INTERNATIONAL JOURNAL OF LATEST TECHNOLOGY IN ENGINEERING,
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ISSN 2278-2540 | DOI: 10.51583/IJLTEMAS | Volume XIV, Issue IV, April 2025
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Deep Fracture Mapping and Groundwater Potential Assessment
Using Magneto Telluric (MT) Resistivity Imaging in Kilambakkam
Region
Mohamed Afzal J
Department of Geology, University of Madras, Guindy Campus, Chennai, India 600025
DOI : https://doi.org/10.51583/IJLTEMAS.2025.140400033
Received: 19 April 2025; Accepted: 22 April 2025; Published: 05 May 2025
Abstract: Groundwater exploration in hard rock terrains requires advanced geophysical techniques to identify high-yielding
aquifers. This study utilizes Magneto telluric (MT) resistivity imaging to delineate subsurface fracture zones and assess
groundwater potential in the Kilambakkam region. The resistivity profiles reveal a complex hydrogeological setting characterized
by shallow weathered zones (50m-100m depth) with low water yield, deeper fractured aquifers (120m-250m depth) with
moderate yield, and deep-seated fault zones (180m-300m depth) exhibiting high groundwater potential. Two primary borewell
target zones have been identified based on low resistivity anomalies (1-6 Ωm), indicating significant water-bearing formations.
The study emphasizes the importance of integrating geophysical surveys with hydrogeological data to optimize borewell
placement and enhance sustainable groundwater extraction. Further validation through vertical electrical sounding (VES) and
pumping tests is recommended to ensure long-term aquifer viability.
Keywords: Magneto telluric (MT) Resistivity Imaging, Groundwater Exploration, Fracture Zones, Hard Rock Aquifers, Low
Resistivity Anomalies, Hydro geophysics, Fault Zones, Kilambakkam,
I. Introduction
Magnetotelluric (MT) resistivity imaging is a geophysical technique widely used for subsurface characterization, particularly in
groundwater exploration, mineral prospecting, and geothermal studies (Vozoff, 1972). The method relies on natural
electromagnetic (EM) field variations to map resistivity contrasts at different depths, offering insights into geological formations
and hydrogeological structures (Chave & Jones, 2012). Groundwater occurrence in crystalline hard rock terrains, such as
Kilambakkam, is largely influenced by the presence of fractures, faults, and weathered zones (Singhal & Gupta, 2010). These
structures typically exhibit lower resistivity due to water saturation, making MT an effective tool for delineating potential
aquifers. High-resistivity zones correspond to massive rock formations, while low-resistivity anomalies indicate water-bearing
fractures and weathered layers (Kumar et al., 2015). In this study, we analyze MT profiles collected from Kilambakkam to
identify potential groundwater reservoirs. The interpretation of resistivity variations helps in locating suitable drilling sites,
ensuring sustainable water resource management in the region.
Study Area
The study area, Kilambakkam, is located in the southern region of India and is part of the hard rock terrain dominated by
crystalline formations. (Fig 1)The geology of the area is primarily composed of charnockite, granite gneisses, and
weathered/fractured zones, which significantly influence groundwater occurrence and movement (Sathish et al., 2020). Due to
rapid urbanization and increasing water demand, identifying sustainable groundwater resources in this region is crucial.
Kilambakkam is characterized by a semi-arid climate with moderate to low annual rainfall, making groundwater the primary
water source for both domestic and agricultural needs (CGWB, 2019). The hydrogeology of the region is complex due to the
presence of varying resistivity structures, which include low-resistivity zones associated with weathered/fractured formations and
high-resistivity zones representing hard rock formations (Ramesh et al., 2017). To effectively identify groundwater potential
zones, the magnetotelluric (MT) method was applied across multiple profiles in the region. The analysis of resistivity variations
provides a detailed subsurface characterization that aids in mapping aquifer zones and optimizing well locations for sustainable
groundwater extraction (Krishnamurthy et al., 2019).
II. Methodology
The ADMT-300S low-frequency magnetotelluric equipment is used to locate quartzite and gneisses, shale, and granite rocks
beneath the surface of deeper structural formations, which are plotted on a 2D image (Ravindran, A. A., Kingston, J. V., &
Premshiya, K. H. 2020). The natural electromagnetic field's strength correlates to the subterranean creation of the earth's rock and
changes in resistivity recorded in the field.
