1946 Vancouver Island earthquake
Encyclopedia
The 1946 Vancouver Island earthquake was a 7.3 magnitude
earthquake
that struck Vancouver Island
, on the Coast of British Columbia, Canada
, at 10:15 a.m. on Sunday, June 23, 1946. The main shock epicenter
occurred in the Forbidden Plateau
area northwest of Courtenay
. While most of the large earthquakes in the Vancouver
area occur at tectonic plate
boundaries, the 1946 Vancouver Island earthquake was a crustal
event. Shaking was felt from Portland, Oregon
to Prince Rupert, British Columbia
. The earthquake is remembered as one of the most damaging earthquakes in the history of British Columbia. However, damage was restricted because there were no heavily populated areas near the epicenter, where the violent shaking occurred.
This earthquake is Canada's largest historic onshore earthquake. However, the greatest earthquake in Canadian history recorded by seismometer
s was the 1949 Queen Charlotte earthquake
, an interplate earthquake
that occurred on the ocean bottom just off the rugged coast of Graham Island
, which reached magnitude 8.1 on the moment magnitude scale
.
that caused the 1946 Vancouver Island earthquake are poorly known. No surface expression of the offset was noticed, most likely because the epicenter area is very remote and densely forested. A comprehensive examination and computer interpretation of seismic data from over 50 stations has shown that a possible explanation of the earthquake includes a strike-slip fault corresponding to the lengthy axis of Vancouver Island known as the Beaufort Range
Fault. A fault running across Vancouver Island, corresponding to the projection of the underwater Nootka Fault
on the British Columbia Coast
is also a possibility, but this is less likely to be true, because the earthquake should have given evidence of offsets along a series of highways that follows much of the eastern coastline of Vancouver Island, called Island Highway
, and other roads between Courtenay
and Campbell River
. The estimated depth of the earthquake places it within the continental crust
, not at the margin with the Cascadia subduction zone
, and certainly not inside the subduction zone itself. Specifically, the earthquake's epicenter was positioned somewhere in the Forbidden Plateau
region, located in central Vancouver Island
.
In Vancouver
, damage consisted of lofty buildings oscillating violently, and a piece of masonry fell from the local railway station. In addition, within the city, at least one gas line cracked and several power outages occurred. Fires broke out in several chimneys, and at least one swing span bridge was fractured by the shaking. In the Hotel Vancouver, which housed the elderly and caught on fire, more than 500 war veterans' families fled the flames. One writer, George Finley, stated that the Lions' Gate Bridge
"swayed like a leaf", coinciding with a "low, rumbling sound, like a deep growl."
The 1946 Vancouver Island earthquake demolished 75% of the chimneys in the communities of Cumberland
, Union Bay
, and Courtenay
and caused extensive damage in Comox
, Port Alberni
, and Powell River
, on the eastern side of the Strait of Georgia
. Some chimneys were fractured in Victoria
, and people in Victoria and Vancouver experienced great fright, with some seen fleeing into the streets.
Landslide
s created by the earthquake were common throughout Vancouver Island. Land subsidence resulted from the earthquake, most commonly around shorelines on the Strait of Georgia. This included the bottom of Deep Bay which sank between 2.7 m (9 ft) and 25.6 m (84 ft). These measurements were reported by the Canadian Hydrographic Department. Also, a 3 metres (9.8 ft) ground shift occurred on Read Island
. Ships throughout the region were affected, and those on board them during the earthquake described it as similar to having run over a sand bar
or striking a rock. Undersea power lines were destroyed in the long narrow Alberni Inlet and near the city of Powell River
. All lighthouse keepers in the surrounding area felt the earthquake, and experienced damages including shattered windows and smashed dishes. A tsunami
struck the west coast of Texada Island
with two waves, the first was 2 metres (6.6 ft) high and the second 1 metres (3.3 ft) high. The earthquake caused a landslide near Mount Colonel Foster
. One fortunate occurrence allowed researchers afterward to review the effects of the earthquake: an aerial photographic survey of Vancouver Island had commenced in 1946, soon after the earthquake; these photographs were eventually studied by a geoscientist in the late 1970s.
South of the Canada–United States border in Washington State, some chimneys fell at Eastsound
and on Orcas Island
and a concrete mill was damaged at Port Angeles
. In Seattle, some damage occurred on upper floors of tall buildings, and one bridge was damaged. The shock was strongly felt at Bellingham
, Olympia
, Raymond
, and Tacoma
. The earthquake was powerful enough to knock the needle off a seismograph at the University of Washington
, and was sustained for about a minute even in Seattle.
