H. Reid Miller
Geo- 380
Bob Dziak
Cascadian Tsunami "Barely had they set foot in the city in mourning the death of their benefactor, they feel the earth shake beneath their feet, the sea rises bubbling in the harbor, and breaks the vessels that are to anchor. Swirls of flames and ashes covered the streets and public places; houses collapsed, roofs are reversed on the foundations, and foundations disperse, and thirty thousand inhabitants of all ages and sexes were crushed under the ruins, said the sailor, whistling and swearing: ʽ There will be something to win here. - What can be the sufficient reason of this phenomenon? said Pangloss. - Here is the last day of the world!’ Cried Candide” (Voltaire, 1759 translated by Google translate) Some of the first descriptions of tsunamis are grim at best this excerpt came from Voltaire’s Candide a French satire published during Europe’s Age of Enlightenment. This gives a chilling view of Lisbon on All Saint’s Day (November first) in 1755. What had occurred is a 200 km offshore 8.5-9.0 magnitude earthquake that resulted in a large-scale tsunami and rampaging fires, effectively killing thousands of people. This is one of the deadliest tsunamis recorded in history, but how do tsunamis function and what do we know about their inner workings. Tsunamis since the early 1600s have been synonymous with some form recording of “shaking of the earth”. Very rarely do you see other forms of tectonic activity such as volcanic eruptions or glacier calving that can create a tsunami. The integral part to the large-scale tsunamis that we see is plate tectonics. The plates converge, diverge, or transform to create a Figure [ 1 ]: Shows an example of what is happening in a subduction related tsunami zone. (PNSN, 2013)
Figure [ 1 ]: Shows an example of what is happening in a subduction related tsunami zone. (PNSN, 2013) displacement in the sea floor that corresponds to the sea level.

