Field Demonstrations of Five Geophysical 

Methods that Could Be Used to Characterize 

Deposits of Alluvial Aggregate

U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2007–5226
Field Demonstrations of Five 

Geophysical Methods that Could Be 

Used to Characterize Deposits of Alluvial 

Aggregate

By K.J. Ellefsen, B.L. Burton, J.E. Lucius, S.S. Haines, D.V. Fitterman, J.A. Witty, 

D. Carlson, B. Milburn, and W.H. Langer

Scientific Investigations Report 2007–5226

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2007

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Suggested citation:

Ellefsen, K.J., Burton, B.L., Lucius, J.E., Haines, S.S., Fitterman, D.V., Witty, J.A., Carlson, D., Milburn, B., and Langer, 

W.H., 2007, Field demonstrations of five geophysical methods that could be used to characterize deposits of alluvial 

aggregate: U.S. Geological Survey Scientific Investigations Report 2007–5226, 20 p.
iii

Contents

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................1

Background.....................................................................................................................................................1

Regional Geology..................................................................................................................................1

Description of the Field Site................................................................................................................2

Geophysical Surveys.....................................................................................................................................3

Introductory Remarks...........................................................................................................................3

Time-Domain Electromagnetic Sounding .........................................................................................3

Description of the Method .........................................................................................................3

Data Collection.............................................................................................................................4

Data Processing...........................................................................................................................4

Typical Results..............................................................................................................................4

Electrical Resistivity Profiling ............................................................................................................5

Description of the Method .........................................................................................................5

Data Collection.............................................................................................................................5

Data Processing....................................................................................................................................6

Typical Results..............................................................................................................................6

S-wave Reflection Profiling ................................................................................................................7

Description of the Method .........................................................................................................7

Data Collection.............................................................................................................................8

Data Processing...........................................................................................................................8

Typical Results..............................................................................................................................9

S-wave Refraction Profiling................................................................................................................9

Description of the Method .........................................................................................................9

Data Collection.............................................................................................................................9

Data Processing...........................................................................................................................9

Typical Results..............................................................................................................................9

P-wave Refraction Profiling..............................................................................................................11

Description of the Method .......................................................................................................11

Data Collection...........................................................................................................................12

Data Processing.........................................................................................................................12

Typical Results............................................................................................................................12

Interpretation................................................................................................................................................12

Time-Domain Electromagnetic Soundings .....................................................................................12

Electrical Resistivity Profiles ............................................................................................................14

S-wave Reflection Profiles................................................................................................................15

S-wave Refraction Profiles ...............................................................................................................15

P-wave Refraction Profiles ...............................................................................................................16

Consistency of Interpretations .........................................................................................................16

Conclusions and Implications....................................................................................................................16

Acknowledgments.......................................................................................................................................17

References Cited..........................................................................................................................................18

References to Previous Investigations of Alluvial Aggregate .............................................................19
iv

Plates

1. Locations of geophysical profiles, geophysical soundings, and drill holes

2. Selected drill-hole logs

3. Geophysical and geological cross sections

Figures

1. Generalized stratigraphic column near the field site .............................................................2

2. Photograph showing a portion of the field site, looking northwesterly from Road 1........2

3. Photograph showing receiver coil and data recorder used for TEM soundings ..............3

4. Graphs showing typical results from a TEM sounding. A, Apparent resistivities

and their standard deviations. B, Electromagnetic model estimated from the 

apparent resistivities....................................................................................................................5

5. Photographs showing A, Electrode and cable attachment used for electrical 

resistivity profiling. B, Electrodes and the associated cables used to collect one 

set of measurements. C, Instrument used to collect and record the electrical 

resistivity data ...............................................................................................................................6

6. Typical results from an electrical resistivity profile................................................................7

7. Photographs showing equipment used for S-wave seismic reflection and refraction 

profiling. A, Clog source. B, Golf shoe source. C, Geophone used to detect the

S-wave. D, Seismograph used to record the time-varying voltages generated by

the geophones ..............................................................................................................................7

8. S-wave seismic reflection and refraction data recorded in the farm field ........................8

9. Typical results from an S-wave reflection profile...................................................................9

10. Typical results from an S-wave refraction profile. A, Measured and calculated 

traveltimes. B, Cross section showing the S-wave velocities estimated from the 

measured traveltimes. C, Cross section showing the number of rays passing 

through each block in the seismic cross section..................................................................10

11. Photographs showing equipment used for P-wave refraction profiling. A, Truckmounted, weight-drop source. B, Close-up view of the truck-mounted, 

weight-drop source. C, 9.1-kg sledgehammer source. D, Geophone used to

detect P-waves ...........................................................................................................................11

12. P-wave refraction data recorded in the farm field ...............................................................12

13. Graphs A and B, showing interpretations of two time-domain electromagnetic 

soundings, including the driller’s logs from the holes that are closest to the 

soundings ....................................................................................................................................13
v

Tables

1. Acquisition parameters for the electrical resistivity profiles................................................6

2. Acquisition parameters for the S-wave seismic reflection and refraction profiling .......8

3. Procedures used to process the S-wave reflection data......................................................8

4. Acquisition parameters for the P-wave refraction profiling ...............................................12

5. Summary of the field demonstrations, indicting whether a geologic or hydrologic 

feature was detected or measured by each geophysical method.....................................17
 
Abstract

Personnel from the U.S. Geological Survey and Martin 

Marietta Aggregates, Inc., conducted field demonstrations 

of five different geophysical methods to show how these 

methods could be used to characterize deposits of alluvial 

aggregate. The methods were time-domain electromagnetic 

sounding, electrical resistivity profiling, S-wave reflection 

profiling, S-wave refraction profiling, and P-wave refraction profiling. All demonstrations were conducted at one site 

within a river valley in central Indiana, where the stratigraphy 

consisted of 1 to 2 meters of clay-rich soil, 20 to 35 meters of 

alluvial sand and gravel, 1 to 6 meters of clay, and multiple 

layers of limestone and dolomite bedrock. All geophysical 

methods, except time-domain electromagnetic sounding, 

provided information about the alluvial aggregate that was 

consistent with the known geology. Although time-domain 

electromagnetic sounding did not work well at this site, it has 

worked well at other sites with different geology. All of these 

geophysical methods complement traditional methods of 

geologic characterization such as drilling. 

Introduction

Companies that mine aggregate need to know the geology of a deposit when they are determining whether it can be 

profitably mined, when they are selecting methods to mine it, 

and when they are calculating their reserves. The geology of 

a deposit can be determined, in part, with surface geophysical 

surveys. For these surveys, instruments on the surface of the 

ground generate signals such as sound waves, radio waves, 

or electrical currents. These signals are sent into the ground 

where they interact with geologic heterogeneity. The modified 

signals return to the ground surface where they are detected 

and recorded by other instruments. These modified signals 

are then processed to develop a geophysical cross section of 

the ground, and this cross section is interpreted in terms of the 

geology. 

About 15 geophysical investigations of aggregate deposits have been published (Ellefsen and others, 1998; Ellefsen 

and others, 2005; and the section “References to Previous 

Investigations of Alluvial Aggregate”). These investigations, 

with one exception, focused on obtaining geologic information using just one geophysical method. The exception is 

Ellefsen and others (1998) who conducted demonstrations of 

four different geophysical methods to show how they could 

characterize an aggregate deposit. These four methods were 

time-domain electromagnetic sounding, frequency-domain 

electromagnetic profiling, electrical resistivity sounding, and 

ground-penetrating radar. 

In this study, five different geophysical methods are demonstrated to show how they could characterize an aggregate 

deposit. These five methods, with one exception, are different 

from the four methods that were previously demonstrated by 

Ellefsen and others (1998). The five methods are time-domain 

electromagnetic sounding, electrical resistivity profiling, 

S-wave reflection profiling, S-wave refraction profiling, and 

P-wave refraction profiling. These field demonstrations show 

the advantages and limitations of the various methods.

This study involved personnel from both the U.S. 

Geological Survey and Martin Marietta Aggregates, Inc. 

The field site for the study was leased for mining by Martin 

Marietta, and so the exact location of the field site (that is, the 

latitude and the longitude) is not stated in this report because 

of an informal non-disclosure agreement. For the same reason, 

the names of the roads adjoining the field site are altered for 

this report. Nonetheless, the approximate location of the field 

site is stated, and the geology of the site is fully described.

Background

Regional Geology

The field site is located near Columbus, Indiana (pl. 1), 

and is within the physiographic area called the “Scottsburg 

Lowland” (Gray, 2000). The field site lies within the Flatrock 

Field Demonstrations of Five Geophysical Methods 

that Could Be Used to Characterize Deposits of Alluvial 

Aggregate

By K.J. Ellefsen, B.L. Burton, J.E. Lucius, S.S. Haines, D.V. Fitterman, J.A. Witty, D. Carlson, B. Milburn, and 

W.H. Langer
2 Field Demonstrations of Five Geophysical Methods that Could Be Used to Characterize Deposits of Alluvial Aggregate

River Valley whose sediments were deposited by meltwater 

of the Wisconsin glacier about 15,000 to 20,000 years ago 

(National Cooperative Soil Survey, 2002). 

The stratigraphy pertinent to this study is shown in 

figure 1. The deepest sedimentary bedrock layer is shale and 

shaley limestone of the Upper Ordovician Series, which is 

60 m or more thick (Thompson, 1996). The next overlying 

layer is limestone and dolomite of the Silurian System, which 

is as much as 45 m thick (Maier, 2004). The next layer is 

limestone and dolomite of the Middle Devonian Series, which 

is as much as 23 m thick. These sedimentary layers dip gently 

to the west into the Illinois Basin tectonic feature (Maier, 

2004; Rupp, 1997). The limestone and dolomite layers form a 

freshwater aquifer.

Overlying the bedrock are three layers of unconsolidated sediments (fig. 1). The deepest is a clay layer, which 

is 1 to 6 m thick (Maier, 2004). The next layer is alluvium, 

which is 15 to 30 m thick and mostly consists of sand and 

gravel. This alluvium is outwash from the Wisconsin glaciation and was deposited mostly as valley train (Indiana 

University, 2005). (Valley train is defined as a long, narrow body of outwash that was deposited in a river valley, far beyond the margin of an active glacier [Bates and 

Jackson, 2005].) The uppermost layer is soil, which is 1 to 

2 m thick and is characterized as silt loam, silty loam, and 

silty clay loam (National Cooperative Soil Survey, 2002). 

