Standard Guide for Using the Seismic Refraction Method for Subsurface Investigation

SIGNIFICANCE AND USE
Concepts:  
This guide summarizes the equipment, field procedures, and interpretation methods used for the determination of the depth, thickness and the seismic velocity of subsurface soil and rock or engineered materials, using the seismic refraction method.
Measurement of subsurface conditions by the seismic refraction method requires a seismic energy source, trigger cable (or radio link), geophones, geophone cable, and a seismograph (see Fig. 1).
The geophone(s) and the seismic source must be placed in firm contact with the soil or rock. The geophones are usually located in a line, sometimes referred to as a geophone spread. The seismic source may be a sledge hammer, a mechanical device that strikes the ground, or some other type of impulse source. Explosives are used for deeper refractors or special conditions that require greater energy. Geophones convert the ground vibrations into an electrical signal. This electrical signal is recorded and processed by the seismograph. The travel time of the seismic wave (from the source to the geophone) is determined from the seismic wave form. Fig. 2 shows a seismograph record using a single geophone. Fig. 3 shows a seismograph record using twelve geophones.
The seismic energy source generates elastic waves that travel through the soil or rock from the source. When the seismic wave reaches the interface between two materials of different seismic velocities, the waves are refracted according to Snell's Law (4, 8). When the angle of incidence equals the critical angle at the interface, the refracted wave moves along the interface between two materials, transmitting energy back to the surface (Fig. 1). This interface is referred to as a refractor.
A number of elastic waves are produced by a seismic energy source. Because the compressional P-wave has the highest seismic velocity, it is the first wave to arrive at each geophone (see Fig. 2 and Fig. 3).
The P-wave velocity Vp  is dependent upon the bulk modulus, the sh...
SCOPE
1.1 Purpose and Application—This guide covers the equipment, field procedures, and interpretation methods for the assessment of subsurface conditions using the seismic refraction method. Seismic refraction measurements as described in this guide are applicable in mapping subsurface conditions for various uses including geologic, geotechnical, hydrologic, environmental (1), mineral exploration, petroleum exploration, and archaeological investigations. The seismic refraction method is used to map geologic conditions including depth to bedrock, or to water table, stratigraphy, lithology, structure, and fractures or all of these. The calculated seismic wave velocity is related to mechanical material properties. Therefore, characterization of the material (type of rock, degree of weathering, and rippability) is made on the basis of seismic velocity and other geologic information.
1.2 Limitations:  
1.2.1 This guide provides an overview of the seismic refraction method using compressional (P) waves. It does not address the details of the seismic refraction theory, field procedures, or interpretation of the data. Numerous references are included for that purpose and are considered an essential part of this guide. It is recommended that the user of the seismic refraction method be familiar with the relevant material in this guide and the references cited in the text and with appropriate ASTM standards cited in 2.1.
1.2.2 This guide is limited to the commonly used approach to seismic refraction measurements made on land. The seismic refraction method can be adapted for a number of special uses, on land, within a borehole and on water. However, a discussion of these other adaptations of seismic refraction measurements is not included in this guide.
1.2.3 There are certain cases in which shear waves need to be measured to satisfy project requirements. The measurement of seismic shear waves is a subset of seismic refraction. ...

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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: D5777 – 00 (Reapproved 2006)
Standard Guide for
Using the Seismic Refraction Method for Subsurface
Investigation
This standard is issued under the fixed designation D5777; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope of these other adaptations of seismic refraction measurements
is not included in this guide.
