Abstract

New paleoseismic studies have been undertaken on the Wellington–Hutt Valley (W-HV) segment of the Wellington fault to characterize its late Holocene record of surface-rupturing earthquakes. Trenches and radiocarbon dates from Te Kopahou and Te Marua have provided evidence and improved timing for the four most recent earthquake ruptures.

These events have been recognized on the basis of upward-terminating faults, coseismic deposition, progressive displacement, and faulting of colluviums. At Te Kopahou, colluvial and scree deposition, resulting from surface rupture and strong earthquake shaking, buries old ground surfaces associated with peat and/or soil development. At Te Marua, the timing of the two youngest events has been refined by bracketing the ages of the youngest faulted and unfaulted alluvial terraces of the Hutt River.

Assuming that the W-HV segment acts as a rupture segment along its length, the approximate timings of these faulting events is as follows: the most recent faulting event (event I) occurred between 110 and 310 cal yr B.P. (A.D. 1640–1840); the penultimate faulting event (event II) between 790 and 930 cal yr B.P.; event III occurred between 1835 and 2340 cal yr B.P.; and event IV between 2460 and 4900 yr B.P.

The minimum and maximum earthquake recurrence intervals derived from the four youngest events are ∼715 and 1575 yr, respectively, with a median value of 1145 yr. Revisions of the earthquake timing, recurrence interval data, and, recently, the single-event displacement and slip rate, collectively reduce the seismic hazard for the W-HV segment of the Wellington fault. A four-event paleoearthquake record from the Pahiatua section of the Wellington fault is statistically similar to that from the W-HV segment. This has significant implications with respect to the rupture length and magnitude, or clustering, of future surface-rupturing earthquakes on the Wellington fault.

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