Age (Ma) Lithology

0.015-0.020

360-410

410-440

440-446

1 - 2

15 - 30

1- 6

up to 23

up to 45

60 or more

loamy soil

sand

and

gravel

till, clay

limestone

and

dolomite

limestone

and

dolomite

shale and

shaley

limestone

Thickness

(m) Time Unit

Period Epoch

Quaternary Pleistocene

Devonian

Silurian

Ordovician Late

power lines and a buried telephone line; on the east side of this 

road is a farmhouse and associated farm buildings. Near the 

intersection of Roads A and 2 is an electrical power station, 

which is not shown on the plate. Along Road A are electrical 

power lines; on the east side of this road is a farmhouse and 

associated farm buildings. Between this farmhouse and a pivot 

irrigator, which is in the middle of the field, is an electrical 

power line that is buried beneath the ground surface. 

The farmland at the field site is practically flat (fig. 2). 

Because the geophysical data were collected during March, 

the farm fields were not planted with crops but were littered 

with remnants of crops from the previous year (for example, 

parts of corn stalks). The soil in the fields was dry and somewhat hard because neither rain nor snow had fallen recently. 

On the southeastern side of the farm field, the soil was covered 

by sand, which was apparently deposited by the Flatrock River 

during a recent flood. The farmhouse yards were fenced with 

barbed wire. 

Figure 1. Generalized stratigraphic column near the field site 

(adapted from Indiana University, 1986; and Thompson, 1996).

Description of the Field Site

The field site is in farmland (pl. 1), which is bordered on 

its east side by the Flatrock River; on its north side by Road 3; 

on its west side by Roads A, 2, and B; and on its south side 

by Road 1. Road 3 had moderate automobile and truck traffic; 

all other roads had little traffic. Along Road B are electrical 

Figure 2. A portion of the field site, looking northwesterly from 

Road 1 (pl. 1). In the foreground is sand, which is overlying the 

soil. In the distance is the pivot irrigator.

The field site was drilled, and the cuttings were logged to 

determine the stratigraphy. The locations of the drill holes are 

shown on plate 1. Drilling stopped either when the drill penetrated the clay layer beneath the sand and gravel layer (fig. 1) 

or when the drill stem reached its maximum length, 30.5 m 

(100 ft). For the latter case, the drill logs lack information 

about the stratigraphy at depths greater than 30.5 m (100 ft). 

Beneath the soil, the logs record the dominant sediments 

within depth intervals of about 3 m (10 ft). 

To help visualize the geology, selected logs are plotted along two profiles whose locations are shown on plate 1. 

Profile LL ́ is oriented along the river valley, whereas profile MM ́ is oriented across the river valley. In every log (pl. 2), 

the top layer is soil. Its thickness ranges from 0.6 to 2.4 m (2 

to 8 ft), and the median thickness is 1.2 m (4 ft). Beneath the 

soil is a layer of coarse gravel and sand. Its thickness ranges 

from 3.0 to 11.6 m (10 to 38 ft), and the median thickness is 

5.2 m (17 ft). Beneath the coarse gravel and sand is a layer of 

fine gravel and sand, except in drill holes 28 and 29. Its thickness ranges from 0.0 to 12.2 m (0 to 40 ft), and the median 
Geophysical Surveys 3

thickness is 6.1 m (20 ft). Beneath the fine gravel and sand is a 

layer of sand, which includes gravel and cobbles in a few drill 

holes. Its thickness ranges from 4.9 to at least 21.3 m (16 to at 

least 70 ft). 

The thicknesses of the individual layers (that is, the soil 

layer, the coarse gravel and sand layer, and the fine gravel and 

sand layer) are generally constant along LL ́ and MM ́ (pl. 2) 

except for a few anomalies such as drill hole 25. However, 

the combined thickness of the all layers increases from 

L to L ́ — that is, from the southwest corner to the northeast 

corner of the site. If the thickness of the clay layer is approximately constant (within the range of 1 to 6 m [fig. 1]), then 

the depth to the bedrock increases from the southwest to the 

northeast corner. Between M and M ́, the drill logs, except 

those for holes 29 and 64, extend to their maximum depth, 

30.5 m (100 ft). Thus, the depth to the bedrock is unknown but 

must be greater than 30.5 m (100 ft). 

In several drill holes, the depths to the water table were 

measured just after drilling (pl. 2). The depths range from 

0.6 to 1.5 m (2 to 5 ft), and the median depth is 1.2 m (4 ft). 

Thus, the water table is close to the ground surface, and 

almost all of the alluvium is saturated. In a few drill holes, the 

depths to the water table were measured again, one day after 

the drilling. In these holes, the depths decreased about onehalf meter (1 to 2 ft), but this decrease is insignificant in this 

investigation.

Geophysical Surveys

Introductory Remarks

This section briefly describes the five geophysical 

methods — time-domain electromagnetic sounding, electrical 

resistivity profiling, S-wave reflection profiling, S-wave refraction profiling, and P-wave refraction profiling. Each description includes the procedures used to collect the data at the field 

site, the procedures used to process the data, and some typical 

results. 

The goal of this effort is not to characterize the entire 

field site but rather to demonstrate how these five geophysical methods could be used to characterize a deposit of alluvial 

aggregate. Consequently, only enough data were collected to 

meet this goal. Thus, regions where data were collected tended 

to be small compared to the entire site. The exception is timedomain electromagnetic sounding: the soundings covered most 

of the site.

The data for all five methods were collected during 

March 2005. The atmospheric temperature was usually 

between 0 to 10°C (30 to 50°F). The sky was clear, partly 

cloudy, or cloudy; the wind was calm to moderately strong. 

Rainfall and snowfall were insignificant. The locations of the 

geophysical measurements were surveyed with the Global 

Positioning System; the error in the locations is less than 

2 centimeters.

Time-Domain Electromagnetic Sounding

Description of the Method

Time-domain electromagnetic (TEM) sounding is used to 

estimate how the electrical conductivity of the ground changes 

with depth. The technique was initially developed for mineral 

exploration but has become widely used in ground water, 

environmental, and engineering studies (McNeill, 1990). TEM 

soundings typically are made using an electrical wire that is 

laid on the ground in the shape of a square. The wire square is 

connected to a TEM transmitter, which produces a steady electrical current in the wire square. This current, in turn, produces 

a steady magnetic field. When the transmitter interrupts the 

current, the magnetic field starts to decay, and consequently 

another current is induced in the ground below the wire 

square. Although this induced current attempts to maintain the 

magnetic field, the induced current both decays and diffuses; 

consequently, the magnetic field continues to decay. The 

decay of the induced current, and hence the magnetic field, 

is affected by the electrical conductivity of the ground: The 

decay is slow where the ground is conductive, but the decay 

is rapid where the ground is less conductive. In other words, 

these interlinked processes relate the decay of the magnetic 

field to the electrical conductivity of the ground.

The decay of the magnetic field is monitored with a 

receiver coil, which is placed at the center of the wire square 

(fig. 3). The receiver coil generates a time-varying voltage, 

which is called a “transient.” Because of the aforementioned 

processes, the transient contains information on how the 

conductivity of the ground varies with depth: The initial part 

Figure 3. Receiver coil and data recorder used for TEM 

soundings.
4 Field Demonstrations of Five Geophysical Methods that Could Be Used to Characterize Deposits of Alluvial Aggregate

of the transient contains information about the electrical 

conductivity at shallow depths, whereas the later part of the 

transient contains information about the electrical conductivity at greater depths. Through a process called “inversion,” 

the transient is used to estimate the electrical conductivity as 

a function of depth. The results of the inversion commonly 

are reported as the reciprocal of conductivity, which is called 

“resistivity.” Additional information about the method is in 

Fitterman and Labson (2005).

Data Collection

The size of the wire square was 40 m by 40 m, and the 

receiver coil was placed in the center of the square, a configuration called “central induction loop.” The transmitter, the 

receiver coil, and the data recorder were a Geonics Protem 

47 TEM system. To reduce errors in the data, multiple transients are recorded and averaged, using a cyclical transmitter 

waveform, which is called a “50% duty-cycle square wave.” 

The electrical current in the wire square flows in one direction for one-fourth of the period. During the next quarter 

period the current is turned off, and the transient is measured. 

The second half of the waveform is similar to the first half, 

except that its polarity is reversed. By increasing the period of 

the transmitter waveform, longer transients can be recorded, 

and hence information about the electrical conductivity at 

greater depths can be obtained. Initially, data were collected 

at transmitter repetition rates of 315 and 30 Hz (which are 

referred to as “ultra high frequency” and “high frequency,” 

respectively) to estimate the transient at early and late times. 

Six sets of transients were typically collected at each repetition 

frequency so that the data could be averaged to further reduce 

the uncertainty in the measurements. Because of the relatively 

high resistivity of the alluvium, the transient decayed rapidly 

and the 30-Hz data were not usable. 

Twenty-eight soundings were made across the site (pl. 1). 

The locations of the soundings were chosen to uniformly 

cover the site, while avoiding underground pipes and electrical 

power lines that would corrupt the data.

Data Processing

The averaged transients were converted to a quantity 

called “apparent resistivity,” using the formulas in Fitterman 

and Labson (2005). The apparent resistivities were plotted and 

visually checked for data quality (fig. 4A). With good data, the 

apparent resistivity changes smoothly as a function of time, 

and the standard deviations in the resistivity are less than about 

10 to 15 percent. In the figure 4A example, these two criteria 

were not met by four apparent resistivities, and so these four 

were removed from the data set before the inversion.

Despite our efforts to avoid underground pipes and power 

lines, several soundings were affected by the buried power line 

to the pivot irrigator (pl. 1). The effects appear as discontinuities in the plots of apparent resistivity, usually between 0.05 

and 0.3 millisecond (ms). If the discontinuities were deemed 

small, the apparent resistivities were still used in the inversion.

