Hope Fault

The Hope Fault is an active dextral (right lateral) strike-slip fault in the northeastern part of South Island, New Zealand. It forms part of the Marlborough Fault System, which accommodates the transfer of displacement along the oblique convergent boundary between the Indo-Australian Plate and Pacific Plate, from the transform Alpine Fault to the Hikurangi Trench subduction zone.

The Hope Fault branches off from the Alpine Fault south of Hokitika and then runs in a nearly straight line for about 230 km to the east coast of South Island just north of Kaikoura, with an offshore continuation of at least 13 km. It consists of several segments, from the southwest end, the Kelly Fault, then the Hurunui, Hope River, Conway and Seaward segments. It takes its name from the Hope River, which follows the trace of much of the Hope River segment.

The junction between the Hope fault and the Alpine Fault is complex. The Kelly Fault forms a major splay of the Hope Fault from just west of Harper Pass; it splays again to the west into the Newton and Hura faults. From repeat GPS surveying on the region near Arthur's Pass, the Kelly Fault marks a sharp reduction in velocities to the northwest of the Kelly and Hura faults.

This 42 km long segment runs from Harper pass to the junction of the Hope and Boyle rivers. The maximum slip-rate estimated from the offset of a stream is about 13 mm/yr. A minimum slip-rate has also been estimated from offset of channels in a late Holocene alluvial fan complex of 8.1-11.0 mm/yr. The average recurrence interval for earthquake slip events on this segment is 310–490 yr.

The Hope River segment runs about 30 km from the confluence of the Boyle and Hope rivers as far as the Hanmer Basin. From the offset of dated river terraces, a late Holocene horizontal slip-rate of about 10 mm/yr and a vertical slip-rate of about 0.6 mm/yr have been calculated for this segment. The displacement is thought to have occurred by repeated slips which, if similar to that which caused the 1888 earthquake, indicate a return period of about 140 years.

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