Did you feel that? Probably not, but deep beneath your feet the ground is shaking. In fact, due to Memphis’ proximity to the New Madrid fault, all of us are standing on shaky ground almost every day.
In recent months, earthquakes have spawned tsunamis and volcanic eruptions around the globe. But what will happen if a big one hits the Mid-South? No one can predict with certainty the effects of a major quake, but local experts have a pretty good idea, and it’s not pretty.
The New Madrid seismic zone extends 150 miles south from Cairo, Illinois, through New Madrid, Missouri, to Marked Tree, Arkansas. It reaches into Kentucky and Tennessee and crosses the Mississippi River in three places. The zone averages almost a quake a day, and scientists say it poses the greatest earthquake risk east of the Rocky Mountains.
Three of the largest earthquakes in North American recorded history occurred in the New Madrid zone during the winter of 1811-1812. During a three-month period, a series of more than 100 earthquakes, the most severe estimated at magnitudes of at least 8.0 on the Richter scale, rocked the central United States and changed the landscape of the area. Although no actual seismic measurements were made, the resulting destruction has given scientists a good indication of the earthquakes’ strength and duration.
Since then, two other damaging earthquakes have occurred in the New Madrid zone: a magnitude 6.4 near Marked Tree in 1843 and a magnitude 6.8 near Charleston, Missouri, in 1895. In March 1976, a magnitude 5.0 occurred, followed by a 4.8 in September 1990. Because scientists cannot predict or prevent earthquakes, they rely on history and earthquake cycles to determine future quake possibilities. Quakes up to a magnitude of 6.5 have a reoccurrence rate of 75 to 100 years. Those 7.5 and above occur approximately every 500 years. Scientists estimate that the probability of a magnitude 6.0 or larger quake occurring in the next 50 years is between 25 and 40 percent.
Making Forecasts
When the magnitude 9.0 earthquake occurred in Southeast Asia on December 26th, it set off a tsunami that killed more than 286,000 people and displaced millions more. Media reports focused on the tsunami and for the most part ignored the seismic activity responsible for the killer wave. Here in the New Madrid zone, a tsunami is not possible, of course, but damage from a major earthquake could still be devastating.
Jim Wilkinson coordinates the Central United States Earthquake Consortium (CUSEC), headquartered on Holmes Road. The organization’s purpose is to protect and prepare the eight-state area comprising the New Madrid seismic zone. CUSEC partners with several federal and local emergency management agencies. “We don’t have to worry about a tsunami here, but earthquakes are a very real situation,” says Wilkinson. “We know, based on historical evidence and science, that we’re due for a damaging earthquake. But the reality is that because we haven’t had one in so long, it’s not a priority in people’s view. It doesn’t get a lot of press, but we are facing a situation in which the clock is ticking.”
Earthquakes can be felt when they reach a magnitude of 3.0. Minor damage, such as dishes rattling off kitchen shelves, occurs at 4.0 to 5.0 magnitude. Chimneys and eaves and overhangs can fall during a magnitude 6.0. And quakes reaching a magnitude of 8.0 or larger are considered “great earthquakes” and can cause large splits in the ground, burst utility lines, flooding, and other severe damage. Although the New Madrid zone produces a quake a day, most are too small to be felt. CUSEC scientists monitor this minor seismic activity for signs of possible larger eruptions. The New Madrid zone is not as active as the California fault zones, which can produce several quakes a day, but because of its composition and location, it can be equally dangerous.
The Center for Earthquake Research and Information (CERI) at the University of Memphis is an organization of seismologists and geologists that also monitors and records activity of the New Madrid fault system. “Unlike the fault along the California coast, which is visible to the naked eye, we can’t see the [New Madrid] fault because it is buried deep below layers of sediment,” says geologist Eugene Schweig. “Quakes are occurring along the Mississippi Valley and the river is constantly overflowing and dumping more and more layers of sediment on top of the [seismic zone]. [In California] scientists study the zone and pick up rocks from the fault and make pretty accurate determinations. Here, all we have telling us that there is an earthquake threat is the earthquakes themselves [after the fact.]”
The old, hard rock and sediment of the New Madrid fault carries seismic waves farther than in California quakes, which travel through softer, more newly formed rocks. Quakes of similar magnitude would probably produce greater damage in the New Madrid area than in California. “Quakes in California can be compared to hitting the side of a sandbox,” says Schweig. “The waves just don’t travel very far through that sand. But in the New Madrid zone, it’s like hitting the end of a metal pipe. The waves shoot to the other end.”
A geologist with the U.S. Geological Survey (USGS), housed at CERI, Schweig works with engineers, scientists, and emergency managers to provide information on seismic activity. Schweig says scientists estimate the frequency of earthquakes by examining artifacts or geology and charting small quakes. “We can’t predict earthquakes, so we focus on earthquake forecasting,” he says. “There is a relationship between large and small earthquakes everywhere in the world. If you had a good idea of the number of small ones, you could predict the number of larger ones. But what we’ve done is examine the effects of past earthquakes from things buried out in fields.” CERI and the USGS have determined that quakes similar to those in 1811-1812 also occurred in 900 A.D. and 1,500 A.D., confirming the average reoccurrence rate of 500 years.