The model used for the inversion consisted of horizontal 

layers; each layer was parameterized by an electrical resistivity and a thickness. The thicknesses and resistivities for the 

entire model were determined by a nonlinear, least-squares 

inversion that is implemented in commercial software available from Interpex Ltd. The starting model for the inversion 

was chosen according to two criteria: The model had as few 

layers as possible, and its calculated apparent resistivities 

adequately matched the measured apparent resistivities. Additional information about model calculation and data interpretation procedures can be found in Kaufman and Keller (1983), 

Ward and Hohmann (1988), Hohmann and Raiche (1988), and 

Fitterman and Labson (2005).

Typical Results

Typical results from a TEM sounding are shown in 

figure 4A. The measured apparent resistivities are about 

55 ohm-m at 0.007 ms; they rise to about 130 ohm-m at 

0.14 ms and decrease thereafter. The associated standard 

deviations range from 0.1 to 10.0 percent before 0.215 ms and 

range from 20 to more than 40 percent at later times. Indeed, 

the later standard deviations are so large that their apparent 

resistivities were not used in the inversion. 

Typical results of an inversion are an electromagnetic 

model (fig. 4B). The vertical axis indicates the depth beneath 

the ground surface. The horizontal axis indicates the electrical resistivity. The model shows three depth intervals within 

which the electrical resistivity is constant; for example, the 

electrical resistivity is about 50 ohm-m at depths between 

0 and 14 m. Each constant-resistivity interval corresponds to 

a horizontal layer in the electromagnetic model. The deepest layer extends to infinite depth. Of course, such a layer is 

impossible; consequently, the deepest layer should be interpreted as having a thickness that is too great to be delineated 

by the TEM sounding. 

The aforementioned trends in the apparent resistivity 

(fig. 4A) suggest that the resistivity of the ground initially 

increases with depth and subsequently decreases. These 

changes are manifested in the estimated model (fig. 4B): The 

top, middle, and bottom layers have estimated resistivities of 

50, 220, and 33 ohm-m, respectively. The calculated apparent 

resistivities for this model had the best match to the measured 

apparent resistivities, so this model is termed “most-likely.” 

There are suitable alternative models for which the match 

between the calculated and the measured apparent resistivities 

is almost as good as the match for most-likely model; these 

models are determined by using a procedure called “equivalence analysis.” These alternative models have the same trend 

in resistivity: The resistivites of the top, middle, and bottom 

layers are always low, high, and low, respectively. For these 

alternative models, the thickness of the top layer ranges from 

11 to 19 m, and the thickness of the middle layer ranges from 

79 to 107 m. 
Geophysical Surveys 5

Electrical Resistivity Profiling 

Description of the Method

Electrical resistivity is a property that indicates how 

much a material opposes the flow of electrical current. The 

resistivity of rock or sediment generally depends upon the 

electrical resistivities of the constituent minerals, of the air in 

the pores, and of the water in the pores, as well as the relative 

abundances of the minerals, air, and water. 

To measure the electrical resistivity of the ground, 

direct electrical current is injected into the ground through a 

metal stake, which is called an “electrode,” and the current is 

extracted with another electrode (fig. 5A). The voltage is measured between two other electrodes that are collinear with the 

current electrodes. Various orderings of the four electrodes and 

the spacings between them are used to probe the ground to different depths. To this end, many electrodes (for example, 16 to 

100) are arranged in a straight line, and the spacing between 

all electrodes is constant (fig. 5B). From this large number of 

electrodes, a data-collection instrument (fig. 5C) selects four 

for a single measurement. This instrument rapidly changes 

the combination of electrodes so that there are measurements 

for all orderings and spacings. Additional information about 

the electrical resistivity method and electrical resistivities of 

typical geologic materials can be found in Zohdy and others 

(1974), Reynolds (1997), and Zonge and others (2005).

Data Collection

Electrical resistivity data were collected using a 

SuperSting R8 IP system manufactured by Advanced Geosciences, Inc. The data were collected with 100 stainless-steel 

electrodes. The ordering of the four electrodes involved in a 

single measurement was an “inverse Schlumberger array,” for 

Apparent resistivity (ohm-meters)

Time (milliseconds)

Depth (meters)

A B

Resistivity (ohm-meters)

1,000

100

10

1

0

50

100

150

0.001 0.01 0.1 1 10 1 10 100

Figure 4. Typical results from a TEM sounding (Sounding 20, pl. 1). A, Apparent resistivities and their standard deviations. Circles 

represent measured apparent resistivities that were used in the inversion; squares represent measured apparent resistivities that were 

not used in the inversion; vertical lines represent standard deviations of the apparent resistivities; and the solid, curved line represents 

the calculated apparent resistivity for the most-likely electromagnetic model. B, Electromagnetic model estimated from the apparent 

resistivities. The heavy, solid line represents the most-likely model; the dashed lines represent suitable, alternative models. 
6 Field Demonstrations of Five Geophysical Methods that Could Be Used to Characterize Deposits of Alluvial Aggregate

which the two innermost electrodes were used to inject current 

into the ground, and the two outermost electrodes were used 

to measure the voltage. An advantage of the inverse Schlumberger array is that the signal to noise ratio of a measured voltage is often greater than that of other array types. To further 

improve the signal to noise ratio, each voltage measurement is 

repeated three times and then averaged. 

Electrical resistivity data were acquired along six lines 

or profiles (pl. 1 and table 1). Two profiles were near the 

middle of the field and were perpendicular to one another. The 

remaining four profiles were adjacent to Road 1. For these 

four profiles, the spacing of the electrodes varied to determine 

how spacing affects the delineation of the geologic heterogeneity. All four profiles were centered at the same point. The 

acquisition parameters for all six profiles are summarized in 

table 1.

Table 1. Acquisition parameters for the electrical resistivity 

profiles. The locations of the profiles are shown on plate 1.

Parameter Value

Electrode spacing (meters) 4.0 (Profile BB’)

4.0 (Profile EE’)

3.0 (Profile HH’)

2.0 (Profile II’)

1.0 (Profile JJ’)

0.5 (Profile KK’)

Profile length (meters) 297.0 (Profile BB’)

198 (Profile EE’)

99.0 (Profile HH’)

49.5 (Profile II’)

396 (Profile JJ’)

396 (Profile KK’)

Measurement time (milliseconds) 1,200

Maximum input current 

(milliAmperes)

1,000

Data Processing

The measurements of voltage were used to estimate 

the electrical resistivity with an inversion; the software that 

performed the inversion was chosen to be EarthImager 2D 

(Advanced Geosciences, Inc., 2003). The inversion is based on 

a model that is similar to a geologic cross section except that 

it displays electrical resistivity. The electrical resistivity may 

vary within the vertical plane of the model, but not perpendicular to this plane. For the inversion, voltages and currents are 

combined into a single parameter called “apparent resistivity” 

(Zohdy and others, 1974); the apparent resistivities calculated 

from the field measurements and from the model are matched 

during the inversion by varying the electrical resistivities 

within the model. 

Typical Results

A typical cross section of electrical resistivity is shown 

in figure 6. The vertical axis indicates the elevation, and the 

horizontal axis indicates the horizontal distance along the 

ground. The cross section represents a vertical slice through 

the ground, beneath the line of electrodes. The top of the cross 

section corresponds to the ground surface. The shape of the 

cross section is trapezoidal. Only this trapezoidal region was 

thoroughly probed with electrical current; other regions that 

were partially probed are not shown. The colors in the cross 

section indicate the estimated electrical resistivity: the red and 

orange colors indicate high resistivity; the purple and blue 

colors indicate low resistivity. 

Figure 5. A, Electrode and cable attachment used for electrical 

resistivity profiling. B, Electrodes and the associated cables used 

to collect one set of measurements. C, Instrument used to collect 

and record the electrical resistivity data.

A

C

B
Geophysical Surveys 7

S-wave Reflection Profiling

Description of the Method

S-wave reflection profiling uses S-waves, which are also 

called “shear waves,” to delineate geologic heterogeneity in 

the ground. The S-waves are generated by specially designed 

sources. One source is a wooden platform with metal plates 

on either side (fig. 7A). One of the metal plates is struck with 

a small sledgehammer, and the force impulse is transmitted 

into the ground, generating an S-wave. This source is called 

the “clog,” and it is similar to a source used by the Canadian 

Geological Survey. Another source is a heavy, metal box with 

spikes on its bottom that mechanically couple the box to the 

ground (fig. 7B). The side of the box is struck with a large 

sledgehammer, generating an S-wave. This source is called the 

“golf shoe” (Hasbrouck, 1983). 

After the S-waves are generated by the source, they 

propagate downward, reflect from interfaces such as the alluvium/bedrock interface, then propagate upward. At the ground 

surface, the reflected waves are detected by geophones, each 

of which generates a time-varying voltage that is digitally 

recorded (fig. 7C and D). The recorded voltage from each 

geophone is called a “trace,” and it contains fluctuations in the 

voltage that correspond to reflected waves, as well as other, 

unwanted waves and background noise. Using various computer algorithms, the unwanted waves and noise are removed 

from the traces, effectively leaving the reflections. These 

reflections are subsequently manipulated to generate an image, 

which is somewhat similar to a geologic cross section. This 

cross section is markedly improved if the subsurface interfaces 

have been thoroughly probed with the S-waves. To achieve 

this, traces must be recorded for many different locations of 

the source and the geophones. Additional information about 

seismic reflection profiling is in Pelton (2005). Elevation (meters)

E

0 

180

50 100 150 200 250 300 350

160

140

120

Horizontal distance (meters)

Resistivity 

(ohm-meters)

E’

380

340

300

260

220

180

140

100

60

Figure 6. Typical results from an electrical resistivity profile (profile EE ́ on pl. 1).

Figure 7. Equipment used for S-wave seismic reflection and 

refraction profiling. A, Clog source. B, Golf shoe source. The 

arrows indicate where the golf shoe is struck by a sledgehammer 

to generate an S-wave. C, Geophone used to detect the S-wave. 

D, Seismograph used to record the time-varying voltages 

generated by the geophones. 

