Liquefaction Potential in the 

Central Mississippi Valley 

Liquefaction Potential in the 

Central Mississippi Valley 

By STEPHEN F. OBERMEIER 

US. GEOLOGICAL SURVEY BULLETIN 1832 
DEPARTMENT OF THE INTERIOR 

DONALD PAUL HODEL, Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

UNITED STATES GOVERNMENT PRINTING OFFICE: 1988 

For sale by the Books and Open-File Reports Section, 

U.S. Geological Survey, Federal Center, 

Box 25425, Denver, CO 80225 

Library of Congress Cataloging in Publication Data 

Obermeier, Stephen F. 

liquefaction potential in the central Mississippi Valley 

(U.S. Geological Survey bulletin ; 1832) 

Bibliography: p. 

1. Soil mechanics-Mississippi River Valley. 2. Soil liquefaction-Mississippi 

River Valley. I. Title. II. Series. 

QE75.89 no. 1832 624.1'5136 8~00375 

[TA710.3.M74] 
CONTENTS 

Abstract 1 

Introduction 1 

Overview of liquefaction 2 

Conditions for liquefaction 3 

Materials prone to liquefaction 4 

Consequences of liquefaction 5 

Flow landslides 5 

Lateral-spread landslides 5 

Quick-condition failures 6 

Differential settlements 6 

Engineering evaluation of liquefaction potential 6 

Liquefaction and historical earthquakes 8 

1811-12 earthquakes 8 

Alluvium in St. Francis and Western Lowlands Basins 8 

Sand blow deposits in St. Francis Basin 9 

Energy release center 10 

Accelerations in alluvium 11 

Accelerations in bedrock 11 

Farthest liquefaction 12 

Other historical. earthquakes 12 

Earthquake intensity and ·liquefaction 12 

Suggested methods for evaluating liquefaction potential 13 

Simplified procedure of Seed and Idriss 13 

Magnitude method 15 

Application of methods 17 

Liquefaction susceptibility and geologic origin 18 

Braided stream and meander belt deposits 18 

Glacial lake deposits 19 

Modern flood plain deposits, exclusive of very young sediments 19 

Very young sediments 19 

Eolian deposits 19 

Reworked eolian deposits 19 

Summary 19 

References cited 20 

FIGURES 

1, 2. Maps showing: 

1. Northern Mississippi embayment of the Gulf Coastal Plain showing the 

major physiographic features of the area, the distribution of Quaternary 

alluvium, and Cretaceous sediments 2 

2. Late Quaternary alluvial deposits in the St. Francis and Western 

Lowlands Basins 3 

3, 4. Diagrams showing: 

3. Idealized field loading conditions 4 

4. Zone of liquefaction during earthquake shaking 5 

Contents Ill 
IV Contents 

5, 6. Graphs showing: 

5. Evaluation on level ground of liquefaction potential of sand deposits for 

different magnitude earthquakes 7 

6. Correlation on level ground between field liquefaction behavior of sand 

deposits and modified penetration resistance for surface-wave magnitude 

M8 =7.5±0.3 7 

7, 8. Maps showing: 

7. Distribution of vented sand blow deposits on alluvium, excluding modem 

flood plains 9 

8. Modified Mercalli intensities for the December 16, 1811, earthquake 13 

9-11. Diagrams showing: 

9. Curves for peak horizontal ac9eleration on stiff soils versus epicentral 

distance for various body-wave magnitudes and for back-calculated 

December 16, 1811 , accelerations for St. Francis Basin alluvium 13 

10. Maximum distance from the epicenter of liquefaction in sand as a 

function of earthquake magnitude 16 

11. Maximum distance from fault rupture zone of liquefaction in sand as a 

function of earthquake magnitude 17 

12. Regional intensity map showing estimated Modified Mercalli intensity values for 

an 1811-sized earthquake having an epicenter anywhere along the New Madrid 

seismic zone 18 

TABLES 

1. Relative density of sands according to results of Standard Penetration Test blow 

counts 4 

2. Earthquake magnitude scales 4 

3. Ground slope and expected failure mode of coarse-grained deposits liquefied during earthquakes 5 

4. Modified penetration resistance values in selected settings in the Western Lowlands and St. Francis Basins 10 

5. Locations, intensities, and liquefactions of Central Mississippi Valley historical 

earthquakes having body-wave magnitudes greater than 5. 3, exclusive of 1811-12 

earthquakes 12 
Liquefaction Potential in the Central 

Mississippi Valley 

By Stephen F. Obermeier 

Abstract 

Liquefaction-induced ground failure caused by the 

1811-12 New Madrid earthquakes was commonplace over 

large areas, even far from the epicenters. Recurrence of 

strong earthquakes in the New Madrid seismic zone 

(which lies near the middle of the central Mississippi 

Valley) would undoubtedly cause severe liquefaction 

again and lead to the destruction of many bridges, buildings, and other constructed works. There is a need to 

predict, for different earthquake. magnitudes, the circumstances under which unconsolidated materials may liquefy. 

Estimated accelerations presented in this paper for 

the 1811-12 earthquakes are based on the pattern of sand 

blows caused by those earthquakes and mechanical properties of sands. From these acceleration data and from 

modern seismicity data, accelerations for liquefaction 

analysis can be estimated for any magnitude earthquake. 

The Simplified Procedure of Seed and ldriss can then be 

used to evaluate liquefaction potential. (The terms "liquefaction potential" and "liquefaction susceptibility" are 

used in the sense defined by T.L. Youd and D.M. Perkins 

("Mapping liquefaction-induced ground failure potential," Proceedings of the American Society of Civil Engineers, Journal of the Geotechnical Engineering Division, 

v. 104, no. GT4, p. 433-446.) Liquefaction susceptibility is 

largely a measure of material property and indicates the 

degree of susceptibility to liquefaction (such as low or 

high) during strong earthquake shaking only. Liquefaction 

potential describes the level of susceptibility at a site 

combined with the likelihood that the site will be subjected to earthquake shaking severe enough to trigger 

liquefaction.) Because of uncertainties in predicting 

strong earthquake accelerations, another method is also 

presented. This method, called the magnitude method, is 

based on occurrences of liquefaction from scattered sites 

around the world, from the 1811-12 earthquakes, and 

from other historical earthquakes in the central Mississippi Valley. It is recommended that the level of liquefaction potential be judged on the basis of both the Simplified Procedure of Seed and ldriss and the magnitude 

method. 

Sand and silt deposits in the central Mississippi 

Valley are the most susceptible to liquefaction. large areas 

of terraces and flood plains in the region are underlain by 

moderately dense to loose clean sands and silty sands. 

Relating the properties of these deposits to their liquefaction potentials is reasonably easy and straightforward. 

However, there are also many thick glacial lake deposits, 

eolian deposits, and reworked eolian deposits made up of 

silt-rich and day-bearing materials in the valley. Most of 

these deposits have low liquefaction susceptibility, but, 

locally, some may have high susceptibility. Field methods 

for assessing their properties are crude, and laboratory 

data are so scarce that no simple guidelines are available 

for evaluating liquefaction potential. laboratory tests are 

needed to supplement field studies for many silt-rich and 

day-bearing deposits. 

INTRODUCTION 

Both historical accounts of the 1811-12 New Madrid 

earthquakes and present-day evidence show that 

liquefaction-induced ground failure was very commonplace 

and widespread in alluvial lowlands, especially between the 

towns of New Madrid, Mo., and Marked Tree, Ark. (shown 

in fig. 1). This ground failure was typically manifested by 

sand blows, lateral spreads, ground fissures, and localized 

distortion and warping of the ground surface (Fuller, 1912). 

Many landslides along streams were doubtlessly caused by 

liquefaction. If the 1811-12 earthquakes were to recur 

today, liquefaction-induced ground failure would probably 

make impassable much of the Interstate highway system in 

the St. Francis Basin (shown in fig. 2) from Cairo, Ill., to 

nearly as far south as Memphis, Tenn. Many highway 

bridges would probably be knocked down or badly damaged 

by lateral spreads or collapse of the stream banks. The 

pavement would be so damaged by ground fissures and 

warping that it would be impassable at many places. Many 

other constructed works would also be damaged. In addition, there might be widespread flooding (Saucier, 1977) 

owing to venting to the ground surface of liquefied sand and 

water. Many houses and other structures would also be 

destroyed by the effects of liquefaction. 

Recounting what took place in 1811-12 and what 

would take place today, given the recurrence of strong 

earthquakes, makes it clear that liquefaction would be 

Introduction 1 
EXPLANATION 

Quaternary alluvium 

Tertiary sediments 

Cretaceous sediments 

I 

I 

I 

I 

I 

I 

I 

I 

I 

0 25 MILES I 

6YsKILOMETERS I 

I 

MISSOURI 

goo 

I 

ILLINOIS INDIANA 

-380 

KENTUCKY 

~-----------

TENNESSEE 

-340 

Figure 1. Map of the northern Mississippi embayment of the Gulf Coastal Plain showing the major physiographic 

features of that area, the distribution of Quaternary alluvium, and Tertiary and Cretaceous sediments. 

responsible for much of the total damage. In a reasonably 

analogous situation, the 1964 Alaska earthquake, liquefaction-induced ground failure caused more than half the 

economic losses (Mosaic, 1979). 

Given the possibility of such consequences, exactly 

where and under what circumstances can liquefactioninduced ground failure be anticipated? Liquefaction generally takes place only in unconsolidated sands or silts, but 

not all sands or silts have even approximately the same 

material properties and thus the same liquefaction susceptibility. Important factors other than material properties are 

earthquake magnitude and ground response characteristics. 

This paper will present information for evaluating the 

regional liquefaction potential of different materials in the 

central Mississippi Valley for different-strength earthquakes. To that end, this paper is organized as follows: (1) 

a brief review of factors that cause liquefaction and 

liquefaction-induced ground failure, (2) a description of the 

historical earthquakes in the central Mississippi Valley, (3) 

an examination and discussion of two methods that can be 

used to evaluate liquefaction potential, and (4) a presenta2 Liquefaction Potential in the Central Mississippi Valley 

tion of sediment properties for the geographic area (basically, the alluvial area of fig. 1) where there is a moderate 

to high probability of liquefaction, given a recurrence of 

1811-12-strength earthquakes. This development permits a 

regional assessment of the liquefaction potential for any 

earthquake strength. 

Because this paper is meant to be understood by 

geologists, seismologists, and engineers, some replication 

of common knowledge within each profession is necessary. 

Where words have different meanings within the different 

professions (for example, "soil"), it is the commonly 

accepted engineering interpretation that is intended. Important terms are defined in the text. 

Terminology for the relative density of sand strata 

conforms to usage in table 1. Different earthquake magnitude scales are used in the text. Equivalent values for the 

different scales are given in table 2. 

OVERVIEW OF LIQUEFACTION 

Liquefaction is defined as "the transformation of a 

granular material from a solid state into a liquefied state as 
N 

l 

TENN 

---iiiss 

RIVER 

0 

I 

0 

20 MILES 

I I 

20 KILOMETERS 

EXPLANATION 

Alluvium on small streams 

Mississippi River meander belts 

Late Wisconsinan glacial outwash 

~ Early Wisconsinan glacial outwash 

~ Undifferentiated pre-Wisconsinan 

depositional terraces 

c=J 

Uplands 

Figure 2. Late Quaternary alluvial deposits in the St. Francis and Western Lowlands Basins (from Saucier, 1974). 

a consequence of increased pore water pressures" (Y oud, 

1973). In the liquefied state, the material basically behaves 

as a fluid mass. 

Conditions for Liquefaction 

The application of cyclic shear stresses induced by 

earthquake ground motions causes a buildup of pore-water 

pressure in saturated cohesionless soils (Seed, 1979). These 

stresses are due primarily to the upward propagation of 

shear waves. A soil element on level ground undergoes 

loading conditions as depicted in figure 3, the shear stress 

applications being somewhat random but nonetheless 

cyclic. Because of this shearing, cohesionless soils that are 

sufficiently loose would become more compact if porewater drainage were to occur. Because drainage is usually 

impeded during the short span of an earthquake, pore-water 

pressure increases and intergranular stress decreases. If the 

application of cyclic shear stresses continues, the pore 

pressure of sands that are packed loosely enough can 

approach the initial static confining pressure, even though 

the shear strains are still small. Further cyclic shearing can 

cause the pore pressure to increase suddenly to the initial 

confining pressure and thus lead to large shear straining and 

also flowage. 