III. Results and Discussion
Detailed Analysis of Magnetotelluric (MT) Resistivity Profiles
Color Representation and Resistivity Distribution in Low Resistivity Zones (40-90 Ωm, Blue to Purple) Primarily on the right
side and in deeper parts of the section (~200m and below). Geological Implication Likely corresponds to water-saturated zones,
INTERNATIONAL JOURNAL OF LATEST TECHNOLOGY IN ENGINEERING,
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clay-rich formations, or fault zones. Possible aquifer presence if linked to porous sedimentary layers. May indicate fluid
movement influenced by fractures or faults.
Moderate Resistivity Zones (100-140 Ωm, Green to Yellow) Found throughout the section, transitioning between high and low
resistivity zones.Geological Implication: Represents weathered rock layers, fractured bedrock, or semi-saturated formations.
Partial saturation suggests groundwater presence but not dominance. Crucial for understanding water recharge areas and
hydrogeological connectivity.
High Resistivity Zones (150-175 Ωm, Red to Orange) Found on the left side and in upper sections. Geological Implication
Represents compact bedrock, igneous intrusions, or dry formations. Could be granite, basalt, or metamorphic formations with
minimal porosity. Acts as water barriers or structural boundaries.
Structural and Fault Identification
Sharp Resistivity Transitions Areas of abrupt resistivity change suggest faults or lithological boundaries Steep gradients between
red (high resistivity) and blue (low resistivity) may indicate fault systems. Faults may act as conduits or barriers to fluid
movement. Localized Anomalies (Blue Pockets in High-Resistivity Areas) Small blue patches within high-resistivity zones
suggest trapped water pockets or localized fractures. Potential groundwater reservoirs or mineralized zones.
Depth-wise Analysis
In 0–100m Depth Mixed resistivity values suggest weathered rock, topsoil, and partially saturated layers. Potential for shallow
aquifers connected to deeper conductive zones. In 100–200m Depth More structured resistivity variations indicate fractured
formations or lithological transitions. Important for understanding groundwater movement and rock properties. In 200m+ Depth
Dominated by blue and purple areas, indicating high conductivity. Suggests deep-seated water-bearing formations or potential
mineralized zones. Possible target depth for groundwater exploration.
Comparative Analysis of MT Profiles (Profile 1&2)
High-Resistivity Zones (150-270 Ωm)
First MT Profile Dominated by high resistivity, indicating compact basement rock (igneous/metamorphic formations). Less
permeable, acting as barriers to fluid flow. Second MT Profile More fragmented, suggesting lithological variations or partially
weathered formations. More favorable for groundwater storage (Table1)(Fig 2).
Low-Resistivity Zones (<100 Ωm)
First MT Profile shows Small, scattered low-resistivity areas indicating localized water-bearing formations. Limited connectivity.
Second MT Profile shows Large conductive zones on the right side, extending deeper. Suggests continuous groundwater-bearing
formations associated with faults or fractures. (Table1)(Fig 2).
Structural Features (Faults & Fractures)
First MT Profile Shows Some resistivity changes indicate possible faults but not sharply defined. Transitions suggest gradual
lithological changes rather than major faulting. Second MT Profile Displays steeper resistivity gradients, indicating clear fault
zones. Presence of conductive anomalies near fault lines suggests fluid movement. (Table1)(Fig 2).
IV. Groundwater Potential & Drilling Recommendations
Groundwater Potential Comparison
First MT Profile Shows Moderate potential with small water-bearing zones. Limited connectivity means restricted recharge
potential. Second MT Profile Larger, connected conductive zones indicate better groundwater storage and recharge potential.
Right side of the profile is a strong drilling target.
Drilling Recommendations
For Groundwater Exploration Second MT Profile Target blue conductive zones on the right (~150-250m depth). First MT Profile
Focus on localized blue zones (~100-200m depth), but expect limited yield. (Table1)(Fig 2).
For Stable Bedrock (Construction/Mining): First MT Profile represents Left side dominated by high-resistivity formations
(compact basement rock). Second MT Profile: More fractured, requiring additional geotechnical evaluation. (Table1)(Fig 2).
For Mineralization Exploration: Low-resistivity zones could indicate sulfide mineralization. Second MT Profile’s deep blue areas
are promising for further geophysical testing. The Second MT Profile is more favorable for groundwater exploration, with larger
and better-connected conductive zones. The First MT Profile shows more compact, resistive formations, making it suitable for
geological stability but less ideal for water storage. Structural features (faults/fractures) are more pronounced in the Second
Profile, suggesting better pathways for fluid movement.
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Resistivity Variations and Subsurface Lithology
The results of the Magnetotelluric (MT) survey across Kilambakkam reveal significant resistivity variations corresponding to
different lithological units. High resistivity zones (above 150 Ωm) are observed at shallow depths, indicating the presence of
massive crystalline rocks such as charnockite and granite gneiss (Sathish et al., 2020). In contrast, low resistivity zones (below 60
Ωm) correspond to weathered/fractured rock formations and potential groundwater-bearing zones (Krishnamurthy et al., 2019).