A

B

C

D
8 Field Demonstrations of Five Geophysical Methods that Could Be Used to Characterize Deposits of Alluvial Aggregate

Data Collection

Data were collected along profiles AA ́, CC ́, and GG ́

(pl. 1); the acquisition parameters for each profile are summarized in table 2. Profile AA ́ was parallel to Road B, and 

the clog source was placed on the road to minimize the 

surface wave, which is a type of unwanted wave. The source 

and geophone spacing were small so that alluvium/bedrock 

interface, which reflected the S-waves, was thoroughly probed. 

Profile GG ́ was in the farm field, and its acquisition parameters were identical to those for profile AA ́, except that a 

heavier sledgehammer was used. Profile CC ́ was also in the 

farm field and was collinear with profile GG ́. The acquisition parameters for profile CC ́ were chosen to give the best 

head waves, which are needed for refraction profiling (see the 

section “S-wave Refraction Profiling”). The reason was that 

profile GG ́ was originally intended to be a refraction profile, 

not a reflection profile. However, when the traces were later 

analyzed, it was discovered that they also recorded reflected 

waves. Consequently, profile GG ́ was also analyzed as a 

reflection profile. Analyses of the seismic cross sections for 

these two profiles indicate how they are affected by different 

acquisition parameters.

An example of some S-wave reflection data from 

profile GG ́ is shown in figure 8. Each trace is plotted at the 

horizontal distance of the associated geophone. The waves 

that are pertinent to this study are highlighted. The direct wave 

propagates directly from the source to the geophones, through 

the alluvium. The reflected wave reflects from the interface 

between the alluvium and the bedrock; such waves are used to 

generate the reflection image. The head wave is described in 

the section “S-wave Refraction Profiling.”

Data Processing

The procedures used to process the reflection data are 

summarized in table 3, and information about these procedures is in Yilmaz (1987). The purpose of this processing is to 

convert the traces into something similar to a geologic cross 

Table 2. Acquisition parameters for the S-wave seismic reflection and refraction profiling. The locations of the profiles are shown on 

plate 1. 

Parameter Profile AA’ Profile CC’ Profile GG’

Number of geophones 48 96 48

Geophone spacing (meters) 2.5 4.0 2.5

Natural frequency of geophone (Hertz) 10 10.0 10

Component of particle velocity detected by geophone horizontal 

(perpendicular 

to seismic line)

horizontal 

(perpendicular 

to seismic line)

horizontal 

(perpendicular 

to seismic line)

Number of shot positions 49 24 49

Shot spacing (meters) 2.5 24.0 2.5

Source type clog golf shoe clog

Sledgehammer weight (kilograms) 1.8 9.1 3.6

Duration of traces (seconds) 0.8 0.6 0.8

Sample interval (milliseconds) 0.5 0.5 0.5

Table 3. Procedures used to process the S-wave reflection data.

Procedure Purpose

Stacking of common 

source gathers

Check the shot quality, remove P-waves 

and other noise

Sorting of traces to 

produce common 

midpoint gathers

Position reflection points beneath geophones

Frequency-wavenumber 

(f-k) filtering

Remove noise

Surgical muting Remove refracted waves

Normal moveout correctionFlatten reflected arrivals

Stacking of common 

midpoint gathers

Convert each common midpoint gather 

into a single trace for image

Frequency filtering Remove noise

Automatic Gain Control Balance amplitudes of weaker (later) 

reflections

Frequency-offset (f-x) 

deconvolution

Enhance lateral coherency, minimize 

spurious energy

0.1

0.0

0.2

0.3

0.4

Time (seconds)

Horizontal distance (meters)

25 50 75 100

Head wave

Direct wave

Reflected wave

Source

location

Figure 8. S-wave seismic reflection and refraction data 

recorded in the farm field (profile GG ́ on pl. 1).
Geophysical Surveys 9

section, which can be readily understood and interpreted. The 

cross section is often called a “reflection image,” and its accuracy depends upon the properties of the S-waves, the properties of the geology, and the quality of the processing.

Typical Results

The reflection image along profile AA ́ is shown in 

figure 9. The vertical axis indicates depth; the horizontal axis 

indicates the horizontal distance along the ground. The positive and negative values in the image are represented by red 

and blue colors, respectively. The prominent horizontal line at 

about 33-m depth corresponds to a wave reflected from a horizontal interface. Such coherent features in the cross section 

correspond to geologic features such as interfaces. 

The goal of processing the S-wave refraction data is the 

same as that of processing the S-wave reflection data — to 

generate a seismic cross section that can be readily related 

to the geology. However, because the nature of head waves 

differs significantly from that of reflected waves, the processing differs significantly. The details of the processing are 

described in the subsection “Data Processing.”

S-wave refraction profiling is somewhat new compared to 

other geophysical methods, so only a few publications describing this method are available (Ellefsen and others, 2005). 

Because S-wave and P-wave refraction profiling are somewhat 

similar, the references listed in the section on P-wave refraction profiling may be helpful. 

Data Collection

Originally, profile CC ́ was intended to be an S-wave 

refraction profile, and profiles AA ́ and GG ́ were intended 

to be S-wave reflection profiles. However, when the data 

from profiles AA ́ and GG ́ were analyzed, head waves were 

observed, so the data from these two profiles were also processed as S-wave refraction profiles. The data collection for 

all three profiles is described in the section “S-wave Reflection Profiling,” and the parameters used to collect the data are 

listed in table 2.

Data Processing

The processing consists of three steps. First, the traces 

are stacked to improve the signal to noise ratio. Second, the 

times at which the direct and the head waves arrive at the geophones are measured; these measured times are often called 

“traveltimes.” Figure 10A shows an example of the traveltimes 

along profile GG ́. The horizontal axis refers to the horizontal 

distance along the seismic profile, and the vertical axis refers 

to the traveltime. The colors indicate the confidence in the 

accuracy of the traveltime, which can be high, moderate, or 

low. The third step in the processing is to generate a seismic 

cross section from the measured traveltimes. To this end, 

a seismic cross section is proposed, and to each part of the 

cross section an S-wave velocity is assigned. Traveltimes for 

this proposed section are calculated and then compared to the 

measured traveltimes. The differences between these calculated and measured traveltimes indicate how the cross section 

should be revised. This procedure is called “traveltime inversion” and is a type of optimization. 

Typical Results

The seismic cross section for profile GG ́ is shown in 

figure 10B. The vertical axis indicates the elevation, and 

the horizontal axis indicates the horizontal distance along 

profile GG ́. The top of the cross section corresponds to the 

ground surface, and the other sides indicate the region probed 

by the S-waves. The cross section appears blocky because the 

Figure 9. Typical results from an S-wave reflection profile 

(profile AA ́ on pl. 1).

S-wave Refraction Profiling

Description of the Method

S-wave refraction profiling, like reflection profiling, uses 

S-waves to delineate geologic heterogeneity in the ground. 

Indeed, the sources and the geophones used for reflection 

profiling are also used for refraction profiling (fig. 7). Despite 

the usage of the same equipment, the methods are different. To 

understand this, consider an S-wave propagating through the 

ground and then impinging on an interface, say the interface 

between alluvium and bedrock. A portion of the S-wave is 

reflected from the interface — this reflected wave is used in 

reflection profiling. The remaining portion of the S-wave is 

transmitted through the interface — this transmitted wave is 

used in refraction profiling. Because of changes in the S-wave 

velocity, the transmitted wave is bent or refracted, just as light 

is refracted as it passes from air to glass. This transmitted 

wave in the bedrock is subsequently refracted again into the 

alluvium, and it propagates to the ground surface where it is 

detected by geophones. This twice-refracted wave is called 

a “head wave,” and an example of a head wave is shown in 

figure 8. 

Horizontal distance (meters)

Depth (meters)

0 10 20 30 40 50 60 70 80 90 100 110 120

0

20

30

10

40

50

60
10 Field Demonstrations of Five Geophysical Methods that Could Be Used to Characterize Deposits of Alluvial Aggregate

traveltime inversion uses blocks to represent the ground. The 

cross section has three layers: In the top layer, the S-wave 

velocity is less than 150 m/s; in the middle layer, the S-wave 

velocity ranges from about 150 to 450 m/s; and in the bottom 

layer, S-wave velocity is greater than 2,140 m/s. 

The reliability of the seismic cross section may be qualitatively assessed in at least two different ways. First, the calculated traveltimes for the cross section should be compared 

to measured traveltimes (fig. 10A). For this cross section, the 

measured and calculated traveltimes are similar, indicating 

that the cross section may be reliable. Second, the number of 

rays passing through each block should be checked (fig. 10C). 

Where the number is low, the estimated velocity is unreliable; 

in contrast, where the number is high, the estimated velocity 

may be reliable. For example, near 250-m horizontal distance 

and 170-m elevation, no rays passed through the blocks, so 

the estimated velocity is unreliable. On the other hand, near 

300-m horizontal distance and 158-m elevation, more than 32 

rays passed through the blocks, so the estimated velocity may 

be reliable. Notice that no rays pass through the blocks along 

the perimeter of figure 10C; these blocks are omitted from the 

cross section in figure 10B.

Figure 10. Typical results from an S-wave refraction profile (profile GG ́ on pl. 1). A, Measured and calculated 

traveltimes. B, Cross section showing the S-wave velocities estimated from the measured traveltimes. C, Cross section 

showing the number of rays passing through each block in the seismic cross section. M, millisecond; m, meters; s, second.

200 250 300 350 400

Horizontal distance (meters)

150

160

170

180

190

200

Elevation (meters)

Slowness 

(millisecond/meter) 

Velocity 

(meter/second) 

0.300 

0.467 

0.727 

1.133 

1.764 

2.747 

4.277 

6.660 

200 250 300 350 400

Horizontal distance (meters)

150

160

170

180

190

200

Elevation (meters)

Number 

of rays 

0 

1 

2 

4 

8 

16 

32 

240 260 280 300 320 340 360

Horizontal distance (meters) 

0.00

0.05

0.10

0.15

0.20

0.25

0.30

Time (seconds) 

150 

234 

364 

567 

883 

1,370 

2,140 

3,330 

High confidence

Moderate confidence

Low confidence

Calculated traveltime

A

B

C

Measured traveltimes
Geophysical Surveys 11

P-wave Refraction Profiling

Description of the Method

P-wave refraction profiling uses direct P-waves and head 

P-waves to delineate geologic heterogeneity in the ground. 

