The Clarence Fault is an active dextral (right lateral)

strike-slip fault In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...

in the northeastern part of

South Island The South Island, also officially named , is the larger of the two major islands of New Zealand in surface area, the other being the smaller but more populous North Island. It is bordered to the north by Cook Strait, to the west by the Tasman ...

, 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 The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At , it is the largest tectonic plate. The plate first came into existence 190 million years ago, at the triple junction between the Farallon, Phoenix, and Iza ...

, from the transform Alpine Fault to the

Hikurangi Trench The Hikurangi Trench, also called the Hikurangi Trough, is an oceanic trench in the bed of the Pacific Ocean off the east coast of the North Island of New Zealand, lying between the southern end of the Cook Strait and the Chatham Rise. It is the ...

subduction zone Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the ...

Extent

The Clarence Fault extends from about 5 km south of

Haupiri Haupiri is a locality in the West Coast region of New Zealand's South Island. Greymouth lies to the west. The Ahaura and Haupiri Rivers run through the area. The population of the Haupiri statistical district, which covers a much larger area than ...

, close to the Alpine Fault to about 10 km west of Ward. This fault is the only member of the Marlborough Fault System to have neither a clear junction with the Alpine fault to the southwest nor a northeastward continuation to the coast. The southwestern part of the fault consists of many fault traces and has a transpressive "pop-up" geometry. To the northeast the strands merge to form a single fault trace in the middle of the Waiau Toa / Clarence River valley, from which the fault gets its name. At the surface the displacement on this continuous trace appears to be nearly pure horizontal, but continuous uplift of the neighbouring Inland Kaikōura Range over the same period, suggests that some of the dip-slip component thought to be present at depth on the fault zone is transferred onto thrust or reverse faults under the range. An extra 10° of clockwise rotation has been recognised within the block that lies northeast of the tip of the Clarence fault.

Elliott Fault

The Elliott Fault branches from the central portion of the Clarence Fault and then rejoins it. A recurrence interval for earthquakes along this fault is estimated to be 2000–3500 years.

Recent seismicity

Measurements from the southwestern part of the fault suggest 76–80 m of dextral displacement since the Late Pleistocene, about 18,000 years ago. This gives an average slip rate of 3.6–4.4 mm/yr with an average slip of about 5 m for each event. In the northeastern part of the fault, the estimated slip-rate is somewhat higher, 4.7 mm/yr and the average slip also higher at about 7 m. A recurrence interval of about 1500 years has also been estimated for this part of the fault. The timing of the most recent earthquake on the northeastern fault segment is poorly constrained, but is likely to be in the range 950–2000 years ago.

Seismic hazard

The likelihood of a significant earthquake happening on the Clarence Fault in the next 50–100 years is regarded as moderate to possibly high, although poorly constrained by the available data.

References

{{Seismic faults of New Zealand Seismic faults of New Zealand Strike-slip faults