Earthquake Preparedness Salt Lake City

The Earthquake Threat in Salt Lake City
In 1994, a magnitude 6.7 earthquake struck Northridge, a heavily populated area in the State of California. The earthquake struck early in the morning. Buildings were damaged, but only 60 people were killed, most by a collapsing section of freeway during the morning commute. Fast forward 11 eleven years to 2003, where an earthquake, also magnitude 6.7 and occurring early in the morning, occurred centered in the town of Bam, which had a population of close to 100,000 people. The Bam, Iran earthquake killed 40,000 and devastated the city and surrounding area. (Zahrai and Heidarzadeh 1-6).
Though both quakes had the same magnitude, were centered in densely populated areas, and occurred at roughly the same time of day, the results were much different. In a heavily populated area of California during roughly the same time of day, an earthquake of the same magnitude as that of the Bam earthquake only produced only 60 fatalities (Earthquakes In United States FEMA). The Bam, Iran quake resulted in almost 7,000 times the number of casualties as the Northridge quake. Why?
The key difference between Bam and Northridge was not the earthquake codes. In fact, the code used in Iran and the code used in the California are almost identical in their requirements. The key difference is that California had applied the code to its buildings better than Iran had. As a result there were less collapses, less fatalities and therefore a greater chance of economic recovery for survivors of the Northridge earthquake. A key lesson to take away from the Bam/Northridge comparison is that simply preparing current and future buildings for earthquakes is not a sufficient earthquake mitigation strategy for high risk areas (Zahrai and Heidarzadeh 1-6).
Utah contains one of the most active faults in the United States, but no one knew about the fault when Utah was settled. In 1912 G. K. Gilbert, a famous geologist, visited the Wasatch Front hoping to solve a technical dispute. The dispute centered on how the mountains running parallel to Wasatch valleys had formed. Gilbert noted that, with the exception of the mountains near Salt Lake City, nearly all the mountains had small cliffs at their bases. He recognized these cliffs as scars from powerful earthquakes (or fault scarps). He deduced that each time an earthquake occurred, the valley sunk six to seven feet and the Wasatch Range rose a little higher (Yeats 246). Gilbert further postulated that the lack of a fault scarp near Salt Lake City suggested pressure buildup in tectonic plates beneath the city. He predicted the Wasatch Fault would produce a large earthquake centered near Salt Lake City (Yeats 246). Modern geologists have concurred with Gilbert’s prediction and kept the warning in effect for nearly one hundred years (Yeats, 246).
Despite this early recognition of earthquake potential, residents of the Salt Lake Valley took little or no preemptive action in regards to earthquakes for many years. In part, this was because few people in the early 1900s understood risks associated with earthquakes. As a result, many of the early structures in the state do not conform to seismic codes because they were built before the codes were adopted. These buildings pose major risks in the event of an earthquake. If a large earthquake fails to strike before these structures age past usability, and are torn down, the state will save money by not having invested to bring them up to code. On the other hand, if there is a large earthquake while pre-code infrastructure is still standing, it might devastate the region.
It is this balancing of risk and reward that should inform Utah’s earthquake preparedness strategy. Based on the potential probability and estimated magnitude of seismic events, the state needs to adopt an approach that balances practical economic and development concerns against an acceptable level of risk. Utah’s current approach to earthquake risk falls short because it tolerates a level of risk that is too high. Currently, especially for an area with a relatively high degree of earthquake potential, Utah’s infrastructure is woefully unprepared, and a large earthquake would have disastrous human and economic impacts. To avoid a result similar to what happened in Bam, Utah needs to take immediate steps to provide adequate incentives, or to fund directly, the seismic retrofitting of its infrastructure. This paper discusses the risks and potential damages of a large magnitude earthquake along the Wasatch Front and makes some suggestions about how Utah could alter its preparation strategy to better manage its earthquake risk.
Earthquake Probability as it Contributes to Risk
Probability is one of the factors that should determine how much effort and money the state should put into preparing for an earthquake. The purpose of this section is to examine the probability of a large earthquake occurring along the Wasatch Front.
There is a relatively high probability of a large earthquake striking the Wasatch Front. A large earthquake is one in which the magnitude exceeds 6.5 (Eldredge 1) Geologists estimate that there is a “25 percent chance of a magnitude 7.5 earthquake occurring somewhere along the Wasatch Front in the next 100 years (Eldredge 16).” Other reasonable estimates based on different theories give a probability closer to 57 percent for an earthquake of the same magnitude (Cook, 1).

Smaller, yet still destructive, earthquakes have a much higher chance of occurring. Large earthquakes (as discussed earlier) with a magnitude between 6.5 and 7.5 normally occur once every 350 years on the Wasatch Front (Eldredge 1-16). But, earthquakes with magnitudes of less than 6.5 have an average recurrence interval of 50 years (Eldredge 1-16). Even an earthquake of this magnitude would damage buildings in compliance with seismic codes and devastate buildings not in compliance with seismic codes.