The earthquake caused somewhat astounding movement among structures, moving one 300 feet (91.4 m) wall about 35 feet (10.7 m) and caused one home to shift for 5 feet (1.5 m) off its foundation. The total affected area in Canada and the United States was about 260000 square kilometre.
Moment magnitude scale
The moment magnitude scale is used by seismologists to measure the size of earthquakes in terms of the energy released. The magnitude is based on the seismic moment of the earthquake, which is equal to the rigidity of the Earth multiplied by the average amount of slip on the fault and the size of...
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...
that struck Vancouver Island
Vancouver Island
Vancouver Island is a large island in British Columbia, Canada. It is one of several North American locations named after George Vancouver, the British Royal Navy officer who explored the Pacific Northwest coast of North America between 1791 and 1794...
, on the Coast of British Columbia, Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
, at 10:15 a.m. on Sunday, June 23, 1946. The main shock epicenter
Epicenter
The epicenter or epicentre is the point on the Earth's surface that is directly above the hypocenter or focus, the point where an earthquake or underground explosion originates...
occurred in the Forbidden Plateau
Forbidden Plateau
The Forbidden Plateau is a small, hilly plateau in the east of the Vancouver Island Ranges in British Columbia, located northwest of Comox Lake roughly between Mount Albert Edward to the southwest and Mount Washington to the northeast. The gently sloping sub-alpine terrain is broken by small,...
area northwest of Courtenay
Courtenay, British Columbia
Courtenay is a city on the east coast of Vancouver Island, in the Canadian province of British Columbia. It is the largest city in the area commonly known as the Comox Valley, and it is the seat of the Comox Valley Regional District which replaced the Comox-Strathcona Regional District...
. While most of the large earthquakes in the Vancouver
Vancouver
Vancouver is a coastal seaport city on the mainland of British Columbia, Canada. It is the hub of Greater Vancouver, which, with over 2.3 million residents, is the third most populous metropolitan area in the country,...
area occur at tectonic plate
Plate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...
boundaries, the 1946 Vancouver Island earthquake was a crustal
Crust (geology)
In geology, the crust is the outermost solid shell of a rocky planet or natural satellite, which is chemically distinct from the underlying mantle...
event. Shaking was felt from Portland, Oregon
Portland, Oregon
Portland is a city located in the Pacific Northwest, near the confluence of the Willamette and Columbia rivers in the U.S. state of Oregon. As of the 2010 Census, it had a population of 583,776, making it the 29th most populous city in the United States...
to Prince Rupert, British Columbia
Prince Rupert, British Columbia
Prince Rupert is a port city in the province of British Columbia, Canada. It is the land, air, and water transportation hub of British Columbia's North Coast, and home to some 12,815 people .-History:...
. The earthquake is remembered as one of the most damaging earthquakes in the history of British Columbia. However, damage was restricted because there were no heavily populated areas near the epicenter, where the violent shaking occurred.
This earthquake is Canada's largest historic onshore earthquake. However, the greatest earthquake in Canadian history recorded by seismometer
Seismometer
Seismometers are instruments that measure motions of the ground, including those of seismic waves generated by earthquakes, volcanic eruptions, and other seismic sources...
s was the 1949 Queen Charlotte earthquake
1949 Queen Charlotte earthquake
The Queen Charlotte Islands earthquake of 1949 was a magnitude 8.1 interplate earthquake that struck the sparsely populated Queen Charlotte Islands and the Pacific Northwest coast on August 22, 1949. It is one of the world's greatest earthquakes. The main shock epicenter began in the ocean bottom...
, an interplate earthquake
Interplate earthquake
An interplate earthquake is an earthquake that occurs at the boundary between two tectonic plates. If one plate is trying to move past the other, they will be locked until sufficient stress builds up to cause the plates to slip relative to each other...
that occurred on the ocean bottom just off the rugged coast of Graham Island
Graham Island
Graham Island is the largest island in the Haida Gwaii archipelago , lying off the coast of British Columbia, Canada. It is separated only by a narrow channel from the other principal island of the group, Moresby Island Graham Island is the largest island in the Haida Gwaii archipelago (formerly...
, which reached magnitude 8.1 on the moment magnitude scale
Moment magnitude scale
The moment magnitude scale is used by seismologists to measure the size of earthquakes in terms of the energy released. The magnitude is based on the seismic moment of the earthquake, which is equal to the rigidity of the Earth multiplied by the average amount of slip on the fault and the size of...
