Earthquakes

As I look at the destruction that surrounds the earthquake and subsequent tsunami that occurred in Japan, I pray for the people whose lives are suddenly destroyed, both literally and figuratively. It is a cruel reminder that as human beings, we are so fragile, so inconsequential, and significantly unprepared for natural disasters of any kind. We live in constant unawareness of the dangers surrounding us, for somehow we feel that nothing really horrible could happen to us. Yet, I am reminded of the paper I wrote several years ago, when I was taking a geology class about the natural disasters of the Pacific Northwest. Following are a few excerpts from it. Clearly, we are unprepared for this type of disaster.


The Pacific Northwest is deceptively beautiful. The foundations of the various breathtaking dramatic landscapes lie in the plethoric diversity of hazards, from the slumbering Mt. Rainier to the vastly magnificent Pacific Ocean, whose waves could wipe out cities. Many of these potent hazards are the result of the plate tectonic setting of the Pacific Northwest. Situated on the North American Plate, Washington is at the crossroads of a type of convergent boundary called a subduction zone. Washington and Oregon lie on the North American plate, while westwards in the Pacific lies the Juan de Fuca Plate, which is currently being subducted underneath the aforementioned North American plate, creating the “Cascadia subduction zone.” The result of this movement is that volcanoes form on the subduction zone, explaining the existence of mountain ranges like the Cascades. Additionally, the powerful movement of the plates can result in substantially powerful earthquakes and tsunamis (Hyndman, 2006), known as subduction zone earthquakes. In addition to these powerful earthquakes, the Puget Sound Area is susceptible to deep earthquakes and crustal fault earthquakes, all of which are hazardous to the region (See Image 1).

The largest of these earthquakes, Subduction Zone earthquakes, occur when the boundary is ruptured between the subducting Juan de Fuca plate and the North American plate, at about 20 miles under the surface (PNSN, 2003). These earthquakes have the potential to produce catastrophic damage from British Columbia to Northern California, reaching a magnitude of 9 or more (PNSN, 2003), far outreaching the damage seen in the recent Nisqually Earthquake. Though damaging, these earthquakes usually only roughly once every 300-500 years (PNSN, 2003), with the last four earthquakes occurring in 1700, 900, 750, and 400 AD (CREW, 2005). In addition to this damaging earthquake that would shake for minutes rather than seconds (PNSN, 2003), there would be aftershocks with magnitudes reaching 7.5 (PNSN, 2003), causing further loss.

When this devastating Cascadia Subduction Zone earthquake occurs, it will affect the Puget Sound region's infrastructure and lifelines. Many of the utilities will take time to repair, making it difficult for people to obtain warmth, clean water, food, and shelter. Also, the phone lines will be down for at least a few days until they are repaired, leaving some stranded for assistance and without a way to call for help. Additionally, landslides and debris will cover the roadways in some areas, and some bridges will be unstable or have collapsed, making it difficult or impossible to travel by car. Some airports will be able to operate, but many will be shut down because of instabilities. In addition, railways and docks will be damaged, making it difficult for help to come in these ways. Older buildings and unreinforced masonry will suffer substantial damage from the Cascadia earthquake. Other homes might also be affected or deemed unfit to live in. Clearly, the infrastructure and lifelines of the Puget Sound are vulnerable in the event of an earthquake (CREW, 2005).

In addition to the devastating damage the Cascadia Zone Earthquake will have upon the Puget Sound area's infrastructure, it will devastate the region's economy. First of all, the transportation will be affected throughout the Cascadia region, which will make it difficult for support to come and for businesses to continue, thus forcing some businesses to shut down, hurting the area economically. In addition, many companies will revert shipping to other ports that remain undamaged, never returning, and thus hurting the Pacific Northwest economy. Also, many businesses may temporarily revert their headquarters or stations to east of the Cascades, impairing Puget Sound's economy further. Clearly, Puget Sound will be affected in more than one way as they attempt to rebuild their city and economy in the aftermath of a massive subduction zone earthquake (CREW, 2005).

The Puget Sound community is certainly unprepared for the damage that an earthquake along the Cascadia Subduction Zone would make. First of all, many do not realize the scope of such an earthquake, nor do they realize the extensive area that it would affect. Also, numerous individuals are unaware of the threat of tsunamis that could result from this large earthquake, and thus be unprepared to deal with the consequences of this. Also, many would be unprepared to face several days without food, water, electricity, etc., because many of them do not have earthquake kits or stored food or water and would be completely unprepared if such a disaster were to occur. Clearly, the Puget Sound is not prepared for such a threat, and thus extremely vulnerable in the event of a Cascadia Zone Earthquake.

