What is the Richter Scale?
The most common standard of measurement for an earthquake is the Richter scale, developed in 1935 by Charles F. Richter of the California Institute of Technology. The Richter scale is used to rate the magnitude of an earthquake – the amount of energy it released. This is calculated using information gathered by a seismograph.
The Richter scale is logarithmic, meaning that whole-number jumps indicate a tenfold increase. In this case, the increase is in wave amplitude. That is, the wave amplitude in a level 6 earthquake is 10 times greater than in a level 5 earthquake, and the amplitude increases 100 times between a level 7 earthquake and a level 9 earthquake. The amount of energy released increases 31.7 times between whole number values.
On the Richter Scale, magnitude is expressed in whole numbers and decimal fractions.
Information courtesy howstuffworks.com.
Diane and Steve Henry were in their Hoisington home Saturday night when something rocked their world.
They were not alone.
The earthquake which measured 5.6 on the Richter Scale that shook eastern Oklahoma Saturday evening was felt as far away as Omaha, Neb., St. Louis, Mo., Amarillo, Texas, and Wisconsin, the United States Geological Survey office in Denver reported. The trembler followed smaller foreshocks earlier in the day that did not reach as far.
“It was really strange,” Diane Henry said. This was the first time she’d ever felt an earthquake like that.
“I was in bed reading and the bed shook,” she said. Her husband was in the living room watching television and felt his recliner move as well.
According to the USGS, there have been dozens of aftershocks recorded following the Saturday quake and its magnitude 4.7 foreshock that occurred on the same day. These aftershocks will continue for weeks and potentially months, but will likely decrease in frequency.
This is not an unusual amount of aftershock activity for a magnitude 4.7 to 5.6 quake. The earthquake sequence that started Saturday occurred close to where a magnitude 4.1 earthquake occurred on Feb. 27, 2010.
The earthquakes that occurred on Saturday are typical of the larger areas of North America east of the Rocky Mountains that have infrequent earthquakes large enough to cause minor to major damage.
Earthquakes are not unusual in Oklahoma, but they often are too small to be felt, the USGS noted. From 1972-2008 about two to six earthquakes a year were recorded by the USGS National Earthquake Information Center.
In 2008, earthquake activity began to increase, with over a dozen earthquakes recorded that year. In 2009 the rate continued to climb, with nearly 50 quakes recorded – many big enough to be felt.
The earthquakes from 1973-2007 were scattered broadly across the east-central part of the state. The events since 2007 have been more clustered in the vicinity northeast and east of Oklahoma City and generally southwest of Tulsa, where the recent magnitude 5.6 earthquake occurred.
There is always a small possibility of an earthquake of larger magnitude following any earthquake, information from the USGS said. But the occurrence of the magnitude 5.6 earthquake, and the increase in activity in recent years does not necessarily indicate that a larger more damaging earthquake will occur.
Earthquakes east of the Rocky Mountains, although less frequent than in the West, are typically felt over a much broader region. East of the Rockies, an earthquake can be felt over an area as much as ten times larger than a similar magnitude earthquake on the west coast. A magnitude 4.0 eastern U.S. earthquake typically can be felt at many places as far as 60 miles from where it occurred, and it infrequently causes damage near its source. A magnitude 5.5 eastern U.S. earthquake usually can be felt as far as 300 miles from where it occurred, and sometimes causes damage as far away as 40 25 miles.
