Crazy Seismic Question 2

[DaveAtkins]

I am designing a one story, wood framed, "prototype" coffee shop (that is, it can be built anywhere in the country). It turns out that Florida wind loads governed the lateral analysis, but I came across something curious when checking seismic loads.
Unless I am reading the maps in IBC incorrectly, the "worst" seismic situation (based on the highest Ss and S1) is not in California at all, but rather at the New Madrid fault in Missouri. Is this correct?

DaveAtkins

 

[Lion06]

I believe you are correct! Surprising, isn't it?

 

[csd72]

I have never figured out how that works, how you can get a seismic hotspot in the middle of the tectonic plate.

There is a similar situation in the middle of Australia but it is not as active and the population is minimal.

 

[DaveAtkins]

Well, the New Madrid area experienced a major, major earthquake in the 1800's, I think, but as far as I know, nothing since then. I've heard the earthquake in the 1800's changed the path of the Mississippi River.

DaveAtkins

 

[blake989]

There are small ones in that area every few years, Northeast Arkansas experienced one a few years ago......4.0 magnitude if a I remember correctly. I've done some design in Memphis, not fun.

 

[MiketheEngineer]

I am from Missouri and it is HIGH. It has to do with soil conditions (horrible - maybe a bit better than peat in some areas) and of course the fault. There is a very NASTY fault line running thru that area. Starting in about 1810 this area suffered the worst earthquakes maybe ever experienced in the world. Some said they might have been as high as 10 on the Richter Scale!! The quakes and after shocks lasted 2 years!! Tepees fell over!! People fell over!! Log homes collapsed. The Mississippi River ran BACKWARDS for 6 hours as it filled the newly formed Reelfoot Lake!! - from the depression. The quakes rang church bells in Philadelphia - like 900 miles away!!

I haven't done any work in CA - but when you get to Southern Missouri (hell - even St. Louis - at least we have decent soils) its gets nasty and some the Public Works departments have taken it to heart. Unfortunately - most of Missouri is NOT enforced. Sure we are supposed to follow Code - but NO ONE enforces it except in the larger cities and counties.

And the next one is due any day ---- some people say??!!

 

[structuralaggie]

We briefly studied that earthquake in my environmental loads class. There was nor Ricter scale then, so it was all based on the mercalli intensity scale which was measured on historical data. There weren't many people around, and most of who were weren't literate, so the data was hard to come by. At any rate, they estimated that earth quake was the worst ever on the north american continent.

The Mississippi is actually located in a failed rift in the middle of the North American Plate.

 

[prost]

Yes, most of the quakes on the New Madrid fault (near the bootheel of Missouri, USA) are small. There were a series of powerful earthquakes, largest was about 6.5 on Richter scale, during period 1811-1812, over a span of about 2 years. One was so powerful the ground shifted so much so that the Mississippi was temporarily flowing north in sections of the river, finally the riverbed shifted to another spot. There were few people in that area at the time, so that far as we know, no one was killed. I am no seismic expert, so I can guess why it is considered such a hot spot--the earth's crust there is solid rock in many places, making the ground almost ideal for transmitting seismic shock waves; the waves propagated so well that church bells in Boston, Massachusetts allegedly rang when the shock waves reached Boston. You may not have major plates coming together there, but it is obvious the crust is fractured there, as they are able to find and monitor action on the New Madrid Fault.

Lots of links here

http://quake.ualr.edu/public/nmfz.htm

 

[mrMikee]

There aren't many earthquakes in that area and they are small, but there is a fairly consistent activity. I used to check the map linked to below regularly and was a little surprised to almost always find something on the map.

http://earthquake.usgs.gov/eqcenter/recenteqsus/

Regards,
-Mike

 

[haynewp]

I went to a seismic seminar a few years ago and they spent a long time talking about that fault line. It is supposed to be due (in a geological time table sense) for a large earthquake that everyone on the east coast will feel. It does have something to do with the overall soil of the east coast and the way the waves will travel.

 

[ashleyassociates]

I am a student of the NW Tennessee area....heck I am also a large landowner there as well....you are correct in saying this is the most seismically active area in the US. The area is overdue for an earthquake....the seismic coefficient (Sa) for the area that I own property (Dyersburg) is 2.2, as opposed to Montgomery, AL where I live that currently has an Sa of 0.20. Reelfoot Lake was formed is the early 1800's as was alluded to before when the Mississippi river ran backwards for 2 days filling this lake as it formed from the major earthquake of 1802 +/-.

 

[SteelMover]

To add to what is said above...