CUSEC studies estimate that potential losses from future earthquakes of 5.5 or greater would be significant in the central United States because of the high population density of cities such as St. Louis and Memphis. There are a large number of structures in the zone that are not designed to withstand earthquakes. The presence of thick sediments will amplify the quakes, leading to destruction that would impact an area 10 times larger than an equivalent California quake.
In the New Madrid zone, quakes are most often felt by people in rural areas, where automobiles and machinery and pavement are less likely to impede or resemble vibrations. The latest notable earthquake in the area occurred last Friday in Enola, Arkansas. It measured 2.7 on the Richter scale. “With each increase of one magnitude, the amount the ground moves increases 10 times,” says Schweig. “And the amount of energy released, or the strength of the quake, increases about 32 times.”
The size of an earthquake also depends on the type of soil in the zone. The soft soil of the Memphis bluffs, for example, offers advantages and disadvantages, says Schweig. For short seismic waves, which affect single-story dwellings such as houses, soft soil is better because it reduces the damaging vibrations. Longer waves, which affect multi-story buildings and bridges, cause more damage when traveling through soft soil. (The USGS and CERI are currently completing surface maps based on soil composition in Shelby County.)
“We don’t need to be afraid of an earthquake, but we need to be prepared,” says Schweig. “A devastating quake is quite unlikely during your lifetime, but as we found out with the tsunami — which was an event which may have been more unlikely than a New Madrid quake — we see it can happen. Earthquakes are low probability and high consequences.”
Reducing the Risk
Seismologists say earthquakes don’t kill people, buildings kill people. In the New Madrid seismic zone, scientists are well aware of this mantra and are taking measures to reduce the risk of damage from a high-magnitude earthquake.
In California, where earthquakes are more frequent than in in the New Madrid area, city governments began instituting seismic building codes as early as the 1950s.
Memphis and Shelby County governments have been slow to catch up. According to Wilkinson, local codes did not include seismic requirements until the early 1990s. The CUSEC sees seismic codes as the most important step local governments can take to minimize damage and casualties.
“Under the old building code, the costs to modify buildings to meet seismic regulations was about 2 or 3 percent, in addition to normal building costs,” says Wilkinson. “A lot had to do with whether the building was designed correctly on the front end, instead of retrofitting the building, which can get expensive.”
A new, universal (and international) code is expected to be completed soon. For West Tennessee builders that has been a point of contention. “Costs to comply with the new code have been estimated by builders to be as high as 40 percent [in addition to building costs],” says Wilkinson. “But until we have a tangible study that gives specific costs, we’ll just be throwing numbers around.”
Some companies, such as AutoZone, have already built to higher earthquake-resistant standards. The company’s downtown office building rests on shock absorbers. The building’s base is constructed to allow for sway.
The National Civil Rights Museum has retrofitted its original structure to comply with seismic codes and constructed its expansion building to even more stringent codes.
CUSEC is working with city governments to upgrade bridges, including the I-40 bridge over the Mississippi River. They have also created a team of engineers and architects to inspect buildings after a catastrophe. CUSEC representatives also work with builders and contractors on cost-effective approaches to reduce damage.
“In my opinion, the public sector is aware of the potential for disaster, but a lot of individuals in the area do not have it on their radar,” says Red Cross spokesman Rick Roberts. The Mid-South chapter of the Red Cross has long offered disaster training as well as first aid and CPR. In March, the organization will launch its “Get Ready, Mid-South” initiative, designed to prepare residents for disasters such as terrorism, tornadoes, and earthquakes. “The same items that we were sending to tsunami victims would be the same things that we would need,” says Roberts. “You have to ask yourself, ‘What would happen if?’ And, ‘Will I be prepared?'”
According to Wilkinson, the worst-case scenario for a large earthquake in this area would be for it to occur during the day in mid- to late-winter, when melting snow would have begun to flood the Mississippi River.
CUSEC hosts educational seminars with school children, teaching earthquake preparedness using Seismo, a seismic-wave character. Memphis City Schools does not have a specific earthquake emergency plan, but it is covered in the district’s overall Response Procedures and Guidelines manual.
MLGW Preparedness
Perhaps the most notable advances in the public sector have been made by the company that would be most affected in the event of a major earthquake. CUSEC says Memphis Light, Gas, & Water is exemplary in its earthquake preparedness. According to utility spokesman Mark Heuberger, MLGW has retrofitted all electrical substations and the 14 water-pumping stations within the Memphis/Shelby County area. The company has placed generators at all stations, replaced old metal water pipes with flexible duct pipes, and secured equipment inside stations to prevent falls.
“We didn’t just do this for earthquakes. We did it because it was practical,” says Heuberger. “If an earthquake were to occur, we would need to get our services on-line as soon as possible, and these are some of the ways to do that.” Because the utility’s corporate building in downtown Memphis doesn’t meet some of the code provisions to handle seismic and other major disasters, some operations have been moved to more secure facilities. The utility conducts impromptu crisis scenarios three times a year, including at least one earthquake situation.
Even with these advances, scientists say that much more needs to be done to prepare for a quake. “What we end up with is a large inventory of structures that weren’t designed for earthquakes, and that’s worrisome,” says Wilkinson. “Our ultimate goal is to protect people and property. That is a challenge with all of the other budget priorities out there. We want to get to a point where it’s safe, but we have to look at real-world issues. It’s a balancing act.”
