Catchy title right? lol
When you hear about an earthquake, what’s the first thought that pops into your head? California, right? West Coast, right? Far the hell away from me as possible, right? Well you’d like to think so. Most people aren’t aware of the fact that the Midwestern United States has been known to be a seismically active region. Granted, there aren’t as many earthquakes there as there are west of the Rocky Mountains, but there are still some.
This past week, I have been hearing about earthquakes that have struck my old home state of Illinois. When I heard about this, I immediately jumped up and started websurfing. As a person that has been studying earthquakes since the 6th grade, I was immediately excited but equally nervous. Lemme just start off by saying that I am NOT a seismologist nor do I work for the USGS (United States Geological Survey). I’m just an average dude that likes to read about earthquakes and plate tectonics.
For those of you that can’t understand these articles about the earthquake on April 18th and/or April 21st over at the USGS’s website or just don’t feel like clicking the link, lemme give you some back info via a block quote courtesy of the USGS.
This large region borders the much more seismically active New Madrid seismic zone on the seismic zone’s north and west. The Illinois basin – Ozark dome region covers parts of Indiana, Kentucky, Illinois, Missouri, and Arkansas and stretches from Indianapolis and St. Louis to Memphis. Moderately frequent earthquakes occur at irregular intervals throughout the region. The largest historical earthquake in the region (magnitude 5.4) damaged southern Illinois in 1968. Moderately damaging earthquakes strike somewhere in the region each decade or two, and smaller earthquakes are felt about once or twice a year. In addition, geologists have found evidence of eight or more prehistoric earthquakes over the last 25,000 years that were much larger than any observed historically in the region.
Earthquakes in the central and eastern U.S., although less frequent than in the western U.S., 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 100 km (60 mi) 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 500 km (300 mi) from where it occurred, and sometimes causes damage as far away as 40 km (25 mi).
Earthquakes everywhere occur on faults within bedrock, usually miles deep. Most bedrock in the Illinois basin – Ozark dome region was formed as several generations of mountains rose and were eroded down again over the last billion or so years.
At well-studied plate boundaries like the San Andreas fault system in California, often scientists can determine the name of the specific fault that is responsible for an earthquake. In contrast, east of the Rocky Mountains this is rarely the case. The Illinois basin – Ozark dome region is far from the nearest plate boundaries, which are in the center of the Atlantic Ocean, in the Caribbean Sea, and in the Gulf of California. The region is laced with known faults but numerous smaller or deeply buried faults remain undetected. Even the known faults are poorly located at earthquake depths. Accordingly, few earthquakes in the region can be linked to named faults. It is difficult to determine if a known fault is still active and could slip and cause an earthquake. As in most other areas east of the Rockies, the best guide to earthquake hazards in the Illinois basin – Ozark dome region is the earthquakes themselves.
Back in 1811-1812, the adjacent New Madrid Seismic Zone was the setting for 4 major earthquakes which ranged from 7.0-8.2 on the Richter Scale. These earthquakes were strong enough to shake church bells all the way out in Boston, Massachusetts. Another thing about earthquakes is that in some cases, major quakes are preceded by foreshocks (smaller earthquakes that could occur in succession months, weeks, or days before a large earthquake), and these foreshocks could also be located within a totally different seimic zone or fault system than that of a major earthquake. The major reason why the New Madrid earthquakes did not cause much damage was because of the fact that the area surrounding the earthquakes was sparsely populated at the time. As we all know, this is far from the truth today. The cities of St. Louis, Missouri, Chicago, Illinois Louisville, Kentucky and other major cities are at a far greater risk of being affected if a major earthquake were to strike this area today.
I’m definitely not trying to scare anyone to death, or to have anyone home all day bolting their belongings to their bookshelves which in turn would be bolted to the walls and floors. I’m just trying to inform people (since our govt. loves to keep us informed about things…) of what could happen. Granted the chances are not great, but anything is possible. For more info on earthquakes, check out the links below.
Random Thought of the Moment: “Dammit! I’m late for class again….smh”
The Song of the Moment: “Paper Planes” by M.I.A.