1.1 Purpose and Application—This guide covers the equip-
1.2.3 There are certain cases in which shear waves need to
ment, field procedures, and interpretation methods for the
be measured to satisfy project requirements. The measurement
assessment of subsurface conditions using the seismic refrac-
of seismic shear waves is a subset of seismic refraction. This
tion method. Seismic refraction measurements as described in
guide is not intended to include this topic and focuses only on
this guide are applicable in mapping subsurface conditions for
P wave measurements.
various uses including geologic, geotechnical, hydrologic,
1.2.4 Theapproachessuggestedinthisguidefortheseismic
environmental (1), mineral exploration, petroleum exploration,
refraction method are commonly used, widely accepted, and
and archaeological investigations. The seismic refraction
proven; however, other approaches or modifications to the
method is used to map geologic conditions including depth to
seismic refraction method that are technically sound may be
bedrock, or to water table, stratigraphy, lithology, structure,
substituted.
and fractures or all of these. The calculated seismic wave
1.2.5 Technical limitations and interferences of the seismic
velocityisrelatedtomechanicalmaterialproperties.Therefore,
refraction method are discussed in D420, D653, D2845,
characterization of the material (type of rock, degree of
D4428/D4428M, D5088, D5730, D5753, D6235, and D6429.
weathering, and rippability) is made on the basis of seismic
1.3 Precautions:
velocity and other geologic information.
1.3.1 It is the responsibility of the user of this guide to
1.2 Limitations:
follow any precautions within the equipment manufacturer’s
1.2.1 This guide provides an overview of the seismic
recommendations, establish appropriate health and safety prac-
refraction method using compressional (P) waves. It does not
tices, and consider the safety and regulatory implications when
address the details of the seismic refraction theory, field
explosives are used.
procedures, or interpretation of the data. Numerous references
1.3.2 If the method is applied at sites with hazardous
are included for that purpose and are considered an essential
materials, operations, or equipment, it is the responsibility of
part of this guide. It is recommended that the user of the
the user of this guide to establish appropriate safety and health
seismic refraction method be familiar with the relevant mate-
practices and determine the applicability of any regulations
rial in this guide and the references cited in the text and with
prior to use.
appropriate ASTM standards cited in 2.1.
1.4 This standard does not purport to address all of the
1.2.2 This guide is limited to the commonly used approach
safety concerns, if any, associated with its use. It is the
to seismic refraction measurements made on land. The seismic
responsibility of the user of this standard to establish appro-
refraction method can be adapted for a number of special uses,
priate safety and health practices and determine the applica-
onland,withinaboreholeandonwater.However,adiscussion
bility of regulatory limitations prior to use.
1.5 This guide offers an organized collection of information
or a series of options and does not recommend a specific
ThisguideisunderthejurisdictionofASTMCommitteeD18onSoilandRock
and is the direct responsibility of Subcommittee D18.01 on Surface and Subsurface
course of action. This document cannot replace education or
Characterization.
experienceandshouldbeusedinconjunctionwithprofessional
Current edition approved July 1, 2006. Published August 2006. Originally
judgment. Not all aspects of this guide may be applicable in all
approved in 1995. Last previous edition approved in 2000 as D5777 – 00. DOI:
10.1520/D5777-00R06. circumstances. This guide is not intended to represent or
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D5777 – 00 (2006)
FIG. 1 Field Layout of a Twelve-Channel Seismograph Showing the Path of Direct and Refracted Seismic Waves in a Two-Layer Soil/
Rock System (a = Critical Angle)
c
replace the standard of care by which the adequacy of a given 4. Summary of Guide
professional service must be judged, nor should this document
4.1 Summary of the Method—Measurements of the travel
be applied without consideration of a project’s many unique
time of a compressional (P) wave from a seismic source to a
aspects. The word “Standard” in the title of this guide means
geophone(s) are made from the land surface and are used to
only that the document has been approved through the ASTM
interpret subsurface conditions and materials. This travel time,
consensus process.
along with distance between the source and geophone(s), is
interpreted to yield the depth to refractors refractors (refracting
2. Referenced Documents
layers).The calculated seismic velocities of the layers are used
2.1 ASTM Standards:
to characterize some of the properties of natural or man-made
D420 Guide to Site Characterization for Engineering De-
man subsurface materials.
sign and Construction Purposes
4.2 Complementary Data—Geologic and water table data
D653 Terminology Relating to Soil, Rock, and Contained
obtained from borehole logs, geologic maps, data from out-
Fluids
crops or other complementary surface and borehole geophysi-
D2845 Test Method for Laboratory Determination of Pulse
cal methods may be necessary to properly interpret subsurface
Velocities and Ultrasonic Elastic Constants of Rock
conditions from seismic refraction data.
