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

424 PATA Days 2024 The main weighting factors in the methodology are slopes, distance to the fault and the geological- geotechnical characteristics of the materials. This study updates susceptibility maps for Santiago foothills (Lara et al. 2018) including the effects of SRF. Slopes and topographic amplification Keefer (1984) indicates that from 40° slope onwards rock falls are generated and from 35° slope onwards disintegrated rock slides occur. According to Zhao et al. (2019), 70% of the landslides triggered by the Nyingchi earthquake (Mw 6.4) occurred on slopes between 35° and 55°. In the case of landslides, Keefer (1984) notes that disintegrated landslides (generally of the translational type) occur from 15° onwards. In dynamic analysis studies of slope stability, it has been observed that slopes are related to topographic amplification effects, which tend to intensify on inclinations greater than 15° and 30° (European Commission, 2012). Previous seismic events could have deteriorated the quality of the rocks, making steep areas more unstable. Topographic amplification occurs when seismic waves interact with specific geomorphological features, such as steep slopes in regions with significant topographic relief. This interaction leads to increased ground motion amplitudes near the ridge crests (e.g., Meunier et al., 2008; Sepúlveda et al., 2005; Shao et al., 2022) Ground accelerations at mountain peaks can be three to six times greater than at the base (Wang et al., 2012; Wang et al., 2018 as cited in Serey 2020). This increased acceleration makes the upper parts of slopes more prone to landslides. In some studies, on earthquake- induced mass movements, a significant concentration near ridges has been observed. For instance, the 6.1 Mw Lushan earthquake (Shao, 2022) and the 6.2 Mw Aysén earthquake (Sepúlveda 2010), both occurring at shallow depths, exhibited this pattern. However, there are also cases where mass movements cluster near the ridge and close to rivers, as seen in the Finisterre Mountains during the 1993 earthquake (Meunier, 2008), as well as in the Northridge, Chi-Chi, and Wenchuan earthquakes. These patterns result from a combination of seismic mechanisms and geological controls (Rault et al., 2019). Distance to Fault Faults are structures that may have associated deterioration, through fracturing and weathering/ alteration, in the outcrops they affect. Brittle faults show mainly two structural domains, a central core and its surrounding damage zones. The fault core is the result of highly localised deformation and intense shear that accommodates most of the displacement within the fault zone and generally consists of a number of recurrent slip surfaces and fault rocks such as salbands, cataclasites and breccias; the damage zones are characterised by less intense deformation compared to the fault core, and these zones generally exhibit several second order structures such as subsidiary faults, fractures and veins, as well as fault-associated folds in some cases (Choi et al., 2016). In general, there is consensus that faults influence susceptibility to landslide generation, however, there is no consensus on the distance to which they influence (e.g. Mitchell and Faulkner, 2009; Lima Celestino et al., 2020; Naquira, 2009; Farías, 2017; Muñoz, 2013; Alfaro et al., 2018). In this work we propose to consider a distance to the SRFof 300mas aparameter for assessing susceptibility. Lithology/geotechnics The lithology of the Santiago Mountain range corresponds mainly to rocks of the Abanico Formation and some minor intrusives. The slopes have a soil cover that does not exceed 1 m in thickness and the rock is generally moderately to slightly weathered.