Another type of earthquake that poses a credible hazard to the Puget Sound area is shallow crustal earthquakes. These earthquakes are fairly mysterious to scientists in that their recurrence interval is unknown; however, they do know that they can produce up to a M 7.5 earthquake along pre-existing crustal faults (Stewart, 2005). They usually occur less than 15 miles beneath the surface of the earth as a result of stress on the crust, with many aftershocks reaching a magnitude of 6.5 (PNSN, 2003). They occur on pre-existing crustal faults, like the Seattle or Tacoma faults. Prior earthquakes of this type include one in 1872, two on Vancouver Island since 1918, and one in 900 in Seattle: in all, of the earthquakes discovered so far, there have been four or more magnitude 7 or higher earthquakes of this kind within the past 1100 years (PNSN, 2003).

In the event of a crustal earthquake on the Seattle Fault Line, the infrastructure and many lifelines of the Puget Sound area will be damaged. Many of the water lines and tanks will be ruptured, and areas affected by liquefaction will be hardest hit, especially if the pipelines are cast iron, and will take weeks to repair. The sewage lines may be ruptured in many places, and the treatment centers will be vulnerable as well, causing waste to spill into lakes and rivers, and taking weeks to replace as well. On a slightly more positive side, though many will experience power outages, they will likely have their power back within approximately three days, unless a substation is affected by the earthquake, in which case it will take substantially longer to repair. In addition, the communication lines will be affected, as many will tie up the phone lines after the earthquake. Wireless phone lines will be difficult to use, but the wired phone lines will be somewhat more intact. The natural gas lines are built in more sound soil; therefore, they are less vulnerable to damage. However, the liquid fuel lines cross the Seattle Fault, and are likely to rupture and cause fire damage (Stewart, 2005).

In addition to the damage the earthquake will cause to lifelines if it occurs, the transportation systems will be damaged significantly. Roads and highways will be closed or damaged due to liquefaction, sinkholes, ruptures, and various other problems, and the roads not damaged will be clogged with commuters and emergency response vehicles. Several airports will close down, though the Sea-Tac Airport shouldn't be affected too significantly by this earthquake (damage-wise). Also, many ferry docks will be damaged and ferries will have to be re-routed to safe and undamaged docks. In addition, many railroads will be damaged and take significant time and money to repair (Stewart, 2005).

Additionally, many buildings will be destroyed or become unsafe for humans to occupy. This will cause problems, as many will be left homeless and in need of shelter. In addition, many schools and business buildings will be in disrepair, preventing citizens from going to work and school (Stewart, 2005).

Though the Seattle Fault would likely cause the most damage because of its intimacy with the greater Seattle area, the Tacoma Fault and the Southern Whidbey Island Fault could produce similar impacts if they were to produce an earthquake. Therefore, the threat that these faults cause must also be taken into account (Stewart, 2005).

Yet another earthquake that threatens the Puget Sound area is deep earthquakes. These earthquakes occur about 30-40 miles underground, and can reach up to a magnitude of 7.5 (PNSN, 2003). These earthquakes occur quite frequently, about every 20-30 years; in fact, there have been six such earthquakes exceeding a magnitude 6 since 1900 (PNSN, 2003).

Perhaps the most well known recent examples of these quakes occurred in 1949, 1965, and the recent Nisqually Earthquake in 2001. The damage that occurred in the 1965 in Des Moines was "felt by all in community: frightened few. Damage slight. Some dishes and windows broke. Plaster cracked and fell. Knickknacks and books fell. Small objects shifted. Vases and small objects overturned, trees and bushes shaken strongly. Rapid motion proceeded few seconds by loud earth noises (Thorsen, 1986).” Conversely, the 1949 earthquake rattled Tacoma and caused “One death, [and] at least a dozen injured. Many buildings damaged and parts fell. Many chimneys damaged and toppled. Several houses slid into Puget Sound. One smokestack fell. One 23 ton cable saddle was thrown from the top of tower of Tacoma Narrows Bridge, causing considerable loss. Railroad bridges south of Tacoma were thrown out of line. Tremendous rockslide followed earthquake when a half mile section of a 300 foot cliff slid into Puget Sound. Considerable damage to brick, plaster, windows, walls, and ground cracked (Thorsen, 1986).” The damage that occurred in these earthquakes could be similar if the Puget Sound area were to experience another deep earthquake.

In addition to the risk that these three types of earthquakes present, there is a substantial risk of liquefaction. Liquefaction occurs in areas with water saturated sediments; when shaking occurs, this water comes to the surface and mixes with the sediments, which causes damage to structures. The Puget Sound Area is at risk for liquefaction because it experiences a great deal of rain, which causes the ground to have a higher water saturation rate, making it more susceptible to liquefaction, especially in wetland and low-lying areas.


