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

94 PATA Days 2024 The San Ramón Fault (FSR) displays conspicuous geomorphological features like fault scarps (Rauld, 2002; 2011), together with paleoseismological evidence indicating its active nature (Vargas et al., 2014), and seismicity characterizing the neighboring Andean block (Ammirati et al., 2019). This makes the fault as a source for seismic hazard to the capital city of Chile (Easton et al., 2018; 2022). This hazard could be manifested as the generation of surface-rupturing earthquake or by the occurrence of earthquakes without surface rupture. Thus, the city could be affected by surface rupture and by the shaking associated to an earthquake of magnitude in the order of Mw=7.2-7.5 (Armijo et al., 2010; Vargas et al., 2014; Ammirati et al., 2019). Therefore, it is necessary to reassess the hazard posed by this structure based on new knowledge of the trace, through the analysis of geomorphological features along the piedmont of Pirque. M E T H O D S Using a Digital Terrain Model (DTM) with a spatial resolution of 1 meter generated from a LiDAR point cloud (2-10 pulses/m2) and orthoimages with a spatial resolution of 0.25 meters, scarps and other features affecting the Quaternary geomorphological units in the foothills of the Andes in the Metropolitan Region were identified and mapped. To identify and describe the geomorphological features expressing the neotectonic activity of the FSR, 350 topographic profiles were conducted (Fig. 2). These profiles, oriented east-west, were spaced every 50 meters along the piedmont of the Andesan mountain front, between the Maipo River and Quebrada Honda. The identified features include fault scarps, fault scarps with anthropogenic influence, bulging, and regional slope change. The location of the fault is interpreted according to the following hierarchical order: fault scarp, fault scarp with anthropogenic influence, bulging, and change in far-field slope. The fault trace is mapped as observedwhen the recognized feature in the profile is a fault scarp. On the other hand, the trace is interpreted when the observed feature is a fault scarp with anthropogenic influence, bulging, or change in farfield slope. Finally, in profiles where no feature were observed, the trace was inferred by appealing to its lateral continuity. For hazard assessment, we considered previous data (Armijo et al., 2010; Vargas et al., 2014; Ammirati et al., 2019), along with the information gathered in this study. The Hank and Kanamori formula (1979) was used to estimate the moment magnitude.