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This study presents a novel approach to identifying and characterizing active faults in urban areas, using an example from the city of Cusco in Peru, by combining magnetotelluric (MT) exploration and radon gas monitoring. The research aims to improve understanding of the active faults in the Cusco Valley by using the MT method to provide subsurface electrical resistivity data, enabling the mapping of fault structures and determination of fault properties. A 2-D inversion of the MT data resulted in resistivity models that revealed critical information about fault geometry, such as dip and depth. Radon gas measurements complement the MT data by being able to distinguish between active and inactive faults. This is because active faults can exhibit higher permeability due to ongoing tectonic activity. This increased permeability facilitates the migration of radon from deeper rock formations to the surface, leading to detectable anomalies. Active faults are particularly significant as their continued deformation enhances permeability, making radon anomalies a valuable indicator for locating these structures. A clear correlation was found between elevated radon concentrations (>5.9 kBq m−3) and the locations of faults identified through the MT resistivity model, and additional gas sample analyses ruled out the possibility that these anomalies were caused by lithological variations. This integrated approach holds significant potential for detecting active faults in urban areas such as Cusco. In these locations faults such as the Cusco and Alto Qosqo faults may be obscured by construction. The findings uncovered previously unmapped fault lineaments and advanced the understanding of fault kinematics in Cusco, emphasizing the importance of combining MT and radon monitoring for earthquake hazard assessment in urban environments.

The Western flank of the Central Andes presents a high concentration of giant paleo-landslides that are well preserved due to the long-term aridity of the region. However, the precise timing of most of these features remains unknown, hindering our understanding of their forcing factors and frequency. To address these questions, we focused on eight giant paleo-landslides located in the Locumba landslide Cluster, near and around the Aricota rockslide, to explore their possible temporal correlation. We employed cosmogenic nuclide exposure dating to constrain the timing of these failures, sampling a total of 52 boulders. In about half of the cases, the obtained exposure ages exhibited significant scattering, including very old apparent ages up to ∼1 Ma. For these, only probable time of landslide occurrence associated with large uncertainty could be proposed. We attribute this age scattering mainly to the inheritance problem, which is expected to be very strong in these arid regions where most slopes are slowly eroding, likely at steady-state equilibrium, resulting in very high cosmogenic nuclide concentrations at the surface and shallow depths (first 20 m). Nevertheless, we obtained reliable age constraints for five of the landslides, all of which occurred during the Late and Middle Pleistocene, with mean ages of approximately 16 ka, 18 ka, 115 ka, 190–220 ka and ca. 330 ka. When compared to previous dates in the region and other climatic proxies, the time ranges of 16–18 ka and 100–120 ka correspond to two well-defined humid periods, known as Heinrich Stadial 1a, the Ouki event (during MIS5), respectively. More generally, the activity of landslides along the Central Western Andes seems to increase during interglacial periods. These results suggest that past climate changes, particularly shifts from hyper-arid to prolonged wetter conditions, played a primary role in large landslide activity in the Central Andes.

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