Small Earthquake Shakes Southern Illinois

[Texsox]

http://www.breitbart.com/news/2006/01/03/D8ET0RM80.html

 

EQUALITY, Ill.

 

No major damage was reported after a minor earthquake shook areas around this small town in southern Illinois on Monday.

 

The quake struck at 3:48 p.m. and registered magnitude 3.6, according to Rafael Abreu, a geologist at the National Earthquake Information Center in Denver.

 

It was centered near Equality, which is about 120 miles southeast of St. Louis.

 

Abreu said calls from people who felt tremors came from Illinois, Indiana and Kentucky, but the quake was unlikely to have caused any damage.

 

"There might have been some rattling of objects, but not much more," Abreu said.

 

Small earthquakes hit southern Illinois several times a year, said Jim Packett, a meteorologist at the National Weather Service in Paducah, Ky.

[Balta1701]

I swear, Illinois and Indiana have felt more earthquakes than I have since I moved out here...

[NorthSideSox72]

It's amazing to me, but very few people outside that region (and many people inside it) forget about New Madrid. That fault (runs SSW to NNE from NE Arkansas thru to southern IL) is highly likely to produce significant quakes sometime in the next fifty years. Last time it had a big break, it was such a huge quake that it re-directed the Mississippi River and shook bells in Boston (happened around 1811). It was probably the most powerful quake in U.S. history.

 

I lived in Memphis for a few years, and I made sure to have an earthquake rider on my homeowner's policy. That city is completely unprepared for such a thing, and I'm glad I left before it happened (there is only one large building in Memphis built to withstand any sort of tremors: Autozone HQ). If a quake anything close to 1811 happened today, the disaster in Memphis and STL would make Katrina look like child's play.

[YASNY]

It's amazing to me, but very few people outside that region (and many people inside it) forget about New Madrid.  That fault (runs SSW to NNE from NE Arkansas thru to southern IL) is highly likely to produce significant quakes sometime in the next fifty years.  Last time it had a big break, it was such a huge quake that it re-directed the Mississippi River and shook bells in Boston (happened around 1811).  It was probably the most powerful quake in U.S. history.

 

I lived in Memphis for a few years, and I made sure to have an earthquake rider on my homeowner's policy.  That city is completely unprepared for such a thing, and I'm glad I left before it happened (there is only one large building in Memphis built to withstand any sort of tremors: Autozone HQ).  If a quake anything close to 1811 happened today, the disaster in Memphis and STL would make Katrina look like child's play.

 

Those quakes (there were 3, I think) not only rang church bells in Boston, but it changed the course of the Mississippi River, made the river run backward and created Reelfoot Lake in Tennessee. I read some eyewitness accounts and it was pretty amazing. The quakes basically rearranged the landscape in the area. Ponds became mud and fish covered hills. Hills disappeared. Etc.

[whitesoxfan101]

As a person who's been in the middle of a 3.6 earthquake, I can tell you that most of those people probably didn't even notice it as it happened. But yes, the New Madrid fault is always forgotten and sadly it will stay that way until it causes a significant quake like the 1811 one.

[Chisoxfn]

I swear, Illinois and Indiana have felt more earthquakes than I have since I moved out here...

Shutup...your going to jinx it. We are way overdue.

[Balta1701]

Shutup...your going to jinx it.  We are way overdue.

Actually, I think I'd disagree with the statement that "we're way overdue." Roughly speaking, the L.A. Basin should probably expect 1 magnitude 6+ event every 10-20 years. That's for the entire L.A. Basin area...each and every one of those blind thrust faults combined. The last one right here was in 94, Northridge, but there were also 2 major events out in the Mojave in the 90's, so statistically speaking the 90's were pretty active. Doesn't mean that there won't be a magnitude 6 event in the near future, but also doesn't mean there will be one.

 

In terms of the San Andreas...well, there could be one now, or the next one could happen 150 years from now. The remarkable thing about recurrence intervals is that in almost every fault section in the country, they do exist, but they have margins of error on the order of 100% of the recurrence interval. So on the San Andreas, if there was a big quake in 1857, and its recurrence interval is 100-200 years, then you could very well go 50, 100, 150, 200, 250, 300, 350, or 400 years between major movements, entirely based on the mood of the fault. The San Andreas will rupture again, and the odds are it will be within my lifetime, but we're also not "Overdue" for one on it. We would be overdue in about 2100 if there hadn't been one yet, because we would be greater than the estimated recurrence interval.

[juddling]

I remember back in the day at SIU around 89-90 I was up all night cramming for a final when about 4 in the morning....6 or 7 guys wander out into the hall asking what happened??? i was up and couldn't feel a thing and thought they were all crazy. When i got to my final...some other students were talking about the earthquake. I don't remember what it rated on the Richter scale but all i thought was it couldn't have been that bad cause i didn't feel a thing.

 

People down there don't forget the New Madrid fault. The news brings it up all the time down there and every time they get a tremor...it's 2 weeks of news stories about the BIG one and when it is coming.

[Chisoxfn]

Actually, I think I'd disagree with the statement that "we're way overdue."  Roughly speaking, the L.A. Basin should probably expect 1 magnitude 6+ event every 10-20 years.  That's for the entire L.A. Basin area...each and every one of those blind thrust faults combined.  The last one right here was in 94, Northridge, but there were also 2 major events out in the Mojave in the 90's, so statistically speaking the 90's were pretty active.  Doesn't mean that there won't be a magnitude 6 event in the near future, but also doesn't mean there will be one.

