## 1 Introduction  
There are many examples of the application of different geophysical techniques in geological-mining research. The most commonly used techniques include gravimetric, magnetic, electrical, electromagnetic and seismic methods. However, these indirect techniques include a data inversion process, which generates uncertainty in the interpretation of these data (inverse problem). The solution to the inverse problem is not unique, since the same set of field data supports a domain of valid mathematical solutions, and modifications can be made in the measured property (e.g., resistivity) and in the thicknesses of the geological unit with the same measurement results [1]. For this reason, it is advisable to combine indirect techniques that measure different properties and whose results have a good geological significance depending on the direct information available [2; 3; 4; 5]. In this work, the capacities of different geophysical techniques to study geological structures are analysed. For this purpose, the northern boundary of the detrital aquifer of Bailen (southeastern Spain, Figure 1a), characterized by the presence of normal faults in a NE-SW direction with several hundred meters of vertical displacement, was selected as the experimental site. The following two geophysical techniques that measure different properties (elasticity and conductivity) and offer good resolution at several hundred metres depth are used together: seismic and electromagnetic techniques (time-domain electromagnetic (TDEM) method). As a complementary geophysical technique, the magnetic method was chosen. Although its use in the study of fractures is not as frequent in the literature as the previous ones, it was expected that it will provide additional information, such as the strike of the fractures existing in the subsoil and covered by recent materials. In addition, direct field information and groundwater catchment data were available, providing verification and correlation tools for the indirect techniques used in this work. First of all, the information provided by seismic reflection is analysed and compared with stratigraphic data obtained in the field. Seismic methods are the most important  
Figure 1: **(a)** Geographical location and geological map of the Bailén basin. The studied sector is indicated (black box, see Figure 2), as are the positions of two boreholes (1 and 2) and the location of the X–X section. (b) X–X’ geological section, which includes the positions of boreholes 1 and 2. G: granite, P: phyllites; T1: conglomerates and sandstones of the basal Triassic (lower aquifer); T2: lutites of the upper part of the Triassic; M1: rudites and calcarenites from the basal Miocene unit (upper aquifer); M2: marls from the upper part of the Miocene. geophysical technique in terms of accuracy, resolution and penetration depth [1]. The main objective of seismic reflection is to provide information on the geological structures of the subsoil and to identify different boundaries through changes in the acoustic impedance of the materials passed through [6]. Reflection seismology is the most commonly used tool for establishing the fundamental structural and depositional framework, therefore it has been widely used in the analysis of sedimentary basins and in hydrocarbon exploration [7; 8; 9; 10]. Second, the time-domain electromagnetic method (TDEM) is applied in this study. The TDEM operating principle consists of circulating an electric current through a transmitting coil for short periods of time. When the flow of current is abruptly interrupted, a variation in the primary magnetic field occurs, which induces a variable electric current. This, in turn, generates a transient secondary magnetic field. These currents flow in closed paths and migrate in depth, decreasing in intensity over time. Changes in the secondary magnetic field over time induce a transient voltage in the receiving coil.