## 1 Introduction  
The critical zone (CZ) defines the outermost surface layer of the earth, where the atmosphere, meteoric water, biota, soil, and bedrock interact [1, 2]. The CZ extends from the unaltered rock to the top of the canopy of plant vegetation on the ground surface [3] (Figure 1). The CZ hosts life and the energy and resources to sustain it, and it is the subject of an increasing body of research. Researchers and government entities have highlighted the role of the CZ for our society in different economic and environmental aspects, and the need for a correct and robust characterization of this important layer [4, 5, 6, 7]. The CZ, from top to bottom, comprises: the soil (that includes the organic horizon, the surface horizon A, and the subsoil horizon B), regolith, fractured bedrock, and fresh bedrock (Figure 1). The CZ also comprises the near-surface aquifers. The formation of the CZ is a combination of two important processes, namely: (i) soil layer erosion, which can remove weathered materials from the topsoil surface (surface topography), and (ii) rock weathering processes, which occur mechanically and chemically and that can break down rock layers, separating the underlying altered bedrock and fresh bedrock [8; 9; 10]. The thickness of the CZ can range from 0.7 m to 223.5 m, being thicker in midlatitudes [11]. The production of regolith from fractured bedrock can increase the surface area and distribution of weatherable minerals and expose them to increased water intrusion from the surface. The thickness of the regolith controls groundwater storage and flow paths in highly complex system landscapes such as mountainous landscapes and is highly correlated with topographic slopes or gradients [12; 13]. All the activity that occurs in the CZ will greatly determine the level of mass and energy exchange between the biosphere system, the regolith layer, and the earth's atmosphere [14; 15; 16; 17]. Thus, understanding the geometry, area, and physical properties of the CZ is crucial for the sustainability of the surrounding ecosystem. Geophysical methods have been used in the past to try to characterize and constrain the CZ, its formation, and the processes that occur within it, e.g., the analysis of deep rock weathering and groundwater storage potential; studies on transport processes, reactivation, and kinetics processes; imbalances of chemical processes in the water surface boundary plane, and tectonic fracture activity [21; 22; 23; 24]. These processes are interrelated and influence each other in the formation of the CZ. Some works that focused on the study of the CZ used seismic wave velocities and electrical resistivity to demonstrate the influence of topographic stress and fault activity on bedrock fault distribution [25; 26]. Specifically, in the EBSZ, the structure of the CZ was first characterized by P-wave tomography and MASW across the frontal strands of the Carrascoy fault system, namely the Algezares-Casas Nuevas fault (ACNF) [27]--in review. This study revealed the underground structure, the CZ, and the damage zone related to blind faults buried under the Guadalentin Depression. Nevertheless, the along-strike variations of the structure in the EBSZ and the CZ thickness  
Figure 1: Simplified model of the critical zone regarding the weathering profile developed on rock masses (modified from [18; 19; 20]). Zones I to VI defined by the degree of weathering [18]. and properties could not be estimated, requiring a comprehensive geophysical study along with different areas of this fault system. In this study, we investigate the geometry of different fault zones and the distribution of the CZ using coincident seismic and electrical surveys in the EBSZ along four profiles (La Torrecilla, La Salud North, La Salud South, and Carrascoy). To characterize the CZ along the EBSZ, we have used indirect geophysical methods, including P-wave tomography, Multichannel Analysis of Surface Waves (MASW), and Electrical Resistivity Tomography (ERT) on the profiles of La Torrecilla and La Salud North.