.
Background and tectonics
The tectonicsTectonics
Tectonics is a field of study within geology concerned generally with the structures within the lithosphere of the Earth and particularly with the forces and movements that have operated in a region to create these structures.Tectonics is concerned with the orogenies and tectonic development of...
that caused the 1946 Vancouver Island earthquake are poorly known. No surface expression of the offset was noticed, most likely because the epicenter area is very remote and densely forested. A comprehensive examination and computer interpretation of seismic data from over 50 stations has shown that a possible explanation of the earthquake includes a strike-slip fault corresponding to the lengthy axis of Vancouver Island known as the Beaufort Range
Beaufort Range
The Beaufort Range is a mountain range on southern Vancouver Island, British Columbia, Canada, located north of Port Alberni and to the west of Qualicum Beach. It has an area of 448 km2 and is a subrange of the Vancouver Island Ranges which in turn form part of the Insular Mountains.The highest...
Fault. A fault running across Vancouver Island, corresponding to the projection of the underwater Nootka Fault
Nootka Fault
The Nootka Fault is an active transform fault running southwest from Nootka Island, near Vancouver Island, British Columbia, Canada.-Geology:...
on the British Columbia Coast
British Columbia Coast
The British Columbia Coast or BC Coast is Canada's western continental coastline on the Pacific Ocean. The usage is synonymous with the term West Coast of Canada....
is also a possibility, but this is less likely to be true, because the earthquake should have given evidence of offsets along a series of highways that follows much of the eastern coastline of Vancouver Island, called Island Highway
Island Highway
The Island Highway is actually a series of highways that follows much of the eastern coastline of Vancouver Island, British Columbia, Canada....
, and other roads between Courtenay
Courtenay, British Columbia
Courtenay is a city on the east coast of Vancouver Island, in the Canadian province of British Columbia. It is the largest city in the area commonly known as the Comox Valley, and it is the seat of the Comox Valley Regional District which replaced the Comox-Strathcona Regional District...
and Campbell River
Campbell River (Vancouver Island)
The Campbell River is a river on Vancouver Island, British Columbia, Canada, draining into Discovery Passage at the northwest end of the Strait of Georgia, at the City of Campbell River, which is named for the river. The Kwak'wala name for the river, or for the village near its mouth The Campbell...
. The estimated depth of the earthquake places it within the continental crust
Continental crust
The continental crust is the layer of igneous, sedimentary, and metamorphic rocks which form the continents and the areas of shallow seabed close to their shores, known as continental shelves. This layer is sometimes called sial due to more felsic, or granitic, bulk composition, which lies in...
, not at the margin with the Cascadia subduction zone
Cascadia subduction zone
The Cascadia subduction zone is a subduction zone, a type of convergent plate boundary that stretches from northern Vancouver Island to northern California. It is a very long sloping fault that separates the Juan de Fuca and North America plates.New ocean floor is being created offshore of...
, and certainly not inside the subduction zone itself. Specifically, the earthquake's epicenter was positioned somewhere in the Forbidden Plateau
Forbidden Plateau
The Forbidden Plateau is a small, hilly plateau in the east of the Vancouver Island Ranges in British Columbia, located northwest of Comox Lake roughly between Mount Albert Edward to the southwest and Mount Washington to the northeast. The gently sloping sub-alpine terrain is broken by small,...
region, located in central Vancouver Island
Vancouver Island
Vancouver Island is a large island in British Columbia, Canada. It is one of several North American locations named after George Vancouver, the British Royal Navy officer who explored the Pacific Northwest coast of North America between 1791 and 1794...
.
Damage and casualties
Though very destructive, the earthquake caused only two casualties: Jacob L. Kingston, aged 69, and Daniel Fidler, who was 50. One of the two had a heart attack; the other drowned when his dinghy was swamped by a wave.In Vancouver
Vancouver
Vancouver is a coastal seaport city on the mainland of British Columbia, Canada. It is the hub of Greater Vancouver, which, with over 2.3 million residents, is the third most populous metropolitan area in the country,...
