Seismic risk

Seismic risk refers to the risk of damage from earthquake to a building, system, or other entity. 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. [1] A building located in a region of high seismic hazard is at lower risk if it is built to sound seismic engineering principles. On the other hand, a building located in a region with a history of minor seismicity, in a brick building located on fill subject to liquifaction can be as high or higher risk.

A special subset is urban seismic risk which looks at the specific issues of cities. Risk determination and emergency response can also be determined through the use of an Earthquake scenario.

Determination of seismic risk

The determination of seismic risk is the foundation for risk mitigation decision-making, a key step in risk management. Large corporations and other enterprises (e.g., local governments) analyze their 'portfolio' of properties, to determine how to best allocate limited funds for structural strengthening of buildings, or other risk reduction measures such as emergency planning. In calculating the risk of each facility in the 'portfolio', potential life safety and economic losses due not only to structural damage, but also to equipment, contents and business interruption are considered. Public agencies (local, state governments and federal agencies) similarly analyze their portfolios. The interconnections of infrastructures such as water, road and highway, and electric power systems are also considered. Insurance companies routinely employ estimates of seismic risk in their operations, to determine appropriate insurance rates, to monitor over-accumulation of policies in a small area, and to purchase reinsurance. A simplified method of calculating seismic risk for a given city, involves the use of a street survey. [2] If you know the level of seismic hazard, the damage generally follows established patterns.

Seismic risk is often determined using a seismic modeling computer programs which uses the seismic hazard inputs and combines them with the known susceptibilities of structures and facilities, such as buildings, bridges, electrical power switching stations, etc. The result gives probabilities for economic damage or casualties, for example the HAZUS computer program [3]. While the results can be used as a general measure of seismic risk for types of buildings, the actual seismic risk for any individual building may vary considerably and will depend upon its exact configuration and condition. Acquiring and analyzing the specific data for an individual building or facility is one of the most expensive and daunting aspects of seismic risk estimation. Progress is made if one can calculate the 'fragility' or seismic capacity of the components within a structure. [4]

In 1999, ASTM produced guidelines for reporting seismic loss estimates on commercial properties, commonly known as Probable Maximum Loss or PML reviews. These guidelines specify the scope of work, qualifications of the reviewer, and proper nomenclature for reporting loss estimates.[5]

Reduction of seismic risk

Seismic risk can be reduced by active programs that improve emergency response, and improve basic infrastructure. The concepts of earthquake preparedness can help plan for emergencies arising from an earthquake. Building codes are intended to help to manage seismic risk and are updated as more is learned about the effects of seismic ground motion on buildings. This type of active improvement of mitigation of damage from earthquakes is known as seismic retrofit.[6] However, the changes generally do not immediately improve seismic risk in a community since existing buildings are rarely required to be upgraded to meet the revisions.

See also

Notes

  1. ^ Seismic risk evaluation for an urban centre. 250TH ANNIVERSARY OF THE 1755 LISBON EARTHQUAKE
  2. ^ Simple Survey Procedures for Seismic Risk Assessment In Urban Building Stocks
  3. ^ [1]
  4. ^ [2]
  5. ^ "Archived copy". Archived from the original on 2013-09-14. Retrieved 2013-02-26.CS1 maint: archived copy as title (link)
  6. ^ Craig Taylor and Erik VanMarcke, ed. (2002). Acceptable Risk Processes: Lifeline and Natural Hazards. Reston, VA: ASCE, TCLEE. ISBN 9780784406236. Archived from the original on 2013-12-03.

External links

Braced frame

A braced frame is a structural system designed to resist wind and earthquake forces. Members in a braced frame are not allowed to sway laterally (which can be done using shear wall or a diagonal steel sections, similar to a truss).

Coordinating Committee for Earthquake Prediction

The Coordinating Committee for Earthquake Prediction (CCEP) (Japanese: 地震予知連絡会, Jishin Yochi Renraku-kai) in Japan was founded in April 1969, as part of the Geodesy Council's Second Earthquake Prediction Plan, in order to carry out a comprehensive evaluation of earthquake data in Japan. The committee consists of 30 members and meets four times each year, as well as publishing a report on its activities twice each year. The CCEP brings together representatives from 20 governmental bodies and universities engaged in earthquake prediction and research. It has a secretariat within the Ministry of Land, Infrastructure, Transport and Tourism.