The direct and head P-waves are somewhat similar to direct 

and head S-waves, so P-wave refraction profiling is somewhat 

similar to S-wave refraction profiling. Nonetheless, the P- and 

S-waves have different properties, and two differences are 

especially important here: The velocity of P-waves is always 

higher then the velocity of S-waves, and P-waves are strongly 

affected by the fluids in the pores, whereas S-waves are practically unaffected. 

For the refraction profiling, P-waves were generated with 

two different types of sources. The first source was mounted 

on a modified drilling truck (fig. 11A), and the principal 

parts of the source consisted of a metal bar and a metal plate 

(fig. 11B). The metal bar, which weighed over 100 kg, was 

lifted about 2 m off the ground and then released. It hit the 

metal plate, which was firmly implanted in the ground, and 

this impact generated P-waves. This source is called the 

“truck-mounted, weight-drop source.” The second source 

consisted of a sledgehammer and a metal plate (fig. 11C). This 

source generated P-waves when the metal plate was struck by 

the sledgehammer, which weighed about 9.1 kg. This source is 

called the “9.1-kg sledgehammer source.” The P-waves generated by both sources were detected by geophones that were 

especially suitable for P-wave refraction profiling (fig. 11D). 

These geophones differ from those used for the S-wave reflection and refraction profiling because of the inherent differences in the waves. The time-varying voltages generated by 

the geophones are digitized and recorded by the seismograph 

(fig. 7D). Additional information about this method may be 

found in Dobrin and Savit (1988), Telford and others (1990), 

Reynolds (1997), and Pelton (2005).

Figure 11. Equipment used for P-wave refraction profiling. A, Truck-mounted, weight-drop source. B, Close-up view of the truckmounted, weight-drop source. C, 9.1-kilogram sledgehammer source. D, Geophone used to detect P-waves.

B

A C

D
12 Field Demonstrations of Five Geophysical Methods that Could Be Used to Characterize Deposits of Alluvial Aggregate

Data Collection

Data were collected along profiles DD ́ and FF ́ (pl. 1); 

the acquisition parameters for each profile are summarized in 

table 4. Both profiles were in the farm field and were collinear. There was one significant difference between the two 

profiles: the source for profile DD ́ was the 9.1-kg sledgehammer, whereas the source for profile FF ́ was the truck-mounted 

weight-drop. The reason for the two different sources was to 

evaluate how well each type could generate data for refraction 

profiling. 

Table 4. Acquisition parameters for the P-wave refraction 

profiling. The locations of the lines are shown on plate 1. 

Parameter Profile DD’ Profile FF’

Number of geophones 96 48

Geophone spacing 

(meters)

4.0 4.0

Natural frequency of 

geophone (Hertz)

10 10

Component of particle 

velocity detected by 

geophone

vertical vertical

Number of shot positions 24 11

Shot spacing (meters) 24 24

Source type 9.1-kg

sledgehammer

Truck-mounted, 

weight-drop

Duration of traces (seconds)0.6 0.8

Sample interval (milliseconds)0.5 0.5

Horizontal distance (meters)

40 80 120 160

Direct

wave

Head wave from 

alluvium/bedrock 

interface

0.1

0.0

0.2

0.3

0.4

Time (seconds)

Head wave

from water

table

Figure 12. P-wave refraction data recorded in the farm field 

(profile FF ́ on pl. 1).

Some P-wave refraction data from profile FF ́ are shown 

in figure 12. There are three waves that are pertinent to the 

P-wave refraction profiling: the direct wave, which propagates 

directly from the source to the geophones; the head wave from 

the water table (namely, the interface between the unsaturated 

and saturated zones); and the head wave from the interface 

between the alluvium and the bedrock. 

Data Processing

The processing of P-wave refraction data is practically 

identical to that for S-wave refraction data, so information 

about processing may be obtained from the section “S-wave 

Refraction Profiling.” 

Typical Results

The seismic cross sections obtained with P-wave refraction profiling are generally identical to those obtained with the 

S-wave refraction profiling. The only significant difference 

is that the P-wave cross sections show the P-wave velocity, 

whereas the S-wave cross sections show the S-wave velocity. 

Information about the cross sections, as well as the plots of 

traveltimes and ray density, may be obtained from the section 

“S-wave Refraction Profiling.” 

Interpretation

Time-Domain Electromagnetic Soundings

The TEM soundings were interpreted with the simplest 

models that could fit the observations. In general, this could be 

accomplished with three-layer models in which the top layer 

had intermediate resistivities (50 to 90 ohm-m), the middle 

layer had moderately high resistivities (200 to 1,500 ohm-m), 

and the bottom layer had low resistivities (10 to 50 ohm-m). 

Depths to the interface between the top and the middle layers ranged from 13 to 41 m, and the depths to the interface 

between the middle and the bottom layers ranged from 74 to 

110 m. For some of the interpretations, the first layer was 

subdivided into two or three layers to determine whether such 

a subdivision might improve the match between the observed 

and the calculated data and also improve the agreement 

between the TEM models and the driller’s logs. However, 

neither of these two improvements occurred. 

Figure 13 shows examples of two interpretations, including the driller’s logs near the soundings. In the model for 

sounding 13 (fig. 13A), the interface between the top and the 

middle layers is at a depth of 22 m, which corresponds to 

the clay layer in the driller’s log. At this depth, the resistivity increases from 64 to 680 ohm-m, but what is expected is 

that the resistivity should decrease because of the clay layer. 

On the other hand, if the clay layer were merely one or two 

meters thick, then its influence on the sounding would be 

insignificant, and the layer would probably be undetectable. 

Unfortunately, the driller’s log does not provide any information on the thickness of the clay layer. 

In the model for sounding 27 (fig. 13B), the interface 

between the top and the middle layers is at a depth of 41 m, 

which is significantly below the bottom of the driller’s log. 

This depth is within the Devonian limestone and dolomite 

(fig. 1). It is possible that the upper portion of this bedrock 

is weathered and fractured, reducing its electrical resistivity. 
Interpretation 13

In this case, the top layer would include the soil, alluvium, and 

the upper portion of the bedrock. However, such a thick top 

layer would be expected in all TEM models for the site, but it 

appears in only a few. 

The generalized stratigraphic column (fig. 1) indicates 

that the depth to the bedrock ranges from 16 m to more than 

32 m; this range is somewhat similar to the range for the 

interface between the top and the middle layers in the TEM 

models (namely, 13 to 41 m). Thus, the top layer in all TEM 

models roughly corresponds to the combined soil and alluvium. Likewise, the stratigraphic column indicates that the 

top of the Ordovician shale and shaley limestone could be 

as deep as 85 to 106 m; this range corresponds well to the 

range for the interface between the middle and bottom layers 

in the TEM models (namely, 74 to 110 m). Thus, the bottom 

layer in all TEM models corresponds to the shale and shaley 

limestone. By inference, the middle layer in the TEM models 

must correspond to a composite of the Devonian limestone and 

Figure 13. A and B, Interpretations of two time-domain electromagnetic soundings, including the driller’s logs from the holes that 

are closest to the soundings. The sounding number, which is at the top of each graph of apparent resistivity, may be used to locate the 

sounding within the site (pl. 1). Likewise, the drill-hole number, which is at the top of each driller’s log, may be used to locate the drill 

hole within the site (pl. 1). Explanation of the symbols that are used in the graphs are in the caption for figure 4. Explanations of the 

symbols that are used in the driller’s logs are on plate 2. 

1,000

1,000

1,000

1

10

100

0.001 0.01 0.1 1 10

27

0

50

100

150

10 100

27

Time (milliseconds) Resistivity (ohm-meters)

20

1

10

100

0.001 0.01 0.1 1 10

13

0

50

100

150

10 100

13

25

A

B

Apparent resistivity (ohm-meters)

Depth (meters)

Time (milliseconds) Resistivity (ohm-meters)

Apparent resistivity (ohm-meters)

Depth (meters)

1,000
14 Field Demonstrations of Five Geophysical Methods that Could Be Used to Characterize Deposits of Alluvial Aggregate

dolomite and the underlying Silurian limestone and dolomite. 

A general correspondence exists, therefore, between the generalized stratigraphic section and the three-layer TEM models 

(fig. 1). 

The TEM soundings did not delineate the stratigraphy as 

well as expected. The reason for these modest results is probably the shallow target — the soil, gravel, and sand layers in 

the first 14 to 41 m of depth. To obtain information about these 

layers, the transient would have to be sampled at times earlier 

than 6.9 microseconds, and such sampling cannot be done 

with any commercially available equipment. Also, the contrast 

between the high resistivities of the gravel and the sand may 

be too small to be detected by the TEM soundings. Despite the 

modest results, the TEM soundings did estimate the depth to 

the shale and shaley limestone.

Electrical Resistivity Profiles

For profile BB' (pl. 3), the cross section of electrical 

resistivity is interpreted in terms of three layers, which are 

displayed in the geologic cross section. The bottom layer 

extends from 122-m elevation, where the resistivity is greater 

than 380 ohm-m, to 160-m elevation, where the resistivity is 

about 220 ohm-m. The driller’s logs for holes 57 and 61 do 

not record the bedrock; hence, the top of the bedrock must be 

below about 164-m elevation. This bedrock is the Devonian 

limestone and dolomite (fig. 1), and rocks of these types have 

measured electrical resistivities that range approximately from 

50 to 107 ohm-m (Telford and others, 1990, p. 290; Reynolds, 

1997, p. 422). Consequently, the bottom layer is interpreted 

as the Devonian limestone and dolomite. Within this layer, 

the resistivity decreases as the elevation increases, perhaps 

because fracturing and weathering increase. Near the top of 

this layer, which is at about 160-m elevation, the resistivity 

varies slightly with horizontal distance. This variation probably is not due to the geology but rather is due to noise in the 

data or distortion inherent in the processing. 