, damage consisted of lofty buildings oscillating violently, and a piece of masonry fell from the local railway station. In addition, within the city, at least one gas line cracked and several power outages occurred. Fires broke out in several chimneys, and at least one swing span bridge was fractured by the shaking. In the Hotel Vancouver, which housed the elderly and caught on fire, more than 500 war veterans' families fled the flames. One writer, George Finley, stated that the Lions' Gate Bridge
Lions' Gate Bridge
The Lions Gate Bridge, officially known as the First Narrows Bridge, is a suspension bridge that crosses the first narrows of Burrard Inlet and connects the City of Vancouver, British Columbia, to the North Shore municipalities of the District of North Vancouver, the City of North Vancouver, and...
"swayed like a leaf", coinciding with a "low, rumbling sound, like a deep growl."
The 1946 Vancouver Island earthquake demolished 75% of the chimneys in the communities of Cumberland
Cumberland, British Columbia
Cumberland is a town in the Comox Valley on Vancouver Island in British Columbia, Canada.-History:The village was originally named Union, British Columbia after the Union Coal Company, which was in turn named in honour of the 1871 union of British Columbia with Canada. The town was renamed after...
, Union Bay
Union Bay, British Columbia
Union Bay in British Columbia, Canada is a small community approximately 15 kilometres south of Courtenay, British Columbia, the largest city in the Comox Valley. Union Bay is populated by about 1200 people and is an unincorporated site within the Comox Valley Regional District...
, and Courtenay
Courtenay, British Columbia
Courtenay is a city on the east coast of Vancouver Island, in the Canadian province of British Columbia. It is the largest city in the area commonly known as the Comox Valley, and it is the seat of the Comox Valley Regional District which replaced the Comox-Strathcona Regional District...
and caused extensive damage in Comox
Comox, British Columbia
Comox is a town of 12,000 people located on a small peninsula in the Georgia Strait on the eastern coast of Vancouver Island, British Columbia. The warm dry summers, mild winters, fertile soil and abundant sea life attracted First Nations thousands of years ago, who called the area kw’umuxws...
, Port Alberni
Port Alberni, British Columbia
Port Alberni is a city located in the province of British Columbia in Canada. It is the location of the head offices of the Alberni-Clayoquot Regional District. The city has a total population of 17,743, and the census agglomeration area a total of 25,396....
, and Powell River
Powell River, British Columbia
Powell River is a city on the northern Sunshine Coast of southwestern British Columbia, Canada. Most of its population lives near the eastern shores of Malaspina Strait, that part of the larger Georgia Strait between Texada Island and the Mainland...
, on the eastern side of the Strait of Georgia
Strait of Georgia
The Strait of Georgia or the Georgia Strait is a strait between Vancouver Island and the mainland coast of British Columbia, Canada. It is approximately long and varies in width from...
. Some chimneys were fractured in Victoria
Victoria, British Columbia
Victoria is the capital city of British Columbia, Canada and is located on the southern tip of Vancouver Island off Canada's Pacific coast. The city has a population of about 78,000 within the metropolitan area of Greater Victoria, which has a population of 360,063, the 15th most populous Canadian...
, and people in Victoria and Vancouver experienced great fright, with some seen fleeing into the streets.
Landslide
Landslide
A landslide or landslip is a geological phenomenon which includes a wide range of ground movement, such as rockfalls, deep failure of slopes and shallow debris flows, which can occur in offshore, coastal and onshore environments...
s created by the earthquake were common throughout Vancouver Island. Land subsidence resulted from the earthquake, most commonly around shorelines on the Strait of Georgia. This included the bottom of Deep Bay which sank between 2.7 m (9 ft) and 25.6 m (84 ft). These measurements were reported by the Canadian Hydrographic Department. Also, a 3 metres (9.8 ft) ground shift occurred on Read Island
Read Island
Read Island is an island in British Columbia, Canada. It is part of the Discovery Islands between Vancouver Island and the mainland, between the Strait of Georgia and Johnstone Strait....
. Ships throughout the region were affected, and those on board them during the earthquake described it as similar to having run over a sand bar
Shoal
Shoal, shoals or shoaling may mean:* Shoal, a sandbank or reef creating shallow water, especially where it forms a hazard to shipping* Shoal draught , of a boat with shallow draught which can pass over some shoals: see Draft...
or striking a rock. Undersea power lines were destroyed in the long narrow Alberni Inlet and near the city of Powell River
Powell River, British Columbia
Powell River is a city on the northern Sunshine Coast of southwestern British Columbia, Canada. Most of its population lives near the eastern shores of Malaspina Strait, that part of the larger Georgia Strait between Texada Island and the Mainland...
