Structural Controls on Geothermal Manifestations Using Integrated Geophysical Methods: A Case Study of the Tulu Moye Area, Central Main Ethiopian Rift

Structural Controls on Geothermal Manifestations Using Integrated Geophysical Methods: A Case Study of the Tulu Moye Area, Central Main Ethiopian Rift | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Structural Controls on Geothermal Manifestations Using Integrated Geophysical Methods: A Case Study of the Tulu Moye Area, Central Main Ethiopian Rift Dejene Alemu Bekele, Mulugeta Markos Tediso This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9318561/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract This study investigates subsurface geological structures and their influence on geothermal manifestations in the Tulu Moye geothermal field, located in the Central Main Ethiopian Rift. The study area lies between UTM coordinates 512000–514500 mE and 902000–904000 mN, at an elevation of approximately 2090 m above sea level. Integrated geophysical methods, including electrical resistivity and magnetic surveys, were employed to delineate subsurface structures associated with geothermal activity. A total of five Vertical Electrical Sounding (VES) points and three Electrical Resistivity Tomography (ERT) profiles were acquired using a SYSCAL PRO system, while 206 magnetic data points were collected along eleven profiles using a proton precession magnetometer. The resistivity data were processed using IPI2Win, RES2DINV, and Surfer software, whereas magnetic data were analyzed using Oasis Montaj. The results reveal that zones of low resistivity and low magnetic anomalies correspond to areas of potential geothermal fluid accumulation and hydrothermal alteration. The ERT models indicate a laterally continuous low-resistivity zone extending between 480 m and 640 m, interpreted as a fractured and altered zone facilitating fluid flow. Upward continuation of magnetic data highlights deeper structures, with low magnetic anomalies observed in the northeastern, southeastern, and central parts of the study area. Structural analysis using Euler deconvolution and analytical signal techniques indicates that the dominant subsurface lineaments trend in the northwest–southeast direction, acting as conduits for geothermal fluids. Overall, the integration of resistivity and magnetic methods effectively delineates geothermal potential zones and improves understanding of structural controls on geothermal systems in the Tulu Moye area. Geophysics Magnetic anomaly Tulu Moye Geophysical methods geothermal resource Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1. INTRODUCTION The rising of magma towards earth surface during the rifting process results of geodynamic Activities (Ebinger, 2005 ; Keir et al., 2006 ; Komolafe, 2010 ). Due to this geodynamics process surface expression of tectonic lineaments and manifestation of geothermal resources were occurred. The investigations of the subsurface geological structures and tectonic lineaments have crucial role to understand geothermal activities and process associated with active region of geothermal area (Admassu & Worku, 2015 ; Chorowicz, 2005 ).Most of the times subsurface geological structures like lineaments are investigated by geophysical methods to identify the subsurface structures (Telford et al., 1990 ; Keller & Frischknecht, 1966 ). For this study electrical resistivity and magnetic methods were used to investigate the subsurface geological structures that influence the geothermal system (Loke, 1999 ; Blakely, 1995 ). 1.2. Statement of the Problem Different investigations have been carried out at Tulu Moye geothermal resource area which is located in the Main Ethiopian Rift, at different time (Mamo, 2001 ; Admasu & Worku, 2015; Mengistu, 2016 ).Detail investigation of the subsurface geological structures requires localized geophysical survey in addition to geological, geochemical and remote sensing methods. So considering all of these problems detailed geophysical study of the Tulu Moye geothermal area was deployed. This research employed the electrical resistivity and magnetic methods to investigate geological structures that influence geothermal resources. 1.3. Objectives of the Study 1.3.1. General Objective The main objective of this thesis work is to study structures and its effect on geothermal Manifestation of Tulu Moye area using resistivity and magnetic methods. 1.3.2. Specific objectives To indicate the subsurface lithological units To identify surface manifestation of geothermal system. To identify areas of geothermal potential. 2. MATERIALS AND METHODS 2.1. Description of the Study Area The study area is located in the central part of the Main Ethiopian Rift within the Oromia Regional State, Arsi Zone, specifically in the Tulu Moye geothermal field. Geographically, it is bounded by UTM coordinates 512000–514500 mE and 902000–904000 mN, with an average elevation of approximately 2090 m above mean sea level. The area lies about 176 km southeast of Addis Ababa and approximately 32 km northwest of Asela town. This region is characterized by active tectonic features associated with rifting processes, making it a suitable location for geothermal investigations. 2.2. Materials The field data acquisition required several geophysical instruments and supporting equipment. These included an electrical resistivity meter (SYSCAL PRO) along with its accessories, a proton precession magnetometer for magnetic data collection, a Global Positioning System (GPS) device for spatial referencing, batteries for power supply, and basic field tools such as a hammer. 