Spokane is an urban area where not many earthquake preps have been made.
Ranging from magnitude 4 to those not even strong enough to be measured by a seismograph, small earthquakes have been rattling the Spokane area since last May.
Ruth Ludwin, a research scientist with the Pacific Northwest Seismograph Network (PNSN), said the earthquakes have been coming in "bursts" since May.
"In late June we had a magnitude 3.9, then on through early July we had a series of small ones, then it was quiet until the end of September," she said. "We had more in October and then November was busy with more big ones." The strongest occurred Nov. 11, a magnitude 4 quake followed by several more measuring over magnitude 3.
Ludwin said Spokane, a city of almost 200,000 people in eastern Washington, isn't normally a highly active seismographic area so they didn't have much measuring equipment there before the quakes started up in May. Since then, the U.S. Geological Survey has helped them out by bringing in four more devices. "People were reporting many that we weren't able to detect because of the lack of equipment," she said. "And now we're still not detecting all of them because many are too shallow to register."
This kind of burst activity is unusual for Spokane, said Ludwin. "There is some history of single earthquakes in the general area with impact, but not these types of series," she said. The search for the cause of these quakes goes on. "We're working on it, we're studying local geological structures and trying to understand the stress regimes of the area," said Ludwin.
The largest quake in eastern Washington in the last 100 years was a 5.5-magnitude temblor in 1942 centered 35 miles northeast of Spokane. The majority of these recent quakes have been felt in the northern part of the city.
The earthquake activity has some people on edge. Because many of the quakes are so shallow, Ludwin said they cause a lot of noise. The PNSN has been working extensively with the media to let people know of the real hazards and ways to prepare for further earthquakes.
"There's always an earthquake concern in general in this area of the country, but we try to educate people and distribute information when the predictions and rumors start up," said Ludwin. And according to her, some local people are trying to predict upcoming major earthquakes.
"We don't try to counteract these predictions or rumors, we just try to make sure people are ready for any type of quake activity and not carry on those rumors," she said. "Certainly we know where earthquakes can occur, but we can't make strength predictions."
Ludwin said Spokane is not really prepared for any larger quake that could hit. "Spokane is an urban area where not many earthquake preps have been made," she said. "This is an ongoing problem. Sure, earthquakes in eastern Washington aren't as common as they are in the western part, but they are possible. There is a fault underneath Spokane."
The PNSN is working actively with the state's emergency operations office and other local agencies to further mitigation efforts. "We're making sure people know how to turn off their utilities and strap down their water heaters and secure heavy things to the ground or walls," said Ludwin.
"Unfortunately many of these mitigation steps aren't required."
Until then, schools and businesses are preparing with earthquake drills and evacuation plans to be ready for the next tremors.
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