International Journal of Geosciences, 2012, 3, 117-125 Published Online February 2012 (
Geophysics Contribution for the Determination of
Aquifers with a Case Study
Latifa Ouadif1, Lahcen Bahi1, Ahmed Akhssas1, Khadija Baba1, Med Menzhi2
13GIE Laboratory, Mohammadia Engineering School, Mohammed V Agdal University, Rabat, Morocco
2National Centre for Scientific and Technical Research, Mohammed V Souissi University, Rabat, Morocco
Received September 24, 2011; revised November 23, 2011; accepted December 29, 2011
The determination and monitoring of aquifer formations on the eastern border of Moroccan Gharb basin are very diffi-
cult because of their spatial and temporal variation. To delimit these formations, a geophysical survey of 52 geoelectric
soundings was performed with a mesh of 500 m and electrodes distance between 1000 m and 3000 m. Geoelectric sec-
tions and resistivity maps show a horst and graben structure. The correlation of existing oil drillings shows that the Ju-
rassic and Neogene formations are both affected by normal faults causing Jurassic deposits collapse with local thicken-
ing of the Miocene deposits, and reverse faults delimiting tectonic slices due to tension caused by prerifaine nappe ad-
vance. This fact confirms the generated structure by the resistivity method. The isobath map of resistant formations’s
roof show average depths extending from 400 to 800 m for calcareous sandstone that are potential aquifers while oil
drillings indicate over 1000 m depths.
Keywords: Aquifer; Prerifaine Nappe; Resistivity Method; Geophysical Survey; Gharb Basin
1. Introduction
The Gharb Neogene basin is a collapse zone formed on
the margins of the Rif’s chain. The filling deposits of the
basin are characterized by a vertical variation due to a re-
gional geological context. The Gharb basin, which knew
many subsidences during certain periods, with a paroxysm
in the Pliocene, receives the prerifaine nappe which sub-
divides the Miocene in infra-nappe and supra-nappe Mio-
cene [1-5]. The former works reflect the structural com-
plexity of Gharb basin in general and particulary its east-
ern boundary. This makes the determination and moni-
toring of the formations, constituted by permeable depos-
its likely to correspond to aquiferous levels, very difficult
[6-8]. The recognition of this limit is confronted with the
difficulties posed by the lack of data and controversial in-
terpretations about the structure of this limit [9,10]. Thus,
it is necessary to conduct synthetic studies implying local
geology, study of oil drillings and interpretation of all car-
ried out geoelectric soundings. The realization of geoele-
ctric sections and resistivity maps, combined with the cor-
relations of stratigraphic drilling columns, allows eluci-
dating the structure of the eastern boundary of the Gharb
basin-prerifaine ridges which is affected by reverse faults
due to prerifaine nappe advance in the basin and by the
collapse normal faults.
2. Methodology
The study purpose is to identify the major tectonic aspects
of the eastern border of the Gharb basin with prerifaine
ridges and find out the formations that may constitute po-
tential aquifers levels. This approach required the inter-
pretation of 52 geoelectric soundings with AB electrodes
distance varying from 1000 to 3000 m, carried out in the
Sidi Kacem region, and also to study the oil drills data in
the same region that have provided a database on the
petrographic facies of the Jurassic and Neogene deposits
of the basin boundary with prérifaines ridges. North Eas-
South West and North-South drillings correlations show
lateral and vertical various formations evolution of this
complex boundary.
The electrical resistivity method is most used in engi-
neering geology. It identifies and locates, from the earth
surface, the structures which have resistivity contrasts
[11,12]. It consists of conducting geoelectric sounding to
determine, at several points, the vertical succession of
layers of different resistivity. This method is based on the
principle of Ohm’s law: the injection in soil of a direct
current at a very low frequency and then voltage meas-
urement makes it possible to unveil the true resistivity of
crossed formations. Several devices were used among
which the most known is the Schlumberger one. In this
device (Figure 1), we inject a current into two electrodes
opyright © 2012 SciRes. IJG
A and B, and we measure the voltage at the receiving
electrodes M and N. Apparent resistivity is given by:
where K is the geometric factor that depends on elec-
trodes spacing only.
Our geophysical survey covers an area of 20 km2 and
includes 52 geoelectric soundings with a line AB length
extending from 1000 to 3000 m (Figure 2). We interpre-
ted these VES to determine the vertical succession of for-
mations in place and have made geoelectric sections to
Figure 1. Schlumberger array.
show the lateral variation of facies. We have also made
geological sections from oil drilling combined with geoe-
lectric sections to correlate the different data and better
approximate the limit structure between the prerifaines
ridges and the Gharb Basin.
3. Results and Discussions
3.1. Geoelectric Soundings Interpretation
Inverse modeling of the electrical resistivity data is done
using the software IPI2WIN [13]. We distinguish four
groups of geoelectric soundings that generally show re-
spectively from top to bottom the following (Figure 3).