3. Data Acquisition Techniques 3.1 Vertical Electrical Sounding (VES) Data Acquisition Vertical Electrical Sounding (VES) measurements were conducted along two profile lines using a resistivity terrameter. The first profile consisted of three VES stations (VES1, VES2, and VES3) aligned in a northwest–southeast direction, while the second profile included two VES stations (VES4 and VES5) oriented southwest–northeast. The maximum current electrode spacing (AB/2) reached 330 m for each VES measurement. The spacing between VES stations was approximately 100 m along the first profile and 300 m along the second profile. During data acquisition, the current electrode spacing was progressively increased to obtain deeper subsurface information, while the potential electrode spacing (MN) was adjusted as required. Apparent resistivity values were recorded manually in the field. The spatial distribution of VES points and profile lines was later mapped using ArcGIS 10.3 software. 3.2 Magnetic Data Acquisition Magnetic data were collected using a proton precession magnetometer. A total of 206 magnetic data points were acquired along eleven profiles distributed across the study area. The measurements were conducted systematically with consistent station spacing to ensure adequate spatial coverage. A GPS device was used to record the geographic coordinates of each measurement point, ensuring accurate positioning for subsequent data processing and interpretation. 3.3 Data Processing and Interpretation The acquired geophysical data were processed using standard software packages. The VES data were interpreted using IPI2Win and IPI-Res3 software, where iterative inversion techniques were applied to match the observed field curves with theoretical models. The processed resistivity data were then imported into Surfer software to generate pseudo-sections and geoelectrical sections. Electrical Resistivity Tomography (ERT) data were processed using Prosys II for data transfer and preliminary visualization, while RES2DINV software was employed to perform two-dimensional inversion modeling. The inversion process utilized forward modeling and nonlinear least-squares optimization techniques to produce subsurface resistivity distributions (de Groot-Hedlin & Constable, 1990 ; Loke & Barker, 1996 ). Magnetic data processing was carried out using Oasis Montaj software. The data were corrected and gridded to produce total magnetic field maps. Advanced filtering techniques, including analytical signal and upward continuation, were applied to enhance subsurface structural features (Blakely, 1995 ). 4. Results and Discussion 4.1 Electrical Resistivity Interpretation 4.1.1 Resistivity Pseudo-Section The resistivity pseudo-section was constructed from the apparent resistivity data to provide a qualitative representation of subsurface resistivity variations in both vertical and lateral directions. Although pseudo-sections do not represent the true resistivity distribution, they offer an approximate visualization of subsurface features. The pseudo-section reveals significant lateral and vertical variations in resistivity values along the profile. Relatively high resistivity values are observed near the surface around the VES3 location, which may indicate compact or less altered geological materials. In contrast, a zone of low resistivity extends from the near-surface region between VES1 and VES2 downward toward the central part of the profile. This low-resistivity zone is interpreted as a weathered and fractured region saturated with geothermal fluids. The presence of such conductive zones is commonly associated with hydrothermal alteration and increased temperature, suggesting potential geothermal activity within the subsurface. 4.1.2 Geoelectrical Section The geoelectrical section derived from VES data provides a quantitative interpretation of subsurface lithological variations and structural features. The section reveals distinct subsurface layers characterized by variations in resistivity values, which are indicative of different geological units. A fractured zone is identified between VES1 and VES2 at depth, which likely serves as a pathway for hydrothermal fluid circulation. This fracture zone appears to facilitate the movement of geothermal fluids, leading to alteration of surrounding rocks. Beneath VES2, the interaction between hydrothermal fluids and pyroclastic materials has resulted in the formation of clay-rich layers at a depth of approximately 11.6 m. Additionally, deeper sections indicate the presence of intrusive basaltic formations, which have penetrated older geological units. These intrusions are interpreted as potential heat sources contributing to the geothermal system. The structural configuration observed in the geoelectrical section highlights the importance of fractures and lithological contrasts in controlling geothermal fluid flow. 4.2 Electrical Resistivity Tomography (ERT) Interpretation The two-dimensional inversion models derived from Electrical Resistivity Tomography (ERT) data provide a more detailed image of subsurface resistivity distribution. The inversion results indicate resistivity values ranging from approximately 54.7 Ωm to 4253 Ωm, with a maximum investigation depth of about 115 m. The ERT model reveals a prominent low-resistivity zone extending vertically from shallow depths (approximately 2.5 m) down to about 19.9 m. This zone is interpreted as a weathered and hydrothermally altered region that may act as a conduit for geothermal fluids. Laterally, this conductive zone extends across a significant portion of the profile. Below this conductive layer, higher resistivity values are observed, corresponding to relatively unaltered or massive basaltic formations. The model also indicates the presence of intrusive bodies, which are inferred to be magmatic in origin. These intrusions likely serve as heat sources driving the geothermal system (Saemundsson, 2008 ; Grant & Bixley, 2011 ). Fracture zones identified within the ERT model further support the interpretation of fluid pathways. These structural discontinuities enhance permeability, allowing the upward migration of thermal fluids. Therefore, the integration of resistivity data clearly indicates that both lithological variation and structural features play a key role in geothermal fluid circulation. 