1929 Arthur's Pass earthquake
Encyclopedia
The 1929 Arthur's Pass Earthquake occurred at 10.50pm NZMT
on 9 March 1929 (11:20 GMT). The sparsely settled region of the Southern Alps
shook for four minutes. Tremors continued almost continuously until midnight and sporadic strong aftershocks were felt for several days.
The earthquake was measured at 7.1 on the Richter Scale and the intensity of shaking in the epicentral region has been assessed from historical records as level VIII on the Modified Mercalli Scale. Intensities of 6 were observed in Christchurch
and Westport
. The earthquake occurred on the Poulter Fault, which was not identified and mapped until 2001.
and Pacific plate
s. In the South Island
most of the relative displacement between these plates is taken up along a single dextral (right lateral) strike-slip fault with a major reverse component, the Alpine Fault
. In the North Island
the displacement is mainly taken up along the Kermadec-Tonga subduction zone
, although the remaining dextral strike-slip component is accommodated by the North Island Fault System
. The Poulter Fault runs for approximately 50 km Northeast from the junction of the Bealey and Mahinga rivers to the valley of the Hurunui River. Between 16 km and 36 km of the fault ruptured, with dextral displacement of up to 4 metres and dip-slip displacement of 1 – 2 metres (North side up).
and blocking roads. The highway connecting Canterbury and the West Coast via Arthur's Pass was closed for several months. Many water tanks and chimneys were damaged or toppled. Two years after the earthquake, trampers in the Otahake Valley discovered that a 900m high section of the side of a mountain had collapsed, blocking the valley and sending debris 5 km downstream.
Although this is one of the ten largest land-based earthquakes to strike New Zealand since European settlement, it was overshadowed by the more deadly 1929 Murchison earthquake
a few months later.
Time in New Zealand
New Zealand has two time zones. The main islands use New Zealand Standard Time , 12 hours in advance of Coordinated Universal Time , while the outlying Chatham Islands use Chatham Standard Time , 12 hours 45 minutes in advance of UTC.During summer daylight saving time is observed and clocks are...
on 9 March 1929 (11:20 GMT). The sparsely settled region of the Southern Alps
Southern Alps
The Southern Alps is a mountain range extending along much of the length of New Zealand's South Island, reaching its greatest elevations near the island's western side...
shook for four minutes. Tremors continued almost continuously until midnight and sporadic strong aftershocks were felt for several days.
The earthquake was measured at 7.1 on the Richter Scale and the intensity of shaking in the epicentral region has been assessed from historical records as level VIII on the Modified Mercalli Scale. Intensities of 6 were observed in Christchurch
Christchurch
Christchurch is the largest city in the South Island of New Zealand, and the country's second-largest urban area after Auckland. It lies one third of the way down the South Island's east coast, just north of Banks Peninsula which itself, since 2006, lies within the formal limits of...
and Westport
Westport, New Zealand
-Economy:Economic activity is based around fishing, coal mining and dairy farming. Historically, gold mining was a major industry, and coal mining was much more extensive than today . However, the region still is home to New Zealand's largest opencast mining operation in Stockton...
. The earthquake occurred on the Poulter Fault, which was not identified and mapped until 2001.
Tectonic setting
New Zealand lies along the boundary between the AustralianIndo-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....
s. In the 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...
most of the relative displacement between these plates is taken up along a single dextral (right lateral) strike-slip fault with a major reverse component, the 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...
. In the North Island
North Island
The North Island is one of the two main islands of New Zealand, separated from the much less populous South Island by Cook Strait. The island is in area, making it the world's 14th-largest island...
the displacement is mainly taken up along the Kermadec-Tonga subduction zone
Kermadec Trench
The Kermadec trench is one of Earth's deepest oceanic trenches, reaching a depth of . Formed by the subduction of the Pacific Plate under the Indo-Australian Plate, it runs over a thousand kilometres parallel with and to the east of the Kermadec Ridge and island arc, from near the northeastern tip...
, although the remaining dextral strike-slip component is accommodated by the North Island Fault System
North Island Fault System
The North Island Fault System or North Island Dextral Fault Belt is a set of southwest-northeast trending seismically-active faults in the North Island of New Zealand that carry most of the dextral strike-slip component of the oblique convergence of the Pacific Plate with the Australian Plate...
. The Poulter Fault runs for approximately 50 km Northeast from the junction of the Bealey and Mahinga rivers to the valley of the Hurunui River. Between 16 km and 36 km of the fault ruptured, with dextral displacement of up to 4 metres and dip-slip displacement of 1 – 2 metres (North side up).
Effects
Numerous landslides were triggered, damaging the Midland railwayMidland Line
Midland Line refers to the following rail lines:*Midland railway line, Perth, Australia*Midland Line, New Zealand*Midland Line in Massachusetts, United States...
and blocking roads. The highway connecting Canterbury and the West Coast via Arthur's Pass was closed for several months. Many water tanks and chimneys were damaged or toppled. Two years after the earthquake, trampers in the Otahake Valley discovered that a 900m high section of the side of a mountain had collapsed, blocking the valley and sending debris 5 km downstream.
Although this is one of the ten largest land-based earthquakes to strike New Zealand since European settlement, it was overshadowed by the more deadly 1929 Murchison earthquake
1929 Murchison earthquake
The 1929 Murchison earthquake occurred at 10:17 AM on 17 June. It struck the Murchison region of South Island, with an estimated magnitude of 7.8, and was felt throughout New Zealand. There were 17 casualties, mostly as a result of landslides triggered by the earthquake...
a few months later.