Another quake rumbled this morning
By Kim Bell
ST. LOUIS POST-DISPATCH
Monday, May. 05 2008

The U.S. Geological Survey said a 2.7 magnitude quake rumbled this morning. But this time, its epicenter was near Valley Park.

The quake came at 6:25 a.m., centered two miles southeast of Valley Park, according to Jessica Sigala, a geophysicist with the U.S. Geological Survey's National Earthquake Information Center based in Colorado. Its epicenter was somewhere between Valley Park and the Sappington area.

Sigala said this morning's quake was not connected to the 5.2 magnitude quake that struck at 4:37 a.m. on April 18 in the Wabash Valley Seismic Zone, some 140 miles from St. Louis.

When this morning's quake hit, an officer with St. Louis County police in the Affton precinct said he felt the ground shaking for perhaps five seconds and the roof moving, "like someone was moving something around." Police had no reports of damage or injuries.

Timothy M. Kusky, director of the Center for Environmental Sciences at St. Louis University, said today's quake in St. Louis came from "some small faults outside the Wabash and New Madrid zones. They're active every once in awhile." Kusky said he's still studying the readouts from this morning's quake to pinpoint the exact epicenter. But he thinks it was along what's called the Eureka-House Springs fault.

"There are a few faults under Eureka and House Springs that have small quakes every 10 to 20 years," he said. "Generally, they're magnitudes of 2 to 3 or less."

Kusky said the fault had quakes in 1978 and 1998, both of magnitudes between 2 and 3.

Kusky said it's probably just a coincidence that today's came on the heels of the April 18 quake in the Wabash Valley Seismic Zone. Its epicenter was about six miles northwest of Mount Carmel, Ill. That one rattled homes from Memphis to Cincinnati and places in between. About 30 aftershocks have followed -- the largest being a 4.6 magnitude aftershock at 10:14 a.m. on April 18. The most recent aftershock was 1.4 magnitude that came at 7:34 p.m. Friday near Bellmont, Ill.

Kusky said he's worried about shifting sands near levees.

"One thing we have to be kind of worried about is that earthquakes like this have the potential to shake up loose sand .... and some of the levees saturated with water right now might collapse," Kusky said.

Kusky said it could be a concern, especially around the new $49 million levee in Valley Park.

Kusky said it's called liquefaction. It happens in saturated soils. Before the quake, the pressure on soil particles is relatively low. But the violent shaking from an earthquake can cause the water pressure to increase to the point where the soil particles, or sand, moves.

Kusky explains that liquefaction can be responsible for sinking sidewalks, telephone poles and foundations in an earthquake. He cited a famous example in the 1964 Alaskan quake. "Entire neighborhoods slid toward the sea on liquefied sand layers," Kusky wrote in a paper explaining the phenomenon. In 1964 and 1995 quakes in Japan, Kusky said apartment buildings and shipping piers rolled onto their sides.

Kusky added that today's earthquake is "probably too small for catastrophic failure by liquefaction, but if I was in Valley Park, I would want someone, an engineer, to go out and check the levee for signs of seepage, sand boils .... that could indicate a problem."

A spokesman for the Army Corps of Engineers said he would be checking with engineers today to see if such an inspection is necessary.


Original article: Stl Today
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