PALEOSEISMICITY OF THE WELLINGTON HUTT VALLEY SEGMENT OF THE WELLINGTON FAULT, NORTH-ISLAND, NEW-ZEALAND

The Wellington Fault is one of the major active right-lateral strike-slip faults of the southern North Island and represents a significant seismic hazard to the greater Wellington region. Trench excavations across the fault in the Long Gully/Karori Reservoir area and near Kaitoke, along with Quaternary stratigraphic and soil studies at Te Marua, indicate that the most recent surface rupture event along the southern portion of the Wellington Fault was 300-450 cal B.P. (calendar years before A.D. 1950) and the next oldest event was 670-830 cal B.P. The elapsed time between these two events is 220-530 years. Based on the previously reported 6.0-7.6 mm/yr, long-term (c. 140 ka), average, horizontal slip mte calculated at Emerald Hill, and the 3.2-4.7 m single-event offsets (the five most recent events) measured at Te Marua, the average recurrence interval for this portion of the Wellington Fault is 420-780 years. At the Long Gully trench site, two stream channels are laterally displaced by c. 50 m. Displacement has resulted in the ponding of the streams behind an uphill-facing bedrock scarp. The ponding began about 10 ka, as inferred from the age of the oldest organic material exposed in the trench excavations. The average lateral slip rate in the Long Gully area is thus c. 5 mm/yr. Recent surface fault movements at Long Gully, Te Marua, and Kaitoke have similar timings, suggesting that the 75 km long section of the Wellington Fault extending from Cook Strait to Kaitoke comprises a single fault-rupture segment: the Wellington - Hutt Valley Segment.