Although more densely packed cohesionless materials (such as sands having medium or moderate relative 

density) are not nearly as susceptible to large shear straining 

as looser materials, they may still develop a residual pore 

Overview of Liquefaction 3 
GROUND SURFACE GROUND SURFACE GROUND SURFACE JMWtA\\ 

a' • <To' 

IIA\YIA\\ 

o:' D 

l _LT Tj_ 

-CJ-Ko<1o' -ICJJ-K1a0 ' -\~~-K ' 

f 1 T 

Initial stresses Cyclic load sequence 

Figure 3. Idealized field loading conditions (from Seed 

and ldriss, 1971). 'T, earthquake-induced horizontal shear 

stress; a 0', initial vertical effective overburden stress; K0, 

ratio of intial lateral to vertical effective stress. 

pressure equal to the confining pressure. After the cyclic 

stress applications stop, this residual pore pressure generally causes an upward flow of water. It is likely that the 

upward flow of water to the ground surface from an 

underlying layer having a high pore-water pressure is the 

major mechanism for carrying sand to the ground surface 

and causing "sand blows" (Housner, 1958) or "sand boils" 

(Seed, 1979). (Sand blows and sand boils are terms often 

used for the same phenomenon. In this paper, sand blows 

are restricted to earthquake-induced liquefaction features.) 

Liquefaction during earthquake shaking can originate 

in a zone as shallow as 2 m below the ground surface 

(Obermeier and others, 1986) to depths much greater than 

20 m (Seed, 1979). Generally, if the water table is near the 

ground surface (say, within a few meters), the probability of 

liquefaction is significantly increased. However, no simple 

guidelines are available regarding depth of water table and 

depth of liquefiable deposits. Figure 4 illustrates that the 

zone of liquefaction during shaking depends on the relationship between the cyclic shear stresses generated by the 

earthquake and the stress required to initiate liquefaction in 

the soil. 

Seismological factors of prime importance that control liquefaction during shaking include the amplitude of the 

cyclic shear stresses and the number of applications of the 

shear stresses (Seed, 1979). These factors in tum are related 

to field conditions of shaking amplitude (that is, peak 

acceleration) and earthquake magnitude. Analytical engineering methods for evaluating variable and irregular cyclic 

stress applications typical of real earthquakes are well 

developed and yield results that are quite acceptable for 

Table 1. Relative density of sands according to results of 

Standard Penetration Test blow counts 

[From Terzaghi and Peck, 1967] 

No. of blows 

(N) 

0-4 ..................... . 

4-10 .................... . 

10-30 ................... . 

30-50 ................... . 

>50 .................... . 

Relative density 

Very loose 

Loose 

Medium or moderate 

Dense 

Very dense 

4 Liquefaction Potential in the Central Mississippi Valley 

engineering analysis (Seed and others, 1983), providing 

that shaking amplitude-time records can be predicted with 

reasonable accuracy . 

Materials Prone to Liquefaction 

Grain-to-grain bonds and the relative density of 

granular materials are the principal physical controls on 

liquefaction susceptibility. As granular materials age, grainto-grain bonds apparently develop and thereby increase 

resistance to liquefaction; the liquefaction resistance of 

granular materials having high relative densities is much 

higher than that of loosely packed granular materials. Very 

young deposits, less than 500 years in age, are generally 

much more susceptible to liquefaction than older Holoceneage deposits for a fixed relative density (Youd and Perkins, 

1978). As a practical example in the New Madrid region, 

deposits on modem flood plains generally are more susceptible than slightly older deposits on terraces at slightly 

higher elevations, even if the ground-water table is at the 

same depth on the flood plain and terrace (Obermeier and 

Wingard, 1985). 

In areas strong! y shaken by the 1811-12 earthquakes, 

the most common materials susceptible to widespread 

liquefaction are very loose to medium dense, clean, 

medium-grained sands that occupy lowland areas; also 

susceptible are many deposits of gravelly sands and silty 

and very fine grained sands. Hundreds of rivers and creeks 

adjoining terraces and flood plains have high water tables 

and rather loose sands. 

Clean silts containing very small amounts of clay and 

having low cohesion are also susceptible to liquefaction, 

although not to the extent that many of the clean sands are. 

Thick, moderately soft, clean silts, deposited as loess, are 

Table 2. Earthquake magnitude scales 

[This table shows equivalent earthquakes for the central Mississippi 

Valley. Data are from Nuttli and Herrmann (1982)] 

Richter local 

magnitude 

(ML) 

5.0 ......................... . 

5.2 ......................... . 

5.4 ......................... . 

5.6 ......................... . 

5.8 ......................... . 

6.0 ......................... . 

6.2 ......................... . 

6.4 ......................... . 

6.6 ......................... . 

6.8 ......................... . 

7.0 ......................... . 

7.2 ......................... . 

Body-wave 

magnitude 

(mb) 

5.0 

5.2 

5.4 

5.6 

5.8 

6.0 

6.2 

6.4 

6.6 

6.8 

7.0 

7.2 

Surface-wave 

magnitude 

(Ms) 

4.4 

4.8 

5.2 

5.6 

6.0 

6.4 

6.8 

7.2 

7.6 

8.0 

8.4 

8.7 
SHEAR STRESS 0~----~--------------------------------~ 

t 

w 

0 

r 

Zone of liquefaction during 

earthquai shaking 

:\ 

', Cyclic stress required to 

' / initiate liquefaction 

'" in C cycles \ 

Average cyclic shear stress 

developed for C cycles..............: 

by earthquake motions 

\ 

\ 

\ 

' \ 

' ' \ \ \ 

\ 

\ \ 

Figure 4. Zone of liquefaction during earthquake shaking 

(from Seed and ldriss, 1971). C, number of cycles. 

commonplace in many upland areas near major streams that 

carried meltwaters from glaciers. Alluvial lowlands adjacent to these loess-covered uplands often have a rather thick 

veneer of very soft silt, which was originally laid down as 

loess but was later eroded and redeposited in the lowlands. 

Some of the silts in the glacial meltwaters were 

carried into large lakes and deposited on the lake bottoms. 

Thick glacial lake deposits of large areal extent are located 

north and northeast of Cairo. Many of these old lakes have 

high ground-water tables, and the silts are so clean and soft 

that they are susceptible to liquefaction. Beneath the silts in 

these old lake beds are very loose sands at many places. 

Clay-bearing soils that may also liquefy appear to be 

those in which less than 15 percent of the particles are finer 

than 0.005 mm, the Atterberg liquid limit is less than 35, 1 

and the water content1 is nearly equal to or greater than the 

liquid limit (Seed and others, 1983). Almost without 

exception, the only soils exhibiting these properties in the 

central Mississippi Valley are the silt-rich soils that occupy 

alluvial lowlands (discussed above) and possibly very 

. young sediments in modem flood plains and in very wet 

swampy areas. 

1

The liquid limit is the water content at which a remolded sample has 

a soft consistency; at the liquid limit, the sample is on the semisolid-liquid 

boundary. Liquid limit is measured in a standardized test described in any 

elementary soil mechanics text. Water content is the ratio of the weight of 

water to the weight of dry soil, expressed as a percentage. 

It is also possible that clay-rich sediments .that are 

very young (no older than a few tens or hundreds of years) 

and extremely soft (so soft that the sediments are mud or an 

ooze) are susceptible to liquefaction. Such weak clay-rich 

sediments are generally found only adjacent to modem 

streams. 

Consequences of Liquefaction 

Liquefaction can lead to three basic types of ground 

failure (Seed, 1968): flow landslides, landslides having 

limited movement (lateral spreads), and quick-condition 

failures. In addition, ejection of soil by sand blows and 

differential loosening and densifying of soil can cause 

differential settling of the ground surface. For sands, Youd 

( 1978) has suggested that the type of ground failure induced 

by liquefaction is related to the ground surface slope, as 

table 3 shows. 

Thickness and setting (for example, the depth or 

lateral continuity of the sand deposit) also need to be 

considered in determining the probable mode of ground 

failure. A thin, loose sand layer at a depth of 10 m in an 

otherwise nonliquefiable clay deposit is not likely to cause 

a bearing capacity failure, regardless of the ground surface 

slope. However, this condition might lead to a translational 

landslide on steep slopes or magnify ground surface movement due to lateral spreading in flat areas (Anderson and 

others, 1982). 

Flow Landslides 

On slopes steeper than 5 percent, large soil masses 

can move as viscous fluids or blocks of intact materials 

riding on liquefied flows. Liquefaction in sands and silts 

can lead to flows that travel hundreds of meters (see, for 

example, Youd and Hoose, 1978, figs. 20-22). Some of the 

most destructive flows ever recorded originated in loess on 

hill slopes in Russia (Keefer, 1984). 

Lateral-Spread Landslides 

Limited flow can take place on slopes between 0.5 

and 5 percent, underlain by sands or silts that are too dense 

to flow freely. Where loose sands occur on slope inclinaTable 3. Ground slope and expected failure mode of 

coarse-grained deposits liquefied during earthquakes 

[After Youd, 1978] 

Ground surface slope 

(percent) Failure mode 

<0.5 . . . . . . . . . . . . . . . . . . . . Bearing capacity and ground 

oscilliation. 

0.5-5 . . . . . . . . . . . . . . . . . . . . Lateral-spread landslides 

> 5 . . . . . . . . . . . . . . . . . . . . . . Flow landslide 

Overview of Liquefaction 5 
tions of as little as 0.5 percent, horizontal displacements can 

still be many meters and leave large open cracks at the 

surface (Youd, 1978). Generally, lateral spreads develop in 

alluvial lowlands along streams. Lateral spreads are generally longest parallel to the streams. Lengths along streams 

of 150 to 300m are not unusual (see, for example, Fuller, 

1912). Rather large lateral spreads can also develop wherever lateral resistance to movement is reduced by removal 

of only a few meters of soil. Small scarps and manmade 

ditches are likely locations. Lateral spreads are commonplace in alluvium as a result of moderate to strong earthquakes. 

Quick-Condition Failures 

Seepage forces caused by upward-percolating pore 

water can drastically reduce the shear strength of granular 

materials for a period of minutes to days after earthquake 

shaking. If the strength is reduced to the point of instability, 

this state is known as a "quick condition." 

Quick-condition failures are generally found only in 

thick sand deposits that extend from below the water table 

to the ground surface. Loss of bearing capacity is a common 

type of quick-condition failure. During the 1964 Niigata 

earthquake in Japan, high-rise apartment buildings had 

quick-condition bearing-capacity failures and rotated so 

much that people could walk on previously vertical exteriors; embankments also subsided into the weakened sands. 

The buoyant rise of buried tanks, empty swimming pools, 

and water treatment tanks is another common result. 

Differential Settlements 

Wherever seepage forces carry sand and water to the 

surface, buildings can be undermined. Vertical displacement of the ground surface by densification of a liquefied 

soil layer can cause differential settling of buildings. 

Although differntial settling is probably not often totally 

destructive of buildings, it can distort and damage structures. 

Engineering Evaluation of Liquefaction Potential 

Methods developed recently to determine material 

properties include the electric-cone penetration test, the 

cross-hole seismic velocity test, and the pressuremeter test 

(Youd and Bennett, 1983). These test methods, which are 

still somewhat experimental, have yielded so few data in the 

central Mississippi Valley that it is not reasonable to 

consider their use for regional evaluation of liquefaction 

potential. Laboratory dynamic test data on natural soils are 

virtually nonexistent for the central Mississippi Valley, and, 

for a regional evaluation of liquefaction potential, developing an adequate data base by means of dynamic laboratory 

6 Liquefaction Potential in the Central Mississippi Valley 

testing would be prohibitively expensive. The only method 

for which there are abundant data is the Standard Penetration Test (SPT). 

In the field, evaluating the properties of sand deposits 

is most commonly done, at least for preliminary or regional 

analysis, by testing the soil in place with the SPT blow 

count method (American Society for Testing and Materials, 

1978). A sampling tube is driven into the ground by 

dropping a 140-lb (63.5-kg) weight from a height of 30 in 

(176.2 em). The penetration resistance is measured by the 

number of blows required to drive the sampler 1 ft (30.5 

em). The SPT blow counts (N values) are then used in 

conjunction with anticipated earthquake-induced shear 

stresses and number of repetitions of the shear stress (which 

is related to earthquake magnitude) to determine if liquefaction can take place. Figure 5 shows boundary curves 

(Seed and others, 1983) that define where liquefaction is 

likely to occur for earthquakes of different magnitudes. The 

curves apply to clean sands containing almost no silt, on 

level ground. (Figure 5 can be modified for use with silty 

sands and clean silts that plot below the A line on the 

Unified System plasticity chart (Seed and others, 1983, p. 

