Abstract

We use four methods to investigate the earthquake history over the past 600 yr of the central Alpine fault, New Zealand. Trenches across the active fault trace at five locations identify two ruptures on the fault in the past 450 yr. Three other indirect indicators (episodes of landsliding and aggradation, dated either via 14C or from forest establishment on the resulting surfaces, and tree-ring growth anomalies) provide further evidence for these two earthquakes and a greater resolution in estimates of their timing and extent. The most recent earthquake occurred in A.D. 1717 and the rupture extended over a section of fault between Milford and the Haupiri River, a distance of 375 km. About 1630, another earthquake occurred on the fault and this extended between at least the Paringa and Ahaura Rivers (250 km). Regional episodes of landsliding and forest establishment provide evidence for a third earthquake at about 1460 over the same section of fault. The pattern of earthquake recurrence is not regular, but averages ∼200 yr and varies from ∼100 yr to at least 280 yr, which is the lapsed time since the most recent rupture.

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