Seismic Refraction

Some uses of seismic refractionMapping bedrock topography Determining the depth of gravel, sand or clay deposits Delineating perched water tables Determining the depth to the water table Detecting subsurface caverns Estimating rippability Detecting shallow faults and fracture zones Detecting large boulders

ACTIVE STANDARD: D5777-00(2006) Standard Guide for Using the Seismic Refraction Method for Subsurface Investigation $42.90 for PDF Developed by Subcommittee: D18.01 See Related Work by this Subcommittee Adoptions: Book of Standards Volume: 04.09 1. Scope 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, 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.

Refraction Lay Out

Seismic RefractionAdvantagesSimple layoutLow manpower requirementsLimited Equipment RequirementsRapid data reduction and analysis (computer not needed)Easy interpretation

Seismic RefractionDisadvantagesRelatively large energy input requiredRelatively long layout (10 times depth)Limited number of model layersLimited velocity differencesLimited interface geometry (assume smooth)

Rippability versus seismic velocity. (Caterpillar. Handbook of Ripping, 8 th Edition)

Chart1

2.1428571429

4.2857142857

6.4285714286

8.5714285714

10.7142857143

12.8571428571

15

17.1428571429

19.2857142857

21.4285714286

23.5714285714

25.7142857143

27.8571428571

30

32.1428571429

34.2857142857

36.4285714286

38.5714285714

40.7142857143

42.8571428571

45

47.1428571429

49.2857142857

0.00

Meters

miliseconds

Direct Wave

Sheet1

DistanceArival Time in ms

mDirectRefracted

00.00

32.140.0021428571

64.29

96.4315.58213.58

128.5716.242.666666666713.5733333333

1510.7116.913.333333333313.5766666667

1812.8617.58413.5813.5766666667

2115.0018.244.666666666713.5733333333

2417.1418.915.333333333313.5766666667

2719.2919.586

3021.4320.246.6666666667

3323.5720.917.3333333333

3625.7121.588

3927.8622.248.6666666667

4230.0022.919.3333333333

4532.1423.5810

4834.2924.2410.6666666667

5136.4324.9111.3333333333

5438.5725.5812

5740.7126.2412.6666666667

6042.8626.9113.3333333333

6345.0027.5814

6647.1428.2414.6666666667

6949.2928.9115.3333333333

Sheet1

meters

miliseconds

Direct and Refracted Waves

Sheet2

0.00

Meters

miliseconds

Direct Wave

Sheet3

Simple Plot

DistanceTimeDTime R0030683212163418243624323830404036484242564448644654724860805066885272965478104568411258

Chart1

030

832

1634

2436

3238

4040

4842

5644

6446

7248

8050

8852

9654

10456

11258

Distance (meters)

Time (miliseconds)

Sheet1

DistanceTimeDTime R

0030

6832

121634

182436

243238

304040

364842

425644

486446

547248

608050

668852

729654

7810456

8411258

Sheet1

Distance (meters)

Time (miliseconds)

Sheet2

Sheet3

Chart2

00

2.14285714293

4.28571428576

6.428571428615.58

8.571428571416.24

10.714285714316.91

12.857142857117.58

1518.24

17.142857142918.91

19.285714285719.57667

21.428571428620.2433366667

23.571428571420.9100033333

25.714285714321.57667

27.857142857122.2433366667

3022.9100033333

32.142857142923.57667

34.285714285724.2433366667

36.428571428624.9100033333

38.571428571425.57667

40.714285714326.2433366667

42.857142857126.9100033333

4527.57667

47.142857142928.2433366667

49.285714285728.9100033333

meters

miliseconds

Direct and Refracted Waves

Sheet1

DistanceArival Time in ms

mDirectRefracted

00.00

32.140.0021428571

64.29

96.4315.58213.58

128.5716.242.666666666713.5733333333

1510.7116.913.333333333313.5766666667

1812.8617.58413.5813.5766666667

2115.0018.244.666666666713.5733333333

2417.1418.915.333333333313.5766666667

2719.2919.586

3021.4320.246.6666666667

3323.5720.917.3333333333

3625.7121.588

3927.8622.248.6666666667

4230.0022.919.3333333333

4532.1423.5810

4834.2924.2410.6666666667

5136.4324.9111.3333333333

5438.5725.5812

5740.7126.2412.6666666667

6042.8626.9113.3333333333

6345.0027.5814

6647.1428.2414.6666666667

6949.2928.9115.3333333333

Sheet1

meters

miliseconds

Direct and Refracted Waves

Sheet2

0.00

Meters

miliseconds

Direct Wave

Sheet3

Two Equations for Simple Refraction

These two equations should give the same answer. It should be less than half the crossover distance.

Steps in solving for depth1Determine the velocities of both layers in meters per second or feet per second2Determine the crossover distance3Determine the time intercept for V24Determine the depth to layer 2 usingBoth refraction equations (internal check)

Up DipDown Dip

Dipping Bed Equations