4.3 Magnetic Data Interpretation Magnetic data analysis was conducted to identify subsurface geological structures based on variations in magnetic anomalies. The total magnetic field data exhibit both positive and negative anomalies, reflecting the dipolar nature of the Earth's magnetic field and variations in subsurface rock properties. 4.4.Euler Deconvolution Analysis The Euler deconvolution technique was applied to estimate the location and depth of magnetic sources. This method relates the magnetic field and its gradients to the position of causative bodies, with structural indices representing different geological features (Thompson, 1982 ; Reid et al., 1990 ). In this study, a structural index of N = 0 was used, corresponding to contact-type geological structures. The results indicate the presence of multiple subsurface sources at varying depths. Deeper magnetic sources (greater than 300 m) are identified in certain trends, while intermediate and shallow sources are also observed. The clustering of Euler solutions suggests that the subsurface structures are predominantly aligned in a northwest–southeast direction. This structural trend is consistent with regional tectonic patterns and likely plays a significant role in controlling geothermal fluid movement. 4.3.2 Upward Continuation Analysis Upward continuation filtering was applied to the magnetic data to enhance deeper geological features by suppressing shallow anomalies. This technique effectively smooths short-wavelength variations and highlights regional-scale structures (Blakely, 1995 ). The magnetic data were upward continued to elevations of 150 m, 250 m, and 450 m. As the continuation height increases, shallow features become less prominent, and deeper structures are more clearly defined. At 450 m continuation, distinct zones of low magnetic anomaly are observed in the northeastern, southeastern, and central parts of the study area. These low magnetic anomaly zones are interpreted as trends affected by hydrothermal alteration, where magnetic minerals may have been altered or destroyed. Such zones are commonly associated with geothermal systems and may indicate trends of geothermal potential. 4.4 Integrated Interpretation The integration of electrical resistivity and magnetic data provides a comprehensive understanding of the subsurface geological framework. Both datasets consistently identify zones characterized by low resistivity and low magnetic anomalies, which are indicative of hydrothermal alteration and geothermal fluid presence. The dominant structural orientation identified from both ERT and magnetic analyses is northwest–southeast. These structures likely act as zones conduits for geothermal fluids, facilitating the movement of heat and fluids from deeper trends to the surface. Furthermore, the presence of intrusive bodies, fracture zones, and altered trends suggests a well-developed geothermal system. The zones identified through integrated interpretation represent promising targets for further geothermal exploration and development. 5. CONCLUSION This study applied integrated electrical resistivity and magnetic methods to investigate subsurface geological structures and their influence on geothermal manifestations in the Tulu Moye area, located in the Central Main Ethiopian Rift. The results demonstrate that both methods are effective in delineating subsurface features associated with geothermal systems. The resistivity data, including VES and ERT results, revealed zones of low resistivity that are interpreted as weathered, fractured, and hydrothermally altered Zone. These conductive zones are likely associated with elevated temperatures and the presence of geothermal fluids. In particular, the ERT models identified a laterally continuous low-resistivity zone between 480 m and 640 m, suggesting a trend pathway for fluid movement. The magnetic data analysis further supports these findings. Zones characterized by low magnetic anomalies were identified in the northeastern, southeastern, and central parts of the study area. These anomalies are interpreted as zones of hydrothermal alteration where magnetic minerals have been reduced or altered. The application of upward continuation filtering enhanced deeper structural features, while Euler deconvolution provided estimates of source depth and structural configuration. Structural analysis from both resistivity and magnetic datasets indicates that the dominant الاتجاه of subsurface lineaments is northwest–southeast. These structures are consistent with regional tectonic trends and are interpreted as major conduits controlling geothermal fluid circulation. Overall, the integration of resistivity and magnetic methods provides a reliable approach for identifying geothermal potential zones. The trends characterized by low resistivity, low magnetic anomalies, and structurally controlled pathways represent promising targets for future geothermal exploration and development in the Tulu Moye area References Admassu, E., & Worku, S. (2015). Characterization of Quaternary extensional structures in the Tulu Moye geothermal prospect, Ethiopia. Journal of African Earth Sciences, 39, 