3.1. Electrical Resistivity Tomography
After removing noisy data, 563 of the 579 data points that were initially gathered for profile 1 were determined to be appropriate for the inversion process. The resulting ERT inverted section (Fig. 4) clearly shows a low-resistivity material layer in the topsoil, with a resistivity ranging from approximately 5.7 to 50.7 ohm.m., which is interpreted as reddish clay soil. The next layer has resistivity values that are typical of clay soil with quartz, ranging from 50.7 to 152 ohm.m. The resistivity values of anomalies designated B (void zone and weak zone) range from 50.7 to 1359 ohm.m. This indicates that the slate is weathered, moderately fractured, or highly fractured. The slate reaches the base of the profile at depths of approximately 330–420 m and 550–620 m along the profile to a depth of 100 m. Moreover, large basement rocks, represented by anomaly A, have resistivity values between 4065 and infinity.
For electrical resistivity imaging, a total of 579 data points were collected along profile 2. Approximately 578 data points were used for the inversion after the dataset was automatically filtered and noisy data were removed. The layer's upper portion consists of low-resistivity materials, whose resistivity values range from 6.0 to 51.1 ohm.m and whose thicknesses range from 4 to 11 m. It was determined that this uppermost layer was reddish clay. All aquifer strata have thicknesses that increase from 340 to 610 m in a north‒south direction.
The next layer has resistivity values in the range of 51.1 to 149 ohm.m, which is in line with the properties of clay soil mixed with quartz. The resistivity anomalies in the 149–432 ohm.m range point to slate that is somewhat cracked and worn. Furthermore, resistivity readings between 432 and 1258 ohm.m indicate large amounts of slate in depth intervals between 39.6 and 57.5 m and lateral thicknesses between 360 and 420 m and between 540 and 590 m. Massive basement bedrock can be seen in the southern section of the profile, where it extends from 18 meters to 280 meters in depth. The range of high resistivity values in this region of the stratum, which vary from 3657 ohm.m to infinite ohm.m., respectively, indicates the presence of basement rock (see Fig. 5).
Similarly, 574 data points from profile 3 were gathered, kept after removing noisy data, and utilized for the inversion. The model's overall resistivity values vary greatly, suggesting that the underlying geology is not homogeneous and ranges from low to high electrical resistivity values (4.6–16868 ohm/m). It is evident from the 2D inverted section (Fig. 6) that the resistivity values of the top layer range from 4.6 to 476 ohm.m across the profile, with reddish clay being highlighted. The resistivity values in the second layer, which correspond to the properties of clay with quartz soil, range from 47.6 to 154 ohm.m. The variance in resistivity readings between anomalies of 154–498 ohm.m. suggests that the slate is moderately cracked and worn. This aquifer zone has resistivity values ranging from 498 to 1612 ohm.m. The comparatively greater resistivity value suggests a fairly massive slate aquifer at a depth of 18 to 65 m.
After automatic filtering and the removal of noisy data by visual examination from the dataset, approximately 577 data points from profile 4 were chosen for inversion. Reddish clay is indicated by the study region, where the resistivity ranges from approximately 4.1 to 376 ohms. The resistivity of the inverted model of the next layer ranges from 37.6 to 113 ohms, which is typical of the top layer of clay with quartz soil. At a depth of approximately 18.5–110 m, the severely worn and moderately fragmented slate is indicated by an intermediate layer resistivity ranging from 113–1032 ohm. The resistivity variation region at the subsurface shows a resistivity anomaly that varies in the degree of fracture between the high-marked resistivity regions (A, A1, and A2 (massive basement rock)) and the low-marked resistivity regions B, B1, and B2 (week zone area)). One side of the indicated anomaly (A, A1, and A2) has a low-resistivity anomaly. Figure 7 illustrates the properties of the enormous rocks in this region, which exhibit a high resistivity range > 3114 ohm.
