March 3, 2010

Seattle Could Experience Megaquake In Near Future

An earthquake hotspot just 50 miles off the Pacific Northwest coast is on the verge of unleashing itself on Seattle, Portland and Vancouver, similar to the damage that shattered Chile, according to a recent Associated Press report.

The fault has been in the dormant state for over 300 years, but the consequences could be devastating when it awakens.

Recent computer simulations have shown a hypothetical magnitude 9 quake could shake the area between 2 to 5 minutes.  This would be strong enough to potentially cause poorly constructed buildings from British Columbia to Northern California to collapse and severely damage highways and bridges.

A quake of this caliber would send tsunami waves rushing to shore in minutes. 

The Pacific Northwest "has a long geological history of doing exactly what happened in Chile," Brian Atwater, a geologist with the U.S. Geological Survey and University of Washington, told AP. "It's not a matter of if but when the next one will happen."

The last quake hit in 1700, which sent 30- to 40-foot-tall tsunami waves crashing onto the coast and racing across the Pacific. 

Chris Goldfinger, head of the Active Tectonics and Seafloor Mapping Laboratory at Oregon State University, told AP there is an 80 percent chance the southern end of the fault off southern Oregon and Northern California could break in the next 50 years and produce a megaquake. 

Research presented last year at a seismology conference showed that Seattle high-rises built before 1994 were at high risk of collapsing during a superquake. 

Oregon and Washington disaster managers are aware of the risks, and work is ongoing to shore up schools, hospitals and other buildings to withstand a seismic jolt.

"We're definitely being proactive in trying to get those fixed, but we have a long way to go," said Yumei Wang, geohazards team leader with the Oregon Department of Geology and Mineral Industries.

Oregon is said to have 1,300 schools and public safety buildings that are at high risk of collapsing during a major quake.  The state recently budgeted $15 million to two-dozen schools and emergency facilities to start the retrofit process.  State laws say that poorly built public safety buildings need to be upgraded by 2022 and public schools by 2032.

The state is also helping its coastal communities plan for vertical evacuation buildings that could withstand giant tsunami waves.

Seattle plans to retrofit its 34 fire stations.  The city also plans to upgrade 600 buildings considered the most at risk.

"We have been preparing aggressively," said Barb Graff, who heads the city's Office of Emergency Management.

Chile and the Pacific Northwest are all a part of several seismic hotspots around the globe where plates of the Earth's crust grind and dive.  These subduction zones help give height to mountain ranges, ocean trenches and volcanic arcs.  However, they also spawn the largest quakes on Earth.

According to geologist Jian Lin of the Woods Hole Oceanographic Institution, the magnitude-8.8 earthquake that shook Chile occurred in an offshore region that was under increased stressed from a 1960 magnitude-9.5 quake.  This was the largest quake in recorded history.

This quake either badly damaged or destroyed 500,000 homes and killed over 700 people.

Similar tectonic fires are set off the Pacific Northwest, where the Juan de Fuca plate is diving below North America.  Centuries of pent-up stress in the Cascadia subduction zone will eventually cause the plates to slip.  Scientists do not know how to predict when a quake will occur, only that one will happen.

In 2001, a 6.8-magnitude quake centered near Olympia, Washington shook a swath of the Pacific Northwest, but caused no deaths. 

A group of scientists plan to travel to Chile in May for a conference on giant earthquakes and their tsunamis to help better understand megaquakes.


Image Caption: The Contemporary Art Museum building in Santiago was damaged by the January 27th 8.8 magnitude earthquake that rocked Chile. Credit Carlos Varela - Wikipedia