Group 1 (Figure 3(a)):
A thin clay layer;
Sand with 60 m of average thickness;
Thick layer of marl up to 400 m;
Resistant layer formed by calcareous sandstone of the
Group 2 (Figure 3(b)):
A thin clay layer;
Figure 2. Location map of geoe le ctric soundings.
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(a) (b)
(c) (d)
Figure 3. Interpretation of some geoe lectric soundings.
A low resistance formation assigned to marly sands;
A marly formation becomes a little stronger at depth;
These geoelectric soundings have not reached the re-
sistant sandstones of the Miocene.
Group 3 Figure 3(c):
A thin resistant cover made of conglomerates;
Formations of sand little resistant;
Marly formations that reach a depth of 150 m;
A resistant formation formed by sandstone is reached
at a shallow depth of about 200 m.
Group 4 Figure 3(d):
Thin clay formation;
Sixty meters of sand and marl, which become str-
onger at depth.
These geoelectric soundings have not reached the cal-
careous sandstone.
3.2. Geoelectric Cross Section
The Neogene basin of the Gharb has become deformed at
its borders what is due to tectonic movements of the Pre-
rif and prerifaines ridges [14-17]. Geoelectric sections ba-
sed on data from geoelectric soundings performed in two
directions to identify the shape and structure of the bor-
der: A subparallel direction North East-South West to the
ridge of Outita-Draa (Figure 4) and a North West-South
East direction which is perpendicular to the ridge (Fig-
ure 5).
The subparallel sections to the ridge show resistant for-
mations with shape of horst and graben that sink deep
leaving place for marly Neogene deposits. These marly
deposits are very thick reaching 500 m in S4 in north of
the study area.
The perpendicular sections to the ridge also show the
same structure of horst and graben. Approaching the ridge,
the resistant complex is shallower; it is reached at 300 m.
3.3. Structural Analysis
The structural analysis is based on the study of oil drill-
ings. North East-South West correlations drillings show
that the Jurassic and Neogene formations are affected by
normal faults which cause a collapse of both sides of an
upper area formed by Jurassic deposits (boreholes OT8
and KM5) with thickening of the Miocene, and reverse
faults that delimit a tectonic slices. These reverse faults
are mainly due to tension caused by the advance of the
prerifaine nappe in the Neogene Gharb basin. However
the geoelectric soundings show the heterogeneity of for-
mations met in the south-east Jurassic ridge, which de-
monstrates the complexity of this area which is affected
by normal and reverse faults delimiting horsts and gra-
bens (Figure 6).
The North-South correlations, also, show a thickening
of the Miocene at the areas of collapse that is progressif
from Outita link in South towards North in direction of
center of Gharb basin. Reverse faults affecting the preri-
faine nappe and Miocene deposits result from the defor-
mation caused by the advance of the prerifaine nappe in
Gharb basin (Figure 7).
3.4. Map Resistivity
The Resistivity maps for different lengths of lines AB
also show the existence of faults and raising of Miocene
marls which are conductives to the center of our area in a
direction North West-South East (Figure 8). The resis-
tivity map for AB = 200 m indicates that the surface
formations are mainly marly except at the far North West
where we are seeing more resistant formations that can
be attributed to the sandy sandstone. The greater the length
Copyright © 2012 SciRes. IJG
of line AB, where we reaches deeper formations [18,19],
the most of Miocene marls appear in the middle of our
zone in a North West-South East direction. This confirms
once again this tectonic as a horst and graben.
The depth distribution map of the roof of the resistant
complex which may constitute a potential aquifer shows
that he is reached as lenses at shallow depths around 200
m in the central zone and the Far East. At South East, it
is at great depths reaching 800 m, while in the rest of the
area, it is reached at an average depth between 400 and
600 m (Figure 9).
4. Conclusion
Gharb Basin has been the subject of several geological,
geophysical and sedimentological studies; however, the
eastern boundary of the basin remains unknown. The
geoelectric survey has shown the geological complexity
of this boundary. The geoelectric sections and resistivity
maps show a structure in horst and graben. Oil drillings
Figure 4. North East-South West geoele c tric sec t ions, subpar a lle l to Outita-Draa r i dge.
Copyright © 2012 SciRes. IJG
Figure 5. North Weast-South East geoelectric sections, perpendicular to Draa Outita ridge.
Figure 6. North East-South West geological and geoelectric sections.
Copyright © 2012 SciRes. IJG
Figure 7. North South geological and geoelectric sections.
Copyright © 2012 SciRes. IJG
Copyright © 2012 SciRes. IJG
Figure 8. Resistivity maps for AB = 200, 600, 1000 and 3000.
Figure 9. Depth distribution map of resistant roof.
Copyright © 2012 SciRes. IJG
Copyright © 2012 SciRes. IJG
orrelations conducted in Sidi Kacem region show re-
verse faults affecting the Jurassic and the Neogene due to
tension caused by the prerifaine nappe advance. This con-
firms the structure generated by the geoelectric survey.
The originality of our work is the fact that the roof map
of resistant layers gives average depths between 400 and
600 m for calcareous sandstone which could constitute
potential aquifers as opposed to the oil drillings, which
indicate depths over 1000 m.
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