Earthquakes in Indiana? Yes, despite our intraplate setting, Indiana has the occasional earthquake. Just before New Year’s 2011, at 7:55 AM on Thursday, December 30, 2010, Indiana experienced a small 3.8M earthquake just ESE of Kokomo, Indiana. But if we’re intraplate, why do these earthquakes occur? Well, while most of Indiana’s earthquakes are associated with the Wabash Valley Seismic Zone (WVSZ), this one was likely just due to slipping along a buried fault. The Earth’s crust is not one continuous slab! But the Wabash Valley Seismic Zone is a relatively active tectonic setting just across our Illinois border. Click here for a map. Notice in this map that a 7.1M earthquake could be devastating to areas in Indiana, with expected liquefaction occurring around Vincennes. Look at table 6.4 in your textbook while you look at this map. Central Indiana lies within the VII and VI zones. According to our book, we should be ready to run outside of the building if this level earthquake should occur in the WVSV!
I would like to examine to case studies on earthquakes, to allow you to examine the risks discussed before within the context of an earthquake event. We will take a look at the New Madrid Fault Zone, the Anatolian Fault Zone in Turkey, and the Indian Ocean Tsunami.
New Madrid Fault Zone
The New Madrid Fault Zone runs beneath the Mississippi River Valley between Missouri and Arkansas on the west, and Tennessee and Kentucky on the east. Evansville, IN sits at the northern end of the fault zone. This active fault zone last produced a series of three “great” (i.e., M8 or greater) earthquakes in 1812. The earthquake was strong enough to knock the President out of his bed in Washington D.C., and was strong enough to wake everyone up as far away as Canada and Boston. It caused the Mississippi River to run backwards for several days. A map of these events is available from a Missouri environmental consulting firm.
AutoZone Auto parts store built their corporate headquarters in Memphis,
TN to the earthquake building standards of California. (Photo: USGS).The New Madrid Fault Zone has continued to produce numerous small earthquakes since then (see Figure 6.6 in your text). As I stated earlier, large intraplate earthquakes (within a plate) are rare, but this is the one location where they do occur. Geologists are divided regarding the potential for the New Madrid Fault zone to produce another large earthquake in the near future. If it did, the results would be catastrophic, causing enormous damage in Memphis and St. Louis, and moderate damage in Evansville and southern Indiana, and moderate to minor damage in Indianapolis.
The story of the New Madrid Fault zone starts a billion years ago, when the North American plate tried to split apart, but failed. This left a weak zone within the North American plate. As a result, when the forces of plate tectonics are transferred to the plate interior, the New Madrid area is a natural point for brittle failure to occur.
An earthquake in the Eastern U.S. would be much more damaging than the western U.S. The bedrock geology of the eastern U.S. allows the seismic waves to travel much farther. Although buildings built on bedrock will still remain generally safe, the waves could damage buildings built on unconsolidated sediments at great distances from the epicenter.
Even a much less powerful earthquake (say, M6.5) than those of 1812 could cause significant damage to the Mississippi River Valley and destroy natural gas and oil pipelines that run through the fault zone to supply Indiana. Moreover, rail and interstate bridges in the central U.S. could be closed for months. Some cities in this region, including Evansville, have required new major structures to be built to California standards for resistance to shaking. Large buildings like hospitals, high schools, stadiums, bridges, and office buildings would be most likely to collapse. The AutoZone headquaters in Memphis and the I-155 bridge over the Mississippi river are two large structures built to the standards.
If you would like to know more about the risks associated with this fault, you can read this article which was published in the Riverfront Times (St. Louis). The article will help to reinforce much of what was discussed here and will help you to gain a better understanding of how the risks of faults impact the Midwest in the New Madrid Fault Zone.