What a Relief!

new-madrid-fault

New Madrid Fault.

I don’t have the shakes any more!  Today’s Kansas City Star reports that the New Madrid Seismic Zone in the boot heel (southeast) area of Missouri may be quieting down, which is very good news.  A series of earthquakes in the New Madrid seismic zone from 1811-1817 could be felt as far away as Quebec.  One of the earthquakes woke people as far away as Pittsburgh, Pennsylvania, and Norfolk Virginia.  The few people in Kansas City at that time were tossed around in their bedrolls like popping corn.

So many cable television channels are devoting lots of airtime to possible disaster stories — asteroids, mega volcanoes, gamma ray bursts, magnetic pole flipping, climate change, you name it, it’s coming at us.  The news of real events isn’t comforting, either, with earthquakes, tornadoes, hurricanes, floods and fires.  It’s good that we can relax a little about one possible catastrophe.

At the bottom is an explanation from the U.S. Geological Survey of the New Madrid Fault and the earthquakes it has unleashed. You can also read a lot more about the New Madrid Seismic Zone on Wikipedia by clicking here: New Madrid Fault.  Also check out the post by Gallivance noting a book about the New Madrid fault and the Mississippi River, featuring herds of squirrels on the march, a bright, forked comet and pirates!  A Comet, An Earthquake, And The End of The River Pirates

Comparison: the 1895 Charleston, Missouri, earthquake in the New Madrid seismic zone with the 1994 Northridge, California, earthquake. Red indicates area of structural damage, yellow indicates area where shaking was felt.

Comparison: the 1895 Charleston, Missouri, earthquake in the New Madrid seismic zone with the 1994 Northridge, California, earthquake. Red indicates area of structural damage, yellow indicates area where shaking was felt.

The New Madrid Fault Poses Little Threat, Scientists say

(Kansas City Star, April 13, 2009)

The New Madrid fault zone that unleashed a series of violent earthquakes in the early 19th century may be quieting down, two scientists say.

The fault line, which stretches into southeast Missouri, shows no signs of building up the stresses needed for the quakes many seismologists expect to someday rock the region again, the scientists say.

The researchers from Purdue and Northwestern universities said that may mean the little-understood New Madrid Seismic Zone is shutting down or that seismic activity is shifting to adjacent faults in the country’s midsection.

Other scientists call those conclusions premature.

 U.S. Geological Report on the New Madrid Earthquakes 1811-1812

Shortly after 2 o’clock on the morning of December 16, 1811, the Mississippi River valley was convulsed by an earthquake so severe that it awakened people in cities as distant at Pittsburgh, Pennsylvania, and Norfolk, Virginia. This shock inaugurated what must have been the most frightening sequence of earthquakes ever to occur in the United States. Intermittent strong shaking continued through March 1812 and aftershocks strong enough to be felt occurred through the year 1817. The initial earthquake of December 16 was followed by two other principal shocks, one on January 23, 1812, and the other on February 7, 1812. Judging from newspaper accounts of damage to buildings, the February 7 earthquake was the biggest of the three.

In the Mississippi and Ohio River valleys the earthquakes did much more than merely awaken sleepers. The scene was one of devastation in an area which is now the southeast part of Missouri, the northeast part of Arkansas, the southwest part of Kentucky, and the northwest part of Tennessee. Reelfoot Lake, in the northwest corner of Tennessee, stands today as evidence of the might of these great earthquakes. Stumps of trees killed by the sudden submergence of the ground can still be seen in Reelfoot Lake.

Uplift of over 3 meters was reported at one locality several hundred kilometers to the southwest of the epicentral zone where a lake formed by the St. Francis River had its water replaced by sand. Numerous dead fish were found in the former lake bottom. Large fissures, so wide that they could not be crossed on horseback, were formed in the soft alluvial ground. The earthquake made previously rich prairie land unfit for farming because of deep fissures, land subsidence which converted good fields to swamps, and numerous sand blows which covered the ground with sand and mud. The heavy damage inflicted on the land by these earthquakes led Congress to pass in 1815 the first disaster relief act providing the landowners of ravaged ground with an equal amount of land in unaffected regions.

Some of the most dramatic effects of the earthquakes occurred along rivers. Entire islands disappeared, banks caved into the rivers, and fissures opened and closed in the river beds. Water spouting from these fissures produced large waves in the river. New sections of river channel were formed and old channels cut off. Many boats were capsized and an unknown number of people were drowned. There are some graphic eyewitness descriptions in contemporary newspapers made by the boatmen caught on the Mississippi River near Little Prairie, not far from the present-day town of Caruthersville, Missouri.

Although the total number of deaths resulting from the earthquakes is unknown, the toll probably was not large because the area was sparsely populated and because the log cabin type construction that was prevalent at that time withstood the shaking very well. Masonry and stone structures did not fare so well, however, and damage to them was reported at distances of 250 kilometers and more. Chimneys were thrown down in Louisville, Kentucky, about 400 kilometers from the epicentral area, and were damaged at distances of 600 kilometers.

Although it is impossible to know the precise epicentral coordinates of the earthquakes, contemporary accounts of the events suggest that the epicenter of the December 16 shock was close to the southern limit of the area of sand blows. The epicenter of the February 7 shock was closer to the northern limit of the sand blows, near the town of New Madrid, Missouri. There is not sufficient information about the second main shock on January 23 to know its epicenter. Thus the common practice of calling the entire earthquake sequence the “New Madrid earthquakes” is somewhat misleading. From what is known about the present seismicity of the area, it can be inferred that their focal depths were probably between 5 and 20 kilometers. The fault plane — or planes — on which the Earth rupture occurred are inferred to have had a NNE – SSW strike direction, more or less parallel to the Mississippi River.

