Impacts of Climate Change on the Pacific Northwest

August 27, 2019

Geology Blog 3: Topography and Earthquakes

Today was exciting for us as we got a tour of Seattle! Seattle is the largest city in both the state of Washington and the Pacific Northwest region of North America. It is the fastest-growing major city and the most livable city in United States. We started from the university of Washington. Our bus tour of Seattle included: Pike Place Public market, international District, Lake Washington, floating homes on Lake Union, Fremont Troll, Kerry Park, Gas Works Park, Golden Garden Park. We were all shocked by Seattle’s beautiful natural and cultural landscape.

City Seattle View(Photo by Yang Bao)

During the journey, we were surprised how hilly Seattle is. The city is said to lie on seven hills, (Crowley, Walt .January 14, 2003. “Seattle’s Seven Hills”. HistoryLink. Retrieved April 12, 2010.) including Capitol Hill, First Hill, West Seattle, Beacon Hill, Magnolia, Denny Hill, and Queen Anne. Some famous places are all located on hills as well. Many of the hilliest areas are near the city center. The highest point within city limits is at High Point in West Seattle[1]

Seattle Dem Msp(Map by Dayang Zhao)

 

But why is Seattle hilly? From the tour guide, we learned that there was a network of underground passageways and basements named Seattle Underground on the ground floor of downtown Pioneer Square. Seattle Underground was later buried underground and was abandoned due to ground subsidence caused by the earthquake. Now Seattle is built on the Seattle Underground. So we think the hilly topography of Seattle is related to earthquake, such as the ground subsidence caused by the earthquake or plate collision.

Seismic monitoring instruments(Photo by Luhan Wang)

We saw the Seismic monitoring system with several screens when we visited Pacific Northwest Seismic Network Facility. The teacher introduced us to some instruments which were being used to monitor seismic activity. The principles of these instruments are roughly similar, but the size, weight, and spring coefficients are different, allowing them to monitor different levels of earthquakes. The teacher is explaining that it is a precision instrument that can record vibrations in three directions. He opens the panel of the instrument to show us the three-direction recording strip installed inside. By observing these instruments for monitoring earthquakes, we learned that people have been studying natural disasters such as earthquakes since the beginning, and constantly innovating and improving technologies, hoping to minimize the disasters they bring. The records of the monitoring system is available and some videos were uploaded to YouTube so that PNSN can benefit the public.(https://www.youtube.com/user/pnsnseisinfo)

 

We learned from past news reports that there are lots of earthquakes in Seattle. Why so many? According to references (https://www.seattle.gov/emergency-management/hazards/earthquake), The Seattle area experiences three earthquake types with varying consequences, including crustal earthquakes which are expected on the Seattle Fault Zone, intraplate or Deep Quakes which occur at depths of 30-70 km in oceanic crust as it dives under lighter continental crust, and Subduction Zone or Megathrust Quakes which occur on the interface between the North American plate and the Juan de Fuca plate. What’s more, earthquakes on the Seattle Fault poses the greatest risk considering that the Seattle Fault Zone extends east-west through the middle of the city. There is no denying that people will be affected negatively for they could be injured by falling debris as well as secondary impacts such as landslides, tsunami, fires, infrastructure failures, and hazardous materials releases. As for ecosystems, about 15% of Seattle’s total area is soil that is prone to ground failure in earthquakes, and then the vegetation and valleys and so on which are related to soil tightly will be impacted.

Attracted by the fascinating views of Seattle, we are also interested in its unique topography as well as underlying causes. Earthquakes impact Seattle greatly, not only the residents but the ecosystem. Seattle has a large population and diversities of ecosystems. We can’t know when and how big the earthquakes would happen in Seattle. The only thing we can do is to try to better understand the mechanisms of geology and topography, and how to use the disciplines of nature to benefit the residents and ecosystems.