225–238. Amigun, O. J., Afolabi, O., & Ako, D. B. (2012). Euler deconvolution of analytical signal of magnetic anomalies over iron deposits in Okene, Nigeria. International Journal of Geophysics, 2012, 1–10. Arnórsson, S. (2000). Isotopic and chemical techniques in geothermal exploration, development, and use. Vienna: International Atomic Energy Agency. Blakely, R. J. (1995). Potential theory in gravity and magnetic applications. Cambridge: Cambridge University Press. Chorowicz, J. (2005). The East African Rift System. Journal of African Earth Sciences, 43(1–3), 379–410. de Groot-Hedlin, C., & Constable, S. (1990). Occam’s inversion for two-dimensional smooth models. Geophysics, 55(12), 1613–1624. Ebinger, C. J. (2005). Continental break-up: The East African perspective. Astronomical Geophysics, 46(2), 2.16–2.21. Grant, M. A., & Bixley, P. F. (2011). Geothermal reservoir engineering (2nd ed.). Burlington: Academic Press. Hochstein, M. P. (1988). Assessment and modeling of geothermal reservoirs. Geothermics, 17(1), 15–30. Keller, G. V., & Frischknecht, F. C. (1966). Electrical methods in geophysical prospecting. Oxford: Pergamon Press. Keir, D., Ebinger, C., Stuart, G., Daly, E., & Ayele, A. (2006). Strain accommodation by magmatism and faulting as rifting proceeds to breakup: Seismicity of the northern Ethiopian Rift. Journal of Geophysical Research, 111(B5), 1–14. Komolafe, A. A. (2010). Investigation of tectonic lineaments and thermal structures of Lake Magadi, southern Kenya Rift using integrated geophysical methods (Unpublished master’s thesis). Loke, M. H. (1999). Electrical imaging surveys for environmental and engineering studies: A practical guide to 2D and 3D surveys. Malaysia: Geotomo Software. Loke, M. H., & Barker, R. D. (1996). Rapid least-squares inversion of apparent resistivity pseudosections. Geophysical Prospecting, 44(1), 131–152. Mamo, T. (2001). Geological and surface alteration report of the Tulu Moye–Gedemsa area. Addis Ababa. Mekonnen, T. K. (2004). Interpretation of geophysical data using aeromagnetic datasets of Zimbabwe and Mozambique (M.Sc. thesis). International Institute for Geo-information Science and Earth Observation. Mengistu, Y. (2016). Detection of geothermal energy anomalies using Landsat thermal infrared data in the Tulu Moye geothermal prospect (M.Sc. thesis). Addis Ababa University. Nabighian, M. N. (1972). The analytical signal of two-dimensional magnetic bodies with polygonal cross-section. Geophysics, 37(3), 507–517. Reid, A. B., Allsop, J. M., Granser, A. J., & Somerton, I. W. (1990). Magnetic interpretation in three dimensions using Euler deconvolution. Geophysics, 55(1), 80–91. Saemundsson, K. (2008). Structural geology, tectonics, volcanology and geothermal activity. Short Course III on Exploration for Geothermal Resources, ISOR, Iceland. Telford, W. M., Geldart, L. P., & Sheriff, R. E. (1990). Applied geophysics (2nd ed.). Cambridge: Cambridge University Press. Thompson, D. T. (1982). EULDPH: A new technique for making computer-assisted depth estimates from magnetic data. Geophysics, 47(1), 31–37. Additional Declarations The authors declare no competing interests. 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INTRODUCTION","content":"\u003cp\u003eThe rising of magma towards earth surface during the rifting process results of geodynamic\u003c/p\u003e \u003cp\u003eActivities (Ebinger, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Keir et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Komolafe, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). Due to this geodynamics process surface expression of tectonic lineaments and manifestation of geothermal resources were occurred.\u003c/p\u003e \u003cp\u003eThe investigations of the subsurface geological structures and tectonic lineaments have crucial role to understand geothermal activities and process associated with active region of geothermal area (Admassu \u0026amp; Worku, \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Chorowicz, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2005\u003c/span\u003e).Most of the times subsurface geological structures like lineaments are investigated by geophysical methods to identify the subsurface structures (Telford et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e1990\u003c/span\u003e; Keller \u0026amp; Frischknecht, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e1966\u003c/span\u003e). For this study electrical resistivity and magnetic methods were used to investigate the subsurface geological structures that influence the geothermal system (Loke, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e1999\u003c/span\u003e; Blakely, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e1995\u003c/span\u003e).\u003c/p\u003e \u003cdiv id=\"Sec2\" class=\"Section2\"\u003e \u003ch2\u003e1.2. Statement of the Problem\u003c/h2\u003e \u003cp\u003eDifferent investigations have been carried out at Tulu Moye geothermal resource area which is located in the Main Ethiopian Rift, at different time (Mamo, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2001\u003c/span\u003e; Admasu \u0026amp; Worku, 2015; Mengistu, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2016\u003c/span\u003e).Detail investigation of the subsurface geological structures requires localized geophysical survey in addition to geological, geochemical and remote sensing methods. So considering all of these problems detailed geophysical study of the Tulu Moye geothermal area was deployed. This research employed the electrical resistivity and magnetic methods to investigate geological structures that influence geothermal resources.