What if the Big One hits here?

By Bruce Smith of The Mountain News

After witnessing the destructive power of the massive earthquake and tsunami that hit near Fukushima last month, and now watching the turmoil enveloping Japan in its aftermath, many residents of the Puget Sound region are wondering if the same thing could happen here – or worse.

Seeking specifics from the scientific community, The Mountain News spoke with Steve Bailey, Director of Emergency Management for Pierce County, and Bill Steele, a noted University of Washington geologist. They confirmed that a mega 9.0 earthquake could happen here, and in fact, has done so several times historically. However, certain geological factors would make the local impact here different than what is transpiring in Japan.

As for larger earthquakes, such as in the 10.0 and up range, that is highly speculative in the scientific community.

Bailey told the Mountain News that understanding the likelihood of a mega quake in the 9.0 range, where it would hit and what kinds of destruction it would produce requires an examination of what kinds of earthquakes occur presently.

As a result, our conversation started with an overview of the geology of the earth and its movement, and he explained that there are two different types of earthquakes: subduction zone quakes and fault-line or crustal earthquakes.

The subduction type are deep, powerful quakes formed by the movements of tectonic plates, which are massive slabs of the earth’s crust, and as they slide across one another in a horizontal fashion they trigger an earthquake. The Fukushima earthquake was this type, and scientists are currently pegging this quake to be a 9.1 on the Richter scale.

Bailey said that the area where the plates touch are called subduction zones, and are friction points that receive constant pressure from the underlying dynamics of the earth. When the pressure reaches a certain point a section needs to slip to release the pent-up energy, and the resulting release sends shock waves through the earth.

Not only is the magnitude of energy released by subduction zone earthquakes massive, so is the actual displacement of earth. As the plates move in opposition to each other they form huge trenches, often in the sea bed that can be as deep as 35,000 feet..

Although subduction zone quakes release the most amount of energy, with the largest reaching 9.0-9.5, they only occur in a particular area about once every 300-500 years said Bailey. However, these zones are often located under the oceans, so when a subduction quake happens it is often accompanied by a tsunami, the massive movement of water that forms multiple waves or surges that can reach a height of 35-70 feet, such as those that swept ashore last month in Japan.

Bailey described the Fukushima quake as unique. He said that average subduction quakes move between 20-30 feet, but in Fukushima the plates moved 300 km, or over 180 miles.

Another anomaly of the Fukushima quake is that the movement occurred over a sizeable stretch of the zone.

Crustal or fault-line earthquakes are very different. They are vertical movements along seams in the earth’s surface, and they do not release as much energy as subduction quakes, generally topping out around 7.0. However, they occur more frequently, generally in 20-30 year periods, and are closer to the earth’s surface – and thus closer to urban centers – and therefore tend to be much more destructive than subduction zone earthquakes.

Quakes along the well-known San Andreas Fault in California would be an example of a fault-line earthquake, as was the 6.9 “Nisqually Quake” that hit western Washington in 2001. Bailey said that there are several fault lines running underneath the Puget Sound area, and the region experiences a fault-line quake about once every 20 years, and historically they have averaged 6.0-6.5.

However, UW Professor Bill Steele told the Mountain News that the largest fault line in the Pacific Northwest, known as the South Whidbey Fault, runs from Vancouver Island southeast under Everett, Washington and through to North Bend, east of Seattle. Steele said it could conceivably trigger an 8.0 if it moves simultaneously with another interconnected fault line in the Yakima area.

Professor Steele also discussed the Richter scale, the famous benchmark for measuring the strength of earthquakes, and he offered perspectives on how to gauge the power of a tremor.

Steele said the Richter scale generally reflects the amount of energy released, and that the actual destructive force of a quake is determined by many factors. These include the distance from population centers and how close to the surface of the earth’s crust the release point actually is – plus, how many release points actually engage and how far along the fault line they are located.

Nevertheless, all these factors are related, and for earthquakes to reach the higher numbers they require greater sources of energy, which means more of the earth in motion, either in volume or distance.

For instance, Steele said that for a 10.0 fault-line earthquake to hit the Puget Sound, the earth would probably have to move along a seam so lengthy that the tremor would travel virtually around the entire circumference of the planet.