479) by adding 7.5 to the N1 value.) For a given earthquake 

magnitude, data points below the curve have a high probability of not liquefying, and data points above the curve 

have a high probability of liquefying enough to cause sand 

blows (and landslides and other liquefaction-related ground 

failure). The curves were developed from field and theoretical studies of earthquake-induced liquefaction at many sites 

around the world. 

The field cyclic stress ratio in figure 5 is the ratio, on 

an element in the sand layer, of the average earthquakeinduced horizontal cyclic shear stress ( 'T h avg) to the vertical 

effective stress (a0 ') before the cyclic stresses were applied. 

The field cyclic stress ratio due to earthquake shaking, 

developed in the field, is computed from the following 

equation (Seed and others, 1983): 

'Th avg = 0.65(Amax . Uo . rg) 

ao' g ·ao' 

where Amax is the peak horizontal acceleration at the ground 

surface, a 0 is the total overburden stress on the sand under 

consideration, a0 ' is the initial effective overburden stress 

(total stress minus pore-water pressure) on the sand layer 

under consideration, rg is the stress reduction factor ranging 

from a value of 1 at the ground surface to a value near 0.9 

at a depth of about 10 m, and g is the acceleration of 

gravity. 

For one of the most common field conditions on 

alluvium in the New Madrid earthquake region, where the 

water table is about 2 m below the ground surface and the 

weakest sands are at a depth of 4 to 5 m, the field cyclic 

stress ratio is almost exactly equal to the peak horizontal 

acceleration; that is, if the peak horizontal acceleration is 

0.20 g, the cyclic stress ratio is essentially 0.20. In figure 5, 
0 

-~ 

en 

en 

~ en 

.2 

u 

> 

u 

"l:l 

a; 

u: 

00 

I I I I 

~~/~/ // ~r>i Co (0"1 lr)l lr>f Ill Ill II I "i Cb" 

~~I ~I ~I lt'l 

I 1 I ~I I 1 I 

I / 

I 

10 20 40 

Modified Penetration Resistance N,, in blows per foot 

EXPLANATION 

Average earthquake-induced horizontal 'Th avg 

cyclic shear stress 

cr' D Vertical effective stress 

N, Standard Penetration Test blow count 

measured in field, modified to blow 

count resistance at vertical effective 

stress of 1 ton/ft2 

Figure 5. Evaluation on level ground of liquefaction 

potential of clean sand deposits (average diameter >0.25 

mm) for different ma9,nitude earthquakes (from Seed and 

others, 1983). A is a ata point indicating probable liquefaction for M=6.75 (discussed in text). M is earthquake 

m~nitude (Richter ma~nitude ML or surface-wave magnitu e M 5 , whichever is arger). 

the modified penetration resistance N1 is the SPT blow 

count value measured in the field multiplied by a correction 

factor that accounts for the influence of field stress conditions on the measured blow count; for the field conditions 

just given, the multiplication factor is 1.4 (see Seed and 

others, 1983). 

To illustrate use of the curves, assume that the peak 

horizontal acceleration at the ground surface is 0.20 g for an 

earthquake magnitude (M) of 6. 75 and that the SPT blow 

count in clean sand is 11 (corrected to N1 = 15.4) on a nearly 

level terrace for the depth and water table conditions 

described above. This situation is shown as point A in 

figure 5; liquefaction and production of sand blows would 

be very probable. 

The accelerations required for liquefaction according 

to figure 5 are an approximate lower bound. Figure 6 shows 

the curve for M = 7. 5 and field data from many earthquakes 

around the world. The solid circles in figure 6 represent data 

taken from sites where there was evidence of liquefactioninduced ground failure, such as sand blows. Although no 

evidence for liquefaction was observed at some sites (open 

circles), liquefaction still may still have occurred at depth 

and not been observed because the field setting was not 

conducive to production of sand blows. To illustrate, an 

especially thick, fine-grained cap above liquefied sands 

apparently prevented sand blows from venting to the ground 

surface at many places in the St. Francis Basin during the 

1811-12 earthquakes (Saucier, 1977), yet many dikes and 

sills of liquefied sediment penetrated the cap (S.F. Obermeier, unpublished data, 1979). As another example, especially coarse and permeable deposits above the zone lique0.5 

0.4 

0 

·;:; 

~ 

en 

en 

~ en 

.2 

u 

> u 

"l:l 0.2 ~ 

"l:l 

e 

ltl 

E 

·;:; 

en 

w 

0.1 

~- 0 

-1:: b lI 

I o No liquefaction observed I 

-Curve for Ms=7.5::t:0.3 (same I 

as curve forM= 7.5 on fig. 5) I 

I -- 1.25 times ordinate for curve I 

for Ms = 7.5 ::t: 0.3 

• 'I • fl 

• •I • • I 0 0 • I 

• 0 I • • I'· • g5 og • • 0/ 0 

• 0 , 0 0 0 

• 0 0 

• I 0 

• 0 • o I 0 

•• •¢i. 0 

0 0 

• 0 0 0 • 0 

.,0 0 0 0 00 

•• 0 0 0 0 

.. ~ 0 0 

0 

I;/ 0 00 

• 0 o0 o g 0 

',#:) 

I 

/ 0 0 •I 

/ 

Modified Penetration Resistance N1, in blows per foot 

'Th avg 

o:' D 

EXPLANATION 

Average earthquake-induced horizontal 

cyclic shear stress 

Vertical effective stress 

N, Standard Penetration Test blow count 

measured in field, modified to blow 

count resistance at vertical effective 

stress of 1 ton/ft2 

40 

Figure 6. Correlation on level ground between field liquefaction behavior of sand deposits (average diameter 

>0.25 mm) and modified penetration resistance for 

surface-wave magnitude M 5 =7.5 ±0.3 (from Seed and 

ldriss, 1982). 

Overview of Liquefaction 7 
fied during shaking appear to have dissipated pore pressures 

so fast in many places that sand blows did not develop 

(Obermeier, in press). The data in figure 6 are from many 

types of field settings, scattered around the world, and it is 

not surprising that expressions of liquefaction-related features were not observed, even though liquefaction may have 

occurred. In summary, the solid line in figure 6 is probably 

quite a good bound for estimating accelerations, provided 

that attention is given to the field setting; in addition, it is 

extremely likely that there would be liquefaction at accelerations 25 percent higher than those shown by the solid 

line- bound (see fig. 6). 

Figure 5 is strictly applicable for level or nearly level 

ground only (that is, for slopes less than about 5 percent). 

On steeper slopes, higher accelerations may be required to 

cause liquefaction, and more sophisticated methods must be 

used to determine if liquefaction can develop. Still, using 

figure 5 helps assess the possibility of problems on the 

slopes; if ground failure is indicated by figure 5, the 

potential for problems warrants further investigation. 

The procedure sketched above, known as the Simplified Procedure of Seed and Idriss, indicates only where 

liquefaction is probable. Damaging ground failure may or 

may not result from an occurrence of liquefaction. In 

general, liquefied loose sands are much more likely to flow, 

move large distances, and cause more damage than liquefied medium dense sands are; more rigorous methods are 

necessary for evaluating the complete scenario. 

For clay-bearing soils that plot above the A line on 

the Unified Classification System plasticity chart (Seed and 

others, 1983, p. 479), there are no charts analogous to 

figure 5 . Laboratory test methods must be used at the 

present time to appraise their behavior in any detail. 

However, it is certain that serious liquefaction can take 

place in these materials only if they are very soft. The 

softness of silts and clays can also be crudely estimated by 

the SPT method. Only very weak, clay-bearing soils that 

have index and physical properties (natural water content, 

liquid limit, percentage of clay) in the range discussed 

previously are candidates for liquefaction. 

LIQUEFACTION AND HISTORICAL 

EARTHQUAKES 

Historical earthquakes in the central Mississippi Valley can be used to establish relations between liquefaction, 

earthquake magnitudes, accelerations, and Modified Mercalli (MM) intensities. Liquefaction effects of the 1811-12 

earthquakes are reviewed first; accounts of more recent 

earthquakes having body-wave magnitudes (mb) greater 

than 5.3 follow. 

8 Liquefaction Potential in the Central Mississippi Valley 

1811-12 Earthquakes 

It is well known (Fuller, 1912) that great numbers of 

liquefaction-induced ground failures (hereafter referred to 

as "liquefaction" or "liquefaction features") took place 

many tens of kilometers from the probable epicenters of the 

1811-12 earthquakes and locally were as far away as 400 

km (Fuller, 1912, p. 19). Accounts of areas where the 

farthest liquefaction effects were fairly common typically 

describe disappearing islands in rivers, sand blows near 

streams, and lateral spreads along stream banks. Most, if 

not all, of these farthest liquefaction features were probably 

in very young alluvial sediments. 

The late Quaternary and Holocene sediments in the 

central Mississippi Valley are from a variety of flow 

regimes and, in addition, range in thickness from a featheredge to many tens of meters. There are large differences 

in liquefaction susceptibility and physical properties in 

these sediments (Obermeier and Wingard, 1985) because of 

differences in their ages and modes of deposition. The 

liquefaction susceptibility of deposits on modem flood 

plains commonly is much higher than that of Wisconsinanage sediment. This large variation in physical properties and 

thicknesses also causes wide variations in ground response 

characteristics. Thus, using the regional pattern of liquefaction features to understand earthquake characteristics (such 

as epicenter locations and accelerations) would be 

extremely difficult in a highly variable geologic setting, 

such as one in which all sediment ages and depositional 

modes are present. However, the uniform thickness and 

relatively similar liquefaction susceptibility and physical 

properties of late Quaternary alluvium, which is widespread 

throughout the St. Francis and Western Lowlands Basins, 

present an almost ideal setting for a study of the 1811-12 

earthquakes. 

Alluvium in St. Francis and Western Lowlands Basins 

Figure 2 shows alluvial deposits in the St. Francis and 

Western Lowlands Basins. Almost all the deposits shown in 

the eastern two-thirds of the figure are late Quaternary in 

age; only locally, generally on modem flood plains, are 

there significant deposits of much younger alluvium. Total 

thickness of alluvium is typically between 30 and 50 m 

throughout the St. Francis Basin (Saucier, 1964), and the 

thickness is only slightly less in the Western Lowlands 

Basin (Smith and Saucier, 1971). 

Alluvium in the Western Lowlands Basin and 

between the towns of Cairo and Marked Tree is mostly 

braided stream terraces of glacial outwash. These terraces 

are typically a layered sequence of "topstratum" over 

"bottomstratum" (Saucier, 1964). The top stratum is generally 
~ 

D 

[[] 

+ 

/ 

// 

// 

/ 

/ 

EXPLANATION 

Upland areas 

Alluvium; no observed sand blows 

Alluvium; recognizable vented sand blow deposits (>1 percent ground coverage) but less 

than 25 percent ground coverage 

Alluvium; more than 25 percent of ground surface covered by vented sand blow deposits 

Epicenters for the three strongest 1811-12 

earthquakes, according to Nuttli (1979) 

Fault zone 

Fault 

Fault zones and faults are from 

Hamilton and Zoback (1982) 

0 20 MILES 

I I I I 

0 20 KILOMETERS 

Figure 7. Distribution of vented sand blow deposits on alluvium excluding modern flood plains (Obermeier, in press). 

Sand blows were presumably formed by the 1811-12 earthquakes. Also shown are the energy release center line for the 

December 16, 1811, earthquake and fault zones and faults. 

a 2- to 6-m-thick overbank deposit, composed primarily of 

thick to thin strata that are very rich in clay and highly 

plastic. The clay strata are interbedded with less common 

strata of silt and very fine sand. The contact of the 

topstratum on the bottomstratum is typically gradational 

over a meter. The bottomstratum is a very clean, moderately dense sand, which is generally fine to medium grained 

near the top and grades downward to a coarse sand that has 

gravel at its base. 

Meander belt deposits of the Mississippi River generally have thick strata of clean, fine- to medium-grained 

sand, silty fine sand, and clay within the uppermost 10 to 15 

m. Beneath that are clean sands that coarsen with depth and 

are representative of the bottomstratum. A clay-rich cap of 

overbank deposits covers these meander belt deposits at 

many places, especially in swales and sloughs. The thickness of the clay-rich cap is generally less than 10m. Within 

these meander belts, there are. usually many localities 

(within a few hundred meters of one another) where the clay 

cap is only a few meters thick, and clean sand underlies the 

cap. 

