|USGS earthquakes location map.|
The primary swarm of earthquakes has been centered in northwestern Logan County and northeastern Kingfisher County, about 12 miles north of Crescent, or about 46 miles north of Oklahoma City.
In that cluster, the USGS has recorded 11 earthquakes ranging in magnitude from 2.6 to 4.5 between 10 p.m. CDT Saturday and 7 a.m. Sunday.
A magnitude-4.5 jolt at 9:09 a.m. CDT Sunday became the state’s strongest earthquake so far in 2014. Earlier in the swarm, two earthquakes measuring 4.3 on the moment magnitude scale had been the strongest earthquakes so far in 2014 in Oklahoma, eclipsing a 4.1 jolt centered near Langston on Feb. 8.
|USGS shakemap intensity for the 4.5 magnitude earthquake.|
Those magnitude-4.3 tremors, which occurred at 1:51 a.m. and 3:42 a.m. CDT Sunday respectively, were both felt across a wide area. The “Did You Feel It?” section of the USGS website received reports of shaking as far north as the Kansas City metropolitan area and as far south as Norman, Okla., from both earthquakes. Vibrations were also felt as far east as the Tulsa area from both incidents.
A separate cluster of earthquakes occurred near Choctaw, an eastern suburb of Oklahoma City, on Saturday and Saturday night. Six earthquakes ranging in magnitude from 2.4 to 3.7 were reported between 1 a.m. CDT Saturday and 1 a.m. CDT Sunday. The strongest temblor occurred at 10:08 p.m. Saturday and was felt across much of the Oklahoma City metropolitan area.
Earlier this month, a study confirmed that Oklahoma’s strongest recent earthquake, a damaging magnitude-5.7 quake in 2011 near Prague, was caused by wastewater injection related to hydraulic fracturing, also known as fracking, a method of gas and oil extraction. – Wunderground.
Natural Occurring Earthquake Activity
Most of North America east of the Rocky Mountains has infrequent earthquakes. Here and there earthquakes are more numerous, for example in the New Madrid seismic zone centered on southeastern Missouri, in the Charlevoix-Kamouraska seismic zone of eastern Quebec, in New England, in the New York – Philadelphia – Wilmington urban corridor, and elsewhere. However, most of the enormous region from the Rockies to the Atlantic can go years without an earthquake large enough to be felt, and several U.S. states have never reported a damaging earthquake.
Earthquakes east of the Rocky Mountains, although less frequent than in the West, are typically felt over a much broader region than earthquakes of similar magnitude in the west. East of the Rockies, an earthquake can be felt over an area more than ten times larger than a similar magnitude earthquake on the west coast. It would not be unusual for a magnitude 4.0 earthquake in eastern or central North America to be felt by a significant percentage of the population in many communities more than 100 km (60 mi) from its source. A magnitude 5.5 earthquake in eastern or central North America might be felt by much of the population out to more than 500 km (300 mi) from its source. Earthquakes east of the Rockies that are centered in populated areas and large enough to cause damage are, similarly, likely to cause damage out to greater distances than earthquakes of the same magnitude centered in western North America.
|USGS Oklahoma Seismicity Map – 1973 to March 2012|
Most earthquakes in North America east of the Rockies occur as faulting within bedrock, usually miles deep. Few earthquakes east of the Rockies, however, have been definitely linked to mapped geologic faults, in contrast to the situation at plate boundaries such as California’s San Andreas fault system, where scientists can commonly use geologic evidence to identify a fault that has produced a large earthquake and that is likely to produce large future earthquakes. Scientists who study eastern and central North America earthquakes often work from the hypothesis that modern earthquakes occur as the result of slip on preexisting faults that were formed in earlier geologic eras and that have been reactivated under the current stress conditions. The bedrock of Eastern North America is, however, laced with faults that were active in earlier geologic eras, and few of these faults are known to have been active in the current geologic era. In most areas east of the Rockies, the likelihood of future damaging earthquakes is currently estimated from the frequencies and sizes of instrumentally recorded earthquakes or earthquakes documented in historical records.
As is the case elsewhere in the world, there is evidence that some central and eastern North America earthquakes have been triggered or caused by human activities that have altered the stress conditions in earth’s crust sufficiently to induce faulting. Activities that have induced felt earthquakes in some geologic environments have included impoundment of water behind dams, injection of fluid into the earth’s crust, extraction of fluid or gas, and removal of rock in mining or quarrying operations. In much of eastern and central North America, the number of earthquakes suspected of having been induced is much smaller than the number of natural earthquakes, but in some regions, such as the south-central states of the U.S., a significant majority of recent earthquakes are thought by many seismologists to have been human-induced. Even within areas with many human-induced earthquakes, however, the activity that seems to induce seismicity at one location may be taking place at many other locations without inducing felt earthquakes. In addition, regions with frequent induced earthquakes may also be subject to damaging earthquakes that would have occurred independently of human activity. Making a strong scientific case for a causative link between a particular human activity and a particular sequence of earthquakes typically involves special studies devoted specifically to the question. Such investigations usually address the process by which the suspected triggering activity might have significantly altered stresses in the bedrock at the earthquake source, and they commonly address the ways in which the characteristics of the suspected human-triggered earthquakes differ from the characteristics of natural earthquakes in the region. – USGS.