Hazard Quantification of Seismically Induced Tsunamigenic Subaerial/Submarine Mass Movements

Sancio, Rodolfo (Geosyntec Consultants, Inc.) | Rao, Pramod (Chevron Energy Technology Company) | Hunt, Christopher (Geosyntec Consultants, Inc.) | Umberg, David (Geosyntec Consultants, Inc.) | Greene, Alexander (Geosyntec Consultants, Inc.) | Misra, Shubhra (Chevron Energy Technology Company)


AbstractThis study presents a simplified framework for the quantification of the probability of seismically induced subaerial and submarine mass movements, an essential input for assessment of tsunami risk. The study incorporates the probability of seismically-induced ground motions developed from a Probabilistic Seismic Hazard Analysis (PSHA) and the probability of landslide triggering given an input ground motion, to calculate the joint probability of seismically-induced mass movement.Potential subaerial and submarine sliding masses of sufficient size to trigger a tsunami were identified through a geomorphological analysis of seafloor bathymetry and topographic relief coupled with available regional geological studies of the area. Typical slide volumes were in the range of 107 and 108 m3, consistent with the volumes noted during historical events.In this study, the probability of triggering a mass movement was defined as the probability of exceeding a threshold seismically-induced displacement value along a defined sliding surface beyond which uncontrolled movement of the slide mass was assumed to occur, leading to the potential development of a tsunami wave. The probability of exceeding the threshold displacement was calculated using the Bray and Travasarou (2007) method for estimating earthquake-induced slope displacements.The study treated uncertainty in the input parameters through the use of probability density functions developed using slope stability back analyses and engineering judgement. Material strength parameters were subsequently updated using Bayes theorem.The results of the study indicated that seismically-induced mass movements with potential for triggering a tsunami wave would have an annual probability lower than 1·10−3. Some of the slide scenarios selected in the study were used by others as input into hydrodynamic analyses for tsunami wave generation and propagation, and subsequently to define design inundation levels and design wave events for marine facilities.