Sand Blow Deposits in St. Francis Basin 

Figure 7 shows the distribution and concentration 

(that is, proportion of area covered) of sand blow deposits in 

the St. Francis Basin, excluding alluvium of modem flood 

plains. Figure 7 is based on an investigation by the author, 

who used 1938-40 vintage aerial photographs and more 

recent ones (scale about 1 :20,000) in conjunction with field 

verification. Field and aerial photographic studies represented in figure 7 were restricted to the St. Francis Basin 

and the eastern one-third to one-half of the Western Lowlands Basin (that is, the area of alluvium west of Crowleys 

Ridge). No sand blow deposits were found in the Western 

Lowlands Basin. 

Much of the field and aerial photographic study was 

directed at locating the margin of liquefaction effects, 

Liquefaction and Historical Earthquakes 9 
which was empirically defined as the outer limit where at 

least 1 percent of the ground surface is covered by sand 

blow deposits (smaller percentages are difficult to determine from aerial photographs). In that way, the location of 

the epicenter (more accurately, the "energy release center"2) 

can be estimated for the December 16, 1811 , earthquake, 

and earthquake accelerations can be estimated away from 

near-field earthquake effects by using the relations in shown 

figure 5. 

Energy Release Center 

On the basis of regional earthquake intensity studies, 

Nuttli (1979) estimated that the three largest 1811-12 

earthquakes had the epicenter (energy release center) locations shown in figure 7. Although the epicenter locations 

are very approximate, it is likely that the first strong 

earthquake, the December 16 event, was located considerably southwest of the other two. Thus, it seems reasonable 

to associate the southernmost third of the sand blow 

deposits with the December 16 event. (The three largest 

earthquakes were of approximately the same strength.) 

Estimated epicenters for the other two large events are so 

close to one another that there is less credibility in using the 

distribution of sand blow deposits to locate their energy 

release centers. 

A cursory examination of figure 7 suggests that the 

energy release center for the December 16 earthquake lies 

somewhere along a line centrally located with respect to the 

boundary of sand blow deposits, roughly in the southern 

third of these deposits. In addition, the line trends 

southwest-northeast and has a southern terminus north of 

Marked Tree. This location is based on the premise that the 

alluvium in the region, excluding very young alluvium of 

the modem flood plains, has about the same physical setting 

and engineering properties throughout the area and thus the 

same liquefaction susceptibility. To examine this premise, 

the author investigated alluvium in the St. Francis and 

Western Lowlands Basins by compiling some 400 boring 

logs. Most of the data were collected from files of the U.S. 

Army Corps of Engineers, Memphis District. About 250 of 

the logs had SPT data to depths of about 12 to 15 m. The 

boring locations were scattered throughout the area, but 

most were near levees of large drainage ditches. Data from 

very young alluvium and alluvium along most small streams 

(that is, modem flood plain deposits) were excluded. 

The data are separated in table 4 according to the 

following geographic-geologic settings: braided stream terraces in the Western Lowlands Basin, the southern half of 

braided stream terraces in the St. Francis Basin, and 

2

The epicenter is the point on the Earth's surface directly above the 

earthquake focus (the focus is the point at which strain energy is first 

converted to elastic wave energy). Thus, the epicenter may or may not be 

coincident with the point or zone of maximum energy release (that is, the 

"energy release center"). 

10 Liquefaction Potential in the Central Mississippi Valley 

Table 4. Modified penetration resistance values (N1) in 

selected settings in the Western Lowlands and St. Francis 

Basins 

Geologic-geographic Median Lower No. of 

setting N, 1 quartile N1

1 borings 

Braided stream terrace 

deposits, Western Lowlands Basin .............. 22-23 15 17 

Braided stream terrace 

deposits, southern half, 

St. Francis Basin ......... 26 15-20 105 

Meander belt deposits of 

Mississippi River ......... 25 12-18 48 

1

N1 is the modified penetration resistance, as discussed by Seed and 

others (1983). N1 values are for a depth range of 3 to 10 m. 

Mississippi River meander belt deposits. The southern half 

of braided stream terraces in the St. Francis Basin is further 

subdivided into four large areas. Strata of silty, very fine 

grained sand and of very fine sand are much more common 

in meander belt deposits than they are in braided stream 

terrace deposits, which generally have coarser sands. This 

textural difference required a correction to the SPT blow 

count (the method of Tokimatsu and Yoshimi (1981) was 

used) to account for the influence of grain size on liquefaction potential. There are no substantive differences in SPT 

blow counts or sand textures in braided stream deposits 

throughout the southern part of the St. Francis Basin. 

Table 4 shows "modified penetration resistance" (N1) 

values (N1 is defined in fig. 5), which is the field SPT blow 

count modified to account for the influence of overburden 

pressure and water table location. The N1 values are for a 

depth range of 3 to 10m, which is the range generally most 

susceptible to liquefaction in these basins (at greater depths, 

N1 values are generally higher (Obermeier, in press)). 

Median and lower quartile values (that is, the 50- and 

25-percent values) are given because they are thought by the 

author to realistically bracket the percentage of a sand body 

in this depth range that must be liquefied to form a minor 

regional development of liquefaction, as evidenced by the 

ground being covered by at least 1 percent of vented sand. 

Requiring that half the volume of sand liquefy seems an 

unrealistically high requirement, because liquefaction of a 

single layer of sand 2 to 4 m thick (having N1 values of up 

to 13-15) can be enough to cause liquefaction-induced 

damage to structures (Ishihara, 1985) at a peak horizontal 

acceleration of about 0.2 to 0.25 g and a surface-wave 

magnitude of about 7. 6 to 7. 8 (magnitudes considerably 

lower than those of the three strongest 1811-12 New 

Madrid earthquakes). Liquefaction that is sufficient to cause 

damage to structures is probably more severe than liquefaction that is adequate simply to induce minor regional 

development of sand blows. For a minor regional development of sand blow deposits, however, there must also be 
some significant degree of liquefaction, although the lower 

cutoff is very uncertain and must depend on factors other 

than N1 (for example, important factors in the 1811-12 

earthquake were topstratum thickness and the grain size of 

the liquefied stratum (Obermeier, in press)). The requirement that somewhere between 25 and 50 percent of the sand 

in the depth range 3 to 10 m must have liquefied (that is, 

2-3.5 m must have liquefied) seems consistent with boundary curves proposed by Ishihara (1985, fig. 88) showing 

relations between the thickness of the nonliquefiable cap 

and that of liquefied sand bed for different accelerations. 

Regardless of whether the median or lower quartile or 

a lower value is more appropriate, table 4 shows that, in the 

St. Francis Basin, N1 values are about the same in braided 

stream terrace deposits and in Mississippi River meander 

belt deposits, and N1 values for both types of St. Francis 

Basin alluvium tend to be slightly higher than those for 

Western Lowland braided stream terrace alluvium. The 

topstratum is so thin at many places (less than 3-4 m) in 

both the Western Lowlands and the St. Francis Basins that 

an excessive topstratum thickness could not have been a 

major factor in defining the outer bound of sand blow 

deposits, at least regionally (Obermeier, in press). Thus, the 

energy release center line (hereafter also referred to as the 

energy release line) for the earthquake of December 16, 

1811, should lie approximately central to the outer limits of 

sand blow deposits. This central location establishes the 

southernmost possible terminus and the orientation of the 

energy release line shown in figure 7. The length of the 

energy release line (about 60 km) is based on Nuttli's 

(1983) estimate of the length of rupture. 

Other data strongly suggest that the fault that caused 

the December 16 earthquake was strike-slip and was parallel to and very close to the energy release line in figure 7; as 

examples, modem seismic activity (Stauder, 1982) takes 

place near the energy release line, and the stress field in 

lithified rocks is oriented east-west (Hamilton and Zoback, 

1982). In addition, the overall style of surface deformation 

near Reelfoot Lake is consistent with a fault zone extending 

from the vicinity of the lake toward Marked Tree (Russ, 

1982). Data on modem microearthquakes suggest that the 

rupture depth was between 3 and 13 km (Nicholson and 

others, 1984). 

Accelerations in Alluvium 

Sites generally best suited for back-calculating earthquake accelerations on the basis of liquefaction are outer 

margin locations of sand blow deposits at sites of marginal 

liquefaction, where liquefaction causes only minor changes 

in preearthquake and postearthquake SPT blow counts. This 

outer margin is less than 40 km from the axis and from the 

southern terminus of the energy release line. No SPT data 

were available along the margin of sand blows in figure 7, 

so N1 values are used in the region of liquefaction. 

N1 values of 20 or less comprise at least 25 percent of 

the SPT data points in the depth range 3 to 10m (table 4) in 

the region of sand blows produced by the December 16 

earthquake, shown in figure 7. Using this N1 value of 20 as 

appropriate at the border of sand blows yields a threshold 

acceleration of slightly more than 0. 20 g required to 

generate liquefaction, assuming that the N1 values were not 

greatly changed by the earthquake. This assumption seems 

reasonable in view of the facts that ( 1) SPT blow counts and 

the geologic settings are about the same in both the Western 

Lowlands and the St. Francis Basins and (2) the Western 

Lowlands Basin did not experience significant liquefaction 

during the 1811-12 earthquakes. In summary, it is very 

probable that, 40 to 45 km from the energy release line, the 

peak horizontal accelerations at the ground surface were 

less than 0.20 g. 

Accelerations in Bedrock 

The lack of strong-motion ground response data for 

the New Madrid earthquake region makes it necessary to 

relate the acceleration in alluvium to bedrock motion by 

empirical relations developed elsewhere and by semiquantitative calculations. Seed and Idriss (1982, p. 37) have 

shown that, on average, at 0.20 g, the peak acceleration in 

rock is nearly the same or only slightly higher than that in 

overlying stiff or thick cohesionless soil. These cohesionless soils presumably range from loosely to densely packed. 

For strong earthquakes, Ishihara (1985, p. 353) stated that 

"It may as well be argued that the ratio of acceleration on 

the soil deposit to that on the rock outcrop causing liquefaction in their area is approximately in the range 0.65 to 

0.9 with an average of about 0.8." Sharma and Kovacs 

( 1980), in a micro zonation study of the Memphis area using 

the computer program SHAKE and synthetic seismograms, 

found that the moderately thick (about 30-40 m), medium 

densely packed sands of the area probably have peak 

accelerations that are about the same as those in the 

underlying bedrock for strong earthquakes in the New 

Madrid fault zone (their New Madrid fault zone includes the 

energy release center line in fig. 7); their data show that the 

peak accelerations in these sands should range from about 

equal to but not more than about 20 percent higher than 

those in the underlying bedrock. 3 All the accelerations 

back-calculated from SPT-liquefaction relations in the preceding section are from sites where sand is about 30 to 50 

m thick. Thus, it is likely that, at these sites, the peak 

accelerations at the ground surface were about the same as 

or else only slightly ( ± 20 percent) higher or lower than 

those in the bedrock beneath. 

3

Sharma and Kovacs made acceleration amplification calculations 

both for a basal stratum of sand and of gravel. The author believes that the 

results for sand are most applicable to the southern half of the St. Francis 

Basin because of the preponderance of sand. 

Liquefaction and Historical Earthquakes 11 
Table 5. Locations, intensities, and liquefactions of central Mississippi Valley historical earthquakes having body-wave 

magnitudes greater than or equal to 5.3, exclusive of 1811-12 earthquakes 

location 1 Date 

Mississippi embayment: 

lat 35.2° N., long 90.5° W. . . . . . . . . . . . . . . . . . . . . . . . . 1-4-1843 

lat 36.5° N., long 89.5° W. . . . . . . . . . . . . . . . . . . . . . . . . 8-17-1865 

lat 37.0° N., long 89.4° W. . . . . . . . . . . . . . . . . . . . . . . . . 10-31-1895 

lat 36.9° N., long 87.3° W. . . . . . . . . . . . . . . . . . . . . . . . . 11-4-1903 

Wabash Valley: 

lat 39.0° N., long 87.7° W. . . . . . . . . . . . . . . . . . . . . . . . . 9-27-1909 

Mississippi embayment: 

lat 5S N., long 90.3° W. . . . . . . . . . . . . . . . . . . . . . . . . . 10-28-1923 

lat 36.5° N., long 89.0° W. . . . . . . . . . . . . . . . . . . . . . . . . 5-7-1927 

Wabash Valley: 

lat 38.0° N., long 88.5° W. . . . . . . . . . . . . . . . . . . . . . . . . 11-9-1968 

1

Nuttli and Herrmann (1978). 2

Coffman and von Hake (1973). 

Farthest Liquefaction 

The farthest lateral spreads or flows were about 175 

km from the 1811-12 earthquake epicenters, according to 

Keefer (1984). O.W. Nuttli (oral communication, 1983) 

has found historical accounts that mention sand blow 

activity on the flood plain of the Mississippi River, near St. 

