1929 Grand Banks earthquake

1929 Grand Banks earthquake
Date November 18, 1929 (1929-11-18)
Origin time 20:32 UTC [1]
Magnitude 7.2 Mw [2]
Depth 20 km (12 mi) [2]
Epicenter 44°32′N 56°01′W / 44.54°N 56.01°W / 44.54; -56.01 [1]
Areas affected Newfoundland
Canada
Saint Pierre and Miquelon
Total damage $400,000 [2]
Max. intensity (VI Strong tremor)[3]
(VIII Severe)(Natural Resources Canada 1929 earthquake revised)[3]
Tsunami Yes
Aftershocks ~3 [3]
Casualties 27 or 28 killed

The 1929 Grand Banks earthquake (also called the Laurentian Slope earthquake and the South Shore Disaster) occurred on November 18. The shock had a moment magnitude of 7.2 and a maximum Rossi–Forel intensity of VI (Strong tremor) and was centered in the Atlantic Ocean off the south coast of Newfoundland in the Laurentian Slope Seismic Zone.

Earthquake

The earthquake was centred on the edge of the Grand Banks of Newfoundland, about 400 kilometres (250 mi) south of the island. It was felt as far away as New York City and Montreal. The quake, along two faults 250 kilometres (160 mi) south of the Burin Peninsula, triggered a large submarine landslide displacing (200 km3 or 48 cu mi). It snapped 12 submarine transatlantic telegraph cables and led to a tsunami that arrived in three waves. Newfoundland, Canada and Saint Pierre and Miquelon had the largest impact, both from the snapped 12 submarine cables, and the tsunami. This was Canada's largest submarine landslide ever recorded, up to 500 times the size of 1894 Saint-Alban subaerial slide.[2]

In 2002 Natural Resources Canada and the United States Geological Survey, created an intensity map by using the Revised Modified Mercalli scale[4]

Tsunami

The tsunami waves had an amplitude of 3–8 metres (9.8–26.2 ft), and a runup of 13 metres (43 ft) along the Burin Peninsula.[2] It destroyed many south coastal communities on the Peninsula, killing 27 or 28 people and leaving 1,000 or more homeless.[5] All means of communication were cut off by the destruction, and relief efforts were further hampered by a blizzard that struck the day after. It was recorded as far away as Lagos, Portugal 4,060 km (2,520 mi), 06:47 after the earthquake.[2]It took 02:23 hrs to strike Burin, Newfoundland 340 km (210 mi) from the epicenter and, only 02:00 hrs; to be observed in Bermuda 1,445 km (898 mi).[2] This was Canada's largest submarine landslide ever recorded, up to 500 times the size of 1894 Saint-Alban landslide.[2]

Tsunami travel times demonstrate the strong anisotropy of the propagating waves. The waves reach open ocean islands such as Bermuda in about 2 h[hours] (mean speed ~700 km/h) and the Azores in about 4 h (~630 km/h). At the same time, tsunami wave speeds are much slower in the direction of the North America[n] coast: they require 2.7 h to reach Halifax (~230 km/h) and 4.2 h to reach Atlantic City (~380 km/h).
— W.H Berninghausen, [2]

Prince Edward Island

Prince Edward Island had felt the earthquake the intensity was rated at the time IV (Slight tremor) - VI (Strong tremor) on the Rossi-Forel scale.[3] In PEI it ranged from an intensity of a III (Weak) - V (Moderate).[3]

Saint Pierre and Miquelon

On the French islands of Saint Pierre and Miquelon,[6] about 18 kilometres (11 mi) west of the Burin Peninsula, people were woken around 16:30h by the earthquake that lasted approximately one minute. At 17:20, the tsunami reached the island of Saint-Pierre, submerging the docks. The worst damage was reported on the island then named Île-aux-Chiens (meaning Island of the Dogs till; 1931), now known as L'Île-aux-Marins (The Island of the Sailors). The tsunami hit from the south, rising above the height of the south bank that protects the south coast, flooding the lower part of the island. It damaged and moved some of the houses, there were no reported injuries or casualties from the islands.[6] The quakes intensity on the island was V (Moderate tremor) - VI (Strong tremor),[3] and on the revised Modified Mercalli Intensity scale; IV (Light) - V (Moderate)[4]

Aftermath

It took more than three days before the SS Meigle responded to an SOS signal with doctors, nurses, blankets, and food. Donations from across Newfoundland, Canada, the United States and United Kingdom totaled $250,000. There was never an accurate official list of the victims produced by any branch of the Newfoundland government. In the report entitled "Loss of Life," the Honourable Dr. Harris Munden Mosdell, Chairman of the Board of Health Burin West, reported: "The loss of life through the tidal wave totals twenty-seven. Twenty-five deaths were due directly to the upheaval. Two other deaths occurred subsequently and were due to shock and exposure." Later research attributed an additional death to the earthquake.[7]

In 1952, American scientists from Columbia University put together the pieces of the sequentially broken cables that led to the discovery of the landslide and the first documentation of a turbidity current.2016 Scientists have examined other layers of sand believed to be deposited by other tsunamis in an effort to determine the occurrence rates of large earthquakes. One sand layer, thought to be deposited by the 1929 tsunami, at Taylor's Bay was found 13 centimetres (5.1 in) below the turf line. The occurrences of large tsunamis, such as the one in 1929, are dependent upon deposition of sediments offshore because it was the landslide that made the tsunami so powerful. The deposition of such a large volume of sediments will take a while before there is enough to form an underwater landslide the same size as that in 1929.

See also

References

Citations

  1. 1 2 Engdahl 2016.
  2. 1 2 3 4 5 6 7 8 9 Fine; I.V. 2016.
  3. 1 2 3 4 5 6 RossiForel 2002.
  4. 1 2 GBMMI 2016.
  5. ↑ Ruffman;Hann 2016.
  6. 1 2 Ruffman, Alen 2016.
  7. ↑ Heezen;Ewing 2016.

Sources

External links

Further reading

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