Seattle's Earthquake Vulnerability (Essay Sample)

Seattle's Earthquake Vulnerability
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Seattle's Earthquake Vulnerability
Memo
Cities along the Northwest coast of the U.S. face a significant hazard in the form of megathrust (subduction) earthquakes and tsunami. In the case of Seattle, Washington, their earthquake vulnerability does not stop there. In addition, there are a series of active faults within the crust in the vicinity of Seattle have the potential to host earthquakes greater the M 7. It is therefore important to assess the specific vulnerabilities that Seattle has in the face of such earthquakes since earthquakes is the most serious hazard that Seattle is facing today. Studies have shown that the whole of Pacific Northwest coast is at risk of being hit by a 9.0 earthquake and this magnitude is more or less the same as the one that has hit Seattle previously. This study has come at a time when previous studies suggest Seattle has a 40 percent chance of experiencing an earthquake with a much bigger magnitude in the next fifty years. The goal in this study is to identify these vulnerabilities and incorporate them into a development of a set of recommendations and priorities for mitigating the risks.
Executive summary
The aim of this report is to assess earthquake vulnerabilities facing Seattle and come up with recommendations for this hazard. Seattle is prone to other hazards, both natural and artificial, but earthquake has proved to be more destructive than other hazards facing this coastal city. It is therefore important to note that earthquake is regarded as the most serious hazard facing Seattle. Even though Seattle faces other catastrophic hazards, it has always experienced and will continue to experience earthquakes with bigger magnitudes that are more destructive.
Seattle tends to experience three types of earthquakes and each has a different level of destruction. The first type of earthquake that Seattle has experienced is shallow earthquakes. These earthquakes are common in the North America plate especially along active faults. In comparison to other types of earthquakes, there is always intense shaking at the epicenter but tends to diminish with time. Shallow earthquakes are the most common earthquakes that are likely to be experienced at Seattle Fault zone. This is the primary source for Seattle’s shallow earthquakes.
This will further analyze deep earthquakes as the second type of quakes experienced at Seattle. Deeps earthquakes are common in regions ranging from 30 to 70km within oceanic crust. Because of this depth, this earthquake has a minimal effect on buildings above the region where the motions are taking place. The last time Seattle experienced a deep earthquake was in 2001 and it was referred to as Nisqually Earthquake. The final type of earthquake which this earthquake will analyze is subduction zone or the megathrust earthquakes. This earthquake is so common at the region where North American plate meets the San Juan de Fuca plate. Ideally, San Juan de Fuca plate is a minor plate stretching from the northern part of California all the way to British Columbia. This said, it is important to note that any earthquake occurring at the Seattle Fault should be considered as a destructive earthquake because of the risk associated with it.
Since earthquake is the most destructive natural hazard being experienced at Seattle, it will be important for this report to outline some of the measures the city needs to take to mitigate this hazard. In other words, everybody needs to play a role in mitigating this hazards, it should not just be left to those who are at risk of suffering the effects of the earthquake. This report will therefore highlight some of the most important measures that need to be taken to secure residents of this city from the risk of being hit by earthquakes.
Earthquakes in Northwest Pacific
Until the mid 1980s, most residents of Seattle City thought they were far away from active faults not to worry about being hit by a destructive hazard like an earthquake. Researchers thought the Cascadian subduction zone beneath the Pacific Northwest was not of the type that could cause earthquakes. They arrive at this conclusion because this region had not generated any earthquake after a long time. It then dawned to them on February 28, 2001 that earthquake was a reality when they experienced an earthquake whose magnitude was 6.8 last for about 45 seconds. This earthquake was too destructive to extent of causing injuries to about 250 people (Shipman, 2004). After this earthquake, geologists had to change their view about the Cascadian subduction zone. Since then, scientists and residents of this region have come to realize that this type of subduction forms a potential threat for earthquakes. It has the ability of causing earthquakes of even great magnitudes that may exceed 8 units, similar to the most destructive earthquake that was experienced in Indonesia in 2004. In addition to the active seismicity, this realization is deemed to have originated from studies that have identified numerous paleo-earthquakes and tsunami deposits from local earthquakes (National Wildlife Foundation, 2007).