Dampierre Nuclear Power Plant

The Dampierre nuclear power plant is located in the town of Dampierre-en-Burly (Loiret), 55 km upstream of Orleans and 110 km downstream of Nevers, it uses water from the Loire for cooling.

Approximately 1,100 people work at the site.

Earthquake cloud

Earthquake clouds are clouds claimed to be signs of imminent earthquakes. They have been described in antiquity: In chapter 32 of his work Brihat Samhita, Indian scholar Varahamihira (505–587) discussed a number of signs warning of earthquakes, including extraordinary clouds occurring a week before the earthquake. In modern times, a few scientists claim to have observed clouds associated with a seismic event, sometimes more than 50 days in advance of the earthquake. Some have even claimed to accurately predict earthquake occurrences by observing clouds. However, these claims have very little support in the scientific community.

Earthquake insurance

Earthquake insurance is a form of property insurance that pays the policyholder in the event of an earthquake that causes damage to the property. Most ordinary homeowners insurance policies do not cover earthquake damage.

Most earthquake insurance policies feature a high deductible, which makes this type of insurance useful if the entire home is destroyed, but not useful if the home is merely damaged. Rates depend on location and the probability of an earthquake loss. Rates may be lower for homes made of wood, which withstand earthquakes better than homes made of brick.

In the past, earthquake loss was assessed using a collection of mass inventory data and was based mostly on experts' opinions. Today it is estimated using a Damage Ratio (DR), a ratio of the earthquake damage money amount to the total value of a building. Another method is the use of HAZUS, a computerized procedure for loss estimation.

As with flood insurance or insurance on damage from a hurricane or other large-scale disasters, insurance companies must be careful when assigning this type of insurance, because an earthquake strong enough to destroy one home will probably destroy dozens of homes in the same area. If one company has written insurance policies on numerous homes in a particular city, then a devastating earthquake will quickly drain all the company's resources. Insurance companies devote much study and effort toward risk management to avoid such cases.

In the United States, insurance companies stop selling coverage for a few weeks after a sizeable earthquake has occurred. This is because damaging aftershocks can occur after the initial quake, and rarely, it may be foreshock. Although aftershocks are smaller in magnitude, they deviate from the original epicenter. If an aftershock is significantly closer to a populated area, it can cause much more damage than the initial quake. One such example is the 2011 Christchurch earthquake in New Zealand which killed 185 people following a much larger and more distant quake with no fatalities at all.

Earthquake light

An earthquake light (EQL) is a luminous aerial phenomenon that reportedly appears in the sky at or near areas of tectonic stress, seismic activity, or volcanic eruptions. Skeptics point out that the phenomenon is poorly understood and many of the reported sightings can be accounted for by mundane explanations.

Earthquake preparedness

Earthquake preparedness is a set of measures taken at the individual, organisational and societal level to minimise the effects of an earthquake. Preparedness measures can range from securing heavy objects, structural modifications and storing supplies, to having insurance, an emergency kit, and evacuation plans.

Earthquake warning system

An earthquake warning system is a system of accelerometers, seismometers, communication, computers, and alarms that is devised for notifying adjoining regions of a substantial earthquake while it is in progress. This is not the same as earthquake prediction, which is currently incapable of producing decisive event warnings.

Earthquake weather

Earthquake weather is a type of weather popularly believed to precede earthquakes.

James A. FitzPatrick Nuclear Power Plant

The James A. FitzPatrick (JAF) Nuclear Power Plant is located in the Town of Scriba, near Oswego, New York, on the southeast shore of Lake Ontario. The nuclear power plant has one General Electric boiling water reactor. The 900-acre (360 ha) site is also the location of two other units at the Nine Mile Point Nuclear Generating Station.