The middle layer extends approximately from 160- to 

193-m elevation. Interpretation of this layer is somewhat difficult because its resistivity varies considerably in both the 

horizontal and the vertical directions. Nonetheless, there is a 

general trend in the vertical direction: the resistivity decreases 

from 220 ohm-m at 160-m elevation to about 80 ohm-m at 

180-m elevation and increases thereafter. At drill holes 57 and 

61 and between the elevations of about 164 and 193 m, this 

layer consists of sand, fine gravel and sand, and coarse gravel 

and sand. Clays, sands, and gravels have measured electrical 

resistivities that range from 1 to 800 ohm-m (Reynolds, 1997, 

p. 422). Consequently, the middle layer is interpreted as a 

composite of the clay, the sand, the fine gravel and sand, and 

the coarse gravel and sand. 

The top layer extends approximately from 193- to 

194-m elevation, which is the surface of the ground. The 

ground surface was covered with soil, and the driller’s 

logs for holes 57 and 61 indicate soil at approximately the 

aforementioned elevations. Consequently, the top layer is 

interpreted as soil. 

The measurements of the depth to the water table indicate 

that almost all of the alluvium is saturated (pl. 2). This saturated alluvium probably has low electrical resistivity because 

the pore water has low resistivity due to dissolved salts and 

nitrates from fertilizer. In contrast, the unsaturated alluvium 

and soil probably have a somewhat higher resistivity, simply because they lack pore water. Despite this hypothesized 

significant contrast in resistivity, the cross section of electrical 

resistivity does not show separate layers for the saturated and 

the unsaturated zones (pl. 3). The reason is that the electrode 

spacing is 4.0 m (table 1), which is too large to detect the thin, 

unsaturated zone. 

Although clays usually have significantly lower resistivities than sands and gravels (Reynolds, 1997, p. 422), the cross 

section of electrical resistivity does not have a separate layer 

for the clay that is at the bottom of the alluvium (fig. 1 and 

pl. 3) because this clay is too thin and too deep to be detected. 

In the middle layer, which represents the alluvium, 

the lateral changes in resistivity might be caused by lateral 

changes in the composition of the alluvium because the 

driller’s logs indicate different compositions in holes 57 and 

61. Alternatively, the lateral changes might be caused by 

changes in the electrical resistivity of the ground water, which 

in turn might be caused by changes in the concentration of dissolved salts and nitrates. Selecting the more likely of these two 

interpretations, or even another interpretation, is inappropriate 

without additional information such as geophysical well logs.

The cross section of electrical resistivity in profile EE ́

appears similar to that in profile BB ́ (pl. 3); indeed, where 

the profiles intersect, the estimated resitivities are practically 

identical. Consequently, the interpretation of the cross section 

in profile EE ́ is identical to that in profile BB ́. Likewise, the 

cross section in profile HH ́ (composite) appears similar to that 

in profile BB ́; the only significant difference is the elevation 

of the interface between the middle and the bottom layers: this 

elevation is about 170 m in HH ́ (composite) but is at about 

160 m in BB ́. Thus, the interpretation of HH ́ (composite) is 

similar to that of BB ́, except that the top of the bedrock is at 

170-m elevation. This change in the elevation of the bedrock is 

consistent with the change inferred from the driller’s logs (see 

“Description of the Field Site”). 

The cross sections of electrical resistivity in KK ́, JJ ́, 

II ́, and HH ́ were developed from measurements for which 

the electrode spacings were 0.5, 1.0, 2.0, and 3.0 m, respectively (table 1 and pl. 3). The sizes of these four cross sections 

increase as the electrode spacing increases, simply because 

more ground is probed with electric current. To see a subtle 

change in all four cross sections, examine, for example, the 

anomaly at the ground surface at 150-m horizontal distance. 

The size, the shape, and the resistivity of this anomaly vary 

from cross section to cross section. Because these three features depend upon the electrode spacing, the interpretation of 

any anomaly must account for the electrode spacing. Notice 

that all four cross sections lack variations near their bases. 
Interpretation 15

Assuming that there are indeed such small anomalies within 

the ground, the electric resistivity profiling was unable to 

detect them. Thus, the capability to detect small anomalies is 

high near the ground surface but decreases with depth, and the 

interpretation of any anomaly must account for its depth. 

S-wave Reflection Profiles

In profile AA ́ (pl. 3), the S-wave reflection image is interpreted in terms of four layers, which are shown in the interpreted geologic cross section. The reflection image is dominated by two horizontal events. The lower event, whose top is 

at about 160-m elevation, has high amplitude and is coherent 

across the image. The driller’s log for hole 69 does not record 

the bedrock; hence, the top of the bedrock must be below 

about 164-m elevation. Because the alluvium and the bedrock have very different S-wave velocities (see the following 

section, “S-wave Refraction Profiles”), the interface between 

them will generate a reflection. Consequently, the horizontal 

event at about 160-m elevation is interpreted as the interface 

between the alluvium and the bedrock, which is the Devonian 

limestone and dolomite.

There is an alternative, more sophisticated interpretation of this horizontal event. During surveys in other areas, 

reflected S-waves are sometimes generated at interfaces 

between sand and clay layers (Benjumea and others, 2001a; 

Benjumea and others, 2001b), and so during this survey a 

reflected wave may also be generated at the interface between 

the sand and clay layers. However, because the clay layer is 

merely 1 to 6 m thick (fig. 1), the reflected wave from the 

sand/clay interface would be superimposed on the reflected 

wave from the clay/bedrock interface. For this reason, the 

horizontal event at about 160-m elevation could be interpreted 

as a superposition of two reflections. The reflection from the 

clay/bedrock interface probably has higher amplitude than that 

from the sand/clay interface because the change in the S-wave 

velocities is greater. We believe that this interpretation is more 

likely to be correct than the previous interpretation, but we 

have no information to substantiate this belief.

The upper horizontal event, whose top is at about 180-m 

elevation, has moderate amplitude and is partially coherent 

across the reflection image. Because of its elevation, this event 

must be caused by changes within the alluvium. The driller’s 

log for hole 69 indicates that, at about 180-m elevation, the 

sediments change from fine gravel and sand to sand (pl. 3). 

Consequently, this horizontal event is interpreted as the interface between the layer of fine gravel and sand and the layer of 

sand.

The top layer in the geologic cross section is soil. 

Although this layer does not generate any reflection, it is 

indicated in the driller’s log for hole 69 and is observed at the 

ground surface. Consequently, the soil layer is included in the 

cross section.

In profile GG ́ (pl. 3), the reflection image is dominated 

by one horizontal event. This event has the same amplitude, 

coherence, and elevation that the corresponding event in AA ́

has; consequently, the interpretation is identical. The reflection image for GG ́ lacks the horizontal event at about 180-m 

elevation, which was observed in the image for AA ́ (pl. 3). 

Because the geology along the two profiles is practically identical (pl. 2), this difference may seem surprising. However, the 

data for AA ́ were collected along Road B (pl. 1), where the 

sediments at the ground surface are highly compacted. This 

compaction significantly reduces the generation of a wave that 

propagates along the ground surface (namely, a Love wave). 

In contrast, the data for GG ́ were collected within the farm 

field (pl. 1), where the sediments at the ground surface are not 

compacted. Here, high-amplitude Love waves are generated, 

and they overlapped reflections from interfaces within the 

alluvium. Thus, these Love waves obscured these reflections, 

making them unobservable in the reflection image. 

The interpretation of the reflection image for CC ́ is 

identical to that for GG ́, and consequently the interpretation is 

not discussed. Instead, consider the general appearance of the 

two cross sections: The horizontal event at 160-m elevation is 

partially coherent in CC ́ but is almost completely coherent in 

GG ́. The background random noise is significant in CC ́ but 

is practically insignificant in GG ́. The reason for these two 

differences is the acquisition parameters (table 2). The spacing 

between the sources and the spacing between the receivers 

both are much larger for CC ́ than they are for GG ́. Consequently, both the extent to which the ground is probed and the 

suppression of random noise are much less for CC ́ than they 

are for GG ́.

S-wave Refraction Profiles

Along AA ́ (pl. 3), the S-wave refraction velocities are 

interpreted with two layers. The top layer is a composite of the 

top three layers in the geologic cross section; in other words, it 

is a composite of the fine-grained alluvium, the coarse-grained 

alluvium, and the soil. The velocities in this top composite 

layer range from 425 m/s at 161-m elevation to 180 m/s 

at 195-m elevation. Within this range of elevations at drill 

hole 69, the sediments consist of sand, fine gravel and sand, 

coarse gravel and sand, and soil. Such sediments typically 

have measured S-wave velocities that range approximately 

from 75 to 700 m/s (Suyama and others, 1988; Williams and 

others, 2000), and their velocities typically increase with depth 

because the stress increases (Hunter, 1998; Zimmer and others, 2007). Consequently, this top composite layer is interpreted as alluvium. 

The bottom layer, which is needed to interpret the 

refraction velocities, corresponds to the bottom layer in the 

geologic cross section (pl. 3). Within this layer, the S-wave 

velocities are about 2,500 m/s and are confined to elevations 

approximately between 150 and 161 m. The driller’s log for 

hole 69 does not record the bedrock; hence, the top of the 

bedrock must be below about 164 m elevation. The bedrock is 

the Devonian limestone and dolomite (fig. 1); limestone has 
16 Field Demonstrations of Five Geophysical Methods that Could Be Used to Characterize Deposits of Alluvial Aggregate

measured S-wave velocities that range approximately from 

2,490 to 3,590 m/s (Press, 1966, p. 202; Domenico, 1984; 

Wilkens and others, 1984; Wang, 2002), and dolomite has 

measured S-wave velocities that range approximately from 

3,000 to 3,500 m/s (Wang, 2002). Consequently, this bottom 

layer is interpreted as the limestone and dolomite bedrock.

The refraction velocities in GG ́ and CC ́ are practically 

identical to those in AA ́, with one exception. The exception 

is at the very top, near 195-m elevation, where the velocities 

are as low as 110 m/s. Here, the ground is covered with soil 

that has not been compacted. Because such soils typically have 

measured S-wave velocities that range approximately from 

75 to 300 m/s (Kudo and Shima, 1970; Suyama and others, 

1988), the low velocities at the very top probably are due to 

the uncompacted soil.

