There will be noticeable earthquakes in U.S., Illinois in future - Quad-Cities Online: Editorials

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There will be noticeable earthquakes in U.S., Illinois in future

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Posted: Friday, January 22, 2010 2:52 pm

You can't predict earthquakes, according to Robert Bauer, engineering geologist with the Illinois State Geological Survey. "Predict means time and place and magnitude," he said. "Earthquakes occur throughout our state and large earthquakes can be felt over many states, so yes, there will be noticeable earthquakes in the future." There have been some noticeable earthquakes in the past few years in Illinois.

There was a strong earthquake in 1968 in southern Illinois that was the strongest felt since 1895. The July 10, 1987 earthquake near Olney was a magnitude of 5.1 even,t according to Mr. Bauer. That earthquake was felt by many living in the Quad-Cities. On Sept. 2, 1999 there was a magnitude 3.5 earthquake in Northern Illinois centered near Dixon. That earthquake was between the Peru Monocline and the Sandwich Fault Zone. On Jun. 28, 2004 an earthquake of roughly a little less than 4.5 occurred about 60 miles west of Chicago in LaSalle County. "The April 18, 2008 magnitude 5.4 earthquake near Mt. Carmel was felt in 28 states and Canada," said Mr. Bauer.

During the seven days preceding Jan. 18, there were 918 earthquakes in the U.S. and adjacent areas. (It should be noted here that the U.S. Geological Survey has not used the Richter scale as a measurement of earthquakes for a long time.) Most were small earthquakes. The closest to the Quad-Cities in Illinois were at Burlington and Sandwich. Areas in Oklahoma experienced a 4.0 earthquake. There was a 4.1 in the San Francisco Bay area on Jan. 7 and an offshore earthquake in Northern California on Jan. 10 of 6.5 magnitude. California has about 10,000 earthquakes per year. Most of them are too small to be felt. The U.S. Geological Survey Earthquake Hazards Program has an animated earthquake map for seven-day periods. You can see the earthquakes and their intensities appear on maps of the U.S. or the world has they occurred during that period.

The largest intensities for Jan. 12 appear in the Haiti region.

The USGS shows eight earthquakes in the Haiti Region on Jan.12 of varying degrees. The first quake was of 4.5 magnitude. The last was 7.0 magnitude.

"The fault cutting east-west through Haiti is a boundary between two plates just like the San Andreas Fault," explained Mr. Bauer. "The plates are sliding past each other. Earthquake scientists knew there was a probability of an earthquake of this magnitude but cannot predict when or where specifically along the fault. The fault goes all the way through Jamaica.

"On our west coast for the boundary between two plates scientists can forecast probability of some magnitudes occurring over a few decades," said Mr. Bauer. "This can be done since the two plates slide past each other at known rates and the scientists look at segments of the fault that are locked up and are not having any earthquakes. The amount of energy locked up over the length of time of nearly no earthquakes let scientists estimate the energy-magnitude that is locked up. We don't have that setting for the rest of the U.S.," he said.

"What we do at the Illinois State Geological Survey is to produce maps on how the soils resting on the bedrock will amplify earthquake ground motions. These maps are used by other agencies -- U.S. Geological Survey and the Mid-American Earthquake Center to produce estimates of how much damage from various earthquakes can be expected.The latest report just came out for a magnitude 7.7 event on the New Madrid faults which are near the southern tip of Illinois," said Mr. Bauer.

There is a section on the USGS website for working with the probabilities of future earthquakes of at least 5.0 magnitude (http://earthquake.usgs.gov/earthquakes/step/). The site uses the 2008 USGS National Seismic Hazard Mapping Project (NSHMP). The region of model validity is the conterminous (lower 48 states) USA and Alaska.

When I went to the site I put in Port Bryon's zip code and worked with a 10 year and a 50 year time frame. The results showed zero chance of a 5.0 earthquake in the area during those times. Other areas won't be so lucky. The San Francisco Bay area has a probability of at least a 5.0 earthquake in the next 10 years. It has a 61 percent chance of having a 6.7 earthquake within 30 years. Cairo, Ill., has a 12 percent chance of a 5.0 in the next 25 years. The probability scale on the side of the map that comes up after you have put in your information is just the integer number, according to Mr. Bauer. "You can turn those numbers into percentages by multiplying by 100 so the top of the scale is 100 percent."

Since scientists have predicted the probability of a massive earthquake in Haiti for years, I asked Mr. Bauer why the relief agencies weren't better prepared for one. "Aid agencies are typically not working with mitigation effects from natural hazards ahead of time," he replied.

(More on New Madrid faults next week. There are three. And there are massive plans for the mitigation effects for a magnitude 7.7 event there. )

Marlene Gantt of Port Byron is a former Rock Island school teacher.

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