The presence of alternating resistivity layers suggests a heterogeneous subsurface with varying degrees of weathering and
fracturing. The deeper conductive anomalies (below 50 Ωm) are indicative of saturated fracture zones, which are significant for
groundwater potential evaluation (Ramesh et al., 2017).
Identification of Potential Groundwater Zones
Based on the MT profiles, potential groundwater zones are identified in areas where resistivity values range between 30–100 Ωm,
signifying weathered and fractured formations. These zones are primarily located between 100–250 meters depth, where deep-
seated fractures may act as confined aquifers (CGWB, 2019). The resistivity contrast in these zones suggests that they are
hydraulically connected to deeper aquifers, supporting sustainable groundwater extraction(fig 2,3,4 &5).
The variation in resistivity values indicates a transition from shallow weathered zones to deeper fractured aquifers, which is
consistent with previous studies on hard rock hydrogeology in Tamil Nadu (Sathish et al., 2020). The integration of geophysical
data with hydrogeological knowledge provides a reliable approach for delineating water-bearing formations (Krishnamurthy et
al., 2019).
Implications for Groundwater Management
The study highlights the importance of using geophysical methods like MT to map groundwater resources in hard rock terrains.
The findings emphasize the need for sustainable groundwater extraction, as overexploitation of these fractured aquifers can lead
to reduced recharge potential and groundwater depletion (Ramesh et al., 2017).
To optimize groundwater utilization, it is recommended that future borewell sites be selected based on the identified low-
resistivity zones. Additionally, long-term monitoring of groundwater levels and recharge rates should be conducted to ensure
sustainable water management in Kilambakkam (CGWB, 2019).
Analysis of the MT Profile and Water Zones (Profile 5)
Identified Low-Resistivity Zones (Potential Water-Bearing Areas)
The resistivity profile highlights significant low-resistivity anomalies (1-6 Ωm), which indicate:Shallow aquifer possibilities
(weathered zone). Deep fracture-controlled aquifers in the hard rock system. (Table 2)(Fig4)
Recommended Borewell Drilling Targets
Central Fractured Zone (~120m - 250m depth, 60m-100m horizontal distance) High groundwater storage probability. Fractures
act as conduits for groundwater flow. Recharge is likely from rainfall infiltration. Recommended drilling depth: 250m-
300m.Deep-Seated Fault Zones (~180m - 300m depth, 0-40m & 120-150m) Highly fractured, deep groundwater pockets. Suitable
for long-term groundwater extraction. Recommended drilling depth: 280m-320m.The central fracture zone (~120m-250m depth)
and deep tectonic zones (~180m-300m depth) exhibit high water potential. Drilling in these areas is recommended for sustained
groundwater availability. (Table 2& fig 4) The local geology supports groundwater storage in fractured rock systems, making
these zones viable for future groundwater exploration.
Borewell Placement & Geological Mapping Strategy
Borewell Site Selection
Based on the resistivity results, two primary drilling targets are identified for maximum groundwater yield:
Borewell Drilling Recommendations
Depth of Drilling Minimum Depth: 250m (to tap into deep aquifers). Maximum Depth: 300m - 320m (if additional fractures are
encountered). Expected Water Yield Shallow weathered zones (~50m-100m depth): Low yield (~0.5 - 2 LPS) Fractured rock
aquifer (~120m-250m depth): Moderate to high yield (~3 - 5 LPS). Deep fault zone (~180m-300m depth): High yield (~5 - 7+
LPS). (Table 3& Fig 3) This study provides a scientific approach to groundwater exploration, ensuring sustainable water resource
management for the Kilambakkam region. Further geophysical and hydrogeological studies may enhance the accuracy of
groundwater predictions.
V. Conclusion
The comparative analysis of the two Magnetotelluric (MT) profiles has provided significant insights into subsurface resistivity
variations, structural geology, and groundwater potential. The key findings are summarized as follow Resistivity Variation &
Geological Interpretation the MT Profile shows a higher dominance of resistive formations (77–269 Ωm), indicating compact
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bedrock with limited fluid presence. The MT Profile has a broader range (40–175 Ωm) with more prominent low-resistivity
zones, suggesting potential groundwater-bearing formations. The Second MT Profile is more favorable for groundwater
exploration due to its well-connected, larger conductive zones, particularly on the right side of the profile at depths of 150–
250m.The First MT Profile has fewer conductive zones, suggesting localized water-bearing formations with limited connectivity
and recharge potential. The Second MT Profile shows steeper resistivity transitions, indicating well-defined fault structures that
may enhance groundwater movement. The First MT Profile displays more gradual resistivity transitions, suggesting lithological
variations rather than distinct fault zones. Implications for Drilling & Exploration If targeting groundwater, the Second MT
Profile offers more promising drilling locations within its deep conductive zones (~150-250m). If seeking stable bedrock for
construction or mining, the First MT Profile’s high-resistivity formations are more suitable. Potential mineralization zones could
be present in the low-resistivity regions of the Second MT Profile, requiring further geophysical assessment.