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e1.3. Objectives of the Study\u003c/h2\u003e \u003cdiv id=\"Sec4\" class=\"Section3\"\u003e \u003ch2\u003e1.3.1. General Objective\u003c/h2\u003e \u003cp\u003eThe main objective of this thesis work is to study structures and its effect on geothermal\u003c/p\u003e \u003cp\u003eManifestation of Tulu Moye area using resistivity and magnetic methods.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section3\"\u003e \u003ch2\u003e1.3.2. Specific objectives\u003c/h2\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003eTo indicate the subsurface lithological units\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eTo identify surface manifestation of geothermal system.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eTo identify areas of geothermal potential.\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"2. MATERIALS AND METHODS","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Description of the Study Area\u003c/h2\u003e \u003cp\u003eThe study area is located in the central part of the Main Ethiopian Rift within the Oromia Regional State, Arsi Zone, specifically in the Tulu Moye geothermal field. Geographically, it is bounded by UTM coordinates 512000\u0026ndash;514500 mE and 902000\u0026ndash;904000 mN, with an average elevation of approximately 2090 m above mean sea level. The area lies about 176 km southeast of Addis Ababa and approximately 32 km northwest of Asela town. This region is characterized by active tectonic features associated with rifting processes, making it a suitable location for geothermal investigations.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e2.2. Materials\u003c/h2\u003e \u003cp\u003eThe field data acquisition required several geophysical instruments and supporting equipment. These included an electrical resistivity meter (SYSCAL PRO) along with its accessories, a proton precession magnetometer for magnetic data collection, a Global Positioning System (GPS) device for spatial referencing, batteries for power supply, and basic field tools such as a hammer.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Data Acquisition Techniques","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Vertical Electrical Sounding (VES) Data Acquisition\u003c/h2\u003e \u003cp\u003eVertical Electrical Sounding (VES) measurements were conducted along two profile lines using a resistivity terrameter. The first profile consisted of three VES stations (VES1, VES2, and VES3) aligned in a northwest\u0026ndash;southeast direction, while the second profile included two VES stations (VES4 and VES5) oriented southwest\u0026ndash;northeast.\u003c/p\u003e \u003cp\u003eThe maximum current electrode spacing (AB/2) reached 330 m for each VES measurement. The spacing between VES stations was approximately 100 m along the first profile and 300 m along the second profile. During data acquisition, the current electrode spacing was progressively increased to obtain deeper subsurface information, while the potential electrode spacing (MN) was adjusted as required. Apparent resistivity values were recorded manually in the field. The spatial distribution of VES points and profile lines was later mapped using ArcGIS 10.3 software.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Magnetic Data Acquisition\u003c/h2\u003e \u003cp\u003eMagnetic data were collected using a proton precession magnetometer. A total of 206 magnetic data points were acquired along eleven profiles distributed across the study area. The measurements were conducted systematically with consistent station spacing to ensure adequate spatial coverage. A GPS device was used to record the geographic coordinates of each measurement point, ensuring accurate positioning for subsequent data processing and interpretation.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Data Processing and Interpretation\u003c/h2\u003e \u003cp\u003eThe acquired geophysical data were processed using standard software packages. The VES data were interpreted using IPI2Win and IPI-Res3 software, where iterative inversion techniques were applied to match the observed field curves with theoretical models. The processed resistivity data were then imported into Surfer software to generate pseudo-sections and geoelectrical sections.\u003c/p\u003e \u003cp\u003eElectrical Resistivity Tomography (ERT) data were processed using Prosys II for data transfer and preliminary visualization, while RES2DINV software was employed to perform two-dimensional inversion modeling. The inversion process utilized forward modeling and nonlinear least-squares optimization techniques to produce subsurface resistivity distributions (de Groot-Hedlin \u0026amp; Constable, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e1990\u003c/span\u003e; Loke \u0026amp; Barker, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e1996\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eMagnetic data processing was carried out using Oasis Montaj software. The data were corrected and gridded to produce total magnetic field maps. Advanced filtering techniques, including analytical signal and upward continuation, were applied to enhance subsurface structural features (Blakely, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e1995\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Results and Discussion","content":"\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e4.1 Electrical Resistivity Interpretation\u003c/h2\u003e \u003cdiv id=\"Sec15\" class=\"Section3\"\u003e \u003ch2\u003e4.1.1 Resistivity Pseudo-Section\u003c/h2\u003e \u003cp\u003eThe resistivity pseudo-section was constructed from the apparent resistivity data to provide a qualitative representation of subsurface resistivity variations in both vertical and lateral directions. Although pseudo-sections do not represent the true resistivity distribution, they offer an approximate visualization of subsurface features.