Open Journal of Geology, 2013, 3, 7-12
doi:10.4236/ojg.2013.32B002 Published Online April 2013 (http://www.scir p.org/journal/ojg)
Integration of Seismic Refraction and 2D Electrical
Resistivity in Locating Geological Contact
Nisa’ Ali, Ro sl i Saad, M. M. Nordiana
Geophysics Sectio n, School of Physics, Universit i Sain s Malaysia, Pen ang, Malaysia
Received 2013
ABSTRACT
The aim of this research is to locate the geological contact for engineering purpose appl ying seismic refraction and 2D
electrical re sistivity method. Resistivit y and seismic re fraction method was conducted on four survey lines with 3 lines
runni ng from NW to SE whic h about pa rallel t o each ot her and 40 m apa rt while the fourth li ne was run ning fro m SW
to NE. The 2D resistivity survey used minimum electrode spacing of 5 m and the survey used pole-dipole array with
mini mum c urr ent was 2 mA a nd maxi mum was 2 0 mA. The seismic refraction survey used 5 m geophone spacing with
offset shot was + 30 m and - 30 m. Resistivity results generally show the area was divided into two main zones, allu-
vium wit h resisti vity value of 10 - 800 ohm-m, and granite bedro ck with resistivi ty value of > 2500 o hm-m. There is a
geological contact between granite and alluvium. The seismic results show the area consists of two layers. The first
layer (top layer) with velocity of 460 - 900 m/s which was alluvium mixed wit h b oulders. The second layer wit h veloc-
ity of 2060 - 3140 m/s with depth 71 - 90 MSL. The thickness of the overburden is 5 - 15 m.
Keywords: Geological Contact; 2D Elec tr ic a l Resistivit y; Seismic Re fra c tion
1. Introduction
A geological contact is a boundary between two units
that is identified on t he basi s o f a co mpositio nal, text ural,
structural, or temporal difference between units [1]. The
ways in whic h rock bodies fit together are deduced from
geologic mapping, supplemented wherever possible by
drilling and geophysical data [2].
The 2D electrical resistivity method is most suitable
for interpreting geological structures in subsurface while
seismic method is valuable for mapping depth of bedrock
and fracture zones but fail to indicate the depth or dip
direction of the zone as 2D resistivity method could [3].
Thus, integration of seismic refraction and 2D electrical
resistivity met hod will give useful a nd better information
on delineating contact and faults for engineering purpose.
The refraction seismic method depends on seismic ray
paths being bent at velocity discontinuities. A compres-
sional wave that impinges on a boundary separating two
media with different acoustic impedances is partially
reflected and partially refracted into the lower medium
[4]. Measurements of travel-time as a function of range
can be transformed into a graph of velocity as a function
of depth. Velocity boundaries usually coincide with geo-
logical boundaries and a cross-section on which velocity
interfaces are plotted may therefore resemble the geo-
logical cross-section, although the two are not necessari-
ly the same [5]. Figure 1 shows seismic wave velocities
in earth materials.
Resistivity methods are used in engineering geological
investigatio ns o f sites pr ior to co nstructio n [6]. The resis-
tivity measurements are normally made b y injecting cur-
rent into the ground through two current electrodes and
measuring the resulting voltage difference at two poten-
tial electrodes [7]. Resistivity surveys give a picture of
the subsurface resistivity distrib ution. The spatial contact
between rocks will be identified based on the variation of
resi stivi ty va lues . The d istribu tion of the re sistivit y o f the
earth material will be used to interpret the geolog y of the
subsurface based on the resistivity value for common
geologic mater ia ls ( Tabl e 1).
Figure 1 . Seismic P-wave velocities in earth materials.

N. ALI ET AL.
8
2. Survey Area
The study area is located at PT 8088, Mukim Batu,
Gombak, Selangor, Malaysia with the coordinate of 3°
15’ 37.2” N and 101° 38’ 48.22” E. The area was cut and
filled with undulating surface and some bushes [9] with
fine grained granite comprising granite porphyry and
microgranite as the main rock material [10].
