An approach to time-probabilistic evaluation of seismically induced landslide hazard

The need for effective strategies for preventing and mitigating damage caused by earthquake-induced landslides has stimulated recent developments of techniques for the assessment of seismic-landslide exposure at a regional scale. However, for a rational risk management, a crucial element is represented by the time horizon of the hazardous events. A new way to incorporate the time factor in seismic-landslide hazard assessment is proposed here. It consists of evaluating the temporal recurrence of seismically induced slope failure conditions inferred from the Newmark's model: First, by adopting Arias Intensity to quantify seismic shaking, well-established methods of seismic hazard assessment are employed to obtain the occurrence probabilities for different levels of seismic shaking in a time interval of interest. Then, some-empirical relations, based on the Newmark's model, are employed to evaluate the slope critical acceleration a(c) for which a prefixed probability exists that seismic shaking would result in landslide triggering. The obtained a(c) values represent the minimum slope resistance required to keep the probability of seismic-landslide triggering within the prefixed value. Therefore, the space distribution of the calculated a(c) values can be promptly compared with the actual in situ ac values of specific slopes to estimate whether these slopes have a significant probability of failing under seismic action in the future. An example of this approach, applied to an, area in southern Italy (Daunia region), shows that the introduction of the time factor significantly modifies the representation of the spatial hazard and allows evaluation of the relevance of seismicity as a landslide triggering agent.