Landslides as Paleoseismological Indicators: Experiences Using Geotechnical Back-analyses in the Andes

SEPULVEDA S.A.; JUNQUERA-TORRADO S.; MOREIRAS S.M.; PINTO L; URREJOLA J.T.

Bellevue

Congreso; SSA Annual Meeting; 2022

Seismological Society of America

Large volume landslides are often triggered by earthquakes in seismically active mountain regions. Recent examples in the central Andes and the usually clustered geographic distribution of older landslides suggest that the most likely source of coseismic rock slides and rock avalanches are shallow crustal earthquakes from nearby active faults. Using this as a working hypothesis, large volume, well preserved prehistoric landslides can be studied using geomorphological, engineering geological and geotechnical tools, including Newmark-type, limit equilibrium and numerical modelling back-analyses. We present recent and ongoing examples of studies in the Chilean and Argentinean slopes of the central Andes. Research in the Argentinean region of San Juan-Mendoza (31-33°S) allowed the development of a methodology to identify nearby faults as potential sources of earthquakes that may have induced the slope instabilities, combining the geotechnical analyses and ground motion prediction equations. This methodology is now being applied in similarly distributed megalandslides along the Pocuro fault zone in the Chilean side (32°-33°S). The coseismic nature of paleolandslides cannot be assured from geotechnical studies alone, as other factors such as post-glacial debutressing and climate may also induce large slope collapses in these mountain environments. However, the combination of geoengineering analyses with geochronological and neotectonic studies may provide useful information on the age and magnitude of ancient, large shallow crustal earthquakes, contributing to the characterization of seismic hazard in mountain regions.This work is funded by ANID-Fondecyt 1201360 and 1200871 grants in Chile and by grants from ANLAC program (Res. 571/15), and the SeCTyP (Cod. A06/669; Res. 3820/2016) of National University of Cuyo and the Ministry of Defence (PIDEF 05/18) in Argentina.