3. Methodology
In this survey, two geophysical survey has been carried
out which are 2D resistivity method and seismic refrac-
tion survey.
Four resistivity lines were set with three lines (SELA1-
SELA3) were about 40 m apart and parallel to each other
while the other one (SELA4) was set up crossing the
three lines (Figure 2). Inc luded in Figure 2 are the loca-
tions of the boreholes (BH3 & BH5). BH3 situated 14.5
m from SELA2 and 37.5 m from SELA4. BH5 located
8.0 m from SELA2 and 17.0 m from SELA4. This re-
search was carried out by plant in the electrodes into the
ground in a straight line with a constant spacing of 5 m.
A multi electrode selector will be used to select the ac-
tive electrodes for each measurement. The value was
collected by the resistivity meter, which is ABEM
SAS4000 system using pole-dipole array with minimum
current of 2 mA and maximum was 20 mA. The values
of resistivity obtained from each measurement are plotted
on a pseudo-section and contoured.
Four seismic spread was set up in line with resistivity
method, SELA1 – SELA4 (Table 2). The length of each
seismic spread is 115 m with offset shot +30m and -30m.
Table 1. Resistivity of common geologic materials [8].
Material Resistivity (Ωm)
Granite 300 - 1000 000
Sandstones 1 - (7.4 × 108)
Alluvium and sand 10 - 800
Cla ys 1 - 100
Figure 2. The survey are a with sur vey lines and boreh ol es.
Table 2. Distance and position of resistivity and seismic
survey lines.
Resistivity Seism ic spread (refer to resi stivity line)
SELA1
0 - 200 m
55 - 170
m
SELA2
0 - 180 m
55 - 170 m
SELA3
0 - 190 m
55 - 170 m
SELA4 0 - 200 m 45 - 160 m
The study was conducted by utilizing a 16 lb sledge-
hamme r as sour ce of wave , 24 units o f 24 H z geopho nes
and ABEM M K6 se ismogr aph. The s urve y line uses 5 m
geophones spacing and 7 shot points for each spread.
4. Results and Discussion
The results obtain from seismic refraction and 2D resis-
tivity is supported by borehole records. Seismic cross
sections have provided the depth profile of the survey
area while the resistivity pseudosections gave the resis-
tivity va lue of the subsurface.
4.1. Seismic Refraction
The results from the se i smic cro s s sectio ns (Figures 3-6),
show that the survey area consists of two layers. The
seismic velocities for the first layer range from 460 m/s
to 900 m/s and consist of alluvium mix with boulders.
The second layer velocitie s range from 2060 m/s to 3140
m/s with depth 71 - 90 MSL. The thickness of the first
layer is 5 - 15 m. Based o n these results, the se co nd laye r
abrupt velocity change has outlined the geological con-
tact between the top layer and the bedrock.
4.2. 2D Resistivity
Resistivity results (Figures 7-10) are pseudo-sections
showing the resistivity value of the subsurface with the
red line is the second layer of the seismic refraction re-
sult. Generally, the area was divided into two main zones,
alluvium with resi sti vi t y val ue o f 10 - 800 Ωm, and gra n-
ite bedro ck with resi stivity value o f > 2500 Ωm. There is
a contact zone between granite and alluvium which pro-
duce s faults.
Figure 3. Seismic cross-s ection of SELA1.

N. ALI ET AL.
9
Figure 4. Seismic cross-s ection of SELA2.
Figure 5. Seismic cross-s ection of SELA3.
Figure 6. Seismic cross-s ection of SELA4.
Legend
Sand
Silt
Granite
1.50m
4.50m
9.00m
12.00m
17.00m
BH5
1.50m
7.50m
18.00m
25.50m
30.50m
BH3
Figure 7. Cross section of borehol e data BH3 and BH5.
4.3. Borehole Records
Borehole data, BH5 (Table 3) and BH3 (Table 4) show
that the study area is covered by alluvium, mostly sand.
