Urban seismic risk
Encyclopedia
Urban seismic risk is a subset of the general term seismic risk
which describes the problems specific to centers of population when they are subjected to earthquake
s. Many risks can be minimised with good earthquake construction, and seismic analysis
. One of the best ways to deal with the issue is through an Earthquake scenario
analysis.
, Ontario
, Canada
is used as an example city in this article. The general issues are common to all cities subject to earthquakes.
Cities are a mixture of old and new construction as in this picture. Note the old brick building mixed in with the new highrises, and the famous Toronto CN Tower
. Similar to methodologies used in nuclear reactor
s, a seismic walkdown of the city is the best way to identify vulnerabilities and possible places for improvement.
Toronto is located on the shores of Lake Ontario
, the site of much microseismicity. Historic records indicate that energetic earthquakes occur infrequently in the region, as with many other cities in the world, though Toronto was struck by a 5.0 magnitude earthquake on June 23, 2010
.
Most new construction complies with strict building codes, and buildings designed for loads that go beyond seismic. For example, Toronto's highrises are, for the most part, firmly situated on bedrock (for settlement reasons), and are designed for hurricane wind loads. They are not expected to have any problems structurally during an earthquake, although they may sway noticeably.
There are many places where the risk of seismic damage to older buildings is quite high. Old brick buildings on poor soils are highly vulnerable to earthquake damage, particularly when the mortar
holding the bricks together has decayed. This picture shows an elevated expressway on filled land. Although there may not be total collapse, there will be sufficient damage to incapacitate the structure. Problems increase if there is the possibility for soil or earthquake liquefaction.
Even in buildings which are capable of withstanding an earthquake without structural failure there may be risk to people due to interior hazards. Items such as suspended ceilings and light fixtures have almost no seismic ruggedness. Warehouse stores where heavy merchandise is stacked are a particular hazard.
Seismic risk
Seismic risk uses the results of a seismic hazard analysis, and includes both consequence and probability. Seismic risk has been defined, for most management purposes, as the potential economic, social and environmental consequences of hazardous events that may occur in a specified period of time...
which describes the problems specific to centers of population when they are subjected to 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...
s. Many risks can be minimised with good earthquake construction, and seismic analysis
Seismic analysis
Seismic Analysis is a subset of structural analysis and is the calculation of the response of a building structure to earthquakes...
. One of the best ways to deal with the issue is through an Earthquake scenario
Earthquake scenario
Earthquake scenario is a planning tool to determine the appropriate emergency responses or building systems in seismic risk areas. It uses the basics of seismic hazard studies, but usually places a set earthquake on a specific fault, most likely near a high-population area...
analysis.
Toronto
TorontoToronto
Toronto is the provincial capital of Ontario and the largest city in Canada. It is located in Southern Ontario on the northwestern shore of Lake Ontario. A relatively modern city, Toronto's history dates back to the late-18th century, when its land was first purchased by the British monarchy from...
, Ontario
Ontario
Ontario is a province of Canada, located in east-central Canada. It is Canada's most populous province and second largest in total area. It is home to the nation's most populous city, Toronto, and the nation's capital, Ottawa....
, 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...
is used as an example city in this article. The general issues are common to all cities subject to earthquakes.
Cities are a mixture of old and new construction as in this picture. Note the old brick building mixed in with the new highrises, and the famous Toronto CN Tower
CN Tower
The CN Tower is a communications and observation tower in Downtown Toronto, Ontario, Canada. Standing tall, it was completed in 1976, becoming the world's tallest free-standing structure and world's tallest tower at the time. It held both records for 34 years until the completion of the Burj...
. Similar to methodologies used in nuclear reactor
Nuclear reactor
A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid , which runs through turbines that power either ship's...
s, a seismic walkdown of the city is the best way to identify vulnerabilities and possible places for improvement.
Toronto is located on the shores of Lake Ontario
Lake Ontario
Lake Ontario is one of the five Great Lakes of North America. It is bounded on the north and southwest by the Canadian province of Ontario, and on the south by the American state of New York. Ontario, Canada's most populous province, was named for the lake. In the Wyandot language, ontarío means...
, the site of much microseismicity. Historic records indicate that energetic earthquakes occur infrequently in the region, as with many other cities in the world, though Toronto was struck by a 5.0 magnitude earthquake on June 23, 2010
2010 Central Canada earthquake
The 2010 Central Canada earthquake was a magnitude 5.0 earthquake that occurred in Central Canada on June 23, 2010, at about 13:41:41 EDT and lasted about 30 seconds....
.
Most new construction complies with strict building codes, and buildings designed for loads that go beyond seismic. For example, Toronto's highrises are, for the most part, firmly situated on bedrock (for settlement reasons), and are designed for hurricane wind loads. They are not expected to have any problems structurally during an earthquake, although they may sway noticeably.
There are many places where the risk of seismic damage to older buildings is quite high. Old brick buildings on poor soils are highly vulnerable to earthquake damage, particularly when the mortar
Mortar (masonry)
Mortar is a workable paste used to bind construction blocks together and fill the gaps between them. The blocks may be stone, brick, cinder blocks, etc. Mortar becomes hard when it sets, resulting in a rigid aggregate structure. Modern mortars are typically made from a mixture of sand, a binder...
holding the bricks together has decayed. This picture shows an elevated expressway on filled land. Although there may not be total collapse, there will be sufficient damage to incapacitate the structure. Problems increase if there is the possibility for soil or earthquake liquefaction.
Even in buildings which are capable of withstanding an earthquake without structural failure there may be risk to people due to interior hazards. Items such as suspended ceilings and light fixtures have almost no seismic ruggedness. Warehouse stores where heavy merchandise is stacked are a particular hazard.