The Utah Geological Survey believes the most likely places where the next large earthquakes will occur are Brigham City and Salt Lake City. Both predictions are based on the time interval spacing of ancient earthquakes in the same locations and the observation that neither of the two segments of the fault are moving. Scientists worry when faults bind up and stop moving. As long as a fault is moving pressure on the plate is released at a slow rate. If a tectonic plate stops moving it often signals that an earthquake is imminent. The worst case scenario for the state of Utah is a large earthquake striking Salt Lake City (Eldredge, 14).
Geological Factors Increasing Earthquake Damages
The Wasatch Front has certain physical characteristics that increase the damaging effects of seismic waves on structures. Although other places may have the potential for stronger earthquakes in terms of magnitude, other characteristics of the Wasatch Front region increase the damage potential. These factors include material amplification and liquefaction potential that exist along the Wasatch Front. The purpose of this section is to discuss how these factors elevate the risk for extensive earthquake damage along the Wasatch Front (Andrus 2).
Deep pockets of loosely packed sediment amplify the effect of seismic waves. Utah’s Valleys are full of loosely packed soils. The soils sank to the bottom of ancient Lake Bonneville and subsequently pooled up in valley floors. All valley towns along the Wasatch Front are built on compiled sediment (Lake Bonneville’s Cycles). The unconsolidated soil acts like a bowl of jelly when an earthquake occurs. For example, if someone kicks a bowl of jelly the bowl almost immediately stops shaking because it’s hard and the vibrations bleed out quickly. But, the jelly might continue to shake violently long after the vibrations within the solid bowl have become undetectable. Some building codes increase the damage ratings, in terms of ground acceleration, for seismic waves for extremely poor soil conditions (Reavely, Russel and Wiggins 1-17).
The Wasatch Front is also prone to liquefaction. Liquefaction occurs when vibrations from seismic waves move ground water upward through sandy soils. As the seismic waves continue to vibrate the mix of water and sand loses its stiffness (Andrus, 2). Whole buildings can tip over as the soil beneath their foundations turns to mud (Eldredge, 9). This was observed in two earthquakes in 1964 and has since been studied intensely (Andrus, 2). In order to have liquefaction you need a water table close to the surface of sandy soils (Andrus, 2). This condition exists both near Utah Lake and the Great Salt Lake.
Man Made Factors Contributing to Earthquake Risk Along the Wasatch Front
In an earthquake the type and quality of buildings in the affected region can make a big difference in the overall outcome. Areas that are well prepared may still sustain damages, but the loss of life and damages to the economy are minimized. Regions with poorly designed buildings suffer higher loss of life, and take longer to recover in the event of an earthquake. The purpose of this section is to illustrate the value of having well designed buildings and to assess how well Utah’s buildings would hold up in the event of a large magnitude earthquake.
Utah is somewhere in between the extreme example of poor building practices observed in Bam and the more model building practices observed in earthquake prone California. Utah has many older buildings that fall into the category of unreinforced masonry buildings. These buildings will continue to pose hazards until something is done to remedy the situation. Buildings built after 1970 have much lower levels of risk because seismic codes were mandated by the government from that time forward. Buildings built in compliance with the Uniform Building Code have had excellent track records during earthquakes (Eldredge 1-16).
Even though adopting a building code has done much good there are still many pre-code buildings still standing in Utah. In 2004 the associated press published the opinion of the University of Utah structural engineer in regards to the campus’s Marriott Library. The campus engineer predicted the library would collapse on itself like a stack of pancakes in the event of a magnitude 5.0 earthquakes (Foy 1). Yet students still used the library every day. On any given school day the library had thousands of people go in and out (Foy 1). Happily, plans were made to renovate the library and the Department of Homeland Security allotted some funds to fix the building. Not all buildings are in the same precarious situation as the Marriot Library; however, the Marriot Library illustrates the idea that many buildings are not ready for such a disaster (Shaky in Utah).
Many of the schools and homes in the Salt Lake City are not up to seismic codes. Sections of the schools are still being used that were built before the state applied building codes (Cook). Other sections of the schools might have been built while the code was applied to the construction. The level of seismic readiness in schools varies from school district to school district (Cook). For example, a school district in Box Elder County has repaired 24 of 29 schools. But in Davis County there are 37 schools that need to be repaired. Seismically retrofitting schools is expensive: one school building costs approximately 12 million dollars (Cook). A Salt Lake City newspaper claimed there were 56,000 homes in the Salt Lake Area built of unreinforced brick (Cook). Earthquakes in other cities indicate they will perform poorly in the event of a large earthquake (Nichols 1-2).
Small businesses often rent out older and cheaper buildings in order to save money on rent. As discussed earlier, the older buildings were not built to withstand earthquakes. Some businesses are willing to perform seismic upgrades on their buildings; however, many businesses might not have the means to upgrade their buildings because of small profit margins. Businesses operating in these types of buildings have a high level of earthquake risk (Morelli 1-9).