The power plant was originally built by Niagara Mohawk Power Corporation - FitzPatrick and half of the Nine Mile Point site were transferred to the Power Authority of the State of New York (PASNY) [now called the New York Power Authority (NYPA)]. It was named after Power Authority Chairman James A. FitzPatrick. On November 2, 2015, Entergy Corp. announced its plans to shut down FitzPatrick Nuclear Power Plant in Oswego County after the reactor runs out of fuel in 2016. To avoid closure, Exelon Generation agreed to purchase the plant from Entergy at the price of $110 million.On April 1, 2017, Exelon assumed ownership and operation of the plant.

LaSalle County Nuclear Generating Station

LaSalle County Nuclear Generating Station, located 11 miles (18 km) southeast of Ottawa, Illinois serves Chicago and northern Illinois with electricity. The plant is owned and operated by the Exelon Corporation. Its Units 1 and 2 began commercial operation in August 1982 and April 1984, respectively.

It has two General Electric boiling water reactors. LaSalle's Unit 1 and Unit 2 together produce 2,320 megawatts, which is enough electricity for the needs of 2.3 million American homes.

Instead of cooling towers, the station has a 2,058 acres (833 ha) man-made cooling lake, which is also a popular fishery — LaSalle Lake State Fish and Wildlife Area — managed by the Illinois Department of Natural Resources.

Puente Hills Fault

The Puente Hills Fault (also known as the Puente Hills thrust system) is an active geological fault that is located in the Los Angeles Basin in California. The thrust fault was discovered in 1999 and runs about 40 km (25 mi) in three discrete sections from the Puente Hills region in the southeast to just south of Griffith Park in the northwest. The fault is known as a blind thrust fault, as the fault plane does not extend to the surface. Large earthquakes on the fault are relatively infrequent but computer modeling has indicated that a major event could have substantial impact in the Los Angeles area. The fault is now thought to be responsible for one moderate earthquake in 1987 (the 1987 Whittier Narrows earthquake) and another light event that took place in 2010, with the former causing considerable damage and deaths.

Seismic Hazards Mapping Act

The Seismic Hazard Mapping Act ("The Act") was enacted by the California legislature in 1990 following the Loma Prieta earthquake of 1989. The Act requires the California State Geologist to create maps delineating zones where data suggest amplified ground shaking, liquefaction, or earthquake-induced landsliding may occur ("seismic hazard zones").

The Act requires responsible agencies to approve only projects within seismic hazard zones following a site-specific investigation to determine if the hazard is present and inclusion of appropriate mitigation(s) if so. The Act also requires disclosure by real estate sellers and agents at the time of sale if a property is within one of the designated seismic hazard zones.

The Act called for the creation of an advisory board to the State Mining and Geology Board to advise on the Act's implementation. In a 2004 update to the seismic hazard zone mapping guidelines, this advisory body concluded the amplified ground motion hazard was already sufficiently addressed by the 2001 California Building Code. Consequently, zones for this hazard are not being mapped by the State Geologist.

Seismic hazard

A seismic hazard is the probability that an earthquake will occur in a given geographic area, within a given window of time, and with ground motion intensity exceeding a given threshold. With a hazard thus estimated, risk can be assessed and included in such areas as building codes for standard buildings, designing larger buildings and infrastructure projects, land use planning and determining insurance rates. The seismic hazard studies also may generate two standard measures of anticipated ground motion, both confusingly abbreviated MCE; the simpler probabilistic Maximum Considered Earthquake (or Event ), used in standard building codes, and the more detailed and deterministic Maximum Credible Earthquake incorporated in the design of larger buildings and civil infrastructure like dams or bridges. It is important to clarify which MCE is being discussed.

