The 1929 Murchison earthquake occurred at 10:17 am on 17 June. It struck the Murchison region of the

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 ...

, with an estimated

magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...

of 7.3, and was felt throughout

New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...

. There were 17 deaths, mostly as a result of

landslide Landslides, also known as landslips, are several forms of mass wasting that may include a wide range of ground movements, such as rockfalls, deep-seated grade (slope), slope failures, mudflows, and debris flows. Landslides occur in a variety of ...

s triggered by the earthquake. The rumbling sound of the earthquake was loud enough to be heard at

New Plymouth New Plymouth ( mi, Ngāmotu) is the major city of the Taranaki region on the west coast of the North Island of New Zealand. It is named after the English city of Plymouth, Devon from where the first English settlers to New Plymouth migrated. ...

, more than 250 km (155 mi) away.

Tectonic setting

New Zealand sits astride the boundary between the

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

and the

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 ...

. In the South Island most of the displacement is taken up on the

Alpine Fault The Alpine Fault is a geological fault that runs almost the entire length of New Zealand's South Island (c. 480 km) and forms the boundary between the Pacific Plate and the Indo-Australian Plate. The Southern Alps have been uplifted on the f ...

passing to the north onto a set of strike-slip faults, the

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 ...

. The sense of displacement across the plate boundary is oblique and most of the faults have a reverse component of slip. Some of the resulting deformation is accommodated within the plates themselves away from the boundary. The 1929 Murchison earthquake occurred on the White Creek Fault, located in the

Buller Gorge The Buller Gorge is a gorge located in the northwest of the South Island of New Zealand. The Buller River flows through the deep canyon between Murchison and Westport. Land Information New Zealand lists two sections for the gorge, Upper Buller ...

Damage

Nelson College after Murchison earthquake 1929 (cropped)

Although the

epicentre The epicenter, epicentre () or epicentrum in seismology is the point on the Earth's surface directly above a hypocenter or focus, the point where an earthquake or an underground explosion originates. Surface damage Before the instrumental pe ...

was in a sparsely populated area about 65 km (40 mi) north of Murchison, the shaking in the surrounding region was intense enough to cause damage over a wide area. The towns of

Nelson Nelson may refer to: Arts and entertainment * ''Nelson'' (1918 film), a historical film directed by Maurice Elvey * ''Nelson'' (1926 film), a historical film directed by Walter Summers * ''Nelson'' (opera), an opera by Lennox Berkeley to a lib ...

Greymouth Greymouth () (Māori: ''Māwhera'') is the largest town in the West Coast region in the South Island of New Zealand, and the seat of the Grey District Council. The population of the whole Grey District is , which accounts for % of the West Coas ...

and Westport were all affected and roads, buildings and bridges were severely damaged throughout an area estimated at 26,000 km² (10,000 mi²). The worst damage was caused by landslides triggered by the shaking, which destroyed several homes and resulted in 14 of the 17 deaths. Two other deaths were caused by coal mine collapses. Most of the buildings in the Murchison area were built of wood and were warped and moved from their piles, but many brick buildings and chimneys were damaged in Nelson, Greymouth and Westport.

Characteristics

The earthquake was preceded by several

foreshock A foreshock is an earthquake that occurs before a larger seismic event (the mainshock) and is related to it in both time and space. The designation of an earthquake as ''foreshock'', ''mainshock'' or aftershock is only possible after the full sequ ...

s before the mainshock, accompanied by booming sounds in the mountains around Murchison. There was a large

surface A surface, as the term is most generally used, is the outermost or uppermost layer of a physical object or space. It is the portion or region of the object that can first be perceived by an observer using the senses of sight and touch, and is ...

fault rupture visible in the

Buller River The Buller River ( mi, Kawatiri) is a river in the South Island of New Zealand. One of the country's longest rivers, it flows for from Lake Rotoiti through the Buller Gorge and into the Tasman Sea near the town of Westport. Within the Bulle ...

, indicating about 4.5 m (14.8 ft) of vertical movement and 2.5 m (8.2 ft) of lateral movement. The earthquake triggered many landslides and these created 38 new lakes, of which 21 still exist, including Lake Stanley, on Stanley River. The

Maruia Falls The Maruia River is located in the northwestern South Island of New Zealand. It is a major tributary of the Buller River, flowing for 80 km before joining the larger river eight kilometres to the west of Murchison. The Maruia River rise ...

are also a notable by-product of the earthquake. The earthquake was accompanied by unusually loud rumbling noises that were heard as far away as New Plymouth. A maximum intensity of X (''Extreme'') on the

Mercalli intensity scale The Modified Mercalli intensity scale (MM, MMI, or MCS), developed from Giuseppe Mercalli's Mercalli intensity scale of 1902, is a seismic intensity scale used for measuring the intensity of shaking produced by an earthquake. It measures the eff ...

has been estimated for Murchison. Most of the northern part of South Island suffered an intensity of VII (''Very strong'') or greater.

Aftermath

The landslides blocked many roads causing food supplies to run out in some areas near the epicentre. This and the risk of aftershocks and flooding from landslides blocking rivers caused many residents to evacuate the area, mostly on foot.

Karamea Karamea is a town on the West Coast of the South Island of New Zealand. It is the northernmost settlement of any real size on the West Coast, and is located northeast by road from Westport. Apart from a narrow coastal strip, the town of Karam ...

was completely cut off and received no outside help for two weeks, until a

de Havilland Tiger Moth The de Havilland DH.82 Tiger Moth is a 1930s British biplane designed by Geoffrey de Havilland and built by the de Havilland Aircraft Company. It was operated by the Royal Air Force (RAF) and other operators as a primary trainer aircraft. ...

plane landed on the beach. Some of the blocked roads took months to clear.

Importance for studying the earth's interior

Analysing the seismic waves from this earthquake appearing in the

shadow zone A seismic shadow zone is an area of the Earth's surface where seismographs cannot detect direct P waves and/or S waves from an earthquake. This is due to liquid layers or structures within the Earth's surface. The most recognized shadow zone is ...

Inge Lehmann Inge Lehmann (13 May 1888 – 21 February 1993) was a Danish seismologist and geophysicist. In 1936, she discovered that the Earth has a solid inner core inside a molten outer core. Before that, seismologists believed Earth's core to be a sin ...

demonstrated that there must be a solid

inner core Earth's inner core is the innermost geologic layer of planet Earth. It is primarily a solid ball with a radius of about , which is about 20% of Earth's radius or 70% of the Moon's radius. There are no samples of Earth's core accessible for di ...

that reflected

p-waves A P wave (primary wave or pressure wave) is one of the two main types of elastic body waves, called seismic waves in seismology. P waves travel faster than other seismic waves and hence are the first signal from an earthquake to arrive at any ...

References

External links

Landslide blog about the earthquake by Professor Dave Petley, Durham University, UK
* {{Authority control 1929 Murchison New Zealand - Murchison Murchison History of the West Coast, New Zealand History of the Tasman District Murchison earthquake Murchison earthquake 1929 disasters in New Zealand