Another hazard that results from these earthquakes, specifically crustal fault quakes, is ground rupture. This hazard occurs when fault zones are uplifted, and as a result, pose a threat to any structures, pipelines, or roads that straddle the uplifting fault. The Puget Sound area is susceptible to ground rupture because there are many faults in the area, including the Seattle and Tacoma faults, upon which many buildings and roads are situated.

Yet another risk that occurs in the aftermath of these earthquakes is fire. Fire occurs as a result of pipelines being ruptured or bursting in an earthquake, or flammable materials being overturned. In any of the earthquakes that affect the Puget Sound, this could occur in any place that such flammable materials or pipelines exist. Therefore, the Puget Sound is highly susceptible to fire after an earthquake because these materials and pipelines are in great abundance in this highly populated area.

Additionally, landslides pose a credible threat to the Puget Sound area in the aftermath of an earthquake. The shaking from an earthquake can cause unstable sediments to slide downwards, causing a landslide. The Puget Sound is especially apt to experience a number of landslides after an earthquake because of its wet climate, which causes an increased number of landslides in the first place. With the added strain of an earthquake, landslides become abundant.

An additional risk that threatens the Puget Sound area is tsunamis. Though often overlooked, the Puget Sound can receive tsunamis in three different ways. Crustal fault earthquakes underneath the Puget Sound may cause displacement and cause tsunamis in the aftermath of an earthquake. In addition, the Puget Sound can receive tsunamis by landslides in or under the Puget Sound, which can result from any of the three earthquakes. Therefore, the Puget Sound is almost unknowingly threatened by tsunamis in the aftermath of an earthquake.

Clearly, the damage that any one of these earthquakes would create, in addition to the damage of the threats such as landslides and tsunamis that are caused by such earthquakes, would be devastating to our region. The Puget Sound region is highly populated and any combination of these threats would cause millions or billions of dollars in damage, in addition to the possible loss of lives and injuries.

In addition, the Puget Sound is highly underprepared for any of these earthquakes. Many of the buildings in the area are susceptible to collapse, and many more will be uninhabitable after an earthquake. Also, many in the Puget Sound area do not have adequate supplies to sustain them in earthquakes that would prevent them from obtaining food, fuel, water, and other supplies. Therefore, the area is highly vulnerable in the event of these earthquakes.



Works Cited

ABAG (Association of Bay Area Governments), 2003, Impacts of California Earthquakes on Buildings from Shaken Awake, Online at: http://www.abag.org/bayarea/eqmaps/shelpop/bldg.html [01/28/09].

CREW, 2005, Cascadia Subduction Zone Earthquakes: A Magnitude 9.0 Scenario, CREW and DOGAMI (publishers), pp. 21. Also available as DOGAMI O-05-05 and http://www.crew.org/PDFs/CREWSubductionZoneSmall.pdf.

CREW, 2008, Cascadia Deep Earthquakes. CREW and WaDNR (publishers), 25 pp. Also published as OFR 2008-1 by Washington Department of Natural Resources and avaliable at http://www.crew.org/PDFs/Casc%20Deep%20EQ%20web.pdf

Hyndman, Donald, and Hyndman, David, 2006, Natural Hazards and Disasters, 2nd Edition, Belmont, CA: Brooks, pp. 555.

Pacific Northwest Seismic Network (PNSN), 2003, Earthquake Hazards in Washington and Oregon: Three Source Zones; Online: http://www.pnsn.org/CascadiaEQs,pdf.

Palmer, Stephen P., Perkins, William J., and Grant, W. Paul, Washington Division of Geology and Earth Resources, 2003, Liquefaction Susceptibility of the Greater Tacoma Urban Area, Pierce and King Counties, Washington, Geologic Map GM-51, Scale=1:30,000.

Stewart, M. (ed.), 2005, Scenario for a Magnitude 6.7 Earthquake on the Seattle Fault, EERI and EMD (publishers), pp. 162. Also available at http://www.crew.org/PDFs/CREWSubductionZoneSmall.pdf.

Thorsen, Gerald W., 1986, The Puget Sound Lowland Earthquakes of 1949 and 1965: Reproductions of Selected Articles Describing Damage, Olympia, WA: Department of Natural Resources, pp. 112.

Troost, K.G., Booth, D.B., and Borden, R., in review, Geologic map of the Tacoma North 7.5-minute quadrangle, Washington: U.S. Geological Survey Miscellaneous Field Investigation, scale 1:24,000.

USGS, 1999, Lifelines and Earthquake Hazards in the Greater Seattle Area, Open-File Report 99-387. Also available at http://geomaps.wr.usgs.gov/pacnw/lifeline/aboutmap.html.