California Rocks with 800 Earthquakes in the Past Week
NEW YORK (MainStreet) The earthquake this morning in Los Angeles and the 6.9 magnitude offshore temblor last week northwest of San Francisco remind us: California is on a slippery slope. How many quakes have there been just in the past week in the Golden State? You would think just two, but actually there have more than 800 earthquakes registering a magnitude of 3.0 or greater throughout the state in the past seven days, according to data developed by Jon Connoly of the Pacific Northwest Seismic Network.
The 4.4 magnitude L.A. quake at 6:25 a.m. local time this morning was followed by a 2.7 aftershock almost exactly an hour later. In fact, five shakers have been reported throughout the state in the past 24 hours, according to the U.S. Geological Survey.
But California is not the only state rocking. Overnight, a 3.3 quake was recorded in central Oklahoma and a 2.5 magnitude quake was felt in western Montana.
The USGS says earthquake activity in the central U.S. is "not slowing down." Researchers say that the current level of seismic activity in the so-called "New Madrid Seismic Zone," a region generally between St. Louis and Memphis, reflects "the signature of active, ongoing processes that continue to generate stress in the region -- stress that we expect will eventually be released in future large earthquakes."
The New Madrid Seismic Zone in the central United States produced four large earthquakes with magnitudes upwards of 7 over the winter of 1811-1812," the USGS report says. "Over the last two centuries, small quakes have continued to occur in the zone at a higher rate than elsewhere in the central United States."
But the West Coast, California in particular, is most at-risk, with populous areas straddling massive geologic fault lines. In a news conference this morning, USGS seismologist Robert Graves said there was a 5% chance that this morning's LA quake was a foreshock to a larger event.
"Earthquakes are not random events. Earthquakes are clustered in time and space," John Dvorack, a former USGS scientist told Northern California public television station KQED in an interview Friday.
In fact, Dvorack says that with each temblor comes the greater likelihood of another. During any 72 hour period, the odds of a magnitude 7 or greater quake in California are about 1 in 100,000, he said. However, when a magnitude 7 earthquake occurs, the odds of another quake of the same or greater strength occurring within the next three days increases to nearly 1 in 10.
--Written by Hal M. Bundrick for MainStreet