Seattle Earthquake Risk

Seattle’s tallest buildings are at risk of collapse during a rupture of the Cascadia fault zone in the Pacific Northwest, say U.S. seismic experts. The Cascadia subduction zone is likely to produce the strongest shaking experienced from earthquakes in the lower 48 states, said seismic experts from the California Institute of Technology in Pasadena.

While the Pacific Northwest has experienced little seismic activity in 200 years, there is growing consensus the Cascadia subduction zone ruptures in giant earthquakes exceeding 9 on the Richter scale, Caltech scientists Thomas Heaton and Jin Yang said Thursday at the Seismological Society of America’s annual meeting in Monterey, Calif. The Cascadia subduction zone last ruptured in 1700, Heaton and Yang said.

Simulations at Caltech show such earthquakes, which last for more than 4 minutes and are dominated by low-frequency motions, would be exacerbated by the geography of the Seattle basin and cause severe damage among modern high-rises, said Heaton and Yang.

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LA Beach Signs Warn of Tsunami Threat

Like many Californians who put down roots in earthquake country, Robin Rudisill knows the “Big One” could strike without warning. Yet from her Venice beachfront duplex, Rudisill worries about a different massive blow from Mother Nature — a tsunami.

Her 1950s-era home — with its cool ocean breeze and golden sunsets — sits smack in the heart of a potentially deadly tsunami zone. If that big one ever came ashore, scientists say, it could raze the landscape from the sun-kissed beach to about a mile inland.

To alert homeowners and beachgoers that they are in tsunami territory, the city of Los Angeles has begun posting blue and white “TSUNAMI HAZARD ZONE” signs with an image of ominous-looking waves. The signs, which have surfaced in beach parking lots and at major intersections in Venice and other low-lying communities, also point out evacuation routes.

“It makes it clear that we are in an inundation zone, which most people did not previously, and many still do not, know,” said Rudisill, who pushed for the signs.

While a tsunami threat to the Golden State is real, the potential for killer waves is far less likely than the earthquakes, wildfires, landslides and floods that plague the nation’s most populous state.

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Alaska Volcano Has Geologists on Alert

Mount Redoubt, a volcano 100 miles southwest of Anchorage, is rumbling and simmering, prompting geologists to warn that an eruption may be imminent.

Scientists from the Alaska Volcano Observatory have been monitoring activity round-the-clock since the weekend.

On Thursday, the observatory said: “Seismicity remains above background and largely unchanged with several volcanic earthquakes occurring every hour.”
The last time the 10,197-foot peak blew was during a five-month stretch starting in December 1989. It disrupted international air traffic and placed a layer of volcanic dust throughout the Anchorage area.

Volcanoes in Alaska, including Redoubt, typically erupt explosively, shooting ash almost eight miles high. Volcanic ash features small, jagged pieces of rock and glass.
This differs from volcanoes in Hawaii, which usually have slow rolling lava ooze out.
The difference is gas trying to escape gets blocked, possibly by a lava dome or a viscous magma that increases the power from beneath, said observatory geologist Jennifer Adleman.

“Its pressure keeps building and building,” she said.

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Arkansas – Series of Quakes Could Be Sign of Larger Earthquake Coming

A series of small earthquakes that rattled central Arkansas in recent weeks could be a sign of something much bigger to come.

By this weekend, seismologists hope to install three measurement devices to gather data about future temblors in the area. That information could show whether the rumbles come from heat-related geological changes or from an undiscovered fault — which could mean a risk of substantial earthquakes in the future.

“The potential for generating a high-magnitude earthquake is real,” said Haydar Al-Shukri, director of the Arkansas Earthquake Center at the University of Arkansas at Little Rock.

Five earthquakes ranging in magnitude from 2.2 to 2.7 have hit central Arkansas this month. Quakes with a magnitude of 2.5 to 3 are typically the smallest felt by people.

While hundreds of earthquakes occur each year, including several in Arkansas, the location of the recent ones give Al-Shukri pause. Arkansas quakes generally occur in the state’s northeast corner, part of the New Madrid Seismic Zone, where three temblors with magnitudes of around 8 struck during the winter of 1812 and smaller ones continue today.

But central Arkansas does not have any seismic history, Al-Shukri said.

“It is abnormal. It is significant,” he said. “We need to carefully watch this activity.”

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