 

In terms of the San Andreas...well, there could be one now, or the next one could happen 150 years from now.  The remarkable thing about recurrence intervals is that in almost every fault section in the country, they do exist, but they have margins of error on the order of 100% of the recurrence interval.  So on the San Andreas, if there was a big quake in 1857, and its recurrence interval is 100-200 years, then you could very well go 50, 100, 150, 200, 250, 300, 350, or 400 years between major movements, entirely based on the mood of the fault.  The San Andreas will rupture again, and the odds are it will be within my lifetime, but we're also not "Overdue" for one on it.  We would be overdue in about 2100 if there hadn't been one yet, because we would be greater than the estimated recurrence interval.

The only reason I feel the way I do is I remember when I was a kid we had a few big ones all in what seemed like a short span of years and now its been a long time (although about a year ago we had that couple week span where you could feel a few earthquakes and aftershocks).

 

Hell I don't mind earthquakes as long as they ain't the big one. Far better than getting hammered with hurricanes a few times a year if you ask me (although I guess you can see a hurricane coming).

 

Balta, I'm guessing you know more than I do, but what part of the San Andreas is due. I remember in one of my geology classes my professor was talking to us about how they can semi predict where the quakes are going to occur since they kind of happen in a certain pattern (after a quake the stress is relieved from one area and I guess it starts pushing more on another area which needs to be relieved). That sound about right?

[Balta1701]

Balta, I'm guessing you know more than I do, but what part of the San Andreas is due.  I remember in one of my geology classes my professor was talking to us about how they can semi predict where the quakes are going to occur since they kind of happen in a certain pattern (after a quake the stress is relieved from one area and I guess it starts pushing more on another area which needs to be relieved).  That sound about right?

That can happen, but it doesn't always happen. Sometimes a quake on one fault could put stress on another local fault, but that same motion could relieve stress on another fault which was closer to breaking.

 

When a fault ruptures, there are always areas relative to that fault which are put under compression, and others that are put under extension. There is a ton of geometry and rock mechanics involved in determining what exactly will be the results of a quake of a particular strength and direction on a particular fault. We're just now starting to get the computing power where we can take intelligent looks at such questions.

 

There are plenty of examples of 1 earthquake setting off another - the Dec. 26th Sumatran quake clearly was a triggering event for the 2nd quake a few months later, for example. But if a quake happened and relieved stress on a fault, thus delaying a quake, we'd never really know about it for sure, because you can't really quantify a non-event, so I can't give you an example of that. Let's just say that both are possible, and the actual result will depend on the exact circumstances.

 

Edit, oh and to answer your "What part of the san andreas is due" question which I didn't read the first time through...the 1857 rupture along that fault was an absolute monster for that fault. It started off up near Parkfield and ruptured the fault to some degree all the way through the Mojave. However, the displacements were not constant along the entire rupture - roughly 3 m. in the Mojave and as much as 9 m up north of the Transverse ranges.

 

In general, I think the recurrence interval of that whole section south of the Parkfield section is something in the neighborhood of 150-200 years, which is why some people are starting to worry about it - because technically it is due, and there's probably a 50/50 chance it'll undergo a major rupture sometime in our lifetimes, and probably a 98% chance that one will happen before your grand children pass away, barring things like nuclear war.

 

The section north of that, the Parkfield section, is a really interesting one, in that it actually seems to have one of the most accurate recurrence intervals of any fault in the world. A few decades ago, geologist predicted that by the year 2010, there would be a magnitude 6+ quake along that fault. They actually heavily instrumented that section of the fault in order to observe it. The rupture happened about a year ago. That section of the SA has kept to a much tighter recurrence interval than any other section of the SA.

 

The sections north of there ruptured in 1906 in a moderately famous event, but the SA north of Parkfield is not the only fault line to be worried about up there. They Heyward fault, which interestingly enough runs right across the Bay Bridge and right through the football stadium @ UC Berkeley (you can actually see it in the walls I'm told) is probably roughly due. This is the one which has caused them to rapidly try to retrofit the golden gate bridge, and why they are spending a ton of money on a seismically survivable Bay Bridge.

 

So...the Sections of the SA south of Parkfield are starting to approach the time when you'd call them "Due". Most estimates give numbers like 20-30% probability of a quake in the next 20-30 years somewhere along that section. The problem of course is that we don't know which part of that section will rupture, or how big the rupture will be. 1857 was a monster in that it ruptured sections all along the fault which normally don't move together. There is the possibility for a number of quakes along different parts of that fault, most of which will probably experience 1 event during the next 100-200 years.

Edited January 4, 2006 by Balta1701

[WilliamTell]

As a person who's been in the middle of a 3.6 earthquake, I can tell you that most of those people probably didn't even notice it as it happened.  But yes, the New Madrid fault is always forgotten and sadly it will stay that way until it causes a significant quake like the 1811 one.

 

Exactly, I remember hearing about it for the first time in elementary school thinking that earthquakes only happened in California, haha. But people will learn about it when it happens. That's the way most things go.