The 1953 Suva earthquake occurred on September 14, 1953, at 00:27 UTC near Suva

Suva

Suva features a tropical rainforest climate under the Koppen climate classification. The city sees a copious amount of precipitation during the course of the year. Suva averages 3,000 mm of precipitation annually with its driest month, July averaging 125 mm of rain per year. In fact,...

, Fiji

Fiji

Fiji , officially the Republic of Fiji , is an island nation in Melanesia in the South Pacific Ocean about northeast of New Zealand's North Island...

, just off the southeast shore of Viti Levu

Viti Levu

Viti Levu is the largest island in the Republic of Fiji, the site of the nation's capital, Suva, and home to a large majority of Fiji's population.- Geography and economy :...

. This earthquake

Earthquake

An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...

 had a magnitude of M_s 6.75. The earthquake triggered a coral reef platform collapse and a submarine landslide that caused a tsunami

Tsunami

A tsunami is a series of water waves caused by the displacement of a large volume of a body of water, typically an ocean or a large lake...

. Eight people were reported killed; a wharf, bridges, and buildings were severely damaged in Suva.

Tectonic setting

Fiji lies in a complex tectonic setting along the boundary between the Australian Plate and the 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....

. Southwards from Fiji the Pacific Plate is subducting

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"...

 beneath the Australian Plate along the Tonga Trench

Tonga Trench

The Tonga Trench is located in the South Pacific Ocean and is deep at its deepest point, known as the Horizon Deep.The Tonga Trench is a convergent plate boundary. The trench lies at the northern end of the Kermadec-Tonga Subduction Zone, an active subduction zone where the Pacific Plate is being...

 forming the Tonga

Tonga

Tonga, officially the Kingdom of Tonga , is a state and an archipelago in the South Pacific Ocean, comprising 176 islands scattered over of ocean in the South Pacific...

 Ridge island arc

Island arc

An island arc is a type of archipelago composed of a chain of volcanoes which alignment is arc-shaped, and which are situated parallel and close to a boundary between two converging tectonic plates....

 system and the Lau Basin back-arc basin

Back-arc basin

Back-arc basins are geologic features, submarine basins associated with island arcs and subduction zones.They are found at some convergent plate boundaries, presently concentrated in the Western Pacific ocean. Most of them result from tensional forces caused by oceanic trench rollback and the...

. To the southwest of Fiji the Australian Plate is subducting beneath the Pacific Plate forming the Vanuatu

Vanuatu

Vanuatu , officially the Republic of Vanuatu , is an island nation located in the South Pacific Ocean. The archipelago, which is of volcanic origin, is some east of northern Australia, northeast of New Caledonia, west of Fiji, and southeast of the Solomon Islands, near New Guinea.Vanuatu was...

 Ridge island arc system and the North Fiji back-arc basin. Hence, the region has undergone a complex process of plate convergence, subduction, and arc volcanism from the Middle Eocene

Eocene

The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...

 to the Early Pliocene

Pliocene

The Pliocene Epoch is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present. It is the second and youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch...

. Many of the larger islands, such as Viti Levu, are of volcanic origin. Volcanism still exists, and there are Holocene

Holocene

The Holocene is a geological epoch which began at the end of the Pleistocene and continues to the present. The Holocene is part of the Quaternary period. Its name comes from the Greek words and , meaning "entirely recent"...

 volcanos in Fiji.

The Fiji Platform lies in a zone bordered with active extension fault lines around which most of the shallow earthquakes were centered. These fault lines are the Fiji Fracture Zone (FFZ) to the north, the 176° Extension Zone (176°E EZ) to the west, and the Hunter Fracture Zone (HFZ) to the east.

Earthquake

The earthquake lasted between 25 and 30 seconds and had an estimated magnitude of 6.75 on the surface wave magnitude

Surface wave magnitude

The surface wave magnitude scale is one of the magnitude scales used in seismology to describe the size of an earthquake. It is based on measurements in Rayleigh surface waves that travel primarily along the uppermost layers of the earth...

 scale. The calculated focal mechanism

Focal mechanism

The focal mechanism of an earthquake describes the inelastic deformation in the source region that generates the seismic waves. In the case of a fault-related event it refers to the orientation of the fault plane that slipped and the slip vector and is also known as a fault-plane solution...

 is consistent with slightly oblique dextral (right lateral) strike-slip on a NW-SE trending fault plane, matching the orientation of other fault planes measured in the area and a marked bathymetric lineament. The fault parameters calculated for the earthquake are a length of 30 km, a width of 27 km and a slip of one metre.

Tsunami

The first sign of the tsunami was observed about one minute after the earthquake when a disturbance of the sea surface was noticed by the captain of the cutter Adi Tirisa "beyond the reef some 4 to 5 miles southwest of Suva…she was badly shaken and a little later three great spouts burst out of the sea, carrying mud, stones, and part of a long-wrecked vessel…" The location of this disturbance was at the western end of the entrance to the Suva Passage.

Origin

From the type of fault displacement and the magnitude of the event it was clear that the tsunami was not caused by any displacement of the seabed associated with the earthquake. The shaking triggered collapse of part of the barrier reef at Suva into the Suva Canyon. The current reef edge shows the effects of repeated slope failure. The characteristics of the 1953 landslide scar were investigated using a high resolution multibeam echo sounder. The area immediately offshore from the reef is a composite failure surface, within which a fresh scar was identified with a width of 800 m, defining an estimated slide volume of 60 million cubic metres. Numerical modelling of this as the likely source was able to reproduce many aspects of the observed development of the tsunami.

Damage

This earthquake was the most destructive in Fiji's recorded history, killing three people and seriously injuring twenty others. The most serious damage occurred in the southeastern part of Viti Levu. The tsunami caused particular damage to coastal areas not protected by barrier reefs, devastating the villages of Nakasaleka and Makaluva. There were five deaths from the tsunami, three at Suva and two at Nakasaleka. Had the tsunami occurred at high tide, rather than low tide it would have been more damaging.

The landslide that caused the tsunami generated turbidity current

Turbidity current

A turbidity current is a current of rapidly moving, sediment-laden water moving down a slope through water, or another fluid. The current moves because it has a higher density and turbidity than the fluid through which it flows...

s that damaged several underwater cables in the Suva Canyon. The total damage caused by earthquake and tsunami was estimated as $500,000 (at 1953 values).