Granite is found at depth of 12.0 m and this fit with the
resistivity value pseudo-section of SELA2 (Figure 8)
which indicates granite near BH5 ar ea.
Table 4 providing bore log for BH3. Similar to the
previous borehole, the subsurface materials for this
borehole are alluvium and granite. BH3 has granite as
bedrock at depth of 25.5 m.
Figure 11 shows the cross section of borehole data.
From the cross section, the bore log has the same lithol-
ogy thou gh the thicknesses are var y.
Table 3. Bor e hole data, BH5 .
Depth (m) Description
SPTa
N Rec.b
ratio
75 mm 75 mm 75 mm 75 mm 75 mm 75 mm
1.50
1.95
Medi um de nse , m e dium br ow n mo ltl ed g re y si lty fine S A ND w ith
little gravel 2 4 3 3 3 3 12 53%
3.00
3.45
Ditto 3 4 4 9 6 5 24 61%
4.50
4.95 Stiff, medium brownish grey sandy SILT with a little gravel 2 4 3 2 2 2 9 44%
6.00
6.45 Ditto 2 2 3 4 2 3 12 51%
7.50
7.95 Ditto 4 3 4 3 2 2 11 55%
9.00
9.45
Medium dense, light to medium brownish grey silty SAND 5 9 9 7 7 6 29 38%
10.50
10.95 Dense to very dense, light to medium brownish grey silty SAND 5 7 9 8 8 9 34 36%
12.00 Pale to light grey moltled dark grey, moderately fractured,
moderately weathered , medium to strong coarse grain GRANITE
CRc = 1.50 m; CRRd = 0.92 m/1.50 m; RQDe = 35%
13.50 Ditto CR = 1.50 m; CRR = 0.82 m/1. 50 m; RQD = 37%
15.00 Pale to light grey mott led dark grey, hi ghly fractured, moderately
weathered medium to strong coarse grain GRANITE CR = 1.50 m; CRR = 0.80 m/1.50 m; RQD = 8%
16.50
17.00 Ditto CR = 0.50 m; CRR = 0.20 m/0.50 m; RQD = NIL
End of B H5 at depth 17.00 m.b. g.lf
a. Standard Penetration Test; b. Recovery c. Corin g Run; d. Core R ec overy; e. Rock Quality Designation; f. Meters Below Ground Level.

N. ALI ET AL.
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Table 4. Bor e hole data, BH3 .
Depth
(m) Description SPT N Rec. ratio
75 mm 75 mm 75 mm 75 mm 75 mm 75 mm
1.50
1.95 Loose, light grey silty medium SAND with some gravel 2 1 2 2 2 1 7 27%
3.00
3.45 Medi um de nse, l ig ht g rey medium bro w n silty me
dium
SAND with s om e gravel 2 3 3 3 6 4 16 47%
4.50
4.95 Loose, light gr ey striped light brown silty fine SAND 1 0 1 1 1 2 5 53%
6.00
6.45 Very loose, light grey striped light brown silty fine SAND 1 1 1 0 0 1 2 60%
7.50
7.95 Soft to medium st iff, light grayish brown sandy S ILT with s om e gravel 1 0 0 1 2 1 4 67%
9.00
9.45 Medium stiff, light grayish brown sandy SILT with some gravel 1 0 1 1 2 2 6 64%
10.50
10.95 Medium stiff to stiff, light to medium brown moltled grey sandy SILT with some gravel 1 2 2 2 2 2 8 53%
12.00
12.45 Ditto 2 3 2 1 3 2 8 60%
13.50
13.95 Stiff, light to medium grey sandy SILT 2 3 4 2 2 2 10 53%
15.00
15.45 Ditto 3 3 4 3 3 4 14 67%
16.50
16.95 Stiff, medium grayish brown sandy SILT with traces of gravel 2 4 4 3 2 3 12 71%
18.00
18.45 Loose, medium grayish brown silty fine SAND 2 1 2 3 2 2 9 76%
19.50
19.95
Medi um dens e , l ight br ow n l ight g r e y sil ty f ine SA ND
3 3 4 3 5 2 14 71%
21.00
21.45
Medi um dens e , l ight br ow n l ight g r e y sil ty f ine SA ND
4 7 6 7 7 5 25 51%
22.50