D4428/D4428M Test Methods for Crosshole Seismic Test-
ing
5. Significance and Use
D5088 Practice for Decontamination of Field Equipment
Used at Waste Sites
5.1 Concepts:
D5608 Practices for Decontamination of Field Equipment
5.1.1 This guide summarizes the equipment, field proce-
Used at Low Level Radioactive Waste Sites
dures, and interpretation methods used for the determination of
D5730 Guide for Site Characterization for Environmental
the depth, thickness and the seismic velocity of subsurface soil
Purposes With Emphasis on Soil, Rock, the Vadose Zone
and rock or engineered materials, using the seismic refraction
and Ground Water
method.
D5753 Guide for Planning and Conducting Borehole Geo-
5.1.2 Measurement of subsurface conditions by the seismic
physical Logging
refraction method requires a seismic energy source, trigger
D6235 Practice for Expedited Site Characterization of Va-
cable (or radio link), geophones, geophone cable, and a
dose Zone and GroundWater Contamination at Hazardous
seismograph (see Fig. 1).
Waste Contaminated Sites
5.1.3 The geophone(s) and the seismic source must be
D6429 Guide for Selecting Surface Geophysical Methods
placed in firm contact with the soil or rock. The geophones are
usually located in a line, sometimes referred to as a geophone
3. Terminology
spread. The seismic source may be a sledge hammer, a
3.1 Definitions:
mechanical device that strikes the ground, or some other type
3.1.1 The majority of the technical terms used in this guide
3 of impulse source. Explosives are used for deeper refractors or
are defined in Refs (2) and (3). Also see Terminology D653.
special conditions that require greater energy. Geophones
convert the ground vibrations into an electrical signal. This
electrical signal is recorded and processed by the seismograph.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
The travel time of the seismic wave (from the source to the
Standards volume information, refer to the standard’s Document Summary page on
geophone) is determined from the seismic wave form. Fig. 2
the ASTM website.
shows a seismograph record using a single geophone. Fig. 3
The boldface numbers given in parentheses refer to a list of references at the
end of the text. shows a seismograph record using twelve geophones.
D5777 – 00 (2006)
NOTE—Arrow marks arrival of first compressional wave.
FIG. 2 A Typical Seismic Waveform from a Single Geophone
FIG. 4 (a) Seismic Raypaths and (b) Time-Distance Plot for a
Two-Layer Earth With Parallel Boundaries (9)
where:
V = compressional wave velocity,
p
K = bulk modulus,
µ = shear modulus, and
FIG. 3 Twelve-Channel Analog Seismograph Record Showing
r = density.
Good First Breaks Produced by an Explosive Sound Source (9)
5.1.7 The arrival of energy from the seismic source at each
geophone is recorded by the seismograph (Fig. 3). The travel
time(thetimeittakesfortheseismic P-wavetotravelfromthe
5.1.4 Theseismicenergysourcegenerateselasticwavesthat
seismic energy source to the geophone(s)) is determined from
travel through the soil or rock from the source. When the
each waveform. The unit of time is usually milliseconds (1 ms
seismic wave reaches the interface between two materials of
= 0.001 s).
different seismic velocities, the waves are refracted according
5.1.8 The travel times are plotted against the distance
to Snell’s Law (4, 8). When the angle of incidence equals the
between the source and the geophone to make a time distance
critical angle at the interface, the refracted wave moves along
plot. Fig. 4 shows the source and geophone layout and the
the interface between two materials, transmitting energy back
resulting idealized time distance plot for a horizontal two-
to the surface (Fig. 1). This interface is referred to as a
layered earth.
refractor.
5.1.9 The travel time of the seismic wave between the
5.1.5 A number of elastic waves are produced by a seismic
seismic energy source and a geophone(s) is a function of the
energy source. Because the compressional P-wave has the
distance between them, the depth to the refractor and the
highest seismic velocity, it is the first wave to arrive at each
seismic velocities of the materials through which the wave
geophone (see Fig. 2 and Fig. 3).
passes.