Louis. Street and Nuttli (1984) reported sand blows and 

fissures in White County, Illinois, along the Wabash River. 

These sand blows probably formed in deposits in which N1 

values of 10 or less are common (Obermeier and Wingard, 

1985). Both St. Louis and White County are less than 300 

km from the general vicinity of the epicenter for the 

February 7, 1812, earthquake (see fig. 7 for epicenter 

location). 

According to Street and Nuttli (1984), the southernmost limit of the damaged area for the December 16 

earthquake was either Island 53 or Island 57 in the Mississippi River. It is possible that liquefaction caused the 

damage on these islands, which are about 350 km south of 

the probable epicenter (fig. 7) for the December 16 earthquake. 

Other Historical Earthquakes 

Table 5 is a compilation of central Mississipi Valley 

historical earthquakes having body-wave magnitudes equal 

to or higher than 5. 3 and the associated accounts of 

liquefaction and and MM intensities. Liquefaction was 

reported only for the October 31, 1895, earthquake (which 

is also known as the Charleston, Mo., 1895 earthquake). 

Sand blows occurred at scattered locations over a region 

about 16 km in diameter, at places north of Charleston, in 

Charleston, and south and southwest of Charleston (Powell, 

1975). The region where sand blows developed is in Late 

Wisconsinan braided stream (glacial outwash) alluvium (see 

fig. 2), which is only a little less susceptible to liquefaction 

12 Liquefaction Potential in the Central Mississippi Valley 

Modified Mercalli Body-wave 

intensit/ magnitude1 liquefaction2 

VIII (minimum) 6.0 None reported 

VII 5.3 None reported 

VIII 6.2 Commonplace 

VII 5.3 None reported 

VII 5.3 None reported 

VII 5.3 None reported 

VII 5.3 None reported 

VII 5.5 None reported 

than alluvium elsewhere in the Western Lowlands and St. 

Francis Basins (excluding very young alluvium). Thus, a 

reasonable threshold for liquefaction is mb = 5.5 to 6.0 for 

braided stream and meander belt deposits in both basins, 

excluding deposits on modem flood plains. 

Earthquake Intensity and Liquefaction 

Table 5 lists no reports of liquefaction for MM VII4 or 

lower. Alternately, the MM VIII area of the 1895 Charleston earthquake, for which sand blows were reported, is in 

an area where the sediments are medium dense and at least 

moderately difficult to liquefy. It seems incongruous that 

there are no accounts in table 5 of liquefaction for the 1895 

earthquake or any other earthquakes in loose flood plain 

deposits for MM VII, and yet liquefaction did occur in 

moderately dense materials for MM VIII. The author thinks 

it probable that there were sand blows in the flood plain 

alluvium, especially the very young (less than 500 years 

old) alluvium for many of the MM VII-producing earthquakes but that sand blows were not reported. Sand boils 

develop in the flood plain behind both natural and artificial 

levees along the Mississippi River after many of the largest 

annual floods, because of the large difference in hydraulic 

head on opposite sides of the levees. Thus, in 1895, the 

sand blows in these lowland regions may not have received 

special attention. 

Figure 8 is a map prepared by Nuttli (1981) showing 

regional intensity data for the December 16, 1811, earthquake. Locations of farthest sand blows (in the Mississippi 

River flood plain near St. Louis and in the Wabash River 

4

MM intensity values in table 5 are regional values rather than 

absolute maximum values that are present within a region. At a given site, 

intensity values are commonly one unit higher or lower than regional 

values; site MM intensity values are two units higher in exceptional places. 
1 00 200 300 MILES 

I 1 I 1

1 I 1 DO 200 300 KILOMETERS 

Figure 8. Modified Mercalli intensities for the December 

16, 1811, earthquake (from Nuttli, 1981). 

valley) are in the zone of MM VII intensity. Thus, it is 

concluded that a regional MM VII is the liquefaction 

threshold for the very loose flood plain sands, regardless of 

earthquake magnitude. This intensity conforms to Keefer's 

( 1984) findings. 

SUGGESTED METHODS FOR EVALUATING 

LIQUEFACTION POTENTIAL 

Acceleration, magnitude, intensity, and liquefaction 

data are examined in this section to develop independent 

approaches for evaluating liquefaction potential. 

Simplified Procedure of Seed and ldriss 

The Simplified Procedure of Seed and Idriss requires 

an acceleration-epicentral distance relationship for various 

earthquake magnitudes in order to be versatile. Data compiled by Nuttli and Herrmann (1984a) are used in combination with acceleration data at the margin of sand blows 

(from this paper) to develop acceleration-epicentral distance relations. 

Figure 9 is a plot done by Nuttli and Herrmann 

(1984a) showing the arithmetic average of peak values of 

horizontal acceleration (average of two components) for 

stiff soil as a function of epicentral distance and body-wave 

magnitude for the Central United States. Athough Nuttli 

and Herrmann did not so state in their text, their epicenter 

is assumed to be coincident with the point of maximum 

energy release. The Nuttli-Herrman curves of accelerationepicentral distance in figure 9 are based on semitheoretical calculations, in combination with measured accelerations on small- to moderate-sized earthquakes in the New 

Madrid region. The error of estimate for one standard 

deviation for the Nuttli-Herrmann curves is a factor of 1. 74. 

The curves in figure 9 are intended to be applicable to 

stiff soil (Nuttli and Herrmann, 1984a). Stiff soils may (and 

probably do) amplify bedrock accelerations in the New 

Madrid earthquake region, as calculations by Sharma and 

Kovacs (1980) indicate. Bedrock accelerations are amplified a small to moderate amount (that is, by a factor of 

1. 1-1.4) for small to moderate accelerations for earthquakes of the size (mainly mb<5.5) from which figure 9 

was developed. The amount of amplification for unconsolidated materials also varies somewhat as a function of 

epicentral distance, acceleration level, and layer thickness. 

0 

w 

a: 

<( 

~ 

0 

(/) 

0 

z 

0 

u 

w 

(/) 

a: 

w 

0.. 

(/) 

a: 

~ w 

~ 

F 

z 

w 

u 

~ 

z 

0 

~ a: 

w 

_, 

w 

u 

~ 

200 

100 

10 

Conservative (highl estimate 

of peak horizontal acceleration (0.20gl in alluvium at 

margin of sand blows in figure 7, induced by earth· 

quake of Dec. 16, 1811 

(mb=7.11 

10 100 

DISTANCE FROM EPICENTER, IN KILOMETERS 

Figure 9. Curves for peak horizontal acceleration on stiff 

soils (arithmetic average of peak accelerations on the two 

horizontal components) versus epicentral distance for 

various body-wave magnitudes (from Nuttli and Herrmann, 1984a), and back-calculated December 16, 1811, 

accelerations for St. Francis Basin alluvium (this paper). 

Back-calculated December 16, 1811, accelerations are 

based on liquefaction data. A, Minimum possible distance 

(40-45 km) from the epicenter of the December 16, 1811, 

earthquake to the margin of sand blows; B, maximum 

possible distance (110 km) from the epicenter of the 

December 16, 1811, earthquake to the margin of sand 

blows; C, "most probable" epicentral distance (75-80 

km); C\ maximum peak horizontal acceleration in underlying bedrock that can be reasonably associated with the 

most probable epicentral distance (75-80 km). Curves are 

based almost exclusively on modern acceleration data 

from earthquakes where mb <5.5. Standard deviation of 

log acceleration values about the mb = 5.0 curve is 0.24. 

Suggested Methods for Evaluating Liquefaction Potential 13 
Thus, the basis for extrapolation to large earthquakes used 

for the Nuttli-Herrmann curves of figure 9 and the relations 

of the curves to bedrock motions are not clearly known, but, 

for now, it is assumed that the curves are applicable to 

bedrock accelerations. 

The energy release line shown on figure 7 is centrally 

located with respect to the boundary of sand blows in the St. 

Francis Basin; the southern terminus is taken to be the 

center of a semicircle described by the sand blow boundary 

(not shown). It now is assumed that the epicenter of the 

December 16 earthquake was somewhere along the energy 

release line. Given this constraint, some bounds can be 

placed on acceleration as a function of distance from the 

epicenter. The peak horizontal acceleration in bedrock for 

the December 16 earthquake, previously determined in this 

report to be near the margin of sand blow deposits, was 

probably not greater than about 0.20 g. The southern end of 

the energy release line is less than 40 km from the margin 

of sand blows. Using this distance conservatively yields (for 

hazard analysis) a peak horizontal acceleration of 0.20 g at 

40 to 45 km from the epicenter (point A, fig. 9). Point A is 

probably a slightly conservative (that is, high) estimate of 

acceleration at this lower bound epicentral distance 40 to 45 

km from the epicenter. 

The farthest possible northward location of an epicenter is midway between the southern limit of sand blows 

(south of Marked Tree) and the northern limit (near Cairo). 

If the epicenter had been farther north, widespread liquefaction would have occurred beyond the limits of sand 

blows northwest of New Madrid (fig. 7), in the braided 

stream deposits between Sikeston Ridge and Crow1eys 

Ridge (fig. 2), because braided stream deposits throughout 

the St. Francis Basin have about the same liquefaction 

susceptibility and, locally, at many places have about the 

same ability to produce sand blows. Thus, as a maximum, 

the peak horizontal acceleration was 0. 20 g 110 km from 

the epicenter, which would be located near the northern 

terminus of the energy release line in figure 7 (point B, fig. 

9). This upper bound includes the maximum possible 

effects of focusing along a strike-slip fault. Point B is the 

point that the author considers as the absurd upper limit. 

Almost certainly, the northern limits of sand blows were the 

result of the February 7, 1812, earthquake, which probably 

had its epicenter in the general vicinity of New Madrid and 

Reelfoot Lake (Nuttli, 1979). 

A reasonable southern limit for the energy release line 

(not epicenter) for the December 16 earthquake is somewhere in the center of the southernmost large area where 

vented sand covers more than 25 percent of the ground 

surface (fig. 7). Throughout much of this large area, the 

volume of sand vented to the surface was sufficient to form 

a continuous sheet of sand 1 to 1.5 m thick. North of this 

sand sheet area and northeast of the point showing Nuttli' s 

December 16 epicenter, there are only localized places 

where the vented sand is so thick and continuous. The 

14 Liquefaction Potential in the Central Mississippi Valley 

center of the sand sheet area is about 50 to 60 km from the 

farthest margin of sand blow development, south of Marked 

Tree. 

To be consistent with the definition of epicenter used 

for the Nuttli-Herrmann curves in figure 9, the midpoint of 

the energy release line must be used. The midpoint is 

determined by using a rupture (fault) length of 60 km for the 

December 16 earthquake (Nuttli, 1983). Adding half this 

length (30 km) to the distance from the southernmost 

possible limit of the energy release line to the boundary of 

sand blows (40-45 km) yields 70 to 75 km. Adding half the 

rupture length (30 km) to the distance from the center of the 

southern sand sheet to the southwestern boundary of sand 

blows (50-60 km) yields 80 to 90 km. 

An independent assessment of this range of epicentral 

distances is provided by a study of possible epicenters for 

the February 7, 1812, earthquake. The epicentral region for 

this earthquake was probably somewhere in the area of the 

Lake County uplift (Russ, 1982). This uplift, structural in 

origin, extends from about 5 km north of New Madrid to 30 

km south of New Madrid. The southern limit of the dome is 

coincident with intersecting north- and northeast-trending 

faults at a point about 25 km south of Reelfoot Lake (fig. 7). 

The southern limit of doming is also coincident with an area 

where vented sand coverage is exceptionally high (fig. 7). 

The February 7 earthquake (M8 = 8. 8) was stronger 

than the December 16 earthquake (Ms = 8. 3-8. 5), according to Nuttli (1984). Thus, the sand blows formed by the 

February 7 earthquake should presumably have been farther 

from the epicenter than those formed by the December 16 

earthquake. The southern limit of doming is about 70 km 

from the northern limits of sand blows (south of Cairo). It 

is remotely possible that sand blows were formed in terrace 

deposits some few kilometers north of Cairo and that these 

sand blows have been covered by a veneer deposited by 

flooding since 1811-12. Even when this possibility has 

been accounted for, the southern limit of doming is not 

more than 85 km from the northern limit of sand blows. 

Therefore, for the earthquake of December 16, an 

epicentral distance of 75 to 80 km seems reasonable. This 

"most reasonable epicenter" is shown as point C in figure 9. 