Calculations for determining seismic hazard were first formulated by C. Allin Cornell in 1968 and, depending on their level of importance and use, can be quite complex. The regional geology and seismology setting is first examined for sources and patterns of earthquake occurrence, both in depth and at the surface from seismometer records; secondly, the impacts from these sources are assessed relative to local geologic rock and soil types, slope angle and groundwater conditions. Zones of similar potential earthquake shaking are thus determined and drawn on maps. The well known San Andreas Fault is illustrated as a long narrow elliptical zone of greater potential motion, like many areas along continental margins associated with the Pacific ring of fire. Zones of higher seismicity in the continental interior may be the site for intraplate earthquakes) and tend to be drawn as broad areas, based on historic records, like the 1812 New Madrid earthquake, since specific causative faults are generally not identified as earthquake sources.

Each zone is given properties associated with source potential: how many earthquakes per year, the maximum size of earthquakes (maximum magnitude), etc. Finally, the calculations require formulae that give the required hazard indicators for a given earthquake size and distance. For example, some districts prefer to use peak acceleration, others use peak velocity, and more sophisticated uses require response spectral ordinates.

The computer program then integrates over all the zones and produces probability curves for the key ground motion parameter. The final result gives a 'chance' of exceeding a given value over a specified amount of time. Standard building codes for homeowners might be concerned with a 1 in 500 years chance, while nuclear plants look at the 10,000 year time frame. A longer-term seismic history can be obtained through paleoseismology. The results may be in the form of a ground response spectrum for use in seismic analysis.

More elaborate variations on the theme also look at the soil conditions. Higher ground motions are likely to be experienced on a soft swamp compared to a hard rock site. The standard seismic hazard calculations become adjusted upwards when postulating characteristic earthquakes. Areas with high ground motion due to soil conditions are also often subject to soil failure due to liquefaction. Soil failure can also occur due to earthquake-induced landslides in steep terrain. Large area landsliding can also occur on rather gentle slopes as was seen in the Good Friday earthquake in Anchorage, Alaska, March 28, 1964.

Seismic loading

Seismic loading is one of the basic concepts of earthquake engineering which means application of an earthquake-generated agitation to a structure. It happens at contact surfaces of a structure either with the ground, or with adjacent structures, or with gravity waves from tsunami.

Seismic loading depends, primarily, on:

Anticipated earthquake's parameters at the site - known as seismic hazard

Geotechnical parameters of the site

Structure's parameters

Characteristics of the anticipated gravity waves from tsunami (if applicable).Sometimes, seismic load exceeds ability of a structure to resist it without being broken, partially or completely Due to their mutual interaction, seismic loading and seismic performance of a structure are intimately related.

Surface rupture

Surface rupture (or ground rupture, or ground displacement) is the visible offset of the ground surface when an earthquake rupture along a fault affects the Earth's surface. Surface rupture is opposed by buried rupture, where there is no displacement at ground level. This is a major risk to any structure that is built across a fault zone that may be active, in addition to any risk from ground shaking. Surface rupture entails vertical or horizontal movement, on either side of a ruptured fault. Surface rupture can affect large areas of land.

Susquehanna Steam Electric Station

The Susquehanna Steam Electric Station, a nuclear power station, is on the Susquehanna River in Salem Township, Luzerne County, Pennsylvania.

Urban seismic risk

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 earthquakes. Many risks can be minimized with good earthquake construction, and seismic analysis. One of the best ways to deal with the issue is through an earthquake scenario analysis.

Waterford Nuclear Generating Station

The Waterford Steam Electric Station, Unit 3, also known as Waterford 3, is a nuclear power plant located on a 3,000-acre (1,200 ha) plot in Killona, Louisiana, in St. Charles Parish.This plant has one Combustion Engineering two-loop pressurized water reactor. The plant produces 1,240 megawatts of electricity since the site's last refuel in March 2019. It has a dry ambient pressure containment building.

On August 28, 2005, Waterford shut down due to Hurricane Katrina approaching and declared an unusual event (the least-serious of a four-level emergency classification scale). Shortly after Katrina, Waterford restarted and resumed normal operation.

During the 2011 Mississippi River floods, the power plant, which is located about 25 miles (40 km) west of New Orleans, was restarted on May 12, after a refueling shutdown on April 6.The plant also shut down on October 17, 2012, for steam-generator replacement. The plant returned to full power in the middle of January 2013.

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