The Disastrous Effects of Earthquake Soil Liquefaction

Liquefaction is transformation of loosely packed, saturated sand and/or silt into a fluid mass. Liquefaction is a temporary quicksand condition. The term “liquefaction” is distinct from the term “liquification”. Liquification (five syllables) means “melting from heat” and applies to liquefying (melting) solids, such as metals, plastics, ice, and American cheese. Liquefaction (four syllables), by contrast, involves NO heat, only pressure. (1)

Three Causes of Liquefaction

Liquefaction can be induced in three ways. First, it can be induced seismically by earthquake tremors that generate the pressures needed to separate grains of sand saturated with water, resulting in a viscous fluid mixture of water and suspended sand grains likened to a “cement slurry when freshly poured.” (1) Second, liquefaction can be induced hydrologically by groundwater movements, such as water seeking its own level behind levees during flooding. Third, liquefaction can be induced mechanically, such as with vibrating vehicles, locomotives, or other heavy machinery. A farmer “nearly lost a tractor which was parked over a liquefiable area and left running during a lunch break,” according to one story.  The tractor “almost buried itself before the situation was realized,” thus providing an excellent example of mechanically-induced liquefaction. (2)

The only way that loose sand can have any strength is if the grains touch each other, supporting each other’s weight and any burdens coming from above, the sides, or below. Liquefaction disables grains from touching one another. Two short animations of the behavior of sand grains in a soil deposit during liquefaction are at:  http://www.ce.washington.edu/~liquefaction/html/what/what1.html; accessed February 16, 2006.

Liquefaction is Not a Random Geologic Occurrence

Thus, liquefaction is not a random geologic occurrence! The probability of its occurrence increases with the co-existence of the following three variables:

1. Young loose sand/soil, such as found in alluvial deposits—that is, sediment deposited by flowing water, as in a riverbed, flood plain, or delta.

2. A shallow ground water table (less than 50 feet). (3)

3. The presence of active seismic faults.

These three variables exist in the New Madrid Fault Zone (NMSZ) in the alluvial Mississippi Valley, as well as many other places in the United States, including, for example, Las Vegas. The central Mississippi Valley experiences more earthquakes than any other region in the United States east of the Rocky Mountains. (4)

The co-existence of the three variables in the Mississippi Valley is a concern because of two urban areas: Greater St. Louis Area in Missouri (population: 2,764,054 in 2004) and Greater Memphis Area in Tennessee (population: 1,230,303 in 2005). Unfortunately, the built environments of St. Louis and Memphis have not been built to withstand earthquake effects, including soil liquefaction. Engineers are beginning to install apparatus to measure bridge and other fixed-structure movements near Memphis to assess liquefaction-induced changes resulting from the small earthquakes along the New Madrid Seismic Zone, which occur almost continuously.  

What Liquefaction Means for the New Madrid Seismic Zone

The ubiquitous evidence of old and repetitive liquefactions throughout the New Madrid Seismic Zone strongly suggests that liquefaction will be a very big problem if the New Madrid Seismic Zone detonates some zinger earthquakes like it did in 1811-1812. Examples of old liquefaction include sand blow explosion craters, filled explosion craters, earthquake ponds, channel blowouts, simple sand boils, compound sand boils, sand dikes, sand sills, lateral spread sags, linear crevasses, Graben fissures, sand fissures, sunk lands, and earthquake lakes, among others.

Scientists have developed a better understanding of the devastating effects of liquefaction in built areas from the effects of liquefaction during the 1964 Niigata, Japan, and Alaska earthquakes, and destruction to San Francisco’s Marina District during the 1989 Loma Prieta earthquake. Liquefaction can overturn small and large buildings, fell bridges, and cause dams to fail, among other devastation.  

Development of Liquefaction Hazard Maps

Because of the potential adverse effects of seismically-induced liquefaction, engineers have begun to develop “liquefaction hazard maps”. California is far along in this process for obvious reasons. A visit to the following website provides detailed liquefaction hazard maps for the San Francisco Bay Area: http://www.abag.ca.gov/bayarea/eqmaps/liquefac/pickcityliq.html; accessed February 16, 2006. Utah Geological Survey has similar liquefaction hazard maps for Utah at: http://geology.utah.gov/maps/geohazmap/cachevalley.htm; accessed February 16, 2006.