After carrying out a number of studies, the U.S Geological Survey has finally identified three main potential sources for Pacific Northwest earthquakes. From their studies, these scientists have identified the first potential source for these earthquakes to be rupturing process that takes place along the subduction zone. These earthquakes have been found to be too destructive since they are of big magnitudes that range between 6.5 and 7.2. The second potential cause for earthquakes in this region has been found to within the upper plate of the subduction zone. In the past years, Seattle has experienced earthquakes with even bigger magnitudes from this area. The third potential source of earthquakes within Seattle results from ruptures with the shallow part of the subduction zone. This is the most destructive earthquake because these ruptures can be too large to generate tsunamis and other surface movements. The most recent destructive earthquake to be experienced in this region as a result of ruptures within the shallow subduction zone took place in 1700. This earthquake is deemed to have resulted into a huge tsunami that caused a lot of destruction to parts of Japan. Furthermore, the deposits of this tsunami were deposited in areas around north Pacific (Yelin, 1994).
It is important to note that an earthquake with a magnitude of 9 within Cascadian subduction zone would cause a lot of destruction within Seattle city because the shaking would even last for several minutes. In the same way San Francisco had Nimitz Freeway that was brought down by the Loma Prieta earthquake that took place in 1989, Seattle has built various freeways especially on uncompacted landfill and tidal flat deposits (Shipman, 2004). These freeways are at high risk of causing highway collapse because of the mentioned deposits. Recently, geologists have discovered some faults which run through the downtown of Seattle city. The presence of these fault pose a serious danger to the lives people within this region plus their property since faults are the main cause of strong earthquakes within this region. The Seattle faults runs all the way from Puget Sound and stretches to the Kingdome in the downtown. The fault has a width of about 6m and stretches for about 16km.
An even more destructive earthquake would be an earthquake that will take place at the Cascadian subduction zone. Potentially, the magnitude of this earthquake is likely to exceed 9. Apart having the ability of causing tremendous shaking of the ground, an earthquake that originates from this region is likely to generate huge and destructive tsunamis that can easily sweep across the whole coastal region. The presence of sand layers in coastal swamps is evident that this region has experienced many tsunamis n previous years. The most recent tsunami that was experienced within Seattle took place about 300 years ago (Yelin, 1994). However, it is clear that Cascadian subduction zone has the potential of causing earthquakes with very great magnitudes. Despite geologists finding the region’s vulnerability to earthquakes with such big magnitudes, residents of this region are not adequately prepared for this hazard. Apart from Seattle’s residents not being well prepared for the destruction that comes with the region’s earthquakes, other surrounding regions including Washington, northern California, and Portland are not adequately prepared for the events of the earthquake.
Other areas that are away from the region where there are active plate boundaries are also vulnerable to frequent earthquakes. Despite the fact that earthquakes are not so common in the mentioned areas, they tend to be so destructive when they when they occur. Other surrounding areas including South Carolina, Massachusetts, and Boston have been hardly hit by earthquakes over the last few years. However, just like Northwest Pacific, these areas have not adequately prepared for events of earthquakes.
Seattle fault and its effects
Seattle fault is a fault found in Seattle City and is one of the largest faults in the world that have been linked to causing the most destructive earthquakes. Studies have shown that an increasing number of faults in a given region have increased the difficulty of estimating hazards that result from earthquakes. The Seattle fault is quite complicated and has been active for many years. This fault is complicated is a bit complicated owing to the fact that there is much fault segmentation, tear faults, and splays. Studies suggest the offset along this fault have resulted into the subsidence of the adjacent Seattle Basin, which is thought to be the harbor for numerous young rocks. The fault coincides with...