Steele also said that magnitudes of energy are difficult to pin point, particularly in the upper range of the Richter scale, but he said that a rule-of-thumb would be that a 9.0 earthquake would be 32 times more powerful than an 8.0 earthquake, while a 10.0 quake would be 32 times more powerful than a 9.0. Hence, a 10.0 would be 32 times 32 more powerful than an 8.0, which puts it at a thousand times more powerful, and compared to a 7.0 quake, which is our current historical standard for a large fault-line quake, a 10.0 would be 32,000 times more powerful.

So, could a 9.1 earthquake hit western Washington, and what would happen if it did?

The answer to the first question is a simple “Yes.”

Our area is located just east of a subduction zone called the Cascadian subduction fault, and it is formed by the collision between the Juan de Fuca and North American plates.

Professor Steele added that the Cascadian zone runs north and south just west of the Washington and Oregon coastline, and stretches for about 1,000 km from Vancouver Island, BC to northern California.

Further, Professor Steele said that the last time the Cascadian subduction fault triggered a mega quake was January 26, 1700 at 9 pm Pacific Time, and this precision has been determined by examining the historical records of Japanese shoguns, Russian explorers in Alaska, and Spanish missionaries in South America, who had reported a mysterious-but-massive tsunami reaching their shores unaccompanied by any local tremor. In addition, Native American legends from this era also abound with tales of canoes in trees and other artifacts of a giant tsunami.

Since the geological record puts mega 9.0-sized Cascadian quakes at a 300-500 year interval, Bailey simply says, “We’re due.”

As for its destructive capabilities, Bailey stated that The Big One will have a variety of impacts.

He indicated that the coastal areas will be seriouly impacted by the accompanying tsunami, just like in Japan last month, and enormous ocean swells will run up the rivers for miles, perhaps penetrating further inland than in Fukushima as our elevation gain is not as steep as coastal Japan.

Puget Sound will see a large surge of water that will probably destroy harbor facilities and all structures in low-lying areas, such as the Ports of Tacoma, Seattle and Olympia.

However, Bailey doesn’t foresee extensive structural damage from the actual quake as it will be too far away from the cities to do any substantive damage.

He said the destruction in Seattle and Tacoma would be mostly “facial,” and comparable to the damage caused by the Nisqually Quake.

“It’s all about the codes,” he said, indicating that older buildings will lose brick work and masonry facing, but that modern buildings should endure the shock waves with a lot of swaying.

“There’ll be a lot of pain, but we’ll survive,” he said. “But the big problem will be the economy – we’ll have lots of power outages, disruption of the transportation system – that kind of thing. The big question will be how fast we get back on our feet and will people still have businesses and jobs.”

In comparing Washington to Japan, Bailey said our impacts would be similar to those experienced by Tokyo.

“Tokyo is over a hundred miles from the epicenter,” Bailey said. “We’d be about the same. Fortunately, we wouldn’t have an issue with nuclear generating plants – that’s what’s causing the real problems in Japan.”

Washington reportedly has only one nuclear generating plant for electricity – in the Tri-Cities area east of the Cascade Mountains.

Bailey also forecasted a host of psychological problems for Washingtonians that the Japanese do not face.

“They’re tougher,” he said. “They’ve been hardened – they have a lot of experience with earthquakes, tsunamis and other disasters.”

He also characterized Washingtonians as having a dependent, expectant attitude towards governmental relief efforts.

“People have a lot of expectations of government,” he said. “They expect that government will just come in and restore everything – that ‘government will make me whole.’”

To counter that dynamic, Bailey recommends that everyone have enough food, water, and warm clothing to be able to survive-in-place at home, in the car, and at work for at least seven days.

In addition, he recommends that everyone get to know their neighbors and assay the skills and needs of their communities.

“The fabric of society could unravel,” he said.

From an emergency management perspective, Bailey declared the key priority for government in the recovery period is to “get the infrastructure up and running” and re-open schools.

“Getting the schools re-opened is the number one way of keeping a community together,” he said.

© 2011 The Mountain News
Used with permission.

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