Comparing Newmark’s method at regional, sub-regional and site scales: seismically-induced La Paca rock-fall case (Murcia, SE Spain)

Abstract

The Lorca Basin (Murcia) is located in one of the most seismically active regions of Spain. This area is very interesting for studying earthquake-induced slope instabilities as there are well known cases associated to specific earthquakes (e.g., Bullas 2002, La Paca 2005). In this work we present our investigations at regional and site scales. For the regional scale, we have used a GIS to develop an implementation of Newmark’s sliding rigid block method. We have particularly introduced a new variation to consider soil and topographic amplification effects. Subsequently, we have produced “Newmark displacement” maps for both probabilistic and deterministic seismic scenarios. We have found that rock-falls produced during the last earthquakes in Lorca Basin are associated to Newmark displacements lower than 2 cm. To support this hypothesis we have applied the Newmark method to La Paca rock-fall at a site scale. We have performed a back-analysis to estimate the static safety factor and the critical acceleration. Finally, we have compared the Newmark displacement calculated at La Paca rock-fall at a site scale with our GIS estimations in order to improve the calibration of Newmark’s method at the regional scale.