1929 Grand Banks earthquake

1929 Grand Banks earthquake
UTC time	1929-11-18 20:32:00
ISC event	908394
USGS-ANSS	ComCat
Local date	November 18, 1929
Local time	17:02
Magnitude	7.2 Mw
Depth	20 km (12 mi)
Epicenter	44°32′N 56°01′W / 44.54°N 56.01°W
Areas affected	Dominion of Newfoundland ; Canada ; French Republic Saint Pierre and Miquelon
Total damage	$400,000 ($5.6 million in 2017)
Max. intensity	RFS VI (Strong tremor); MMI VIII (Severe)
Tsunami	Yes
Aftershocks	~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, 1929. 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.^[5]

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, which occurred 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.^[1]

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.^[1] It destroyed many south coastal communities on the Peninsula, killing 27 or 28 people and leaving 1,000 or more homeless.^[6] 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) away, 06:47 after the earthquake.^[1] It took 2 hours and 23 minutes to strike Burin, Newfoundland, 340 km (210 mi) from the epicentre, and only two hours to be observed in Bermuda 1,445 km (898 mi).^[1]

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, ^[1]

Prince Edward Island

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

Saint Pierre and Miquelon

In the French Overseas territory of Saint Pierre and Miquelon,^[7] about 18 kilometres (11 mi) west of the Burin Peninsula, residents were startled around 16:30h by an earthquake lasting approximately one minute. At 17:20, the subsequent tsunami reached the island of Saint-Pierre, submerging the docks. The most destruction was reported on the island formerly known as Île-aux-Chiens (The Island of the Dogs, until 1931–now known as L'Île-aux-Marins, The Island of the Sailors); the tsunami approached from the south, rising above the height of the south bank that protects the south coast, and flooding the lower part of the island upon impact. The waves destroyed (and moved) several residences and structures, but there were no reported injuries or casualties from the islands.^[7] The quake's 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

In the immediate aftermath of the tsunami, electricity, radio and telegram communications were unavailable for several days. It took three days for the S.S. Meigle to respond to a distress signal, sending supplies, aid workers, doctors, nurses, blankets, and food. Donations from across Newfoundland, the United States and the United Kingdom totaled around $250k (about CA$4.3 million in 2023). There was never an accurate or official list of victims produced, by any individual or branch of the Newfoundland or Canadian government. In a report entitled "Loss of Life", the Dr. Harris Munden Mosdell (chairman of the board of Health Burin West) reported that "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.^[6]^[8]

In 1952, scientists from Columbia University put together the pieces of the sequentially-broken cables, leading to the discovery of the landslide and the first documentation of a turbidity current.^[9] Scientists have examined layers of sand, believed to be deposited by other tsunamis, in an effort to determine the regional frequency of large earthquakes.^{[citation needed]} 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.^{[citation needed]} The frequency of large tsunamis varies according to the deposition of sediments offshore, as it was the submarine landslide's power that triggered the wave.^[10]

References

Citations

^ ^a ^b ^c ^d ^e ^f ^g ^h Fine et al. 2005.
^ Engdahl & Vallaseñor 2002.
^ ^a ^b ^c ^d ^e Natural Resources Canada 2002.
^ ^a ^b ^c Natural Resources Canada 2018.
^ "90 years later, a tsunami in southern Newfoundland still brings vivid memories". Cbc.ca. Retrieved December 20, 2021.
^ ^a ^b Ruffman & Hann 2006.
^ ^a ^b Ruffman 1992.
^ "The 1929 Magnitude 7.2 "Grand Banks" earthquake and tsunami". Natural Resources Canada. Retrieved August 6, 2023.
^ Heezen & Ewing 1952.
^ "The Tsunami of 1929". heritage.nf.ca. Retrieved August 6, 2023.

Sources

"Le séisme de magnitude 7,2 et le tsunami de 1929 sur les "Grands Bancs"". Natural Resources Canada. Retrieved March 6, 2016.
"Revised Modified Mercalli intensities for the Magnitude 7.2 1929 Grand Banks earthquake". Natural Resources Canada. October 19, 2018. Retrieved November 22, 2016.
Engdahl, E. R.; Vallaseñor, A. (September 12, 2002). "Global seismicity: 1900–1999" (PDF). International Handbook of Earthquake & Engineering Seismology. Part A, Volume 81A (First ed.). Academic Press. p. 675. ISBN 978-0124406520.
Fine, I. V.; Rabinovich, A. B.; Bornhold, B. D.; Thomson, R. E.; Kulikov, E. A. (2005). "The Grand Banks landslide-generated tsunami of November 18, 1929: preliminary analysis and numerical modeling" (PDF). Marine Geology. 215 (1–2). Elsevier: 45–57. Bibcode:2005MGeol.215...45F. doi:10.1016/j.margeo.2004.11.007. Archived from the original (PDF) on June 30, 2007.
Heezen, B.C.; Ewing, M. (1952). "Turbidity Currents and Submarine Slumps, and the 1929 Grand Banks Earthquake". American Journal of Science. 250: 849–873. doi:10.2475/ajs.250.12.849.
Ruffman, A.; Hann, V. (2006). "The Newfoundland Tsunami of November 18, 1929: An Examination of the Twenty-eight Deaths of the "South Coast Disaster"" (PDF). Newfoundland and Labrador Studies: 57. Retrieved March 5, 2016.
Ruffman, Alan (1992). "Archiving Content The 1929 Tsunami In St. Lawrence, Newfoundland" (PDF). Tsunami Runup Mapping as an Emergency Preparedness Planning Tool. 2-Appendices and Enclosures. Emergency Preparedness Protection civile Canada: 294. Retrieved March 4, 2016.

External links

Archival moment: Tsunami hits Burin Peninsula – CBC
The Magnitude 7.2 1929 "Grand Banks" earthquake and tsunami – Natural Resources Canada
The South Shore disaster: Newfoundland's tsunami
Not Too Long Ago (first hand accounts of the tsunami, pp. 51–60)
Newfoundland Tsunami – November 18, 1929 – Library and Archives Canada
Marine Geology Volume 215, Issues 1–2 International Journal of Marine geology, Geochemistry and Geophysics (2004) ISSN 0025-3227
The International Seismological Centre has a bibliography and/or authoritative data for this event.