Linking earthquake-triggered paleolandslides to their seismic source and to the possible seismic event that originated them in a portion of the Argentine Precordillera (31°-33°S)

Abstract

A total of 36 rock slides were selected for analysing a probable seismic source in the active Andean Precordillera (31 degrees-33 degrees S), the most seismic region of Argentina. Seven of these slope instabilities were selected for in-depth analysis in the field as a function of the most frequent class, lithological susceptibility and field accessibility. Reconstructing the topography previous to collapse and using geotechnical parameters extracted from field data in conjunction with geomechanical testing, the rock slides were modelled using pseudostatic limit equilibrium analyses for the obtention of the critical probabilistic acceleration (a(c)) required to generate the instability under unsaturated conditions and considering both the horizontal and vertical seismic components. To perform a probabilistic estimation of a(c), the parameters in relation to the generalized Hoek-Brown failure criterion were selected to operate statistically using 2D SLIDE 8.0 software. Applying inversely Ground Motion Prediction Equations (GMPEs) and concerning the distance to the studied paleolandslide, a possible earthquake inducing a seismic coefficient (k(h)) >= a(c) was determined. Therefore, a near active fault(s) capable of generating an earthquake magnitude inducing a Peak Ground Acceleration (PGA) >= a(c) at the paleolandslide location was designated as the possible seismogenic source of the slope instability. Intersecting these results, potential paleoseismic events which could have caused several slope instabilities were determined. Thus, a new methodology was developed, which allowed to determine the main seismogenic sources capable of inducing the modelled instabilities in each studied subarea in the Precordillera.