events are well-located. Three features of the data are notable: (1) the seismic activity was shallow, concentrated in the depth range 4 to 14 km, and did not define a single fault plane; (2) little activity occurred on the trace of the Alpine fault, but more than 85 per cent of the earthquakes were within 15 km of the fault trace; (3) events often seemed to cluster in time and space, but even within these clusters, the earthquakes did not share a common focal mechanism.
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