When projecting loss estimates as the result of a potential earthquake or extreme wind hazard, the primary focus for many entities is typically on the potential damage to the buildings and possibly the damage or loss to important equipment, and stock and supplies. Also of significant concern to many corporations and public entities is the time that their facility will be out of service or that their capacity to produce their product or service will be curtailed. This level of "downtime" is often referred to as "business interruption" and can be expressed in term of time, dollars, or a combination of both.
In the development of business interruption estimates, the impact of damage to "lifelines" that support a facility is often ignored. Lifelines are the utilities and transportation networks that service a facility. If the critical lifelines are damaged and unavailable for facility operations, significant business interruption may result.
Lifelines that are typically considered as part of an earthquake or extreme wind loss estimate are the utilities and primary transportation networks that serve the facilities or are critical to the delivery of the product. The lifelines most often considered are:
Depending on the business, other transportation systems such as air (airports), water (ports and harbors), and rail (railway bridges) may be critical. Figure 1 shows damaged pipes on fuel jetty at the Port of Kandla, Gujarat, India, after the 2001 India Earthquake.
Figure 1: Pipes on fuel jetty at the Port of Kandla, Gujarat, India, 2001 (Photo by Ballantyne)
Services related to information technology (IT) often are included under the telecommunications category. However, if a facility utilizes highly specialized IT networks or equipment, additional lifeline categories may be added to the list above.
Lifeline system performance is a function of individual system component performance, and their interaction with one another in the system. Component performance is a function of both the hazard and the vulnerability of the particular component to that hazard.
Historically, electric power system outages in earthquakes and other natural disasters have been caused predominantly by damage to electrical substations and their equipment, primarily damage to elevated porcelain equipment at 230 and 500 kV substations. Heavy, unanchored circuit breakers and transformers can also be susceptible to sliding and overturning damage as a result of strong motion.
Major power-generating facilities in California and Japan have seen limited exposure to major earthquakes. However, many of the existing fossil fuel generating facilities serving major metropolitan areas are located adjacent to rivers on what may be liquefiable soils. This may result in damage to the generation facility itself as well as the loss of the ability to move coal to the facilities.
Transmission and distribution lines (both aboveground and underground) may experience isolated pockets of damage in areas of fault rupture or ground failure. Wire slapping may result in short circuits, resulting in tripping of circuit breakers, but can usually be reset within hours
When determining the potential business interruption issues related to the electrical power, attention should focus on the number of electrical substations and distribution networks that currently feed the facility, or that could possibly be rerouted to provide electrical power to the facility in the short term. Even if a facility has dual feeds from different substations, both of those substations may be fed from a single high voltage substation higher up in the system. Facilities located in regions that have only a single source of power are more vulnerable as compared to facilities with multiple sources of power. This can be due either to the configuration of the distribution network and/or the generating facilities.
Water systems are composed of a range of system components for: water supply, transmission, pumps stations, storage, and distribution. Failure of any of these components can result in failure of the overall system.
Treatment plants are particularly vulnerable to power outages, equipment and piping damage, process tank baffle failure, building damage (particularly if constructed of unreinforced masonry), and structure settlement due to liquefaction. Pump stations are vulnerable to loss of power, equipment and piping damage, and building damage. Storage facilities can fail due to shaking of reservoir embankments causing liquefaction, seismically induced hydraulic loading on reservoir walls, sloshing wave impact loads on reservoir roofs, roof displacement due to seismic loading, and damage to connecting piping due to differential movement.
Historically, pipeline damage has had the greatest impact on system operation. Transmission and distribution pipelines are particularly vulnerable if they are constructed of brittle materials, such as cast iron. They are the most vulnerable where the ground deforms as a result of liquefaction or significant settlement.
Water systems following the 1994 Northridge Earthquake in Los Angeles, and the 1995 Kobe Earthquake in Japan, were not fully restored due to pipeline damage for 9 days, and 60 days respectively. Figure 2 shows a tank at a water reservoir that experienced "Elephant's Foot" buckling as a result of the Northridge Earthquake.