\u003c/p\u003e \u003cp\u003eThe pseudo-section reveals significant lateral and vertical variations in resistivity values along the profile. Relatively high resistivity values are observed near the surface around the VES3 location, which may indicate compact or less altered geological materials. In contrast, a zone of low resistivity extends from the near-surface region between VES1 and VES2 downward toward the central part of the profile.\u003c/p\u003e \u003cp\u003eThis low-resistivity zone is interpreted as a weathered and fractured region saturated with geothermal fluids. The presence of such conductive zones is commonly associated with hydrothermal alteration and increased temperature, suggesting potential geothermal activity within the subsurface.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section3\"\u003e \u003ch2\u003e4.1.2 Geoelectrical Section\u003c/h2\u003e \u003cp\u003eThe geoelectrical section derived from VES data provides a quantitative interpretation of subsurface lithological variations and structural features. The section reveals distinct subsurface layers characterized by variations in resistivity values, which are indicative of different geological units.\u003c/p\u003e \u003cp\u003eA fractured zone is identified between VES1 and VES2 at depth, which likely serves as a pathway for hydrothermal fluid circulation. This fracture zone appears to facilitate the movement of geothermal fluids, leading to alteration of surrounding rocks. Beneath VES2, the interaction between hydrothermal fluids and pyroclastic materials has resulted in the formation of clay-rich layers at a depth of approximately 11.6 m.\u003c/p\u003e \u003cp\u003eAdditionally, deeper sections indicate the presence of intrusive basaltic formations, which have penetrated older geological units. These intrusions are interpreted as potential heat sources contributing to the geothermal system. The structural configuration observed in the geoelectrical section highlights the importance of fractures and lithological contrasts in controlling geothermal fluid flow.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003e4.2 Electrical Resistivity Tomography (ERT) Interpretation\u003c/h2\u003e \u003cp\u003eThe two-dimensional inversion models derived from Electrical Resistivity Tomography (ERT) data provide a more detailed image of subsurface resistivity distribution. The inversion results indicate resistivity values ranging from approximately 54.7 Ωm to 4253 Ωm, with a maximum investigation depth of about 115 m.\u003c/p\u003e \u003cp\u003eThe ERT model reveals a prominent low-resistivity zone extending vertically from shallow depths (approximately 2.5 m) down to about 19.9 m. This zone is interpreted as a weathered and hydrothermally altered region that may act as a conduit for geothermal fluids. Laterally, this conductive zone extends across a significant portion of the profile.\u003c/p\u003e \u003cp\u003eBelow this conductive layer, higher resistivity values are observed, corresponding to relatively unaltered or massive basaltic formations. The model also indicates the presence of intrusive bodies, which are inferred to be magmatic in origin. These intrusions likely serve as heat sources driving the geothermal system (Saemundsson, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Grant \u0026amp; Bixley, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2011\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eFracture zones identified within the ERT model further support the interpretation of fluid pathways. These structural discontinuities enhance permeability, allowing the upward migration of thermal fluids. Therefore, the integration of resistivity data clearly indicates that both lithological variation and structural features play a key role in geothermal fluid circulation.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003e4.3 Magnetic Data Interpretation\u003c/h2\u003e \u003cp\u003eMagnetic data analysis was conducted to identify subsurface geological structures based on variations in magnetic anomalies. The total magnetic field data exhibit both positive and negative anomalies, reflecting the dipolar nature of the Earth's magnetic field and variations in subsurface rock properties.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003e4.4.Euler Deconvolution Analysis\u003c/h2\u003e \u003cp\u003eThe Euler deconvolution technique was applied to estimate the location and depth of magnetic sources. This method relates the magnetic field and its gradients to the position of causative bodies, with structural indices representing different geological features (Thompson, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e1982\u003c/span\u003e; Reid et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e1990\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn this study, a structural index of N\u0026thinsp;=\u0026thinsp;0 was used, corresponding to contact-type geological structures. The results indicate the presence of multiple subsurface sources at varying depths. Deeper magnetic sources (greater than 300 m) are identified in certain trends, while intermediate and shallow sources are also observed.\u003c/p\u003e \u003cp\u003eThe clustering of Euler solutions suggests that the subsurface structures are predominantly aligned in a northwest\u0026ndash;southeast direction. This structural trend is consistent with regional tectonic patterns and likely plays a significant role in controlling geothermal fluid movement.