Imaging extensional fault systems using deep electrical resistivity tomography: A case study of the Baza fault, Betic Cordillera, Spain

Abstract

Seismic hazard assessment of present-day tectonic faults may be improved by studying their structure and kinematics. These features have been mainly determined by surface geological studies of exposed fault traces, structural lateral segmentation or paleoseismic trenches. All these approaches rely mainly on two-dimensional analyses of surface outcrops, while knowledge of the faults at depth remain largely inaccessible. To improve on such limitations, geophysical methods can be applied to establish detailed information on fault morphology and segmentation at depth. This work analyzes new results of a deep electrical resistivity tomography survey acquired across the Baza Fault, a present-day tectonic fault that controls the geometry of the Neogene intra-mountainous Baza Basin (Betic Cordillera, Spain). Interpretation of our preferred resistivity model reveals its detailed structure down to approximately 1000 m depth. The survey shows a minimum 2 km wide complex normal fault system, with rotational tilting blocks bounded by potentially listric normal faults. This study presents subsurface evidence of the Baza fault (F3), coincident the main topographic scarps. However, the geophysical model and geomorphic evidence also support a fault branch (F1) that might be an additional active seismogenic source. The geophysical survey technique presented in this study provides essential data to improve assessment of the seismogenic potential of the Baza Fault.