Anticipated Consequences of Earthquake on Wasatch Front
A large earthquake striking the Salt Lake City area now would pose dire consequences. Scientists conducted simulations of a large earthquake in the Salt Lake City Area using “Hazus,” a program that can estimate potential effects of natural disasters. A magnitude 7.0 earthquake centered in Salt Lake City was simulated using HAZUS. According to the software, a magnitude 7.0 event would result in 3,500 fatalities (Reaveley, Russell, Wiggins, 10). Collapsing buildings would likely kill most of these people. Hazus projected that the earthquake would hospitalize 14,000 people (Reaveley, Russell, Wiggins, 10). With such an influx of people into the hospitals it is not likely they would receive proper medical care. Such an earthquake was also projected to leave 45,000 citizens homeless (Reaveley, Russell, Wiggins, 10). If the earthquake occurred in the winter these citizens would encounter cold Utah temperatures which routinely hover in the teens. Furthermore there is a slight possibility the Dams in Provo Canyon could break. Mass flooding would then result. An additional 50,000 citizens would become homeless if either of these dams failed (Tiedemann 420-425)
The Hazus simulation estimated damage costs for three different magnitudes of earthquakes. The software estimated a magnitude 5.5 earthquake would cost the state $830 million (Reaveley, Russell, Wiggins, 10). The $830 million would only cover the cost of repairing damaged buildings in the Salt Lake City Area. A magnitude 6.5 earthquake would cost the state $2.3 billion in damages. A magnitude 7.5 earthquake, the highest magnitude simulated by Hazus, was projected to cost the state $10 billion in repairs (Reaveley, Russell, Wiggins, 10). In addition to the more immediate needs of medical care and shelter, the cost of repairs to infrastructure and homes would place Utah in an immediate economic state of emergency.
Current Preparation for a Large Earthquake
Besides adopting the building code Utah has taken a number of steps to prepare for an earthquake. In 1995 The United States Geological Survey commended Utah for several of these steps (Brown & Machette, 1). Among these steps were seismically retrofitting fire stations along the Wasatch Front, teaching earthquake risk related curriculum in public schools, evaluating schools for seismic vulnerability and retrofitting the state capitol building (Brown & Machette, 1). The school upgrades are often paid for with money obtained through government bonds and or grants (Cook, 1). It is a slow process requiring any project to be halted when funds run low more extensive preparatory measures have not been taken primarily due to this concern over lack of funds.
As a result, businesses are left on their own to complete upgrades. Most of the businesses cannot afford to retrofit a building. Many businesses will neglect retrofitting buildings, gambling that they will be out of the building before a large earthquake occurs. Currently, Utah has no program in place to assist businesses in retrofitting their buildings.
Suggested Alterations in Preparation Strategy
Based on high probability of occurrence and the high potential for damaging effects from an earthquake, Utah’s current practice of slow and voluntary retrofitting is an unacceptable balancing of risk and reward (Olshansky 7-26). Special attention should be paid to retrofitting buildings of the businesses along the Wasatch Front. Although retrofitting these building will certainly be very expensive, the long term risks to economic security are even greater. In the event of an earthquake, property damages are projected to cost the state a great deal of money, and the impact on small businesses would be substantial (Johnson 1-4). For example, after the Northridge earthquake nearly half of all small businesses failed because they were unable to recover economic losses caused by the earthquake (Johnson 1-4). And the Northridge quake occurred in California, which is, generally, much more prepared than Utah. Since so much of Utah’s economic power sits on the Wasatch Front (particularly in the Salt Lake City/ Ogden area), it might take decades for the state to recover from such a setback. While businesses can take a gamble on leaving pre-code buildings before a large magnitude earthquake hits, the state (and its residents) cannot leave, and will always be supported by the businesses that occupy buildings within its cities; it doesn’t matter which business occupies it at the time of the disaster—Utah will always be indirectly influenced by the effects of earthquakes on local businesses. Utah simply cannot afford to keep gambling as the businesses do (Johnson 1-4).
In order to encourage businesses to upgrade buildings the state needs to make it an attainable goal. Free market competition and tiny profit margins make it difficult for a business to invest in seismic upgrades when for them the chance of being affected is low (Morelli 1-9).
There are a number of ways the state could make it more feasible for businesses to bring their buildings up to seismic code standards. For example, the state could give government contracts to businesses that have seismically retrofitted their buildings. This would make seismic retrofitting in the best interest of businesses seeking to compete in the local economy. Also the State could divert money going to less urgent projects, such as light rail extensions, to remedy the high risk situation of earthquakes. There is also a chance more financial aid could be obtained from the Department of Homeland Security such as the Marriot Library case (Shaky in Utah). By encouraging seismic upgrades in these ways, the business sector along the Wasatch Front would increase its seismic resistance. The State of Utah and its residents would also increase their resistance to the disastrous consequences of an event that becomes more likely with every passing year (Curtis).
Conclusion
In Conclusion, Utah’s current level of earthquake risk is not being adequately addressed. The probability of a large earthquake occurring grows each year. The state is not prepared for a large magnitude earthquake, as illustrated by the Department of Homeland of Securities “Hazus” tests. Because, there are too many unreinforced and outdated pieces of infrastructure the consequences of a large earthquake would be horrific. Utah needs to take some action in order to ensure that businesses have incentives to upgrade infrastructure along the Wasatch Front
Works Cited
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