Virtual mega-quake may help big cities to develop early warning systems

Washington, Feb 27 : Scientists have created a supercomputer-driven simulation of a mega earthquake measuring 9.0 magnitudes on the Richter scale for the region of Pacific Northwest, which may help big cities to develop early warning systems.

A team of researchers led by seismologist Kim Olsen of San Diego State University (SDSU) developed the simulation.

The team used this supercomputer-powered "virtual earthquake" program to calculate for the first time realistic three-dimensional simulations that describe the possible impacts of megathrust quakes on the Pacific Northwest region.

In the simulation, peak ground velocities are displayed in yellow and red. The legend represents speed in meters per second (m/s) with red equaling 2.3 m/s.

What the scientists learned from this simulation is not reassuring.

With a rupture scenario beginning in the north and propagating toward the south along the 600-mile long Cascadia Subduction Zone, the ground moved about 1 1/2 feet per second in Seattle; nearly 6 inches per second in Tacoma, Olympia and Vancouver; and 3 inches in Portland, Oregon.

Additional simulations, especially of earthquakes that begin in the southern part of the rupture zone, suggest that the ground motion under some conditions can be up to twice as large.

"We also found that these high ground velocities were accompanied by significant low frequency shaking," said Olsen.

The long-duration shaking, combined with high ground velocities, raises the possibility that such an earthquake could inflict major damage on metropolitan areas - especially on high-rise buildings in downtown Seattle.

Compounding the risks, like Los Angeles to the south, Seattle, Tacoma, and Olympia sit on top of sediment-filled geological basins that are prone to greatly amplifying the waves generated by major earthquakes.

According to Olsen, "One thing these studies will hopefully do is to raise awareness of the possibility of megathrust earthquakes happening at any given time in the Pacific Northwest."

"Because these events will tend to occur several hundred kilometers from major cities, the study also implies that the region could benefit from an early warning system that can allow time for protective actions before the brunt of the shaking starts," he added.

Depending on how far the earthquake is from a city, early warning systems could give from a few seconds to a few tens of seconds to implement measures.

In addition to increasing scientific understanding of these massive earthquakes, the results of the simulations can also be used to guide emergency planners, to improve building codes, and help engineers design safer structures - potentially saving lives and property in this region of some 9 million people.

"The information from these simulations can also play a role in research into the hazards posed by large tsunamis, which can originate from such megathrust earthquakes like the ones generated in the 2004 Sumatra-Andeman earthquake in Indonesia," said Olsen.

ANI