Seattle Research Paper

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How vulnerable is Seattle?

Samhita Kasuganti
Sik5405@psu.edu

The Seattle Fault is a zone of multiple shallow east-west thrust faults that cross the Puget Sound Lowland and through Seattle (in the U.S. state of Washington) in the vicinity of Interstate Highway 90. The Seattle Fault was first recognized as a significant seismic hazard in 1992 when a set of reports showed that about 1,100 years ago it was the scene of a major earthquake of about magnitude 7, an event that entered Indian oral legend. Extensive research has since shown the Seattle Fault to be part of a regional system of faults. Since Seattle is prone to earthquakes, it is important for the city to prepare for the disasters in order to reduce the damages. Below I have listed …show more content…

According to the maps, the North Western part of Seattle is has about 10-11 people per acre so the area is densely populated. This could be vulnerability for Seattle because high-elevated areas cause the maximum destruction. With an earthquake of magnitude 7.5, this area would cause the maximum deaths. We also see that west most part of Seattle is highly prone to landslides (according to the map Liquefaction Zones and Land Slide Prone Areas), but the overall land of Seattle is fairly elevated. Earthquakes are one of the main triggers that cause landslides. Earthquake induced landslides have been documented from as early as 372 BC (Keefer, 1984) and have caused tens of thousands of deaths and billions in economic losses (Keefer, 1984). Landslides have been a product of 40 of 56 documented earthquakes in present times around the world (Keefer, 1984). Topographic relief has an effect on the intensity of the waves propagating through the ground. Seismic waves are made of primary, secondary, and surface waves. Surface waves are the slowest type of wave but they cause landslides most often because they move particles in a swaying motion. Waves are amplified due to topography as seismic waves enter the base of a topographic ridge, are partially reflected back into the rock mass, and …show more content…

Soil liquefaction describes a phenomenon whereby a saturated or partially saturated soil substantially loses strength and stiffness in response to an applied stress, usually earthquake shaking or other sudden change in stress condition, causing it to behave like a liquid. The phenomenon is most often observed in saturated, loose (low density), sandy soils. This is because the loose sand has a tendency to compress when a load is applied; dense sands by contrast tend to expand in volume. If the soil is saturated by water, then water fills the gaps between soil grains. In response to the soil compressing, this water increases in pressure and attempts to flow out from the soil to zones of low pressure (usually upward towards the ground surface). However, if the loading is rapidly applied and large enough, or is repeated many times (e.g. earthquake shaking, storm wave loading) such that it does not flow out in time before the next cycle of load is applied, the water pressures may build to an extent where they exceed the contact stresses between the grains of soil that keep them in contact with each other. These contacts between grains are the means by which the weight from buildings and overlying soil layers are transferred from the ground surface to layers of soil or rock at greater depths. This loss of soil structure causes it to lose all of its strength. According to the

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