Bursts of energy rocked the Earth in the hour right before an earthquake devastated Turkey in 1999 — a new finding that might one day help researchers predict major quakes.
Many large earthquakes are preceded by smaller rumbles known as foreshocks. However, there is apparently no way to distinguish these tremors from other small quakes that don't portend a larger temblor. At the same time, many large earthquakes do not seem to have any foreshocks.
The magnitude 7.6 earthquake that hit near Izmit in northwest Turkey in 1999, killing at least 17,000 people and leaving nearly 500,000 homeless, is now helping to shed light on the anatomy of such catastrophes. The calamity was one of the best-recorded large earthquakes to date, since researchers had seismic recording stations very close to the fault, said seismologist Michel Bouchon of the University of Joseph Fourier in Grenoble, France.
Now, after analyzing the deluge of information from before, during and after the earthquake, Bouchon and his colleagues have detected repeated, accelerating blips of seismic activity before the Izmit quake, near the point where the rupture began.
Theoretical and laboratory studies of earthquakes suggest they should be preceded by slow slipping along a fault in the Earth. Before the Izmit quake began, the research suggests the fault slipped irregularly but near-continuously for 44 minutes, generating the bursts the scientists detected, as well as increasing low-frequency seismic noise.
"This will motivate seismologists to look more for these types of signals before earthquakes," Bouchon told OurAmazingPlanet. "Seismologists have kind of given up finding such signals in the early nucleation phase before earthquakes."
Future research can analyze details of other large, well-recorded earthquakes for similar signals.
"What we found is encouraging, but we don't know how common these signals will be," Bouchon said.
The scientists detailed their findings in the Friday issue of the journal Science.
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Earthquakes continue to rumble
Earthquakes continued to rumble across northeastern Faulkner County on Thursday, with a 3.8 magnitude tremor reported at about 4:49 a.m. Rumbling was felt in Wooster, Greenbrier and Guy.
More than 20 quakes have been registered since Wednesday, sending people to Geological Survey websites to report "I Felt It," calling insurance agencies about earthquake insurance and wondering what to put in an emergency earthquake pack.
Faulkner County Judge Preston Scroggin said his telephone began ringing early Thursday morning, and, in addition to taking those calls from worried residents in his county, he was making a few calls of his own. "I've been visiting with people who know a lot more than I do" about the recent swarm of quakes, Scroggin said.
That included talking to the folks at the Arkansas Geologic Survey and those concentrating on the natural gas distribution industry.
He said the Arkansas Oil and Gas Commission established a six-month moratorium in January on new injection wells in the area. Four companies are operating already-drilled injection wells: SEECO Inc., Chesapeake Operating Inc., Clarita Operating LLC and Deep-Six Water Disposal Services LLC.
The moratorium, which is expected to end in July, is intended to allow time to study the relationship -- if any -- between the injection wells and earthquakes in the area.
Scroggin said he also touched base with his staff members who have spent four years in training for earthquake preparedness.
The Arkansas Department of Emergency Management required county judges to take the lead in preparedness.
Scroggin said the county's personnel, emergency management, road workers, the sheriff's key people and others have been involved in extensive training and have received certification in earthquake preparedness.
"We've been concentrating on this for four years. We've had several table top exercises," he said. "We are very well prepared."
For instance, in addition to emergency personnel trained to help the injured, the foreman of the road department was trained in examination of bridges and roadways to assess damage for the public's safety; the tax assessor was trained in making damage estimates and cost analyses on homes, businesses and other buildings, Scroggin said.
"All types of people will be out in the field if we have a damage-causing event.
"If we need more assistance, we can call for help from across the state," he said.
"Our goal will be to help the injured and get things back to normal," Scroggin said.
For those who feel the quake, he said, the best thing for them to do right now is to go to the US Geologic Survey site online and say: "I Felt It." The address is http://earthquake.usgs.gov/earthquakes/dyfi/
"It's very important to geologists and the Office of Emergency Management to know where the quakes were felt," Scroggin said.
Reporting damage
Any structural damage should be reported to the OEM, said Dirk Sutterfield, deputy director of OEM. That number is 450-4935.
He explained.
"If there were one event large enough to cause significant damage to a lot of property, we could ask the state to declare a disaster area. That would help us and homeowners with resources for reconstruction and repair.
"The county judge would petition the state, declaring that we need help and the damage is beyond our resources to handle," Sutterfield said.
"But if nobody calls to report damage, we have no way of knowing," he said.
Earthquake insurance
Some insurance agents in the county are reporting an increase in calls about earthquake insurance.
Dawn Brown of State Farm Insurance in Conway said their office had received three calls on Wednesday.
"That doesn't seem like too many but it is unusual," Brown said.
Not all agencies offer the insurance, she said.
At State Farm, the insurance is added as an endorsement on a homeowner's current policy.
"It's not that expensive," she said, with the cost related to a homeowner's deductible, price of their home and the rating of the zone where their home is located.
The cost for homeowners in the Faulkner County zone from State Farm could range from $38 a year to as much as $109 a year, Brown said.
Be prepared
The Red Cross, RedCross.org and the Cooperative Extension Service, www.uaex.edu, have fact sheets and brochures giving advice for earthquake preparedness.
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Map of the Guy Swarm Quakes, updated today:
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