Probabilistic assessment of near-field tsunami hazards: Inundation depth, velocity, momentum flux, arrival time, and duration applied to Seaside, Oregon

Abstract

The generation, propagation and inundation for a probabilistic near-field tsunami hazards assessment (PTHA) at the Cascadia Subduction Zone (CSZ) are analyzed numerically. For the tsunami hazard assessment, a new method is presented to characterize the randomness of the fault slip in terms of the moment magnitude, peak slip location, and a fault slip shape distribution parameterized as a Gaussian distribution. For the tsunami inundation resulting from the seismic event, five tsunami intensity measures (IMs) are estimated: (1) the maximum inundation depth, hMax, (2) the maximum velocity, VMax, (3) the maximum momentum flux, MMax, (4) the initial arrival time exceeding a 1m inundation depth, TA, and (5) the duration exceeding a 1m inundation depth, Th, and presented in the form of annual exceedance probabilities conditioned on a full-rupture CSZ event. The IMs are generally observed to increase as the moment magnitude increases, as the proximity of the peak slip becomes closer to the study area, and as the distribution of fault shape narrows. Among the IMs, the arrival time (TA) shows a relatively weak sensitivity to the aleatory uncertainty while the other IMs show significant sensitivity, especially MMax. It is observed at the shoreline that MMax increases by an order of magnitude from the 500-year to the 1000-year event, while hMax increases by a factor of 3, and TA decreases by only factor of 0.05. The intensity of IMs generally decreases inland, but there are also varying dependencies on bathymetry. For example, a shorter inundation duration, Th (<10min) is observed at the higher ground level (z>3m) while a longer Th (~100min) is observed near the river and creek.