Indeed the midcontinental plate is ideal for transmitting seismic waves over long distances with little loss in energy. In California along the San Andreas, the local plates are literally just more broken up due to the consistent action along a strike slip fault. So while the earthquake may possibly release more energy out West the plate has higher damping characteristics, leading to smaller zones of influence and lower energy transfer into the structure.

 

[Qshake]

Lots of good information here and as with all areas some of it good some not so good (incorrect).

I am in the state and have performed seismic analysis and design in this area for a number of years including work for a masters degree.

Yes, there are a lot of earhtquakes, many in the 2-3 range, on a weekly basis but it is not the most seismic active area in the world. I stronly believe that title is held by the Pacific 'Rim of Fire' area. Other seismically active areas include eastern Europe, in places like Turkey and of course, in southeast Asia, such as India.

As for major events, the 3 New Madrid earthquakes and their intensity and magnitude, one in 1811(December) and two in 1812 (January and February) were backed into by Otto Nuttli who was a geoophysicist at St. Louis University where many believe the Jesuit Preist there began the science of seismology very early on and had much in the way of newspaper clippings and articles and felt reports (long before they were called felt reports) to the populated areas to the east of St. Louis and the New Madrid area. Other areas of large magnitude earthquake potential beyond California are Alaska, which is the proud owner of the title to the largest magnitude earthquake in the US not in the lower 48, and the 1960 Chile earhtquake both of those are 9.0+. And let's not forget the 1895 Charleston earthquake on the east coast.

There are a lot of unusual things going on in the New Madrid area including a rift zone, embayment and last but not least volcanic activity. Yes, volcanic activity. Thus this truly was a 'hotspot' in geological time. The eastern edge of the Ozark uplift is an area of long dead volcanic activity. The fault zone is thought to begin around Marked Tree Arkansas and extends into Southern Illinios to almost Evansville Indiana. Perpendicular to that arm is another set of seismic activity that is around north of Cape Giradeau, MO. This delineation is the Benton Hills. Contrary to popular belief there is no single fault that has ever been identified and rock in this area is as much as 2000' below the surface....thus the embayment. Naturally the soil is great for farming but crappy for buildings wanting to stand during earthquakes. There are also a number of great examples of sand blows in the area and that is made prominent during crop growing season because most plants don't grow in sandy soil....so there are bare circular areas you can see from the airplane.

Both Memphis and St. Louis are lax in upholding any real seismic code especially for rehabilitations. While I can't speak for Memphis, I can say that St. Louis will abate any tax and code provision to generate development. Thankfully I work on public structures in heavy infrastructure so I do see a lot of seismic analysis and design.

As most have noted the seismic waves don't attenuate well in the central US due to compact soil and rock. As noted in other posts the fractures in rock will not transmit energy well and seismic waves are easily attenuated over small zones. This translates into a much greater period and frequency content for strong ground motion over larger areas. Thus if we ever had an accelogram of this area you would see a much longer time history than that of California.

The area which is blessed with the Mississippi river is also cursed as many of the towns either sit on bluffs over looking the river or down in the flood plains where river traffic helped the towns to grow. Those in the lowlands have significant liquefaction concerns from the sandy soil, highwater table and potential strong ground motion.

The 1811-12 events were noted to have over 2000 aftershocks and did last for a period of 2 years. This is according to several research geologist at Southeast Missouri State Univeristy, one of which Dan Stewart who co-authored a book on the subject.

well that's enough for now, now you know why my moniker is Qhshake!



Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[mrMikee]

Good post Qshake.

Thanks for the interesting info.

Regards,
-Mike

 

[JStephen]

There was a pretty interesting show on a while back about this area. While the 1811-1812 earthquakes are the ones people speak of, they were able to find sand blows that were evidence of earlier major earthquakes, and the guess was every few hundred years the area has a major quake.

 

[vmirat]

Around 1987, I was living in Kokomo, Indiana. During the summer, I was building a ground level deck for the house. While I was sitting on the ground working on my deck, I suddenly felt vibration in the ground. I thought it was a vibratory roller since they were building houses nearby. Later, I discovered that it had been an earthquake centered in the New Madrid zone. That's a distance of about 300 miles. This was the one and only time I have ever experienced an earthquake.

 

[enginerding]

In the UBC codes, California requires higher levels of seismic design than the New Madrid area. This is not so in the IBC codes. I was told that this is due, in part, to a change in the way we design for seismic events. The UBC seismic design is for "life safety" in a 500 year event. The IBC/ASCE design is for "collapse prevention" in a 2500 year event. The New Madrid area is capable of larger earthquakes, but far less frequent than California. Because the frequency of major earthquakes in the New Madrid area was (it has since changed) estimated to be about 600 years, the 500 year design resulted in lower loads than in California. The 2500 year design frequency causes the design to be more stringent in New Madrid.