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec20\" class=\"Section3\"\u003e \u003ch2\u003e4.3.2 Upward Continuation Analysis\u003c/h2\u003e \u003cp\u003eUpward continuation filtering was applied to the magnetic data to enhance deeper geological features by suppressing shallow anomalies. This technique effectively smooths short-wavelength variations and highlights regional-scale structures (Blakely, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e1995\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe magnetic data were upward continued to elevations of 150 m, 250 m, and 450 m. As the continuation height increases, shallow features become less prominent, and deeper structures are more clearly defined. At 450 m continuation, distinct zones of low magnetic anomaly are observed in the northeastern, southeastern, and central parts of the study area.\u003c/p\u003e \u003cp\u003eThese low magnetic anomaly zones are interpreted as trends affected by hydrothermal alteration, where magnetic minerals may have been altered or destroyed. Such zones are commonly associated with geothermal systems and may indicate trends of geothermal potential.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec21\" class=\"Section2\"\u003e \u003ch2\u003e4.4 Integrated Interpretation\u003c/h2\u003e \u003cp\u003eThe integration of electrical resistivity and magnetic data provides a comprehensive understanding of the subsurface geological framework. Both datasets consistently identify zones characterized by low resistivity and low magnetic anomalies, which are indicative of hydrothermal alteration and geothermal fluid presence.\u003c/p\u003e \u003cp\u003eThe dominant structural orientation identified from both ERT and magnetic analyses is northwest\u0026ndash;southeast. These structures likely act as zones conduits for geothermal fluids, facilitating the movement of heat and fluids from deeper trends to the surface.\u003c/p\u003e \u003cp\u003eFurthermore, the presence of intrusive bodies, fracture zones, and altered trends suggests a well-developed geothermal system. The zones identified through integrated interpretation represent promising targets for further geothermal exploration and development.\u003c/p\u003e \u003c/div\u003e"},{"header":"5. CONCLUSION","content":"\u003cp\u003eThis study applied integrated electrical resistivity and magnetic methods to investigate subsurface geological structures and their influence on geothermal manifestations in the Tulu Moye area, located in the Central Main Ethiopian Rift. The results demonstrate that both methods are effective in delineating subsurface features associated with geothermal systems.\u003c/p\u003e \u003cp\u003eThe resistivity data, including VES and ERT results, revealed zones of low resistivity that are interpreted as weathered, fractured, and hydrothermally altered Zone. These conductive zones are likely associated with elevated temperatures and the presence of geothermal fluids. In particular, the ERT models identified a laterally continuous low-resistivity zone between 480 m and 640 m, suggesting a trend pathway for fluid movement.\u003c/p\u003e \u003cp\u003eThe magnetic data analysis further supports these findings. Zones characterized by low magnetic anomalies were identified in the northeastern, southeastern, and central parts of the study area. These anomalies are interpreted as zones of hydrothermal alteration where magnetic minerals have been reduced or altered. The application of upward continuation filtering enhanced deeper structural features, while Euler deconvolution provided estimates of source depth and structural configuration.\u003c/p\u003e \u003cp\u003eStructural analysis from both resistivity and magnetic datasets indicates that the dominant الاتجاه of subsurface lineaments is northwest\u0026ndash;southeast. These structures are consistent with regional tectonic trends and are interpreted as major conduits controlling geothermal fluid circulation.\u003c/p\u003e \u003cp\u003eOverall, the integration of resistivity and magnetic methods provides a reliable approach for identifying geothermal potential zones. The trends characterized by low resistivity, low magnetic anomalies, and structurally controlled pathways represent promising targets for future geothermal exploration and development in the Tulu Moye area\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAdmassu, E., \u0026amp; Worku, S. (2015). Characterization of Quaternary extensional structures in the Tulu Moye geothermal prospect, Ethiopia. Journal of African Earth Sciences, 39, 225\u0026ndash;238.\u003c/li\u003e\n\u003cli\u003eAmigun, O. J., Afolabi, O., \u0026amp; Ako, D. B. (2012). Euler deconvolution of analytical signal of magnetic anomalies over iron deposits in Okene, Nigeria. International Journal of Geophysics, 2012, 1\u0026ndash;10.\u003c/li\u003e\n\u003cli\u003eArn\u0026oacute;rsson, S. (2000). Isotopic and chemical techniques in geothermal exploration, development, and use. Vienna: International Atomic Energy Agency.\u003c/li\u003e\n\u003cli\u003eBlakely, R. J. (1995). Potential theory in gravity and magnetic applications. Cambridge: Cambridge University Press.\u003c/li\u003e\n\u003cli\u003eChorowicz, J. (2005). The East African Rift System. Journal of African Earth Sciences, 43(1\u0026ndash;3), 379\u0026ndash;410.\u003c/li\u003e\n\u003cli\u003ede Groot-Hedlin, C., \u0026amp; Constable, S. (1990). Occam\u0026rsquo;s inversion for two-dimensional smooth models. Geophysics, 55(12), 1613\u0026ndash;1624.\u003c/li\u003e\n\u003cli\u003eEbinger, C. J. (2005). Continental break-up: The East African perspective. Astronomical Geophysics, 46(2), 2.16\u0026ndash;2.21.\u003c/li\u003e\n\u003cli\u003eGrant, M. A., \u0026amp; Bixley, P. F. (2011). Geothermal reservoir engineering (2nd ed.). Burlington: Academic Press.