Mild earthquake hits Midwest

[PenforPrez]

Did anybody in the Midwest feel the earthquake this morning?

A 5.2 earthquake centered northwest of Evansville, Indiana shook the Midwest shortly after 4:30 Central this morning. One building partially collapsed in Louisville, and part of the Indianapolis airport was briefly evacuated. Buildings shook in the Chicago Loop, according to CNN.

http://www.cnn.com/2008/US/04/18/illinois.earthquake/index.html

It woke me up; I thought it was the refrigerator because shakes and makes noise. :rolleyes: Minor structural damage was reported here in St. Louis, especially in older neighborhoods in the city. It was felt pretty strongly here.

This is St. Louis' wake-up call, earthquake-wise. Another 8.1 earthquake (such as the earthquakes that occurred on the New Madrid Fault in 1811-12) would probably level St. Louis and Memphis. We're not ready at all.

Paul

[PenforPrez]

Had a nice little aftershock about 15 minutes ago. I was with the boss, and she started hyperventilating. :rolleyes:

Paul

[vinsanity]

I heard that for some reason, the flatter geography of the midwest would make buildings more susceptible to structural damage than a similar-strength Cali quake.

I'm not sure I remember the explanation for that, though.

[steph78]

I heard that for some reason, the flatter geography of the midwest would make buildings more susceptible to structural damage than a similar-strength Cali quake.

I'm not sure I remember the explanation for that, though.
You'd think that after four semesters of grad school taking courses like structural dynamics and earthquake engineering that I'd be able to explain this in simple terms...but it's kind of complicated and my memory is getting fuzzy. Basically, it's a different kind of fault system in the midwest than there is in California. The density of the soil also plays a big part in how the waves propagate through the ground away from the epicenter - when you have softer soil the waves can get amplified (this is why the 1989 earthquake in San Fran caused so much damage particularly in the areas down near the water that were built on parts of the harbor that had been filled in with dirt).

Also, little-known fact, but there are actually MORE seismic events in the midwest during any given year than there are on the west coast...but most of them are low magnitude so no one notices them. On occasion there are whoppers, though (the New Madrid quakes of the early 1800s that Pen mentioned). Because of this, anything built around Memphis today has to be designed to withstand a ridiculous seismic event...but the building code has only required this substantial seismic design for a few decades...and there are a LOT of older buildings that wouldn't even come close to meeting today's building code.

[wordsmith]

Also, little-known fact, but there are actually MORE seismic events in the midwest during any given year than there are on the west coast...but most of them are low magnitude so no one notices them. On occasion there are whoppers, though (the New Madrid quakes of the early 1800s that Pen mentioned).


Yep...there are actually a lot of small quakes around the New Madrid fault, and further north, too, along various monoclines, anticlines, and synclines. They're just very rarely large enough to register or be felt. Where I grew up in Northern Illinois, you only get one large enough to feel once or twice a century. We had one in June of 2004, the only one I've ever felt, and even at that rate, it was small, as seismic events go. It was enough to wake me up (it happened at 1 a.m.), but I thought it was a train derailment until I looked out at the tracks I lived near, and saw that nothing had happened. There was also one in 1999, although I was out of state at college at the time, so I didn't feel it, and most people who did feel it thought it was a quarry blast from a neighboring stone quarry.

This (http://www.isgs.uiuc.edu/research/earthquake-hazards/pdf-files/eq-fct-nrth.pdf) talks about it a little.

[NewMrs.]

I work for an insurance company that provides earthquake coverage for some of our policyholders. Before we provide quotes for this coverage we will run a report to see if the policyholder is in one of our "hot spots." The New Madrid fault is a HUGE hot spot. I don't think that I have ever seen us provide earthquake coverage to any policy holder who was located anywhere close to the New Madrid zone.

[steph78]

I work for an insurance company that provides earthquake coverage for some of our policyholders. Before we provide quotes for this coverage we will run a report to see if the policyholder is in one of our "hot spots." The New Madrid fault is a HUGE hot spot. I don't think that I have ever seen us provide earthquake coverage to any policy holder who was located anywhere close to the New Madrid zone.
Ha - I bet you use the same USGS seismic hazard maps that I do in my work! They are probability-based, using the couple centuries of earthquake data that we have. Memphis and Charleston, SC are the two "hot spots" that I have to deal with the most often (my company is based out of Atlanta and most of our jobs are in the southeast.)

[PenforPrez]

I work for an insurance company that provides earthquake coverage for some of our policyholders. Before we provide quotes for this coverage we will run a report to see if the policyholder is in one of our "hot spots." The New Madrid fault is a HUGE hot spot. I don't think that I have ever seen us provide earthquake coverage to any policy holder who was located anywhere close to the New Madrid zone.

Missouri ranks third in earthquake insurance coverage, but a lot of insurers now won't touch that area.

[wordsmith]

Interesting article (http://news.yahoo.com/s/livescience/20080418/sc_livescience/scientistsevenbiggerquakecouldhitmidwest) posted today re: midwestern earthquakes.