After automatically filtering and removing bad data from the dataset via visual examination, 570 electrical resistivity data points from profile 5 were used for inversion. The profile results indicate that as depth increases, so does the subsurface resistivity. Under the profile, the inverted model resistivity (Fig. 8) displays fluctuating low resistivity values < 940 ohm.m. from the surface down to a depth of approximately 57 m. This profile's top layer is made up of reddish clay that ranges in resistivity from 7.6 to 52.3 ohm.m. and is located at a depth of approximately 10–20 meters. The worn-out basement came next. Its upper portion has a resistivity ranging from 52.3 to 137 ohm.m. and is uniformly thick throughout the profile line, displaying a layer of quartz and clay. The following was determined to be slate that was moderately fragmented and heavily worn, with a resistivity value of 137–359 ohm.m. Beneath this layer lies a basement rock, the upper portion of which is regarded as a saturated basement or highly fractured slate. The resistivity of this rock ranges from 359 to 940 ohm.m. The layer's high resistivity values (2462-ohm.m to infinity) in the 80–120 m depth range indicate that the subsurface materials are resistant, leading to the interpretation that the substance is a large basement rock.
Using an automatic filter and an inspection process to remove noisy data, 572 electrical resistivity data points from profile 6 were used for the inversion, which displays the reddish clay, according to the study results from this profile, which shows a resistivity range of 7.0–45.2 ohm.m. The resistivity values of the next layer inverted model, which are typical of clay soil with quartz, vary from 45.2–115 ohm.m. The resistivity values of the next layer inverted model, which are typical of clay soil with quartz, vary from 45.2–115 ohm.m. The sharp resistivity anomaly between 45.2–745 ohm.m contrasts (designated B and B1 (week zone area)) is thus regarded as a degree of weathered, intermediate, and high fracture slate; this anomaly is obtained at 180–290 m and 390–390 m. According to the inverted model resistivity with tomography (see Fig. 9), these high resistivity zones at the locations designated A and A1 (large basement rocks) are larger than 1895 ohm.m.
3D inverted model resistivity (combinations of profiles 1, 2, and 3)
The subsurface of the research area exhibits an anomaly of varying resistivity values, as indicated by the marked portions denoted as A&A1, B&B1, and C&C1 in Figure 10. Week zones that may be connected to the high-aquifer production zones are depicted in the 3D model, with low resistivity values roughly indicating regions A and A1. In the areas indicated at C&C1 (moderate productive aquifer zone), the 3D model has intermediate resistivity values. The subsurface, representing the low-productivity aquifer zone, is represented by a 3D model with high resistivity values around regions identified at B&B1 (large basement rock).
3D inverted model resistivity values (combined profiles 4, 5, and 6)
For every profile, the top surface is uniform and exhibits very low resistivity values (< 36 ohm.m.) (Figure 11). The 3D model with low resistivity values roughly represents the weak zone area (A1), which is an area with good groundwater potential. The locations shown at B1 (massive basement rock) in the 3D model with high resistivity values roughly indicate low discharge potential.
3.2 Complete Bouguer Anomaly Map
Lateral gravity fluctuations in the Earth's underlying materials are generally visible on the entire Bouguer anomaly map. Because no topographic effects have been minimized to suggest that the area is flat, complete Bouguer anomaly values also mirror gravity fluctuations in the Earth's crust and upper mantle (Reynolds, 1997). The lower rock densities beneath the location at the measurement point range from 41.59 to 46.79 mGal, as shown by the low values of the entire Bouguer anomaly. The low-amplitude reflections reflecting a ring-shaped structure suggest the presence of intrusive (cavity) luminous bodies in the subsurface, according to the complete Bouguer anomaly map (Figure 12) displayed in the research area. A high Bouguer anomaly indicates high rock density beneath the measurement point, which ranges from 48.90 to 51.79 mGal. Generally, the existence of deeper denser materials or shallower or near-surface elevated blocks of basement rocks could be the cause of these high-gravity anomaly zones (Sultan et al., 2018).
3.2.1 Regional and residual gravity anomalies
The distribution of the gravity field is depicted in the regional gravity anomaly map (Figure 13(a)). High-gravity anomalies are caused by deeper-density structures. The study's regional trend was a straight line, and the gravity density decreased from the south to the north. The following is a summary of the essential features of the regional gravity anomaly map of the research area. The regional gravity anomaly in the research area varies from 43.95 to 48.52 mGal, suggesting that the deep-seated sources are deeper in the north and shallower in the south. A true representation of the gravity anomaly map distribution in the study area is provided by the residual gravity anomaly map (Figure 13(b)). The following is a summary of the features of the residual gravity anomaly map of the research area: there is a maximum of 5.21 mGal and a minimum of -3.96 mGal for the residual gravity anomaly field in the understudied area.