22.95 Medium dense , light to medium brownish grey silty fine SAND 9 7 7 8 7 6 28 44%
24.00
24.34 Dense to very dense, medium brownish grey silty fine S AND 7 10 12 17
21
40 mm 56%
50
190 mm
25.50 Pale t o l igh t grey moltl ed d ark grey, moderately fractur ed, sligh tly weather ed, stro ng coarse grain
GRANIT E CR = 1.50 m; CRR = 1.38 m/1.50 m; RQD = 40%
27.00 Ditto CR = 1.50 m; CRR = 1.22 m/1.50 m; RQD = 73%
28.50 Ditto CR = 1.50 m; CRR = 1.30 m/1.50 m; RQD = 65%
30.00
30.50
Pale to li g ht g r ey molt led dark grey, m o derately
fractur ed, sligh tly weather ed, stro ng coarse grain
GRANIT E CR = 0.50 m; CRR = 0.49 m/0.50 m; RQD = 24%
End of B H3 at depth 30.50 m.b. g.l
Figure 8. Resist i vit y pseudo-section of survey line SELA1.

N. ALI ET AL.
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Figure 9. Resist i vit y pseudo-section of survey line SELA2.
Figure 10. Resisti vity pseudo-section of s urvey line SELA3.
Figure 11. Resistivity pseudo-section of su rvey line SEL A 4.
5. Conclusions
2D resistivity method and seismic refraction results sug-
gest that the study area consist of granite bedrock and
alluvium mix with boulders. Hence, the geological con-
tact outline is between granite and alluvium. There were
faults along N -S at distance 100 m of SELA1-3.
6. Acknowledgements
The authors would like to extend sincere gratitude to all
Geophysics Department Staff and Postgraduate students
of School of Physics, Universiti Sains Malaysia for their
assistance in acquiring the geophysical data and making
the research a success.
REFERENCES
[1] R. C. Ho we, “Geologic Co ntacts,” Journal of Geoscience
Education, Vol. 45, 199 7, pp. 133-136.
[2] G. H. Davis, “Structural Geology of Rocks and Regions,”
John Wiley & Sons, Inc., 1984, p. 492.
[3] R. Saad, M. M. Nordiana and Edy Tonnizam Mohamad,
“The 2D Electrical Resistivity Tomography (ERT) Study
for Civil and Geotechnical Engineering Purposes,” Elec-
tronic Journal of Geotechnical Engineering, Bund, Vol.
16, 2011 .
[4] F. W. Roe, “The Geology and Mineral Resources of The
Neighbourhood of Kuala Selangor and Rasa, Selangor,
Federation of Malaya, with an Account of The Geology
of Batu Arang Coal-Field,” Geological Survey Depart-

N. ALI ET AL.
12
ment Federation of Malaya, 1953.
[5] R. Saad, “Novel Protocol of Engineering Geophysics In
Urban Environments,” Ph.D. Thesis, University Sains
Malaysia, 2009.
[6] R. L. Sengbush, “Seismic Exploration Methods,” IHRDC
Publishers, 1983.
doi:10.1007/978-94-011-6397-2
[7] D. H. Griffiths and R. F. King, “Applied Geophysics for
Geologists and Engineers: The Elements of Geophysical J
Prospecting,” Pergam on Pres s , 1981.
[8] J. M. Reynolds, “An Introduction to Applied and Envi-
ronmental Geophysics,” John Wiley & Sons, Ltd., 1997,
p. 796.
[9] R. Barker, “Electrical Imaging and its Application in
Engineering Investigations,” Engineering Geology Spe-
cial Publications, Geological Society, London, Vol. 12,
No. 1, 1997, pp. 37- 43.
[10] M. H. Loke, “Electrical Imaging Surveys for Environ-
mental and Engineering Studies,” A Practical Guide to
2-D an d 3-D Su rveys, 1999.www.abem.se