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

It is known that the hanging wall block has a displacement from east to west, and at this point, the fault plane shows a NNW-SSE orientation. Therefore, it is possible that structures of sets 1 and 2 (roughly perpendicular to the main fault), could be associated with extensional fractures or to an oblique component of the movement. Meanwhile, the structures associated with set 4, and eventually those of set 3, which have a similar strike to the main fault, would be related to the principal ENE-WSW dominant stress field. C O N C L U S I O N S The results of this study provide a detailed characterization of the geological features observed at the main outcrop of the eastern branch of the San Ramón Fault in the San Carlos de Apoquindo area, located in Las Condes district at the foothills of the Andes in Santiago. In this area, volcanic rocks associated to the Cenozoic Abanico Formation overthrust Quaternary alluvium. The main fault plane exhibits an R E F E R E N C E S Allmendinger, R., Jordan, T.E., Kay, S., & Bryan, I. (1997). The evolution of the Altiplano-Puna Plateau of the Central Andes, Annual Reviews of Earth and Planetary Sciences, v. 25, 139-174. Annual Review of Earth and Planetary Sciences. 25. 139-174. Armijo, R., Rauld, R., Thiele, R., Vargas, G., Campos, J., Lacassin, R., & Kausel, E. (2010). TheWestAndeanthrust, the San Ramon fault, and the seismic hazard for Santiago, Chile. Tectonics, 29(2). Campillay Horta, N. (2022). Deformación cortical cuaternaria y peligro sísmico asociado a la Falla San Ramón en el piedemonte de Pirque (~33,5°S). https://repositorio. uchile.cl/handle/2250/192623 Choi, J.-H., Edwards, P., Ko, K., Kim, Y.-S. (2016). Definition and classification of fault damage zones: A review and a new methodological approach, Earth- Science Reviews, Volume 152, 2016, Pages 70-87, ISSN 0012- 8252, https: //doi.org/10.1016/j . earscirev.2015.11.006. orientation of strike dip N32W/43E. The fault core is around 50-75 cm thick, and is constituted by an angular, poorly sorted gravel-to-block-size clasts with a sand-to-clay-sized matrix breccia. In the hanging wall, shales interbedded with tuffs are intensively affected by joints which decrease in number per cubic meters at distance greater than 6 m, and abruptly diminish beyond 10 m, defining a wide damage zone from the fault core. The joints are characterized by four main sets, which would indicate both reverse and strike-slip kinematics in this area. At the surface, the outcrop is characterized by a ca. 1 m thick soil, suggesting some development of the surface during Quaternary times. This work contributes to a more detailed understanding of the damage zone of the San Ramón Fault system, improving our knowledge for seismic hazard assessment of the city of Santiago. A C K N O W L E D G E M E N T S We thank FONDECYT projects 1230350 and 1241021. Easton, G., Inzulza Contardo, J., Pérez Tello, S., Ejsmentewicz Cáceres, D., & Jiménez Yáñez, C. (2018). ¿Urbanización fallada? La Falla San Ramón como nuevo escenario de riesgo sísmico y la sostenibilidad de Santiago, Chile. Revista de Urbanismo, 38, 1-20. Horton, B. K. (2018). Tectonic regimes of the central and southern Andes: Responses to variations in plate coupling during subduction. Tectonics, 37, 402–429. https: //doi. org/10.1002/2017TC004624 Iglesias García, T. (2022). Paleosismología y modelación de la Falla San Ramón en el sector oriente de Santiago. https: //repositorio.uchile.cl/ handle/2250/191480 Meier, S., Johanna F.B., & Philipp, S.L. (2015). Fault zone characteristics, fracture systems and permeability implications of Middle Triassic Muschelkalk in Southwest Germany. Journal of Structural Geology 70, 170- 189. https: //doi.org/10.1016/j . jsg.2014.12.005 Peacock, D.C.P., Dimmen, V., Rotevatn, A., Sanderson, D.J. (2017). A broader classification of damage zones, Journal of Structural Geology, Volume 102, 2017, Pages 179- 192, ISSN 0191-8141, https://doi. org/10.1016/j.jsg.2017.08.004. Riesner, M., Lacassin, R., Simoes, M., Armijo, R., Rauld, R., Vargas, G. (2017). Kinematics of the active West Andean fold-and-thrust belt (central Chile): Structure and long- term shortening rate. https: //repositorio.uchile. cl/handle/2250/168829 Thiele, C. (1980). Geología de la Hoja Santiago, Región Metropolitana. Vargas, G., Klinger, Y., Rockwell, T. K., Forman, S. L., Rebolledo, S., Baize, S., Lacassin, R., & Armijo, R. (2014). Probing large intraplate earthquakes at the west flank of the Andes. Geology, 42(12), 1083-1086. https:// doi.org/10.1130/G35741.1