The felt areas of the three largest earthquakes were extremely large. They extended south to the gulf coast, southeast to the Atlantic coast, and northeast to Quebec, Canada. The western boundary cannot be established owing to a lack of population. However, it can be estimated that the area of intensity V or greater effects was approximately 2½ million square kilometers. This can be contrasted with the 1906 San Francisco earthquake, for which the area of intensity V or greater effects was about 150,000 square kilometers. The large difference in felt areas between the Mississippi Valley and San Francisco earthquakes, which had approximately the same magnitude and focal depth, can be explained by differences in attenuation of earthquake waves traveling through the Earth’s outer crust. The crust in the Western United States tends to “soak up” earthquake energy, whereas in the central and eastern regions of the country the seismic energy experiences a much lower rate of absorption. Quantitative studies of recent earthquakes confirm this explanation.

Invariably the three questions that are asked when one describes the 1811-12 earthquakes are (1) could such earthquakes occur again, (2) if so, when will they happen, and (3) what would be the effect of such an earthquake if it were to occur now?

The answer to whether such earthquakes can happen again is yes. Field studies by M. L. Fuller of the United States Geological Survey published in 1912, provided topographic and geological evidence of large magnitude earthquakes predating the 1811-12 sequence. This evidence included ground cracks as large as any caused by the 1811-12 earthquakes in which trees fully 200 years old grew from the bottoms and slopes. Indications of more recent faults and of sandstone dikes filling old earthquake cracks were also found by Fuller. Futhermore, studies of the seismicity since 1812 show that the region is behaving in a manner more or less typical of active seismic zones.

The second question — when will another great earthquake happen — is much more difficult to answer. Extrapolation of magnitude and intensity recurrence curves is presently the only method of prediction available, but this is full of difficulties because the earthquake record covers far too brief a period of time and because earthquakes do not follow an exact cyclical pattern. Although extrapolations of recurrence curves for the region indicate return periods — depending on the investigator — of anywhere between about 400 to 1,000 years for an earthquake the size of the December 16, 1811 event, there is a possibility that such an earthquake might occur as soon as next year or as late as several thousand years hence.

It is easier to speculate on the effects that an earthquake the size of the 1811-12 series would have if it were to occur today than it is to predict when it will happen. In the epicentral area, a repeat of the kind of surficial damage experienced in 1811-12 can expected. However, this would result in a much greater loss of life and property today because of the much larger number of people and man-made structures in the region than were there 162 years ago. Even more awesome is the size of the area that would be affected. The dispersion of the surface waves, combined with their low attenuation, would result in a large amplitude, long duration sinusoidal type of motion with periods in the same range as the natural periods of tall buildings. Although damage to buildings located outside of the immediate earthquake zone would be mostly nonstructural in character, the monetary amount should be expected to be very large. The emotional and psychological effects of a large earthquake in the central part of the country would probably also be considerable, particularly if the earthquake had a long aftershock pattern as the 1811-12 sequence did.

Perhaps the greatest danger of all arises from the sense of complacency, or perhaps total ignorance, about the potential threat of a large earthquake. The frequency of occurrence of earthquakes the size of those that took place in 1811-12 is very low; however, continuing minor to moderate seismic activity in the central Mississippi Valley area is an indication that a large magnitude tremor can someday be expected there again.

Earthquake Information Bulletin, Volume 6, Number 2, March – April 1974, by Otto W. Nuttli.

Advertisements

5 Comments

Filed under History, Kansas City, Life, Personal, Science

5 responses to “What a Relief!

  1. so much for us East Coasters feeling smug and safe

  2. alwaysjan

    It was only after I’d moved to Los Angeles that I heard about the New Madrid Fault. Whew! Dodged that one. But, we were here for the Northridge quake. Holy crap! My entire family slept in our clothes in one bed for the following week ready to evacuate on a moment’s notice.

    I often drive by Caltech, where all those seismologists sit just waiting for things to shake, rattle, and roll. Just talking about this gives me flashbacks. I think I better go check the batteries in the flashlights.

  3. I have been to New Madrid plenty of time (pass through I mean) did not know this.

  4. I live in an area affected by the activity of the NMSZ. Not too many months ago my husband and I were awakened in the middle of the night by a tremor. The next day, another one, was felt with much disconcertion on the 14th floor of the office building where my office is located. It was all anyone could talk about for over a week.

    Somewhat related, Robert Penn Warren’s verse novel Brother to Dragons includes the 1811 earthquake that formed Reelfoot Lake; Warren uses it as a vehicle for action within the story.

  5. Interesting post Catherine, and thanks very much for the link to our post on the 1811 earthquake. You know that I love this stuff, and it’s always good to see others take an interest (I know if I lived in the area, I’d take an interest for sure.) As you may have gathered from your research, earthquakes are notoriously difficult to predict. And from what I’ve read, the USGS still considers the NM area a high risk area for destructive earthquakes.

    This is a quote from the USGS site: “There is broad agreement in the scientific community that a continuing concern exists for a major destructive earthquake in the New Madrid seismic zone. Many structures in Memphis, Tenn., St. Louis, Mo., and other communities in the central Mississippi River Valley region are vulnerable and at risk from severe ground shaking. This assessment is based on decades of research on New Madrid earthquakes and related phenomena by dozens of Federal, university, State, and consulting earth scientists.”

    Ultimately, it depends on which set of experts one believes. Either way, if I lived in the area I’d have a plan in place and be prepared. There’s no reason to panic, but there certainly is no reason to not be prepared. Thanks again for the link. ~James

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s