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Earthquakes 101


Why all the activity of late in-state?

Sara Custer February 3rd, 2011

Six hundred earthquakes rocked Oklahoma County last year. If you think that’s a lot, you’d be right: That marks an increase from 37 felt earthquakes reported in 2008 and 2009, and only seven from 1987 to 2007.

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Seismologists at the Oklahoma Geological Survey (OGS) say the huge jump in numbers is partly due to the increase in instruments used to measure the earthquakes. According to the OGS, it only started monitoring earthquakes 50 years ago, so it’s highly likely such activity has happened before. Most humans feel earthquakes of 2.5 magnitude or higher.

As giant underground blocks of rocks move, they slowly release pressure, putting stress on the areas around them. The hundreds of little earthquakes that occur are the chunks of rock surrounding the fault system relieving this stress.  

Seismologists say the recent increase is inconsistent with collected data, but is natural earthquake activity, considering parallel fault lines that run through Oklahoma just south of Jones, and between Jones and Luther.

MEASURE FOR MEASURE
The Richter scale is no longer the most reliable earthquake-measuring system. Developed in 1935, it was a comparative system based only on California’s earthquakes.

“It was very specific to Southern California,” says Austin Holland, a seismologist at the OGS. “If we applied it here, we would get a magnitude of 4 for an earthquake that was magnitude 3.”

Now scientists measure the amount of energy released in an earthquake and calculate the magnitude by using algorithms. In this complex formula, a magnitude 4 is 32 times stronger than a magnitude 3, so going up one unit on the scale is not as simple as may appear.

In the Sooner State, seismologists measure how the earth rings after a quake. For larger movements, they can measure the amplitude of waves across the area and then take an average.

Seismologists also record the depth of the earthquake. According to the OGS, most earthquakes here occur between 2 and 4.5 miles below the earth’s surface. The Norman earthquake on Oct. 13, 2010, was about 8 miles deep. However, seismologists say that the depth does not affect an earthquake’s magnitude.

Scientists also use the Modified Mercalli scale to express the intensity of damage to a specific location based on observation. The amount of damage caused by earthquakes depends on the building designs and the type of soil in the area.

“We’re pretty well off here in Oklahoma,” says Holland. “We have a lot of rock in the area and the soil is stiff.”

BE PREPARED
Although Oklahoma’s earthquakes are tiny in comparison to full-blown disasters in other parts of the globe, Holland said a chance for home damage always exists.

“Buying earthquake insurance for your home is up to you, but there is a possibility for damage,” he said. “People should generally be prepared for their families in all natural hazards.”

However, he noted, the same emergency kit one would use for a tornado or snowstorm can be applicable in earthquakes.

The largest earthquake measured in Oklahoma was a magnitude 5.5 on April 9, 1952. It reportedly caused damage in El Reno, Oklahoma City and Ponca City.

DOS AND DON’TS
• The most important thing to remember during an earthquake is to stay away from falling debris.
• If you’re inside, stand in a corner away from windows, wall hangings or bookshelves. Even better, if you can, take cover under furniture or a sturdy table. Don’t try to exit the building. Don’t use elevators.
• If you’re outside, move away from crumbling walls or buildings, potentially falling power lines or streetlights. Ground movement during earthquakes is very seldom the cause of death, so don’t worry about falling into huge cracks in the earth.
• If in a moving vehicle, stop as quickly and safely as possible. Don’t get out of the vehicle and don’t stop near trees, overpasses or buildings. —Sara Custer

 
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