. All lighthouse keepers in the surrounding area felt the earthquake, and experienced damages including shattered windows and smashed dishes. 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...
struck the west coast of Texada Island
Texada Island
Texada Island is the largest island in the Strait of Georgia of British Columbia, Canada. Its northern tip is located about southwest of the city of Powell River and west of the Sechelt Peninsula on the Sunshine Coast. A former mining and logging area, the island still has a few quarries and old...
with two waves, the first was 2 metres (6.6 ft) high and the second 1 metres (3.3 ft) high. The earthquake caused a landslide near Mount Colonel Foster
Mount Colonel Foster
Mount Colonel Foster is a mountain located on Vancouver Island in Strathcona Regional District, British Columbia, Canada. At , it is the fourth highest peak on the island.Mount Colonel Foster is located across the Elk River from Elkhorn Mountain...
. One fortunate occurrence allowed researchers afterward to review the effects of the earthquake: an aerial photographic survey of Vancouver Island had commenced in 1946, soon after the earthquake; these photographs were eventually studied by a geoscientist in the late 1970s.
South of the Canada–United States border in Washington State, some chimneys fell at Eastsound
Eastsound, Washington
Eastsound is an unincorporated community on Orcas Island in San Juan County, Washington, United States.Eastsound is the largest population center on Orcas Island, the second-most populated and physically largest of the San Juan Islands...
and on Orcas Island
Orcas Island
Orcas Island is the largest of the San Juan Islands, which are located in the northwestern corner of Washington state in San Juan County, Washington.-History:...
and a concrete mill was damaged at Port Angeles
Port Angeles, Washington
Port Angeles is a city in and the county seat of Clallam County, Washington, United States. The population was 19,038 at the 2010 census. The area's harbor was dubbed Puerto de Nuestra Señora de los Ángeles by Spanish explorer Francisco de Eliza in 1791, but by the mid-19th century the name had...
. In Seattle, some damage occurred on upper floors of tall buildings, and one bridge was damaged. The shock was strongly felt at Bellingham
Bellingham, Washington
Bellingham is the largest city in, and the county seat of, Whatcom County in the U.S. state of Washington. It is the twelfth-largest city in the state. Situated on Bellingham Bay, Bellingham is protected by Lummi Island, Portage Island, and the Lummi Peninsula, and opens onto the Strait of Georgia...
, Olympia
Olympia, Washington
Olympia is the capital city of the U.S. state of Washington and the county seat of Thurston County. It was incorporated on January 28, 1859. The population was 46,478 at the 2010 census...
, Raymond
Raymond, Washington
Raymond is a city in Pacific County, Washington, United States. The population was 2,975 at the 2000 census and decreased 3.1% to 2,882 at the 2010 census. The town's economy is based on logging and fishing, together with a limited amount of tourism....
, and Tacoma
Tacoma, Washington
Tacoma is a mid-sized urban port city and the county seat of Pierce County, Washington, United States. The city is on Washington's Puget Sound, southwest of Seattle, northeast of the state capital, Olympia, and northwest of Mount Rainier National Park. The population was 198,397, according to...
. The earthquake was powerful enough to knock the needle off a seismograph at the University of Washington
University of Washington
University of Washington is a public research university, founded in 1861 in Seattle, Washington, United States. The UW is the largest university in the Northwest and the oldest public university on the West Coast. The university has three campuses, with its largest campus in the University...
, and was sustained for about a minute even in Seattle.
The earthquake caused somewhat astounding movement among structures, moving one 300 feet (91.4 m) wall about 35 feet (10.7 m) and caused one home to shift for 5 feet (1.5 m) off its foundation. The total affected area in Canada and the United States was about 260000 square kilometre.
See also
- List of earthquakes in Canada
- List of earthquakes in the United States
- List of deadly earthquakes since 1900
- 1918 Vancouver Island earthquake1918 Vancouver Island earthquakeThe 1918 Vancouver Island earthquake was a large earthquake that struck British Columbia, Canada at 12:41 a.m. on Friday, December 6, 1918.This was most likely a strike-slip earthquake, with epicenter near the west coast of Vancouver Island....
- 1949 Queen Charlotte earthquake1949 Queen Charlotte earthquakeThe Queen Charlotte Islands earthquake of 1949 was a magnitude 8.1 interplate earthquake that struck the sparsely populated Queen Charlotte Islands and the Pacific Northwest coast on August 22, 1949. It is one of the world's greatest earthquakes. The main shock epicenter began in the ocean bottom...