The author believes that the most reasonable curve of 

acceleration as a function of epicentral distance, for 

mb=7.1 (equivalent to M8 =8.5), goes through point C and 

is parallel to the curves for mb = 7. 0 and mb = 6. 5; point C is 

intended for both bedrock and medium thick (30-50 m), 

medium dense sand in the St. Francis Basin. 

Also shown in figure 9 is a data point (C1

) that 

represents the upper bound of reasonable peak horizontal 

accelerations in bedrock the same distance from the epicenter as point C (75-80 km). The acceleration at C1 is 0.25 g. 

This upper bound is based on the premise that the accelerations based on figure 5 may be as much as 25 percent too 

low. Even assuming that, for the December 16 earthquake, 

the peak acceleration at the border of sand blows may 
possibly have been 20 percent lower than that in bedrock 

(on the basis of a study of bedrock -surface acceleration 

relations anticipated for Memphis by Sharma and Kovacs 

(1980)) yields an acceleration of 0.29 g at an epicentral 

distance of 75 to 80 km; this point in figure 9 (not shown) 

falls almost exactly on the Nuttli-Herrmann curve for 

mb=7.1. 

In summary, Nuttli and Herrmann's curves indicate 

accelerations that are higher than what can be accounted for 

by the liquefaction-based data. It also should be noted that 

the Nuttli-Herrmann relations in figure 9 are the average of 

two components. Liquefaction, however, is controlled primarily by the peak component of acceleration (Seed and 

others, 1975). Again, the Nuttli-Herrmann values seem a 

little too high. 

Comparing predicted accelerations using the NuttliHerrmann curves with occurrences of farthest liquefaction 

(at St. Louis and along the Wabash River in southern 

Indiana) induced by the February 7 earthquake yields a 

similar conclusion. These two sites are in regions that 

represent the two most likely candidates for the focusing of 

energy and thus for the farthest occurrences of liquefaction 

(see fig. 12 for regions of focusing). Both St. Louis and the 

Wabash River sites are about 250 to 275 km from the center 

of the Lake County uplift. Using 250 to 275 km as 

epicentral distance and mb = 7.4 for the February 7 earthquake (Nuttli, 1983) and the Nuttli-Herrmann curves in 

figure 9 yields an acceleration of about 0.10 to 0.11 g. This 

base acceleration is estimated to be amplified by a factor of 

1.5 in the thick alluvium near St. Louis (Higgins and 

Rockaway, 1986, p. 85). Thus, anticipated peak accelerations for the February 7 earthquake are 0.15 to 0. 16 g. In 

contrast, using an N1 value of 10 for flood plain deposits 

(because such low values are common) and the curve for 

M5 =8.5 in figure 5 conservatively yields a field cyclic 

stress ratio of 0. 08. Equating this cyclic stress ratio to a 

typical field situation (using the equation on p. 6) yields an 

acceleration of 0.08 g. Clearly, the difference between the 

liquefaction model and the Nuttli-Herrmann curves is quite 

large (factor of two). It is possible that sand blows occurred 

even farther than 250 to 275 km from the February 7 

epicenter, but, if the accelerations were as large as the 

Nuttli-Herrmann curves predict, sand blows and other types 

of liquefaction-related features in flood plain deposits at St. 

Louis or along the Wabash River should have been commonplace and quite large rather than hardly mentionable. 

Because acceleration for the 1811-12 earthquakes 

indicated by the Nuttli-Herrmann curves in figure 9 is 

higher than that indicated by the liquefaction data, it is 

suggested that, for moderate to great earthquakes, the 

Nuttli-Herrmann curves be considered as the upper bound 

for liquefaction analysis. The set of curves would be for 

peak horizontal accelerations on bedrock. Then, by using 

the curves to determine the acceleration for the magnitude 

and epicentral distance in question and adjusting the accelerations for local ground conditions (such as thickness of 

alluvium and dynamic modulus properties), the liquefaction 

potential can be assessed from figure 5. This assessment 

would be for movement along the axis of a a strike-slip fault 

and thus would be an upper limit estimate of acceleration. 

Magnitude Method 

Both theoretical calculations (Youd and Perkins, 

1978) and field observations of liquefaction features (Kuribayashi and Tatsuoka, 1975; Youd, 1977; Youd and Perkins, 1978; Davis and Berrill, 1983; Keefer, 1984) demonstrate a reasonably well defined relation between the 

farthest extent of significant liquefaction and the distance 

from the epicenter for a given earthquake magnitude and a 

fixed susceptibility to liquefaction. The field observations 

were predominantly in Holocene-age silt, silty sand, or 

sand, which are materials that typically have moderate to 

high susceptibility to liquefaction during strong shaking 

(Youd and Perkins, 1978). 

Figure 10 shows results based on field observations 

and some suggested practical bounds on the limits of 

localized damaging liquefaction. The solid line is the outer 

limit of lateral spreads or flows, based on data by Davis and 

Berrill ( 1983) and by Keefer ( 1984 )5 from more than 46 

earthquakes scattered around the world. (Keefer's compilation includes both natural deposits and artificial fill.) Very 

probably, most of these data are from sites where there was 

at least 40 mm of differential lateral movement, which is 

sufficient to damage structures that are very sensitive to 

deformation. Such structures include some underground 

pipes, concrete-lined canals, and poorly built buildings 

(especially old brick bearing-wall buildings). The dashed 

line is the best fit of data for all types of liquefactioninduced ground failure in Japan, including sand blows, 

reported by Kuribayashi and Tatsuoka (1975). The dotted 

line is, for practical purposes, the outer limit of 

liquefaction-induced ground failure on natural deposits 

from all data sources. Only rarely do data for natural 

deposits lie on the solid line, which shows the outer limit of 

reported data. 

The curves (solid, dashed, and dotted) are for predominantly loose sediments, but the publications containing 

the data used to determine the curves do not report the 

5

The smallest displacements reported by Keefer are at least 40 mm; 

however, at least some (very few) data points that Keefer showed in his 

figures could have had smaller displacements (D.K. Keefer, personal 

communication, 1984). For these reasons, it is presumed that, for practical 

purposes, the lateral displacements were greater than 40 mm. In his 

original compilation, Keefer used moment magnitudes (Mw) for M>7.5; 

a replot of Keefer's data for figures 10 and 11 using surface-wave 

magnitudes (M5 ) shows basically no change in the curve of the outer limit 

of reported data. Values of M5 for the replot of the 1811-12 earthquakes 

are from Nuttli (1983). 

Suggested Methods for Evaluating Liquefaction Potential 15 
EXPLANATION 

----Outer limit of reported data. lateral spreads or 

flows. very probably >4Q-mm movement, 

predominantly loose sediments. Based on 

data from Davis and Berrill (1983) and Keefer 

(1984). Damage to deformation- sensitive 

structures. 

------Best fit for all data in Japan. Outer limit of marginal liquefaction, predominantly loose sediments. Curve from Kuribayashi and Tatsuoka 

(1975). 

................ Outer limit of liquefaction-induced ground failure on natural deposits for practical purposes. 

lateral, spreads or flows. very probably 

>40-mm movement. predominantly loose 

sediments. Based on data from Davis and 

Berrill (1983) and Keefer (1984). Damage to 

deformation-sensitive structures. Curve applies to N, values probably less than 5. 

• Data point, outer limits of sand-blow deposits 

in St. Francis Basin alluvium exclusive of 

modern flood plain and very young meander 

deposits along Mississippi River and small 

streams. 

----Conservative outer limit for marginal liquefaction, 

moderately thick 130-50 m) sand deposits. Data 

from this paper. Damage to deformation-sensitive structures. Curve applies to N1 values 

as high as 15 to 20. 

(I) 

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~ 

X Data point, outer limit of reported damage possibly owing to liquefaction for Dec. 16, 1811, 

earthquake (350 km). Data from Street and 

Nuttli (1984). 

® Data point, outer limit of reported sand-blow 

deposits for Feb. 7, 1812, earthquake (400 

km). Data from Fuller (1912). 

+ Outer limit of reported data (175 km). Lateral 

spreads or flows, very probably >40-mm 

movement, predominantly loose sediments, 

1811-12 earthquakes. Data from Keefer (19841. 

Magnitudes >5.5 are surface-wave magnitudes (Ms); 

values <5.5 are Richter local magnitudes (Md. 

\000 

500 DATA FOR 

200 FARTHEST 

LIQUEFACTION, 

100 1811-12 .-4 EARTHQUAKES 

50 ;'Dec.16, 

1811 

20 I 

10 

;1'895 Charleston 

5 I 

2 I I 

I 

0.5 , 

,lather historical 0.2 earthquakes 

0.1 

4.0 5.0 6.0 7.0 8.0 9.0 

MAGNITUDE (M) 

Figure 10. Maximum distance from the epicenter of liquefaction in sand as a function of earthquake magnitude 

(part of this figure is modified from data by Keefer (1984)). 

thickness of sediments and possible bedrock acceleration 

amplifications. It is likely, though, that very considerable 

16 Liquefaction Potential in the Central Mississippi Valley 

amplification (by a factor of 1. 5 or more) occurred at many 

of the liquefaction sites. 

Figure 10 also shows the liquefaction farthest from 

the 1811-12 earthquake epicenters. Three data points show 

the outer limit of damage possibly due to liquefaction, the 

outer limit of reported sand blows, and the outer limit of 

lateral spreads or flows. Figure 10 shows that, for the 

1811-12 earthquakes, the outer limits of liquefaction did 

not extend an unusually large distance in comparison with 

those for other large earthquakes scattered around the 

world. This observation seems surprising at first, because of 

the huge area over which the 1811-12 earthquakes caused 

high MM intensities. It is possible that occurrences of sand 

blows and other liquefaction-induced features took place 

much further than 400 km from the epicenter (the farthest 

distance on fig. 10) and were not observed, but the author 

does not believe that to be the case. In 1811 , there were 

many settlers in western Kentucky and along the Ohio River 

valley, which has a wide flood plain westward from the 

midlongitude of Indiana. This flood plain contains thick 

deposits of clean sand at many places. Natural levees along 

the Ohio River are generally small, low features, and sand 

blows caused by flooding are not commonplace. Surely, 

because they are unusual, sand blows caused by the 

1811-12 earthquakes would have been noticed and 

reported. Instead, it is more likely that the alluvium in these 

flood plains is not as loose as that in many of the other 

localities exhibiting liquefaction in figure 10. Probably the 

only sediments having very high liquefaction susceptibility 

in the central Mississippi Valley region are modern sand bar 

deposits and very young point bar and abandoned meander 

deposits less than 500 years old; these deposits would be the 

only materials liquefied at the outer limits from the epicenters. The dotted line in figure 10 is, therefore, believed to be 

a practical outer limit for very loose sands in the central 

Mississippi Valley. Only sand deposits for which N1 values 

are less than about 5 would be susceptible at this limit, on 

the basis of data compiled by Davis and Berrill (1983). 

Figure 10 also shows a conservative outer limit for 

marginal liquefaction of alluvial deposits in the St. Francis 

Basin (and, by extension, in the Western Lowlands Basin as 

well); modern flood plain and very young deposits are 

excluded. These limits were determined by using distance C 

on figure 9 (75-80 km) as the maximum distance from the 

epicenter to the outer bound of liquefaction features for the 

December 16 earthquake (the author believes this distance 

to be conservative, because it is the distance on fig. 7 from 

the center of high-intensity sand blow development to the 

southwestward limit of sand blows). For the 1895 Charleston earthquake, the midpoint between the outer limits of 

sand blows is used as the distance from the epicenter; the 

Charleston data are based on a maximum diameter of 16 km 

for sand blows (based on information reported by Powell, 

1975). The data from historical earthquakes in table 5 
provide a third point at M = 5. 5. The shape of the curve also 

has been chosen to be conservative. For magnitudes less 

than 8. 2 and larger than 6. 8, the slope is the same as that for 

much weaker sands; the overall shape conforms to that of 

the outer limit (solid) line. This curve, for the limits of 

marginal liquefaction, probably represents the outer limits 

at which liquefaction would cause some serious structural 

damage to poorly built, old commercial or residential brick 

or block buildings and other deformation-sensitive structures, but well-built masonry buildings and houses would 

experience only some cracking and other minor distressing. 

The curve applies to alluvial deposits at least 30 m thick and 

containing sand in which N1 values as low as 15 to 20 are 

relatively common in the upper 10m (for example, 2-3.5 m 

of sand deposits for which N1 < 15-20). 

For a large earthquake, as Youd and Perkins (1978) 

pointed out, epicentral distance is not a very good measure 

for the type of correlation shown in figure 10, because the 

epicenter does not define the entire zone of energy release. 

