Proceedings of the 12th International INQUA meeting on paleoseismology, active tectonic and archaeoseismology

The eastern border of Santiago has experienced an accelerated urban development in the last four decades with respect to the previous four centuries, with increasing urbanizationdirectly on the fault trace (Easton et al., 2018). Because of the latter a growing population lives directly on its trace as well as in its surroundings, constituting an increasing risk which is necessary to assess (Easton et al., 2022). Improving knowledge on the location of the fault trace is an important and difficult issue given the increasing urbanization of the area. In this work, we present results from ongoing analysis from hydrogeological and geophysical subsurface exploration of the San Ramón Fault. M E T H O D S An Earth Resistivity Tomography (ERT) survey with Pole-Dipole method considering 10m as dipole distance and 590 m of total length, was carried out to explore the San Ramon Fault trace, reaching up to 191 m of exploration depth. Drilling information was used to understand the deep of groundwater levels and to define the hydrogeological units from geoelectrical units defined by the ERT survey. Complementary data from a Digital Elevation Model (LiDARbased-DEM; 1m 2 spatial resolution, 20cmvertical precision,Valderas, 2020), allowedfor thecontextualization of the sitewith respect to the known SanRamon Fault trace in Las Condes district, located immediately to the north of La Reina district (Easton et al., 2022; 2024). R E S U LT S The localization of the San Ramón fault trace was assessed from ERT survey, drilling information, geomorphological and field observations. From the ERT survey (Fig. 2), it was possible to define geolectrical units that correlate with the hydrogeological units showed in Fig. 3. The unit D with the main hydrogeological potential in fissured or fractured rocks showed resistivity values between 20 and 162 Ohm-mwith lower resistivity values most probably controlled by the presence of clay minerals resulted from the alteration of rocks. The unit E, characterized by lower hydrogeological potential showed resistivity values of 162-460 Ohm-m interpreted as rock blocks with low porosity or even low permeability. The unit B showed 20-57 Ohm-m mainly due to the presence Fig. 1: Location of the known San Ramon Fault trace (see Easton et al., 2024), and study area of this work, where ERT prospection and hydrological studies are ongoing.