In Figure 1 we see the tectonic components that lead to a sequence that is similar to the 1700 Cascadian Tsunami. Part one shows a subducting oceanic crust; as the plate is subducting under the continental crust it builds up tension in the accretionary prism area, when it does release pressure and you see failure of the prism you get rapid uplift and subsidence onshore. Any vertical movement of the seafloor immediately changes the sea-surface. The resulting tsunami propagates as a set of waves whose energy is concentrated at wavelengths corresponding to the earth movements (about 100 km), at wave heights determined by vertical displacement (about 1m), and at wave directions determined by the adjacent coastline geometry (NOAA, 1998). This is meaning that the uplift is proportionate to the corresponding wavelength of the water. Tsunamis cause damage by two mechanisms: the smashing force of a wall of water travelling at high speed, and the destructive power of a large volume of water draining off the land and carrying a large amount of debris with it, even with waves that do not appear to be large. While everyday wind waves have a wavelength of about 100 m and a height of roughly 2 m, a tsunami in the deep ocean has a much larger wavelength of up to 200 km. A wave travels at 500 mph, but owing to the enormous wavelength, but the wave frequency takes anywhere from 20 to 30 minutes to complete a cycle and have an amplitude of only about 1 m. As the tsunami approaches the coast the frequency gets quicker but with the frequency increasing the amplitude or height of the wave increases. Essentially as the wave hits the coastal “wall” it is bigger than Figure [ 2 ]: This is a figure showing off the DART Mooring System, a tsunami monitoring device. (NOAA, 1998)
Figure [ 2 ]: This is a figure showing off the DART Mooring System, a tsunami monitoring device. (NOAA, 1998) but not as fast as it was out in the open ocean.
These waves are picked up on what is called the DART Mooring System (DMS). This machine is twofold you have the base that is under water- shown in Figure 2- that records water velocity and also has some seismic tools capable of readouts of underwater seismicity. Then you have the buoy which receives signals from the sea ground monitor and then it sends that information to a satellite. All this information is sent to the corresponding Tsunami Warning Center. These are set up in various parts of the Ring of Fire of the Pacific Ocean area to constantly monitor and hopefully protect our coastlines. Most of this collective knowledge of tsunamis come from Geologists and Seismologists on the Pacific Coast, and it was developed from multiple incidents one of the biggest being the Cascadian Earthquake of 1700. In the 1600s the Pacific Northwest was subject to a large scale mega-thrust earthquake that resulted in tsunamis hitting the coastline in the Pacific Northwest and also places like Japan that didn’t even feel the shaking. The 1700 Cascadia earthquake was a magnitude 8.7 to 9.2 megathrust earthquake that occurred in the Cascadia subduction zone on January 26, 1700. The earthquake was caused by the Juan de Fuca Plate underlying the Pacific Ocean, from Vancouver, Canada, to California along the Pacific Coastline. We know this information mostly from written records that have been published such as The Orphan Tsunami, compiled by Brian Atwater. A new scientific process called dendrochronology is used to see the relative age or sequence of events (pertaining to the seismicity and tsunamis). This technique measures tree rings and relates when events happen in the growth rings of the tree they can find and measure a viable time scale. This part relates to a reoccurrence interval that through the use of dendrochronology and Deep Sea magnetic layering shows an interval of about 500 years. The scary part about the northwest region is that we are susceptible to events like this. We overlie an active margin that is a ticking time-bomb till the next large scale event. If the same event was to happen you could see some theoretical probabilities of what is to happen: Coastline: Widespread damage to infrastructure also liquefaction can obliterate roads making travel to safety impossible and relief efforts more difficult. Major industries such as shipping and importing/exporting of goods are non-existent. Most casualties occur in this region. Willamette Valley/ I-5 Corridor: You see some infrastructure change due to the post-seismic activity, low causalities, and disruption to transportation biggest source of hysteria. East of Cascades: Due to transportation constraints and loss this geographical proportion gets indirect economic effects that happen and might have to ration out supplies.
The next step in the process after all is done is to start to build up what was lost this next list are some effective steps that cover a multitude of problems potentially being faced (CREW, 2005) : 1. Reducing the risk for critical public facilities, such as hospitals, schools, police, and fire —if our essential facilities are not usable after an earthquake, there will be more deaths, less capacity to handle casualties and people made homeless and an increase in response and recovery times. Funding, and possibly legislation, will be required to upgrade these essential services. 2. Retrofitting high risk buildings, such as unreinforced masonry (URM), tilt-up structures, and tall buildings not built to modern codes — In most earthquakes, URMs and tilt-up structures are the leading cause of casualties. In Cascadia, they are often built on poor soils, increasing their risk, and a disproportionate number of schools and some other essential facilities are URMs. In a subduction zone earthquake, we must also consider the risk to tall buildings that are not engineered to resist long duration shaking damage. 3. Protecting transportation infrastructure — Roads and bridges badly damaged by an earthquake will delay emergency response in the hours after the event, and restrict the movement of people and goods for months. Unusable airports, water ports, and railroads could slow down response and recovery efforts for months or years. If our ports closed for an extended time, shippers could permanently move to other ports, reducing our economic opportunities. 4. Continue public education efforts — most people who live in Cascadia know something about the earthquake risk, but they may not know how to prepare. Or they may not know what to do to protect them from a tsunami. Educating both residents and visitors will help prevent loss of life when the quake strikes
Mentioned was the governmental job of coming up with funding this, I believe, is the key part because in current society there is monetary value that is placed with any kind of part, so legislature passing bills to get emergency funding or allow budgeting to allocate certain funds is a necessity.
Figure [ 3 ]: This is a Japanese stylized depiction from The Orphan Tsunami. (Atwater, 2005)
Figure [ 3 ]: This is a Japanese stylized depiction from The Orphan Tsunami. (Atwater, 2005) The Pacific Northwest is host to a very scary and intriguing problem; we have seen the evidence of the past such as the 1700 Cascadian Tsunami and in terms of tectonic activity we are very overdue. Whether we will get the “big one” soon is up to the randomness of our subduction zone. All we can do is prep for the future and try to pool our knowledge to prevent unnecessary casualties.

Works Cited
Brian Atwater, The Orphan Tsunami of 1700, 2005. Pdf compilation book by Atwater, Brian. Accessed February 27, 2014

Cascadia Region Earthquake Workgroup, Cascadia Subduction Zone Earthquakes: A Magnitude 9.0 Earthquake Scenario, 2005. http://www.crew.org/sites/default/files/CREWCascadiaFinal.pdf. Accessed February 22, 2014

Pacific Northwest Seismic Network, Cascadia Subduction Zone, 2013. http://www.pnsn.org/outreach/earthquakesources/csz. Accessed February 20, 2014

National Oceanic and Atmospheric Administration, Tsunami, 1998. http://www.tsunami.noaa.gov/tsunami_story.html. Accessed February 20, 2014

Voltaire, Candide, 1759. Selected Quote and translated with Google Translate. Accessed February 22, 2014