They suggested, therefore, that the seismic source zone (or 

fault rupture zone) is a better point of reference. A plot 

showing the maximum horizontal (map) distances of lateral 

spreads and flows from the fault rupture zone as given in 

reports by Keefer (1984) and Youd (1985) is the primary 

basis for figure 11. (Keefer's curve has been modified in 

accordance with comments by Y oud.) Figure 11 shows the 

outer limits, for practical purposes, for lateral spreads and 

flows exhibiting more than 40 mm of movement in predominantly loose sediments (solid line) and the practical outer 

limit for marginal liquefaction in St. Francis and Western 

Lowlands Basins alluvium, exclusive of modern flood plain 

and very young deposits (long- and short-dashed line). 

Fault rupture locations for the 1811-12 earthquakes 

were estimated from fault zones shown in figure 7. For the 

December 16 earthquake, the fault zone north of Marked 

Tree was used as the point from which to measure the 

farthest liquefaction, which was taken to be the outer bound 

of sand blows southwest of Marked Tree. For the February 

7 earthquake, the fault zone at Reelfoot Lake was used as 

the reference point, and the farthest liquefaction was taken 

to be the northernmost bound of sand blows in the braided 

stream deposits between Sikeston Ridge and Crowleys 

Ridge. The fault rupture for the 1895 Charleston earthquake 

was the location central to the margin of sand blows. 

The solid line in figure 11 is a conservative limit for 

potentially damaging liquefaction in natural loose deposits 

(N15 5). This solid line should be used for the modern 

flood plain deposits and very young alluvium. The longdash-short-dash line is thought to be a conservative bound 

for the alluvium in the St. Francis and Western Lowlands 

Basins, except for deposits on modern flood plains and very 

young alluvium. 

APPLICATION OF METHODS 

Both the Simplified Procedure of Seed and ldriss 

(used in conjunction with acceleration-epicentral distance 

EXPLANATION 

-----Outer limit of reported data. Lateral spreads or 

flows, very probably >4~mm movement, 

predominantly loose sediments. Based on 

data from Keefer (1984). Damage to deformation-sensitive structures. 

..,_ _ _____.Data points and practical outer limit for marginal liquefaction in the St. Francis and Western Lowlands Basins, exclusive of modern 

flood plain and very young deposits. Moderately thick (3~50 m) sand deposits. Data 

from this paper. Damage to deformationsensitive structures. Curve applies to N1 

values as high as 15 to 20. 

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:!E<( w 

u.. 

1,000 

500 

200 

100 

50 

20 

10 

5 

2 

0.5 

0.2 

Magnitudes >5.5 are surface-wave magnitudes (Ms); 

values <5.5 are Richter local magnitudes (Md. 

Feb. 7, 1812 

;--"-

j' Dec. fa. 1811 

I 

j, 895 Charleston 

I 

I 

I 

I 

I 

I 

I Other historical 

earthquakes 

0.1 

4.0 5.0 6.0 7.0 8.0 9.0 

MAGNITUDE (M) 

Figure 11. Maximum distance from fault rupture zone of 

liquefaction in sand as a function of earthquake magnitude (part of this figure is modified from data by Keefer 

(1984) and Youd (1985)). 

curves in fig. 9) and the magnitude method are conservative 

approaches to estimating where liquefaction is likely to 

occur in that they overestimate the geographic region where 

potential liquefaction problems exist. Both methods show 

only the farthest limits, accounting for effects such as 

focusing of energy from the epicenter or source fault. 

Focusing can cause a major distortion in the pattern of 

ground shaking, as the MM intensity contours in figures 8 

and 12 illustrate. Figure 8 shows approximately average 

regional intensities for the December 16, 1811 , earthquake; 

figure 12 is a possible maximum regional intensity map for 

an 1811-sized earthquake having an epicenter anywhere in 

the New Madrid seismic zone (that is, the zone of present 

intense microseismicity). 

Application of Methods 17 
Figure 12. Possible regional intensity map (based on 

historic earthquake data) showing estimated Modified 

Mercalli intensity values for an 1811-sized earthquake 

(M5 =8.6) having an epicenter anywhere along the New 

Madrid seismic zone (from Hopper and others, 1983). 

Intensity values are the highest that can be reasonably 

expected within an area. Tile seismic zone used to make 

the map corresponds approximately to the region of 

concentrated modern epicenters in southeastern Missouri, northwestern Tennessee, and northeastern Arkansas, reported by Stauder (1982). 

Figure 12 is based on data from earthquakes listed in 

table 5. Intensity data from all the larger historical earthquakes ( 1811 , 1843, 1895) having epicenters approximately 

in the zone of most frequent modern seismic activity 

(Stauder, 1982) (from approximately Marked Tree to Cairo) 

have MM intensity values of VII and higher and are 

consistently strongly focused in much the same geographic 

area. Hopper and others (1983) found that the largest MM 

intensities are in a region oriented approximately parallel to 

the zone of modern seismicity; in addition, there is some 

focusing in close proximity to the Mississippi River, 

extending from near Cairo toward St. Louis. Figure 12 was 

made by drawing MM intensity contour maps for the 1843 

and 1895 earthquakes and then scaling them to the 1811 

earthquake. For example, the highest MM intensity for the 

1895 earthquake was VIII, and the highest for 1811 was XI; 

thus, a value of III was added to all the 1895 values. 

Intensity values in figure 12 approach being the highest that 

can be expected in a region, accounting for the influence of 

both focusing of energy and amplification of bedrock 

motions on weak soil. 

Although figures 8 and 12 indicate that there are large 

variations in shaking severity as a function of distance from 

the epicenter, it does not now seem practical or realistic to 

try to quantify these variations on the basis of the two 

18 Liquefaction Potential in the Central Mississippi Valley 

methods developed in this paper. Instead, it is suggested 

that estimates of the farthest limits of liquefaction be based 

both on the Simplified Procedure of Seed and Idriss in 

conjunction with figure 9 and on the magnitude method; in 

addition, reports published elsewhere on the relations 

between epicentral distance, MM intensity, and acceleration (for example, Nuttli and Herrmann, 1984a, b; Krinitzsky and Marcuson, 1983) should be consulted. 

When MM intensity relations are used, it should be 

remembered that, for practical purposes, an average 

regional value of MM VII is the liquefaction threshold for 

modern flood plain deposits, which have very loose sands. 

On a map of maximum intensity values, such as figure 12, 

MM VIII is therefore the threshold for minor occurrences of 

liquefaction of very loose sediments subjected to highly 

amplified bedrock motion; for figure 12, MM IX is probably the intensity threshold at which damaging liquefaction 

becomes relatively commonplace in very loose to loose 

sands. The MM values shown for much of the area in figure 

12 are two units higher than average regional MM values, 

such as those shown in figure 8. 

The final judgment on whether potential problems 

exist must be based on the consequences of an occurrence of 

liquefaction. For example, if all methods show that a high 

probability of liquefaction exists and if a critical structure is 

involved, then some sort of mitigation is in order. For other 

than critical structures, the decision may be quite subjective. 

LIQUEFACTION SUSCEPTIBILITY AND 

GEOLOGIC ORIGIN 

The texture, mode of deposition, and age of deposits 

affect liquefaction potential in a generally predictable way 

(Youd and Perkins, 1978), as discussed earlier. On the basis 

of these criteria, sediments in the central Mississippi Valley 

have been categorized for susceptibility to liquefaction on a 

regional basis (at a scale of 1:1 ,000,000) by means of 

surficial geologic map units (Obermeier and Wingard, 

1985). Surficial geologic maps are available in all States at 

a scale of 1:1,000,000 and, in some States, at scales 

showing much more detail. Maps at a scale of 1:62,000 or 

1:24,000 are optimal but are generally available only for 

localized areas. 

Because many of the deposits shown on the State 

maps have formation names that may change at a State 

boundary, names are not used in this discussion; rather, the 

geologic origin and age are used as a basis. Liquefaction 

potential is given in terms of N1 values whenever possible. 

Braided Stream and Meander Belt Deposits 

The properties of Wisconsinan-age glacial outwash 

(braided stream) deposits and those of Mississippi River 
meander belt deposits, shown in figure 2, have been 

described previously in the text and in table 4 and will only 

be summarized here. Median N1 values are generally near 

25 in the upper 15 m and increase slightly with depth. 

Rarely, N1 values are as low as 10 to 12 within the upper 15 

m. There are abundant thick, clean sands that fine upward 

to a thin stratum of fine or silty sand just beneath a clay-rich 

cap, which is generally 3 to 6 m thick. Glaciofluvial terrace 

deposits possessing about the same properties are present 

along many of the larger streams north of the St. Francis 

Basin. The Wabash and Ohio Rivers have especially large 

volumes of clean sand in Illinois and Indiana. Thicknesses 

of 30 m are not unusual. 

Although rivers farther south did not carry glacial 

outwash, many have terraces that are Late Wisconsinan in 

age or older and are composed dominantly of thick, clean 

sands. The Obion River in Tennessee has some especially 

large terraces. The terrace deposits along the southern rivers 

probably have about the same resistance to liquefaction as 

the braided stream deposits in the St. Francis and Western 

Lowlands Basins do, because they are all about the same 

age, contain minerals having about the same physical 

properties, and have shallow water tables. 

Glacial Lake Deposits 

Large glacial lakes formed along many rivers carrying glacial meltwater, particularly in Indiana, Illinois, and 

Kentucky. Many of these glacial lakes laid down thick 

deposits of sand, silt, and clay. At many places, grain size 

tends to fine upward from a basal sand. Thicknesses of 15 

mare commonplace. 

Near large streams, thick and unusually loose sands 

(N1 =8) about 6 m deep occur at many places. Elsewhere, 

the sands are denser and have much higher N1 values. Very 

soft silts and clayey silts having SPT blow counts of 2 to 3 

are relatively common in low terraces adjoining streams 

throughout Indiana, Illinois, and Kentucky. The higher, 

better drained terraces typically have much higher blow 

counts owing to the effects of dessication and a lower 

ground-water table. 

Modern Flood Plain Deposits, Exclusive of Very 

Young Sediments 

Very young sediments less than about 500 years old 

are excluded from the class of modem flood plain deposits. 

Modem flood plains along major. streams generally have 

thick strata of clean sand, silt, and clay. The sands generally 

have median N1 values of 15 that are commonplace locally. 

Silt-rich strata in some abandoned channels are so soft as to 

be potentially subject to liquefaction. 

Very Young Sediments 

Very young sediments are defined as being less than 

500 years old. Very young sediments typically border 

streams as point bars or are sand bars in streams. However, 

very young meander cutoffs can be far from large streams. 

N1 values of less than 10 are very common in sands. Very 

young meander cutoffs also contain very loose, very soft 

sediments at many places. 

Eolian Deposits 

Thick loess deposits are found in many upland areas 

near major streams that carried large volumes of glacial 

meltwater. The Wabash and Mississippi Rivers have especially thick loess deposits on uplands adjoining the flood 

plain, especially east of the rivers. Near the rivers, thicknesses of 20 to 25 m are not unusual. The loess is 

predominantly silt and exhibits almost no cohesion at some 

places. Even clayey silt loess can have an extremely low 

cohesion and a sensitivity6 as high as 10 and is possibly 

subject to liquefaction under conditions of large shear 

straining or flowing (Randall Jibson, oral communication, 

1984), although landslides in loess caused by the 1811-12 

earthquakes have no features indicative of large flowage. 

Locally, and especially near large rivers, loess has lenses of 

clean, very loose dune sand or water-deposited strata of 

clean sand. In the highly dissected upland areas of thick 

loess, the loess may be only locally or partially saturated far 

beneath the ground surface and is not very susceptible to 

liquefaction except very locally. Where the ground water 

table is high, though, it is possible that slopes in loess are 

potentially subject to flowing failure during earthquakes. 

Reworked Eolian Deposits 

At the base of the high loess bluffs along major 

rivers, there is generally a veneer of silt washed down from 

the hills. This veneer is 6 m thick at many places and is 

commonly very soft in lowland areas. Clearly, many of 

these sediments are weak enough to liquefy in moderate to 

severe shaking, although liquefaction would probably be 

accompanied by limited straining in most cases. To the 

author's knowledge, the only data relevant to evaluation of 

dynamic behavior of reworked eolian materials are in a 

thesis by Puri ( 1983). 

SUMMARY 

There are so few data on strong earthquakes in the 

central Mississippi Valley that each of the methods most 

6

Sensitivity is defined as the ratio of undisturbed unconfined 

compressive strength divided by the remolded unconfined compressive 

strength. 

