Analysis of Deep-Seated Slope Deformations by Paleoseismic Technique

ABSTRACT: Dating the movements and reconstructing the behavior of a deep-seated slope deformation (DSSD) are fundamental steps for geological hazard assessment. We applied paleoseismic techniques with trench excavation across main Holocene deformation zones of mountain slopes of the Alps. We discovered buried deformed paleosoils recording the various stages of the DSSD. By ¹⁴C method we dated at 10,975-10,570 yr BP (calibrated age) the deposits preceding the main slope deformation, and at 7000 yr BP the oldest layers trapped in the deformation zone suggesting the age of inception of the DSSD. The characteristics of the various deposits indicate short-term episodes of deformation alternated by dormant stages. Deformations occurred along subvertical slip planes with relative uplift of the valley-side blocks, accompanied by toppling with fissure opening and slope steepening. The DSSD has not been active since 2295-1895 yr ago at least, posing clarifying data for the hazard and risk assessment.