The NMSZ, which includes parts of Tennessee, Kentucky, Missouri, Arkansas, Illinois, Indiana, and Mississippi, harbors a large liquefaction field. Scientists estimate the probability of a magnitude 6.0 or greater earthquake occurring in the NMSZ within the next 50 years at 25-60 percent according to the US Geological Survey. (4)

Researchers such as Dr. Martitia Tuttle have been studying liquefaction in the NMSZ for a decade. She completed her geology Ph.D. dissertation in 1999 from the University of Maryland, College Park, MD, on “Late Holocene Earthquakes and their Implication for Earthquake Potential of the New Madrid Seismic Zone, Central United States.” (5) Dr. Tuttle notes: “The ground failure that resulted from liquefaction during the New Madrid earthquakes was severe. We’re talking about vertical displacement of 3 to 6 feet (1 to 2 meters), and lateral displacement up to 33 feet (10 meters).A recurrence of that type of event would have severe consequences for engineered structures.” (4)

According to Tuttle, in 1988 a magnitude 5.9 earthquake in Quebec, Canada, produced liquefaction. “Basements cracked, septic fields were disrupted, and people described water and sand shooting into their basements, out of their toilets, and into their bathtubs,” she said. “And that was just a moderate-sized earthquake, not a big one…. If we study modern earthquakes that produce liquefaction, we can better interpret the geologic record of liquefaction during past events. This helps us anticipate what is likely to happen in the future so that we can make informed decisions about reducing and mitigating hazards. It’s one of those things where people tend to think — if it hasn’t happened during my lifetime, then it can’t happen here,” said Tuttle. “But the liquefaction field in the New Madrid region is very large. We’re talking about a huge earthquake that could have a significant impact on society.” (4)

What Can Be Done to Minimize Effects of Liquefaction?

There are three opportunities to reduce liquefaction hazards when designing and constructing new buildings or other structures, such as bridges, tunnels, and roads.

First, construction should be avoided on liquefaction-susceptible soils. There are four ways to test whether soil is susceptible to liquefaction:

1. Historical findings, such as sand blows in the NMSZ, indicating soils are susceptible to liquefaction;

2. Geologic findings, such as the con-existence of loosely consolidated sediments of landfill and a high water table in a seismic zone;

3. Soil composition, meaning that big and small grains, for example, can withstand liquefaction better because the little grains fill in the pores between the big grains when shaken thereby maintaining soil strength; and

4. State findings, meaning soils in a state of subjection to a high effective stress will liquefy more readily than soils subjected to low effective stress.

The second option to reduce liquefaction hazards is to build liquefaction-resistant structures. “If it is necessary to construct on liquefaction susceptible soil because of space restrictions, favorable location, or other reasons, it may be possible to make the structure liquefaction resistant by designing the foundation elements to resist the effects of liquefaction.” (6) For example, when burying utilities, such as sewage and water pipes, emplacement of ductile connections to the structure will accommodate the large movements and settlements that can occur due to liquefaction. Foundation elements in a shallow foundation need to be tied together to make the foundation move or settle uniformly, thus decreasing the amount of shear forces induced in the structural elements resting upon the foundation.

The third option to reduce liquefaction hazards is to improve the soil by improving the strength, density, and/or drainage characteristics of the soil. This can be done using a variety of soil improvement techniques, such as “densifiction” by dynamic compaction. This is performed by dropping a heavy weight of steel or concrete in a grid pattern from heights of 30 to 100 feet and provides an economical way of improving soil for mitigation of liquefaction hazards.