Summary 19 
commonly used for evaluating liquefaction potential, 

whether it is based on accelerations, magnitudes, or intensities, has some uncertainty. However, on the basis of 

production of earthquake-induced liquefaction during the 

1811-12 earthquakes, the Nuttli-Herrmann curves showing 

relations between acceleration and epicentral distance are 

conservative for engineering analysis. Conservative bounds 

have also been established for farthest liquefaction in many 

geologic settings for different earthquake magnitudes. 

There are many large terraces and flood plains in the 

central Mississippi Valley region that contain moderately 

dense to loose clean sands and silty sands. Evaluation of 

their liquefaction potential is reasonably easy and straightforward. 

Many thick glacial lake deposits, eolian deposits, and 

reworked eolian deposits are made up of silt-rich materials 

of generally low but locally high liquefaction susceptibility. 

Even if the silt-rich materials are liquefied, however, it is 

likely that their capacity for large straining is limited. Field 

methods for assessing their liquefaction susceptibility are 

extremely crude at best, and laboratory data appear to be so 

scarce that there are no guidelines based on simple criteria 

such as void ratio, cohesion, and plasticity characteristics. 

REFERENCES CITED 

American Society for Testing and Materials, 1978, Annual book 

of ASTM standards, pt. 19, Designation D 1586-67 (reapproved 1974), standard method for penetration test and split 

barrel sampling of soils: Philadelphia, Pa., p. 235-237 

Anderson, L.R., Keaton, J.R. Aubry, K., and Ellis, S.J., 1982, 

Liquefaction potential map for Davis County, Utah: Salt Lake 

City, Utah, Dames and Moore Consulting Engineers, 49 p. 

Bennett, M.J., Youd, T.L., Harp, E.L., and Wieczorek, G.F., 

1981, Subsurface investigation of liquefaction, Imperial Valley earthquake, California, October 15, 1979: U.S. Geological Survey Open-File Report 81-502, 83 p. 

Coffman, J.J., and von Hake, C.A., 1973, Earthquake history of 

the United States: National Oceanic and Atmospheric Administration Publication 41-1, 208 p. 

Davis, R.O., and Berrill, J.B., 1983, Comparison of a liquefaction theory with field observations: Geotechnique, v. 32, no. 

4, p. 455--460. 

Fuller, M.L., 1912, The New Madrid earthquake: U.S. Geological Survey Bulletin 494, 119 p. 

Hamilton, R.M., and Zoback, M.D., 1982, Tectonic features of 

the New Madrid seismic zone from seismic reflection profiles, in McKeown, F.A., and Pakiser, L.C., eds., Investigations of the New Madrid, Missouri, earthquake region: 

U.S. Geological Survey Professional Paper 1236-F, p. F55-

F82. 

Higgins, J.D., and Rockaway, J.D., 1986, A graphics system for 

seismic response mapping: Bulletin of the Association of 

Engineering Geologists, v. 23, no. 1, p. 77-91. 

Hopper, M.G., Algermissen, S.T., and Dobrovolny, E.E., 1983, 

Estimation of earthquake effects associated with a great 

earthquake in the New Madrid seismic zone: U.S. Geological 

Survey Open-File Report 83-179, 94 p. 

20 Liquefaction Potential in the Central Mississippi Valley 

Housner, G.W., 1958, The mechanism of sandblows: Bulletin of 

the Seismological Society of America, v. 48, p. 155-161. 

Ishihara, K., 1985, Stability of natural deposits during earthquakes, in International Conference on Soil Mechanics and 

Foundation Engineering, 11th, San Francisco 1985, Proceedings: Boston, Balkema, v. 1, p. 321-376. 

Keefer, D.K., 1984, Landslides caused by earthquakes: Geological Society of America Bulletin, v. 95, p. 406--421. 

Krinitzsky, E.L., and Marcuson, W.F., 1983, Principles for 

selecting earthquake motions in engineering design: Bulletin 

of the Association of Engineering Geologists, v. 20, no. 3, p. 

253-265. 

Kuribayashi, E., and Tatsuoka, F., 1975, Brief review of liquefaction during earthquakes in Japan: Soils and Foundations, 

v. 15, no. 4, p. 81-92. 

Mosaic, 1979, When soils start to flow: v. 10, no. 4, p. 26-34. 

Nicholson, C., Simpson, D.W., Singh, S., and Zollweg, J.E., 

1984, Crustal studies, velocity inversions, and fault tectonics: 

Results from a microearthquake survey in the New Madrid 

seismic zone: Journal of Geophysical Research, v. 89, no. 

B6, p. 4545--4558. 

Nuttli, O.W., 1979, Seismicity of the central United States, in 

Hatheway, A.W., and McClure, C.R., Jr., eds., Geology in 

the siting of nuclear power plants: Reviews in Engineering 

Geology, v. 4, p. 67-93. 

---1981, Evaluation of past studies and identification of 

needed studies of the effects of major earthquakes occurring 

in the New Madrid fault zone: Report submitted to Federal 

Emergency Management Agency, Region VII, Kansas City, 

Mo., 28 p. 

---1983, Empirical magnitude and spectral scaling relations 

for mid-plate and plate-margin earthquakes, in Duda, S.J., 

and Aki, K., eds., Quantification of earthquakes: Tectonophysics, v. 93, nos. 3--4, p. 207-223. 

Nuttli, O.W., and Herrmann, R.B., 1978, State-of-the-art for 

assessing earthquake hazards in the United States-Credible 

earthquakes for the Central United States: U.S. Army Corps 

of Engineers Miscellaneous Paper S-73-1, Report 12, 99 p. 

---1982, Earthquake magnitude scales: American Society of 

Civil Engineers Proceedings, Journal of the Geotechnical 

Engineering Division, v. 103, no. GT 5, p. 783-786. 

---1984a, Ground motion of Mississippi Valley earthquakes: 

Journal of Technical Topics in Civil Engineering, American 

Society of Civil Engineers, v. 110, v. no. 1, p. 54-69. 

---1984b, Source characteristics and strong ground motion of 

New Madrid earthquakes, in Gori, P.L., and Hays, W.W., 

eds., Proceedings of the symposium on the New Madrid 

seismic zone: U.S. Geological Survey Open-File Report 

84-770, p. 330-352. 

Obermeier, S.F., in press, The New Madrid earthquakes: An 

engineering-geologic interpretation of relict liquefaction features: U.S. Geological Survey Professional Paper 1336-B. 

Obermeier, S.F., and Wingard, N.E., 1985, Potential for liquefaction in areas of Modified Mercalli intensities IX and 

greater, in Hopper, M.G., ed., Estimation of earthquake 

effects associated with large earthquakes in the New Madrid 

seismic zone: U.S. Geological Survey Open-File Report 

85-457, p. 127-140. 

Obermeier, S.F., Jacobson, R.B., Powars, D.S., Weems, R.E., 

Hallbick, D.C., Gohn, G.S., and Markewich, H.W., 1986, 

Holocene and late Pleistocene(?) earthquake-induced sand 

blows in coastal South Carolina, in U.S. National Conference 

on Earthquake Engineering, 3d, Charleston, S.C., 1986, 

Proceedings: El Cerrito, Calif., Earthquake Engineering 

Research Institute, v. 1, p. 197-208. 
Powell, B.F., 1975, History of Mississippi County, Missouri, 

beginning through 1972: Independence, Mo., BLN Library 

Service. 

Puri, V., 1983, Liquefaction behavior and dynamic properties of 

loessial (silty) soils: Rolla, Mo., University of Missouri, 

unpublished Ph.D. thesis, 295 p. 

Russ, D.P., 1982, Style and significance of surface deformation in 

the vicinity of New Madrid, Missouri, in McKeown, F.A., 

and Pakiser, L.C., eds., Investigations of the New Madrid, 

Missouri, earthquake region: U.S. Geological Survey Professional Paper 1236-H, p. H95-H114. 

Saucier, R. T., 1964, Geological investigation of the St. Francis 

Basin, lower Mississippi Valley: U.S. Army Corps of Engineers Waterways Experiment Station Technical Report 

3--659. 

---1974, Quaternary geology of the lower Mississippi Valley: 

Arkansas Archeological Survey Research Series, no. 6, 26 p. 

---1977, Effects of the New Madrid earthquake series in the 

Mississippi alluvial valley: U.S. Army Corps of Engineers 

Waterways Experiment Station Miscellaneous Paper S-77-5, 

10 p. 

Seed, H.B., 1968, Landslides during earthquakes due to soil 

liquefaction: Proceedings of the American Society of Civil 

Engineers, Journal of the Soil Mechanics and Foundations 

Division, v. 93, no. SM5, p. 1055-1122. 

---1979, Soil liquefaction and cyclic mobility for level ground 

during earthquakes: Proceedings of the American Society of 

Civil Engineers, Journal of the Geotechnical Engineering 

Division, v. 105, no. GT2, p. 201-255. 

Seed, H.B., and ldriss, I.M., 1971, Simplified procedure for 

evaluating soil liquefaction potential: Proceedings of the 

American Society of Civil Engineers, Journal of the Soil 

Mechanics and Foundations Division, v. 93, no. SM9, p. 

1249-1273. 

---1982, Ground motions and soil liquefaction during earthquakes: Berkeley, Calif., Earthquake Engineering Research 

Institute Monograph Series, 134 p. 

Seed, H.B., ldriss, I.M., and Arango, 1., 1983, Evaluation of 

liquefaction potential using field performance data: Proceedings of the American Society of Civil Engineers, Journal of 

the Geotechnical Engineering Division, v. 109, no. GT3, p. 

458-482. 

Seed, H.B., ldriss, I.M., Makdisi, F., and Bannerjee, N., 1975, 

Representation of irregular stress time histories by equivalent 

uniform stress series in liquefaction analyses: Berkeley, 

-k U.S. GOVERNMENT PRINTING OFFICE: 1988 - 201-933 - 226/80025 

Calif., Report EERC 75-28, Earthquake Engineering 

Research Center, University of California, 13 p. 

Sharma, S., and Kovacs, W.D., 1980, Microzonation of the 

Memphis, Tennessee, area: West Lafayette, Ind., Purdue 

University, Report 14-08-0001-17752, 129 p. 

Smith, F.L., and Saucier, R.T., 1971, Geological investigations 

of the Western Lowlands area, lower Mississippi Valley: 

U.S. Army Corps of Engineers Waterways Experiment Station Technical Report S-71-5. 

Stauder, W., 1982, Present day seismicity and identification of 

active faults of the New Madrid seismic zone, in McKeown, 

F.A., and Pakiser, L.C., eds., Investigations of the New 

Madrid, Missouri, earthquake region: U.S. Geological Survey Professional Paper 1236-C, p. C21-C30. 

Street, R.L., and Nuttli, O.W., 1984, The central Mississippi 

Valley earthquakes of 1811-12, in Gori, P.L., and Hays, 

W.W., eds., Proceedings of the symposium on the New 

Madrid seismic zone: U.S. Geological Survey Open-File 

Report 84-770, p. 33--63. 

Terzaghi, K., and Peck, R.B., 1967, Soil mechanics in engineering practice: New York, John Wiley, 566 p. 

Tokimatsu, K., and Yoshimi, Y., 1981, Field correlation of soil 

liquefaction with SPT and grain size: International Conference on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics, Rolla, Mo., 1981, Proceedings, 

v. 1, p. 203-208. 

Youd, T.L., 1973, Liquefaction, flow, and associated ground 

failure: U.S. Geological Survey Circular 688, 12 p. 

---1977, Discussion of brief review of liquefaction during 

earthquakes in Japan by Eiichi Kuribayashi and Fumio 

Tatsuoka, 1975: Soils and Foundations, v. 17, no. 1, p. 

82-85. 

---1978, Major cause of earthquake damage is ground failure: 

Civil Engineering, v. 48, no. 4, p. 47-51. 

---1985, Landslides caused by earthquakes: Discussion: Geological Society of America Bulletin, v. 96, p. 1091-1092. 

Youd, T .L., and Bennett, M.J., 1983, Liquefaction sites, Imperial 

Valley, California: Proceedings of the American Society of 

Civil Engineers, Journal of the Geotechnical Engineering 

Division, v. 109, no. GT3, p. 440-457. 

Youd, T.L., and Hoose, S.N., 1978, Historic ground failures in 

northern California triggered by earthquakes: U.S. Geological Survey Professional Paper 993, 177 p. 

Youd, T.L., and Perkins, D.M., 1978, Mapping liquefactioninduced ground failure potential: Proceedings of the American Society of Civil Engineers, Journal of the Geotechnical 

Engineering Division, v. 104, no. GT4, p. 433-446. 

References Cited 21