Earthquake

Whether you are in your home, a school classroom, a high-rise or other type of building, it is important to know how to protect yourself during an earthquake. Practice what to do during an earthquake with your family members so you can react automatically when the shaking starts.

If you are indoors, follow these steps:

Duck -- Duck or drop down to the floor.

Cover -- Take cover under a sturdy desk, table or other furniture. If that is not possible, seek cover against an interior wall and protect your head and neck with your arms. Avoid danger spots near windows, hanging objects, mirrors or tall furniture.

Hold -- If you take cover under a sturdy piece of furniture, hold on to it and be prepared to move with it. HOLD the position until the ground stops shaking and it is safe to move.

If you are outside when the shaking starts, get into an open area away from trees, buildings, walls and power lines. If driving, stop safely as soon as possible. Do not stop under overpasses or bridges. Turn off the engine and turn on the radio. Stay inside your vehicle below window level until the shaking stops. Do not get out of your vehicle if downed power lines have fallen across it.

Earthquake Hazards

There are two primary "hot spots" for earthquakes in the central United States that will impact Illinois, specifically in the south and southeastern parts of the state.

New Madrid Seismic Zone lies within the central Mississippi Valley, from Cairo, Illinois, through southeastern Missouri, western Kentucky, western Tennessee and northeast Arkansas. The epicenter of the zone is located just west and northwest of Memphis, Tennessee.

Historically, this area has been the site of some of the largest earthquakes in North America. Between 1811 and 1812, four catastrophic earthquakes with magnitude estimates greater than 7.0 occurred during a three-month period. Hundreds, if not thousands, of aftershocks followed over a period of several years.
Wabash Valley Seismic Zone, in southeastern Illinois and southwestern Indiana, is capable of producing ‘New Madrid’ size earthquake events. The epicenter of the zone is located between Mt. Vernon, Illinois, and West Franklin, Indiana (in Posey County).

Since the discovery of this seismic zone, earthquake awareness and preparedness have increased. Geologists in Indiana and Illinois have found liquefaction sites and sand dikes that show evidence of prehistoric earthquakes in the region.

Measuring the Earthquake

There are two ways to describe the size of an earthquake: magnitude and intensity. Magnitude measures the energy released at the earthquake’s source and is determined from seismograph measurements. Intensity measures the strength of shaking produced by the earthquake at a particular site. This table compares the two earthquake characteristics.

It is important to note that as the magnitude measurement increases by one whole number, the size of the earthquake increases by a factor of 10. Therefore, a magnitude 6.0 earthquake is 10 times larger than a 5.0, and a 7.0 earthquake is 100 times larger than a 5.0.

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