Final Recommendations
Further field validation through borehole drilling, hydrogeological testing, and geotechnical studies is advised to confirm
groundwater yield and rock integrity. Additional geophysical surveys (e.g., seismic or borehole logging) could enhance structural
interpretation and resource evaluation. Overall, the study confirms the hydrogeological significance of conductive zones in the
Second MT Profile and highlights structural complexities influencing subsurface fluid movement. The insights gained will help
guide groundwater development, construction planning, and resource exploration efforts.
References
1. Chave, A. D., & Jones, A. G. (2012). The Magnetotelluric Method: Theory and Practice. Cambridge University Press.
2. Kumar, D., Singh, V. S., & Mohan, S. (2015). Identification of groundwater potential zones using resistivity imaging and
GIS techniques. Journal of Hydrology, 529, 1242-1253.
3. Singhal, B. B. S., & Gupta, R. P. (2010). Applied Hydrogeology of Fractured Rocks. Springer Science & Business
Media.
4. Vozoff, K. (1972). The magnetotelluric method in the exploration of sedimentary basins. Geophysics, 37(1), 98-141.
5. CGWB (2019). Groundwater Resources and Development Prospects in Tamil Nadu. Central Ground Water Board, India.
6. Krishnamurthy, N. S., Kumar, D., & Singh, V. S. (2019). Identification of groundwater potential zones in crystalline
terrain using geophysical methods. Journal of Environmental Geology, 78(5), 245-256.
7. Ramesh, S., Rajendran, K., & Kumaravel, P. (2017). Hydrogeophysical investigation in hard rock terrain using resistivity
techniques. Hydrogeology Journal, 25(3), 561-576.
8. Sathish, R., Prabhakar, K., & Balasubramanian, A. (2020). Geoelectrical characterization of groundwater in fractured
rock aquifers of Tamil Nadu. Geophysical Journal International, 221(2), 1005-1018.
9. Ravindran, A. A., Kingston, J. V., & Premshiya, K. H. (2020). Mitigation Dredging in SeabedGeotechnical Engineering
Study Using Marine 2D ERI and Textural Characteristics in ThengapattanamHarbour, South India. Geotechnical and
Geological Engineering, 1-11. https://doi.org/10.1007/s10706-020-01530-z(01
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Fig :1 Study Area Map
Fig:2 Magneto telluric profile 1&2 in the study Area
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Fig :3 Magnetotelluric Profile 3&4 in the study area.
Fig :4 Magnetotelluric Profile 5 in the study area.
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Fig: 5 3D Resistivity Model profile
Table: 1 Comparison analysis of MT Profile 1&2
Feature
First MT Profile
Second MT Profile
Resistivity Range
77–269 Ωm
40–175 Ωm
High-Resistivity Zones
(Red/Orange)
More widespread
Present but fragmented
Low-Resistivity Zones
(Blue/Purple)
Scattered, smaller
pockets
Larger conductive zones, especially on the right side
Fault/Structural Zones
Some steep transitions
More defined transitions suggesting clearer fault
presence
Depth Range
0–300m
0–300m
Table : 2 Identified Low-Resistivity Zones (Potential Water-Bearing Areas)
Depth
Range
Horizontal Distance
Resistivity
(Ωm)
Interpretation
Water
Potential
~60m -
120m
50m - 90m
5-10 Ωm
Possible shallow perched aquifer
(weathered zone).
Moderate
~120m -
250m
60m - 100m
2-6 Ωm
Fractured rock aquifer with groundwater.
High
~180m -
300m
Left (0-40m) & Right (120-
150m)
1-5 Ωm
Deep tectonic fault-controlled aquifer.
High
Table : 3 Borewell Site Selection of Profile 5
Depth Range
(m)
Resistivity
(Ωm)
Water
Potential
Geological Interpretation
120m - 250m
2-6 Ωm
High
Fractured rock aquifer – major water-bearing
zone.
180m - 300m
1-5 Ωm
Very High
Deep fault-controlled aquifer with high
recharge capacity.