5.1.6 The P-wave velocity V is dependent upon the bulk
p
5.1.10 Thedepthtoarefractoriscalculatedusingthesource
modulus, the shear modulus and the density in the following
togeophonegeometry(spacingandelevation),determiningthe
manner (4):
apparent seismic velocities (which are the reciprocals of the
V 5 @~K 1 4/3µ!/r] (1) slopes of the plotted lines in the time distance plot), and the
=
p
D5777 – 00 (2006)
intercept time or crossover distances on the time distance plot
(see Fig. 4). Intercept time and crossover distance-depth
formulas have been derived in the literature (6-8). These
derivations are straightforward inasmuch as the travel time of
the seismic wave is measured, the velocity in each layer is
calculated from the time-distance plot, and the raypath geom-
etry is known. These interpretation formulas are based on the
following assumptions: (1) the boundaries between layers are
planes that are either horizontal or dipping at a constant angle,
(2) there is no land-surface relief, (3) each layer is homoge-
neous and isotropic, (4) the seismic velocity of the layers
increases with depth, and (5) intermediate layers must be of
sufficient velocity contrast, thickness and lateral extent to be
detected.Reference(9)providesanexcellentsummaryofthese
equations for two and three layer cases. The formulas for a
two-layered case (see Fig. 4) are given below.
5.1.10.1 Intercept-time formula:
t V V
i 2 1
z 5 (2)
2 2
=~V ! 2 ~V !
2 1
where:
z = depth to refractor two,
t = intercept time,
i
V = seismic velocity in layer two, and
V = seismic velocity in layer one.
5.1.10.2 Crossover distance formula:
FIG. 5 (a) Seismic Raypaths and (b) Time-Distance Plot for a
x V 2 V Three-Layer Model With Parallel Boundaries (9)
c 2 1
z 5 (3)
Œ
2 V 1 V
2 1
where:
z, V and V are as defined above and x = crossover distance.
2 1 c
5.1.11 Three to four layers are usually the most that can be
resolved by seismic refraction measurements. Fig. 5 shows the
sourceandgeophonelayoutandtheresultingtimedistanceplot
for an idealized three-layer case.
5.1.12 The refraction method is used to define the depth to
or profile of the top of one or more refractors, or both, for
example, depth to water table or bedrock.
5.1.13 The source of energy is usually located at or near
each end of the geophone spread; a refraction measurement is
made in each direction. These are referred to as forward and
reverse measurements, sometimes incorrectly called reciprocal
measurements, from which separate time distance plots are
made. Fig. 6 shows the source and geophone layout and the
resultingtimedistanceplotforadippingrefractor.Thevelocity
obtained for the refractor from either of these two measure-
FIG. 6 (a) Seismic Raypaths and (b) Time-Distance Plot for a
ments alone is the apparent velocity of the refractor. Both
Two-Layer Model With A Dipping Boundary (9)
measurements are necessary to resolve the true seismic veloc-
ity and the dip of layers (9) unless other data are available that
indicateahorizontallayeredearth.Thesetwoapparentvelocity
300 ft). However, with sufficient energy, refraction measure-
measurements and the intercept time or crossover distance are ments can be made to depths of 300 m (1000 ft) and more (6).
used to calculate the true velocity, depth and dip of the
5.2 Parameter Measured and Representative Values:
refractor. Note that only two depths of the planar refractor are 5.2.1 Theseismicrefractionmethodprovidesthevelocityof
obtainedusingthisapproach(seeFig.7).Depthtotherefractor
compressional P-waves in subsurface materials. Although the
is obtained under each geophone by using a more sophisticated P-wave velocity is a good indicator of the type of soil or rock,
data collection and interpretation approach.
it is not a unique indicator. Table 1 shows that each type of
5.1.14 Most refraction surveys for geologic, engineering, sediment or rock has a wide range of seismic velocities, and
hydrologic and environmental applications are carried out to many of these ranges overlap. While the seismic refraction
determine depths of refractors that are less than 100 m (about technique measures the seismic
...

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