P-wave Refraction Profiles

In profile FF ́ (pl. 3), the P-wave refraction velocities 

appear as three distinct layers. In the top layer, which ranges 

approximately from 193- to 195-m elevation, the velocities 

are about 250 m/s. The driller’s log for hole 56 indicates that 

the sediments at these elevations consist of soil and coarse 

gravel and sand. Because this layer is above the water table 

(pl. 2), it is unsaturated. Such unsaturated, unconsolidated 

sands typically have measured P-wave velocities that range 

approximately from 50 to 700 m/s (Bachrach and others, 

1998; Zimmer and others, 2007). Consequently, this top layer 

is interpreted as unsaturated alluvium and unsaturated soil, and 

in the geologic cross section this layer is represented by the 

very top of the alluvium and the soil. 

In the middle layer of profile FF ́, which ranges approximately from 160- to 193-m elevation, the P-wave velocities 

are about 1,800 m/s (pl. 3). The driller’s log for hole 56 indicates that the sediments at these elevations consist of sand with 

a trace of gravel, sand, fine gravel and sand, and coarse gravel 

and sand. Because this layer is below the water table (pl. 2), 

it is saturated. Such saturated, unconsolidated sediments 

typically have measured P-wave velocities that range approximately from 1,700 to 2,200 m/s (Hamilton, 1971; Zimmer and 

others, 2007). Consequently, this middle layer is interpreted as 

saturated alluvium, and in the geologic cross section this layer 

is represented by alluvium, except its very top.

In the bottom layer of profile FF ́, which ranges approximately from 157- to 160-m elevation, the P-wave velocities 

are about 5,000 m/s (pl. 3). The driller’s log for hole 56 does 

not record the bedrock; hence, the top of the bedrock must be 

below 164-m elevation. The bedrock is the Devonian limestone and dolomite (fig. 1); limestone typically has measured 

P-wave velocities that range approximately from 1,700 to 

7,100 m/s (Press, 1966, p. 202; Domenico, 1984; Wilkens and 

others, 1984; Wang, 2002), and dolomite typically has measured P-wave velocities that range approximately from 3,500 

to 6,900 m/s (Press, 1966, p. 203; Wang, 2002). Consequently, 

this bottom layer is interpreted as the limestone and dolomite 

bedrock, and in the geologic cross section this layer is simply 

represented by the bedrock.

In profile DD ́, the P-wave velocities appear as two 

distinct layers, which correspond to the top and middle layers 

in FF ́ (pl. 3). Because the interpretations of these two layers 

in DD ́ are the same as those in FF ́, the interpretations are 

not repeated. The significant difference between DD ́ and FF ́

is their thickness: DD ́ is merely 7 m thick, whereas FF ́ is 

about 45 m thick. In other words, the recorded waves probed 

to a depth of about 7 m for DD ́ but to a depth of about 45 m 

for FF ́. The reason for this difference is the amount of energy 

supplied by the sources: For DD ́, the amount was relatively 

small because the source was the 9.1-kg sledgehammer. In 

contrast, for FF ́, the amount was relatively large because the 

source was the truck-mounted weight drop (table 4). 

Consistency of Interpretations

The results from each geophysical method were interpreted individually. Nonetheless, individual interpretations 

along parallel profiles referred to the same geologic cross 

section. For example, both the interpretation of the S-wave 

reflection image along GG ́ and the interpretation of the 

electrical resistivity along CC ́ referred to the geologic cross 

section along CC ́ (pl. 3). Thus, the individual interpretations 

are consistent with one another. 

Consider just the four geologic cross sections shown on 

plate 3. All cross sections have the same general stratigraphy: 

soil, alluvium, and bedrock. The soil is 1 to 2 m thick throughout the site; the alluvium is about 28 m thick at the northern 

end of the site (cross sections AA ́, BB ́, and CC ́) and about 

25 m thick at the southern end of the site (cross section HH ́). 

Thus, the four geologic cross sections are consistent with one 

another. 

Conclusions and Implications

The results of the field demonstrations are summarized 

in table 5, which indicates whether a geologic or hydrologic 

feature was detected or measured by a particular geophysical 

method. Because the results have been discussed in the section 

“Interpretation,” only a few remarks are necessary. Table 5 

indicates that each geophysical method detected some of the 

major geologic and hydrologic features associated with the 

alluvial aggregate deposit, but no method detected all features. The implication is that no geophysical method should 

be expected to characterize all features of a deposit of alluvial aggregate. Rather, the criterion for selecting a particular 

geophysical method should be its suitability for characterizing 

the important features of the deposit. No geophysical method 

detected the clay layer at the bottom of the alluvium (table 5). 

Nonetheless, a clay layer might be detectable if the stratigraphy were different. For example, if the clay layer were thick 

and embedded in the middle of the alluvium, then it might 
Acknowledgments 17

be detectable with electrical resistivity profiling. The S-wave 

reflection profiling mapped the interface between layers with 

different grain sizes, and this method might be used to map 

such interfaces in other alluvial deposits.

The importance of these field demonstrations is that the 

results, which are summarized in table 5, indicate which geophysical methods might be used to characterize other alluvial 

aggregate deposits. For example, if information about stratigraphy is needed and a road is adjacent to the deposit, then 

S-wave reflection profiling might be helpful. If information 

about the topography of the bedrock is needed, then electrical 

resistivity profiling or most of the seismic methods might be 

helpful. 

The information in table 5 must be used with caution. 

Whether a geophysical method can detect a particular geologic 

or hydrologic feature depends upon the underlying physical 

principles of the method, which are briefly summarized in 

the section “Geophysical Surveys.” Detection depends upon 

the quality and the capabilities of the geophysical equipment 

that is used to collect the data, of the software that is used to 

process the data, and of the software that is used to interpret 

the data. With time, the quality and the capabilities of the 

equipment and the software will likely improve. Thus, the 

geophysical methods that are currently incapable of detecting 

a particular geologic feature might be capable of detecting that 

feature in the future. Detection depends upon the geology, the 

hydrology, and various features such as electric power lines, 

roads, and fences — all of these factors vary significantly from 

site to site. Detection also depends upon those who collect, 

process, and interpret the data. Accounting for all of these factors requires experience. 

Although the time-domain electromagnetic soundings 

did not work well at this site, the method has worked well in 

some alluvial valleys, such as in Colorado where the bedrock 

is shale (Ellefsen and others, 1998). That is, this method can 

accurately estimate the thickness of an alluvial aggregate 

deposit if the alluvium has a high electrical resistivity and the 

layer beneath it has a low resistivity. Thus, this method should 

be considered when characterizing other alluvial aggregate 

deposits.

Acknowledgments

The Mineral Resources Program of the U.S. Geological 

Survey funded the portion of this project that involved USGS 

personnel. 

Table 5. Summary of the field demonstrations, indicating whether a geologic or hydrologic 

feature was detected or measured by each geophysical method.

Geophysical 

method

Geologic or hydrologic feature

Water table Gravel and sand 

layers within the 

alluvium

Clay layer at 

the bottom of 

alluvium

Thickness of 

alluvium

Time-domain 

electromagnetic 

(TEM) sounding

No No No Partly1

Electrical resistivity 

profiling

No Partly2 No Yes

S-wave reflection 

profiling along 

road

No Yes3 No Yes

S-wave reflection 

profiling in field

No No No Yes

S-wave refraction 

profiling

No No No Yes

P-wave refraction 

profiling with 

sledgehammer 

source

Yes No No No

P-wave refraction 

profiling with 

truck-mounted 

source

Yes No No Yes

1

 In the TEM models, the top layer may be interpreted as the alluvium, although its thickness differs considerably from the driller’s logs. 

2

 When the electrode spacing was 0.5, 1.0, 2.0 and 3.0 m, the electrical resistivity cross sections included 

anomalies at the ground surface that were interpreted as lenses of sand or gravel.

3

 The reflection profiling detected an interface between a layer of fine gravel with sand and another layer of 

sand. 
18 Field Demonstrations of Five Geophysical Methods that Could Be Used to Characterize Deposits of Alluvial Aggregate

References Cited

AGI, 2003, EarthImager 2D, Resistivity and IP inversion software instruction manual: Austin, Texas, Advanced Geosciences Inc., 92 p.

Bachrach, Ran, Dvorkin, Jack, and Nur, Amos, 1998, Highresolution shallow-seismic experiments in sand, Part II–– 

Velocities in shallow unconsolidated sand: Geophysics, 

v. 63, no. 4, p. 1234–1240.

Bates, R.L., and Jackson, J.A., 2005, Glossary of geology: 

Falls Church, Virginia, American Geological Institute, 

800 p.

Benjumea, B., Hunter, J.A., Burns, R.A., Good, R.L., and 

Pullen, S.E., 2001a, Use of high-resolution shear-wavereflection methods for determining earthquake fundamental 

site period response near Alfred, Ontario: Geological Survey of Canada, Current Research 2001–D3, 6 p.

Benjumea, B., Pullen, S.E., Hunter, J.A., Burns, R.A., Douma, 

M., and Eaton, D., 2001b, Near-surface seismic methods 

applied to site-response characterization at an earthquake 

monitoring station near London, Ontario: Geological Survey 

of Canada, Current Research 2001–E7, 9 p.

Dobrin, M.B., and Savit, C.H., 1988, Introduction to geophysical prospecting, fourth ed.: New York, McGraw-Hill Book 

Company, 867 p.

Domenico, S.N., 1984, Rock lithology and porosity determination from shear and compressional wave velocity: Geophysics, v. 49, no. 8, p. 1188–1195.

Ellefsen, K.J., Lucius, J.E., and Fitterman, D.V., 1998, An 

evaluation of several geophysical methods for characterizing sand and gravel deposits: U.S. Geological Survey 

Open-File Report 98–221, 26 p. 

Ellefsen, K.J., Tuttle, G.J., Williams, J.M., and Lucius, J.E., 

2005, S-wave refraction survey of alluvial aggregate: 

U.S. Geological Survey Scientific Investigations Report 

2005–5012, accessed July 30, 2007, and available at 

http://igs.indiana.edu/geology/maps/statephysiography/

physiography.cfm

Fitterman, D.V., and Labson, V.F., 2005, Electromagnetic 

induction methods for environmental problems, in Butler, 

D.K., ed., Near surface geophysics, Part 1—Concepts and 

fundamentals: Tulsa, Society of Exploration Geophysicists, 

p. 295–349.

