The Clarence Fault is an active

Active fault

An active fault is a fault that is likely to have another earthquake sometime in the future. Faults are commonly considered to be active if there has been movement observed or evidence of seismic activity during the last 10,000 years....

 dextral (right lateral) strike-slip fault in the northeastern part of South Island

South Island

The South Island is the larger of the two major islands of New Zealand, the other being the more populous North Island. It is bordered to the north by Cook Strait, to the west by the Tasman Sea, to the south and east by the Pacific Ocean...

, New Zealand

New Zealand

New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...

. It forms part of the Marlborough Fault System

Marlborough Fault System

The Marlborough Fault System is a set of four large dextral strike-slip faults and other related structures in the northern part of South Island, New Zealand, which transfer displacement between the mainly transform plate boundary of the Alpine fault and the mainly destructive boundary of the...

, which accommodates the transfer of displacement along the oblique convergent boundary between the Indo-Australian Plate

Indo-Australian Plate

The Indo-Australian Plate is a major tectonic plate that includes the continent of Australia and surrounding ocean, and extends northwest to include the Indian subcontinent and adjacent waters...

 and Pacific Plate

Pacific Plate

The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At 103 million square kilometres, it is the largest tectonic plate....

, from the transform Alpine Fault

Alpine Fault

The Alpine Fault is a geological fault, more specifically known as a right-lateral strike-slip fault, that runs almost the entire length of New Zealand's South Island. It forms a transform boundary between the Pacific Plate and the Indo-Australian Plate. Earthquakes along the fault, and the...

 to the Hikurangi Trench

Hikurangi Trench

The Hikurangi Trench is a linear deep in 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. Though much shallower, it is the southward continuation of the Kermadec Trench and forms part of the...

 subduction zone

Subduction

In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...

.

Extent

The Clarence Fault extends from about 5 km south of Haupiri

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....

, close to the Alpine Fault to about 10 km west of Ward

Ward, New Zealand

Ward is a small town in Marlborough, New Zealand. It is located on State Highway 1, 20 kilometres south of Seddon. Kaikoura is 82 km to the southwest...

. 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

Transpression

Transpression is a geological term used to describe a region of the Earth's crust that experiences strike-slip shear and a component of shortening, resulting in oblique shear. Transpression typically occurs at a regional scale, such as plate boundaries that have an oblique convergence. More...

 "pop-up" geometry. To the northeast the strands merge to form a single fault trace in the middle of the Clarence River

Clarence River, New Zealand

Clarence River is located on South Island of New Zealand. It is 160 kilometres long.For its first 50 kilometres, the river runs in a generally southeastern direction. It then turns northeast, running down a long straight valley between the Inland and Seaward Kaikoura Ranges...

 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 Inner Kaikoura Range

Kaikoura Ranges

The Kaikoura Ranges are two parallel ranges of mountains in the northeast of the South Island of New Zealand.Formed along New Zealand's Marlborough Fault System, they can be seen as the northernmost extension of the Southern Alps in the South Island....

 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

Thrust fault

A thrust fault is a type of fault, or break in the Earth's crust across which there has been relative movement, in which rocks of lower stratigraphic position are pushed up and over higher strata. They are often recognized because they place older rocks above younger...

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. 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.