Figure 2: Northridge Water Reservoir Elephant's Foot Buckling (Photo by Ballantyne)
Communications systems suffer from several types of impacts in earthquakes: overload of the system resources, damage to equipment and facilities, loss of service resulting from power outage, and loss of cooling as a result of loss of water supply. The two-way nature of telephone service distinguishes it from other utilities, where service is limited to one-way delivery of a physical resource. For telephone service, no storage of resources is necessary, and no supplies are imported.
Continuity of service depends on the operation of critical links in the system (i.e., switching facilities and central offices), and operability of local circuits. On a regional and national scale, the flexible nature of the network provides plenty of redundancy and numerous opportunities to reroute service around failed nodes. Locally, loss of a central office will likely result in loss of service.
Little evidence of circuit damage due to strong ground shaking has been seen in previous earthquakes, and there have been several instances of good telecommunications system performance in areas of significant ground failure. Accordingly, damage to underground cables is expected only in the most severe instances of ground failure.
Damage to the central office and its contents may occur in severe ground motion, and be amplified by ground failure. Loss of power is only a concern if the central office lacks adequate backup power capability.
Bridges are vulnerable to earthquakes due to four general damage mechanisms:
Bridge spans fall off supports because of inadequate seat width and/or lack of anchorage of the span to the seat. This can result in catastrophic collapse and an extended period of restoration.
Support columns fail in shear due to inadequate design to carry lateral loading. This can result in minor damage to catastrophic collapse.
Foundations fail due to liquefaction/lateral spreading. This can result in minor damage to catastrophic collapse.
Approaches settle due to consolidation of the soil behind the abutment. This can result in minor damage that can be quickly repaired.
With the exception of foundation failure, all of the above failure mechanisms were observed after the 1994 Northridge Earthquake in Los Angeles. As a result of the bridge failures, traffic was slowed until detour routes were established and alternate transportation modes were established. The California Department of Transportation had experience of extensive bridge damage in the 1989 Loma Prieta earthquake, and had diverted millions of dollars in subsequent years to seismically upgrade bridges. As a result, less than 10 bridges collapsed in the 1994 Northridge Earthquake, a small percentage considering several thousand that were exposed. Without this accelerated program, it would have likely taken years to restore the Los Angeles highway system to its pre-earthquake performance level. In contrast, in the 1995 Kobe Earthquake, all types of failure mechanisms occurred, paralyzing traffic for months.
Components vulnerable to damage in earthquakes include sewers that collect and transmit the sewage, pump stations, and treatment plants. Damage to sewers is normally difficult to detect, other than on the basis of visual spills or odors, because the pipelines flow by gravity, and will continue to flow even when damaged as long as they are not obstructed.
Sewer collapse is unusual except when significant ground movement occurs. In the 1994 Northridge Earthquake in Los Angeles, approximately 10 "pump arounds" were required where sewers collapsed, compared to well over 1,000 water pipeline failures that occurred in the same area. Sewers constructed of brick are dependent on the arching structure of the brick across the crown. If the ground surrounding the sewers liquefies, the sewers may collapse.
Treatment plants and pump stations can fail due to loss of power, damage to inlet or outlet piping, internal equipment and piping damage, building damage due to shaking, and movement due to liquefaction. Many pump stations have emergency generators to keep them functional if the power fails. In most cases, if a treatment plant or pump station fails, raw sewage will overflow into receiving water before it backs up into a building.
Natural gas systems are damaged in earthquakes primarily due to the damage of buried pipelines. Pipelines subjected to permanent ground movement from soil liquefaction/lateral spread are the most vulnerable.
Welded steel and polyethylene pipelines can accommodate most ground movements. Cast iron lines, sometimes used in low-pressure distribution systems and in older systems in many metropolitan areas, are vulnerable to ground deformation and shaking due the brittle nature of cast iron.
When projecting loss estimates as the result of a potential earthquake or extreme wind hazard, attention should be given to the major lifelines that support the facility's operations. Loss of service of key lifelines can lead to increased downtime following a major natural disaster and may result in significantly elevated business interruption costs.
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