It also set off a new round of interest in earthquake science; triggered a flurry of seismic upgrades of bridges, overpasses, office buildings and homes; and helped advance emergency planning.
• The network of seismic monitoring stations throughout the Pacific Northwest has grown by 300 percent since the quake.
• Global positioning technology is now used at 400 stations across the region to keep tabs on earthquake hazards and monitor catastrophic events as they unfold.
• The state has spent more than $40 million on seismic upgrades and repairs on the Capitol Campus.
• The state Department of Transportation has partially or completely retrofitted nearly 500 of the 880 highway bridges in the Puget Sound region that pose the greatest risk to public safety in a powerful earthquake.
But here’s a sobering thought:
The 2001 earthquake – a 6.8-magnitude quake centered 32 miles beneath Anderson Island between Olympia and Tacoma – was not the “big one” that could tear the region apart. That kind of geologic upheaval – 5,000 times the force of the Nisqually earthquake – has occurred in the past and is expected to occur again.
“We recognize we can never be prepared for some scenarios,” said John Schelling, earthquake program manager for the state’s Emergency Management Division. “We live in earthquake country, and we need to take the threat seriously.”
Washington state has the second-highest risk of economic loss from earthquakes in the nation, behind California, according to a study by the Federal Emergency Management Agency. Seattle ranks seventh among cities nationwide at risk of earthquake damage, the study says. Tacoma ranks 22nd.
THREE TYPES OF QUAKES
The Nisqually event was a deep earthquake in the oceanic plate that is slowly diving beneath the North American continental plate in what is called the Cascadia subduction zone. It was akin to the 1949 and 1965 quakes that struck the Puget Sound region. The depth of these quakes helps to buffer some of their force. Deep earthquakes can be deadly and damaging but are not the biggest threat in earthquake country.
A second type of earthquake occurs on faults in the continental plate at much shallower depths – 15 miles or less. The last of these so-called crustal earthquakes in the Puget Sound region struck about 1,100 years ago on the Seattle fault; it had an estimated magnitude of 7.4. Faults are fractured and displaced rock strata that signal earthquake activity.
That earthquake elevated the south end of Bainbridge Island and Alki Beach in West Seattle 15 to 20 feet and generated a tsunami in Puget Sound. As for damage and injury, the central Puget Sound area did not have a built environment or the millions of people who now live here.
It’s the same type of deadly, destructive earthquake that struck beneath Christchurch, New Zealand, on Tuesday.
In 2005, a team of geologists, structural engineers, seismologists and emergency management officials gathered to answer the question: What would happen if a magnitude 6.7 quake occurred on the Seattle fault today?
Here’s their answer: $33 billion in property damage and economic loss, more than 1,600 deaths, more than 24,000 injuries, and nearly 40,000 buildings destroyed or unfit to occupy.
Shallow earthquakes along fault lines that run through Seattle and Tacoma could be among the deadliest of all in the Puget Sound region because of the density of the population. They could cause unimaginable damage close to the epicenter.
But a third type of earthquake could be the most powerful of all. The likelihood exists – it last happened around 1700 – that the oceanic plate and continental plate could lock up, then break loose, creating a seismic shock and tsunami of epic proportions, a so-called subduction zone earthquake on the order of magnitude 9 and similar to the one that killed 250,000 people in Tangshan, China, in 1976, and the earthquake and tsunami that killed 300,000 in Indonesia in 2004.
A subduction earthquake could set off a chain reaction of crustal earthquakes on fault lines running through the Puget Sound region and under Cascade volcanoes. Scientists have evidence of an event roughly 1,100 years ago that sent a lahar – a massive wall of volcanic mud and debris – from Mount Rainier all the way to the Duwamish Valley.
Just where the two plates were to rupture in the Pacific Northwest would have a lot to do with how damaging a subduction zone quake would be, said John Vidale, earth and space sciences professor at the University of Washington and director of the Pacific Northwest Seismic Network.
“The subduction zone is better understood than it was 10 years ago,” he said. “We know the ground breaks, but we don’t know if it would be off the coast of Washington or halfway to Seattle.”
MONITORING HAS IMPROVED
Since 2001, new technology and increased seismic monitoring equipment have been deployed across the region to better understand where and why earthquakes occur. For instance:
• The Pacific Northwest has 100 ground-motion sensors in place – triple what it had 10 years ago – with 40 more on the way, Vidale said. The stations help pinpoint earthquake epicenters and measure the energy released by earthquakes.
• Global positioning systems are being used to detect earthquakes much faster than traditional seismographs, said Tim Walsh, chief hazards geologist for the state Department of Natural Resources.
“It’s getting to the point where you can process information fast enough to immediately direct emergency response to an earthquake,” he said.
• Optical remote sensing technology – called light detection and ranging, or LIDAR – is helping find new faults, including several in the Puget Sound area.
“It’s like getting a new pair of eyeglasses,” Walsh said. “LIDAR lets us see geologic formations through the forests.”
New since the Nisqually earthquake is scientific knowledge of slow-moving earthquakes that last for several weeks and can’t be detected without seismic monitoring equipment but release as much energy as a magnitude 6.5 quake.
The slow-slip earthquakes, which occur about every 15 months, appear to be associated with the Cascadia subduction zone fault where the oceanic and continental plates intersect.
“They’re going to be important in understanding how the subduction zone functions,” Walsh said of the unusual earthquakes.
One of the few good things that came out of the Nisqually earthquake was the release of federal funds that allowed the DNR to map earthquake hazards county by county to show areas prone to strong ground shaking in an earthquake and unstable soils vulnerable to collapse, or liquefaction.
In general, the softer the soil, the more shaking is likely in an earthquake, Walsh said.
Despite the advances in science, predicting when an earthquake will strike is still the domain of pseudoscientists and psychics.
However, scientists here and around the world continue to work on the earthquake prediction question.
“But right now, we can’t even see how that might work,” Vidale said.
BUILDING CODE CHANGES
Since the Nisqually earthquake, the state has revised the building code three times, including a change to the International Building Code, which has fairly strong seismic standards.
Buildings are designed to what is called a maximum considered earthquake, an earthquake that has a 2 percent probability of happening every 50 years.
“New construction is absolutely more seismically secure than it was 10 years ago,” said Tim Nogler, managing director of the state Building Code Council. He noted that the standards vary based on the ground-motion conditions for the building site.
But any building’s ability to avoid damage has much to do with the strength and location of an earthquake, noted Mike Szramek, a structural engineer with MC Squared Inc. of Olympia.
“If Mother Nature wants your building, it’s hers,” he said.
Engineering buildings to withstand the force of earthquakes has advanced incrementally over the years. Typically, major changes in the seismic building code are linked to structural failures observed in major earthquakes, said Szramek.
“The 1971 San Fernando earthquake – that’s when the seismic code changed drastically,” he said.
In that earthquake, Olive View Hospital in Sylmar, Calif., built to the earthquake standards of the day, was destroyed when four five-story wings pulled away from the main building and three stair towers collapsed.
Today, there is more emphasis on tying various components of a major building together to resist the horizontal forces of an earthquake, Szramek explained.
“We’re putting more belts and suspenders on buildings,” he said.
Still, there are no guarantees in earthquake country.
“We gamble every single day,” he said.
John Dodge: 360-754-5444 email@example.com