Gray, H.H., 2000, Physiographic divisions of Indiana: Indiana 

Geological Survey Special Report 61, plate 1; accessed 

July 30, 2007, and available at http://igs.indiana.edu/

geology/maps/statephysiography/physiography.cfm

Hamilton, E.L., 1971, Elastic properties of marine sediments: 

Journal of Geophysical Research, v. 76, no. 2, p. 579–604.

Hasbrouck, W.P., 1983, Sketches of a hammer-impact, spikedbase, shear-wave source: U.S. Geological Survey Open-File 

Report 83–917, 7 p.

Hohmann, G.W., and Raiche, A.P., 1988, Inversion of controlled-source electromagnetic data, in Nabighian, M.N., 

ed., Electromagnetic methods in applied geophysics: Tulsa, 

Society of Exploration Geophysicsts, p. 469–503.

Hunter, J.A., 1998, Shear-wave velocity measurements for 

earthquake hazards studies, Frasier River delta, British 

Columbia, in Bell, R.S., Powers, M.H., and Lawson, T., 

eds., Proceedings of the Symposium on the Application of 

Geophysics to Engineering and Environmental Problems, 

March 22–26, 1998, Chicago, Illinois: Environmental and 

Engineering Geophysical Society, p. 459–469.

Indiana University, 1986, General stratigraphic column 

for Paleozoic rocks in Indiana: The Trustees of Indiana University; accessed July 30, 2007, and available at 

http://igs.indiana.edu/geology/structure/bedrockgeology/

index.cfm 

Indiana University, 2005, Indiana geology—Indiana 

Quaternary geology map: The Trustees of Indiana 

University; accessed July 30, 2007, and available at 

http://igs.indiana.edu/geology/maps/statesurficial/

quaternaryGeology.cfm

Kaufman, A.A., and Keller, G.V., 1983, Frequency and 

transient sounding: Amsterdam, Elsevier, 685 p.

Kudo, Kazuyoshi, and Shima, Etsuzo, 1970, Attenuation of 

shear waves in soil: Bulletin of the Earthquake Research 

Institute, v. 48, p. 145–158.

Maier, R.D., 2004, Bedrock aquifer systems of Bartholomew 

County, Indiana: Indiana Department of Natural Resources, 

Division of Water, Resource Assessment Section, 1 sheet; 

accessed July 30, 2007, and available at http://www.

in.gov/dnr/water/ground_water/ground_water_assessment/

bartholomew/pdf/bartholomew_bedrock.pdf

McNeill, J.D., 1990, Use of electromagnetic methods for 

groundwater studies, in Ward, S.H., ed., Geotechnical and 

environmental geophysics: Tulsa, Society of Exploration 

Geophysicists, p. 191–218.

National Cooperative Soil Survey, 2002, Soil survey of 

Bartholomew County, Indiana: United States Department 

of Agriculture, Natural Resources Conservation Service, 

753 p. plus maps; accessed July 30, 2007, and available at http://www.in.nrcs.usda.gov/mlra11/manuscript_

publications/manuscripts.html
References to Previous Investigations of Alluvial Aggregate 19

Pelton, J.R., 2005, Near-surface seismology––Surface-based 

methods, in Butler, D.K., ed., Near surface geophysics, 

part 1—Concepts and fundamentals: Tulsa, Oklahoma, 

Society of Exploration Geophysicists, p. 219–263.

Press, Frank, 1966, Seismic velocities, in Clark, S.P., Jr., 

Handbook of physical constants (revised ed.): New York, 

Geological Society of America, p. 195–218.

Reynolds, J.M., 1997, An introduction to applied and 

environmental geophysics: Chichester, England, John Wiley 

& Sons, 796 p.

Rupp, J.A., 1997, Tectonic features of Indiana: South Bend, 

Indiana, The Trustees of Indiana University; accessed 

July 30, 2007, and available at http://igs.indiana.edu/

geology/structure/tectonicfeatures/index.cfm

Suyama, K., Imai, T., Ohtomo, H., Ohta, K., and Takahashi, 

T., 1988, Delineation of structures in alluvium and diluvium 

using SH-wave reflection and VSP methods in Danbom, 

S.H., and Domenico, S.N., eds., Shear-wave exploration: 

Tulsa, Oklahoma, Society of Exploration Geophysicists, 

p. 165–179.

Telford, W.M., Geldart, L.P., and Sheriff, R.E., 1990, Applied 

geophysics, second ed.: Cambridge, England, Cambridge 

University Press, 770 p.

Thompson, T.A., 1996, Bedrock geology of Indiana: South 

Bend, Indiana, The Trustees of Indiana University; accessed 

July 30, 2007, and available at http://igs.indiana.edu/

geology/structure/bedrockgeology/index.cfm

Wang, Zhijing, 2002, Seismic anisotropy in sedimentary 

rocks, part 2—Laboratory data: Geophysics, v. 67, no. 5, 

p. 1423–1440.

Ward, S.H., and Hohmann, G.W., 1988, Electromagnetic 

theory for geophysical applications, in Nabighian, M.N., 

ed., Electromagnetic methods in applied geophysics: 

Tulsa, Oklahoma, Society of Exploration Geophysicists, 

p. 131–312.

Wilkens, Roy, Simmons, Gene, and Caruso, Lou, 1984, The 

ratio Vp/Vs as a discriminant of composition for siliceous 

limestones: Geophysics, v. 49, no. 11, p. 1850–1860.

Williams, R.A., Stephenson, W.J., Frankel, A.D., Cranswick, 

E., Meremonte, M.E., and Odum, J.K., 2000, Correlation of 

1- to 10-Hz earthquake resonances with surface measurements of S-wave reflections and refractions in the upper 

50 m: Bulletin of the Seismological Society of America, 

v. 90, no. 5, p. 1323–1331.

Yilmaz, Özdoğan, 1987, Seismic data processing: Tulsa, 

Oklahoma, Society of Exploration Geophysicists, 526 p.

Zimmer, M.A., Prasad, M., Mavko, G., and Nur, A., 2007, 

Seismic velocities of unconsolidated sands, Part 1––Pressure trends from 0.1 to 20 MPa: Geophysics, v. 72, no. 1, 

p. E1–E13.

Zohdy, A.A.R., Eaton, G.P., and Mabey, D.R., 1974, Application of surface geophysics to ground-water investigations: 

U.S. Geological Survey, Techniques of Water-Resources 

Investigations, book 2, chap. D1, 116 p.

Zonge, Ken, Winn, Jeff, and Urquhart, Scott, 2005, Resistivity, 

induced polarization, and complex resistivity, in Butler, 

D.K., ed., Near surface geophysics, Part 1—Concepts and 

fundamentals: Tulsa, Oklahoma, Society of Exploration 

Geophysicists, p. 265–300.

References to Previous Investigations 

of Alluvial Aggregate

Anderson, Heather, 2000, Aggregate resource evaluation 

for a portion of Felton Prairie, Clay County, Minnesota: 

Minnesota Department of Natural Resources, Division of 

Lands and Minerals, Project 334–11, 82 p.

Auton, C.A., 1992, The utility of conductivity surveying and 

resistivity sounding in evaluating sand and gravel deposits and mapping drift sequences in northeast Scotland: 

Engineering Geology, v. 32, p. 11–28.

Barnett, Adrienne, and Ellefsen, K.J., 2000, Assessment of 

the alluvial sediments in the Big Thompson River valley, 

Colorado: U.S. Geological Survey Digital Data Series, 

DDS–66, 1 CD–ROM.

Crimes, T.P., Chester, D.K., Hunt, N.C., Lucas, G.R., Mussett, 

A.E., Thomas, G.S.P., and Thompson, A., 1994, Techniques 

used in aggregate resource analysis of four areas of the UK: 

Quarterly Journal of Engineering Geology, v. 27, part 2, 

p. 165–192.

Ellefsen, K.J., Lucius, J.E., and Fitterman, D.V., 1999, 

Geophysics in exploration for sand and gravel, in Johnson, K.S., ed., Proceedings, 34th Forum on the Geology of 

Industrial Minerals, May 2-6, 1998, Norman, Oklahoma: 

Oklahoma Geological Survey Circular 102, p. 147–149.

Ellefsen, K.J., and Barnett, Adrienne, 2001, An investigation 

of alluvial sediments using S-wave refraction—A case 

study, in Proceedings of the Symposium on the Application 

of Geophysics to Engineering and Environmental Problems, 

March 4–7, 2001, Denver, Colorado: Environmental and 

Engineering Geophysical Society, published on CD–ROM.

Jacobson, R.P., 1955, Geophysical case history of a commercial gravel deposit: Mining Engineering, v. 7, p. 158–162.
20 Field Demonstrations of Five Geophysical Methods that Could Be Used to Characterize Deposits of Alluvial Aggregate

Jol, H.M., Parry, D., and Smith, D.G., 1998, Ground penetrating radar—Applications in sand and gravel exploration, 

in Bobrowsky, P.T., ed., Aggregate resources—A global 

perspective: Rotterdam, A.A. Balkema, Inc., p. 295–306.

Middleton, R.S., 1977, Ground and airborne geophysical 

studies of sand and gravel in the Toronto region: Ontario 

Geological Survey Study GS18, 37 p.

Odum, J.K., and Miller, C.H., 1988, Geomorphic, seismic, and 

geotechnical evaluation of sand and gravel deposits in the 

Sheridan, Wyoming, area: U.S. Geological Survey Bulletin 

1845, 32 p.

Saarenketo, T., and Maijala, P., 1994, Applications of 

geophysical methods to sand, gravel and hard rock aggregate prospecting in northern Finland, in Lüttig, G.W., 

ed., Aggregates—Raw materials giant: Report on the 2d 

International Aggregates Symposium, Erlangen, Germany, 

October 22–27, 1990, p. 109–123.

Singhroy, V.H., and Barnett, P.J., 1984, Locating subsurface 

mineral aggregate deposits from airborne infrared imagery 

(reflected and thermal)—A case study in southern Ontario, 

in Proceedings of the International Symposium on Remote 

Sensing of the Environment, 3d Thematic Conference: 

Remote Sensing for Exploration Geology, p. 523–539.

Wilcox, S.W., 1944, Sand and gravel prospecting by the earth 

resistivity method: Geophysics, v. 9, p. 36–46.