Catastrophic Planning for New Madrid Seismic Zone

On December 22, 2005, the Department of Homeland Security notified US Congressman Harold Ford, Jr., who represents Memphis and Tennessee’s Ninth District (in his fifth term, elected at age 26 years, see http://www.house.gov/ford/), that the Federal Emergency Management Agency (FEMA) had “scheduled a comprehensive initiative to help local, state and federal officials plan for a catastrophic earthquake in the New Madrid Seismic Zone.” This statement came in response to an ascerbic letter sent by Congressman Ford to Secretary of Homeland Security Michael Chertoff in September 2005 following the Katrina catastrophe urging the development of such a plan for the NMSZ to reduce the probability of a repeat of what he perceived as a Katrina federal government-response debacle. (7)

The December 22, 2005, letter from Department of Homeland Security to Congressman Ford continued: “Earlier this year, FEMA began coordinating with the Central United States Earthquake Consortium (CUSEC) (6) to develop meaningful catastrophic disaster response plans for the NMSZ. In this initiative, FEMA and CUSEC will focus on three cities in the NMSZ: Memphis, Tennessee; St. Louis, Missouri; and Cairo, Illinois. Through facilitated workshops, FEMA and CUSEC member states will address: search and rescue, transportation, staging and distribution of critical resources, temporary shelter/housing, hazardous materials, security, debris removal, temporary medical care, fire, and critical infrastructure protection. The individual communities will determine the focus for planning and exercising.

”FEMA is working with the federal, state and local participants and CUSEC, to schedule activities, including exercise related activities, necessary to carry out this initiative. In cooperation with affected state and local governments, this initiative will identify high risk areas and examine loss estimates for a catastrophic incident, current disaster response capabilities, anticipated response shortfalls, and comprehensive planning strategies for addressing such shortfalls.

“Catastrophic planning initiative products will include incident-specific response plans for pre-selected geographic regions within the NMSZ, based upon loss estimating models and capability inventories of affected local, state and federal responders. Additional products will include: a planning template useful for other catastrophic incidents, anticipated response contingencies beyond the National Response Plan, and proposed legislation and/or executive action to facilitate catastrophic disaster response. In the future, FEMA will keep you apprised as it finalizes the schedule of NMSZ activities within the states and CUSEC.” (8)

Summary

Seismically-induced liquefaction effects can be severe. The New Madrid Seismic Zone has demonstrated severe liquefaction effects in the past when it was relatively uninhabited. An earthquake in the zone today would likely cause liquefaction to recur as the three variables—alluvium, high water table, and seismicity—remain present today, as in the past. Two large population centers near the NMSZ are at risk for the effects of liquefaction: Memphis, Tennessee and St. Louis, Missouri. Preparations for such an event have recently gotten underway.

Sources:

1. Ray Knox and David Stewart: “The New Madrid Fault Finders Guide”, Gutenberg-Richter Publications, Marble Hill, MO, 1995, p. 159. This is an excellent book and I recommend every disaster planner in the Midwest have a copy to better understand the geology of earthquakes in this region. I am concerned this book will go out of print and then become scarce.

2. Ibid. pp. 36-39.

3. JJ Criscione, James Werle, D. Burton Slemmon, and Barbara Luke: “A Liquefaction Hazard Map of the Las Vegas Valley, Nevada.” No date. Available at:   http://www.nbmg.unr.edu/nesc/lhlasvegas.pdf#search='A%20Liquefaction%20Hazard%20Map%
20of%20the%20Las%20Vegas%20Valley%2C%20Nevada'; accessed February 16, 2006.

4. Laurie J. Schmidt: “Squeezing water from rock” in “Earth Observatory” June 25, 2003, at: http://earthobservatory.nasa.gov/Study/Earthquake/; accessed February 16, 2006.

5. M. Tuttle & Associates, Specializing in Paleoseismology and Seismic Hazard Assessment, available at: http://www.mptuttle.com/mtuttlevitae.html and http://www.mptuttle.com/mtuttlecollabs.html; accessed February 16, 2006. See also: Tuttle, M.P.: “The use of liquefaction features in paleoseismology: Lessons learned in the New Madrid seismic zone, central United States.” Journal of Seismology. 2001. 5:361-380.

6. “How can liquefaction hazards be reduced?” at: http://www.ce.washington.edu/%7Eliquefaction/html/how/how1.html; accessed February 17, 2006.

7. “Harold Ford Jr. for US Senate 2006 Unofficial Grassroots Blog” at: http://haroldfordjr2006.blogspot.com/2005/12/ford-obtains-fema-pledge-for-new.html; accessed February 16, 2006.

8. “Central United States Earthquake Consortium” website at: http://www.cusec.org/; accessed February 16, 2006.