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Relating Large-Volume Landslides and Potentially Active Faults Using Geotechnical Analyses in the Pocuro Fault System, Central Andes (32°-33°s)

Description: 

Large-volume landslide deposits are frequent in seismically active mountain regions, such as the central Andes. Their clustered geographic distribution close to tectonically active fault systems suggests that their most likely trigger are shallow crustal earthquakes from nearby faults . We investigate landslides along the Pocuro Fault System (PFS) in the Chilean Andes (32°-33°S), using a method developed in the Argentinean central Andes to link large rock slides with potentially active faults by applying geological and geotechnical earthquake engineering tools, including numerical modelling back-analyses and application of ground motion models. Recent studies of the PFS have found that at least one major branch has Quaternary activity. We thus hypothesize that other faults of the system may be potentially active. A landslide inventory was updated for the region, obtaining morphometric parameters of the landslides. Detailed field and lab geotechnical assessments including testing of selected rock slides were performed to be used as models of a representative number of slides that were analysed using 2D seismic slope stability back-analyses. Given the lack of historic ground motion records, seismic records from abroad considering similar source mechanisms and earthquake parameters were selected to run the analyses. Then, the landslides found to be likely seismically triggered were related to nearby faults of the PFS, identifying those faults more probable to have induced the landslides and an earthquake magnitude range consistent with both the fault geometry and the slopes destabilization. Further research will look to combine these results from geo-engineering analyses with pending geochronological studies of the landslides and faults. This would provide useful information on the frequency and magnitude of ancient, large shallow crustal earthquakes, aiding the characterization of seismic hazard in a region where the contribution of shallow seismicity to seismic hazard has not been accounted for to date. This work is funded by ANID-Fondecyt 1200871 grant (L. Pinto) and the FRBC Endowment Fund (S. Sepúlveda).

Session: Learning Across Geological, Geophysical & Model-Derived Observations to Constrain Earthquake Behavior - III

Type: Oral

Date: 5/1/2024

Presentation Time: 02:45 PM (local time)

Presenting Author: Sergio

Student Presenter: No

Invited Presentation: 

Authors