\u003c/li\u003e\n\u003cli\u003eHochstein, M. P. (1988). Assessment and modeling of geothermal reservoirs. Geothermics, 17(1), 15\u0026ndash;30.\u003c/li\u003e\n\u003cli\u003eKeller, G. V., \u0026amp; Frischknecht, F. C. (1966). Electrical methods in geophysical prospecting. Oxford: Pergamon Press.\u003c/li\u003e\n\u003cli\u003eKeir, D., Ebinger, C., Stuart, G., Daly, E., \u0026amp; Ayele, A. (2006). Strain accommodation by magmatism and faulting as rifting proceeds to breakup: Seismicity of the northern Ethiopian Rift. Journal of Geophysical Research, 111(B5), 1\u0026ndash;14.\u003c/li\u003e\n\u003cli\u003eKomolafe, A. A. (2010). Investigation of tectonic lineaments and thermal structures of Lake Magadi, southern Kenya Rift using integrated geophysical methods (Unpublished master\u0026rsquo;s thesis).\u003c/li\u003e\n\u003cli\u003eLoke, M. H. (1999). Electrical imaging surveys for environmental and engineering studies: A practical guide to 2D and 3D surveys. Malaysia: Geotomo Software.\u003c/li\u003e\n\u003cli\u003eLoke, M. H., \u0026amp; Barker, R. D. (1996). Rapid least-squares inversion of apparent resistivity pseudosections. Geophysical Prospecting, 44(1), 131\u0026ndash;152.\u003c/li\u003e\n\u003cli\u003eMamo, T. (2001). Geological and surface alteration report of the Tulu Moye\u0026ndash;Gedemsa area. Addis Ababa.\u003c/li\u003e\n\u003cli\u003eMekonnen, T. K. (2004). Interpretation of geophysical data using aeromagnetic datasets of Zimbabwe and Mozambique (M.Sc. thesis). International Institute for Geo-information Science and Earth Observation.\u003c/li\u003e\n\u003cli\u003eMengistu, Y. (2016). Detection of geothermal energy anomalies using Landsat thermal infrared data in the Tulu Moye geothermal prospect (M.Sc. thesis). Addis Ababa University.\u003c/li\u003e\n\u003cli\u003eNabighian, M. N. (1972). The analytical signal of two-dimensional magnetic bodies with polygonal cross-section. Geophysics, 37(3), 507\u0026ndash;517.\u003c/li\u003e\n\u003cli\u003eReid, A. B., Allsop, J. M., Granser, A. J., \u0026amp; Somerton, I. W. (1990). Magnetic interpretation in three dimensions using Euler deconvolution. Geophysics, 55(1), 80\u0026ndash;91.\u003c/li\u003e\n\u003cli\u003eSaemundsson, K. (2008). Structural geology, tectonics, volcanology and geothermal activity. Short Course III on Exploration for Geothermal Resources, ISOR, Iceland.\u003c/li\u003e\n\u003cli\u003eTelford, W. M., Geldart, L. P., \u0026amp; Sheriff, R. E. (1990). Applied geophysics (2nd ed.). Cambridge: Cambridge University Press.\u003c/li\u003e\n\u003cli\u003eThompson, D. T. (1982). EULDPH: A new technique for making computer-assisted depth estimates from magnetic data. Geophysics, 47(1), 31\u0026ndash;37.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Magnetic anomaly, Tulu Moye, Geophysical methods, geothermal resource","lastPublishedDoi":"10.21203/rs.3.rs-9318561/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9318561/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study investigates subsurface geological structures and their influence on geothermal manifestations in the Tulu Moye geothermal field, located in the Central Main Ethiopian Rift. The study area lies between UTM coordinates 512000\u0026ndash;514500 mE and 902000\u0026ndash;904000 mN, at an elevation of approximately 2090 m above sea level. Integrated geophysical methods, including electrical resistivity and magnetic surveys, were employed to delineate subsurface structures associated with geothermal activity. A total of five Vertical Electrical Sounding (VES) points and three Electrical Resistivity Tomography (ERT) profiles were acquired using a SYSCAL PRO system, while 206 magnetic data points were collected along eleven profiles using a proton precession magnetometer. The resistivity data were processed using IPI2Win, RES2DINV, and Surfer software, whereas magnetic data were analyzed using Oasis Montaj. The results reveal that zones of low resistivity and low magnetic anomalies correspond to areas of potential geothermal fluid accumulation and hydrothermal alteration. The ERT models indicate a laterally continuous low-resistivity zone extending between 480 m and 640 m, interpreted as a fractured and altered zone facilitating fluid flow. Upward continuation of magnetic data highlights deeper structures, with low magnetic anomalies observed in the northeastern, southeastern, and central parts of the study area. Structural analysis using Euler deconvolution and analytical signal techniques indicates that the dominant subsurface lineaments trend in the northwest\u0026ndash;southeast direction, acting as conduits for geothermal fluids. Overall, the integration of resistivity and magnetic methods effectively delineates geothermal potential zones and improves understanding of structural controls on geothermal systems in the Tulu Moye area.\u003c/p\u003e","manuscriptTitle":"Structural Controls on Geothermal Manifestations Using Integrated Geophysical Methods: A Case Study of the Tulu Moye Area, Central Main Ethiopian Rift","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-04-07 16:49:18","doi":"10.21203/rs.3.rs-9318561/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"d3c86fef-c03e-4ce5-8a5b-20dd8d476756","owner":[],"postedDate":"April 7th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":65860226,"name":"Geophysics"}],"tags":[],"updatedAt":"2026-04-07T16:49:18+00:00","versionOfRecord":[],"versionCreatedAt":"2026-04-07 16:49:18","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9318561","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9318561","identity":"rs-9318561","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}