|Abstract or Summary
- Damage estimates to the built environment from tsunamis are important for disaster mitigation, including planning emergency response and recovery. This dissertation evaluates the damage states of buildings in a small urban coastal city, Seaside, Oregon, from tsunami hazards generated by a Cascadia Subduction Zone (CSZ) event. This study is separated into two parts: (1) tsunami hazard assessment, and (2) tsunami damage assessment of buildings.
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, h[subscript Max], (2) the maximum velocity, V[subscript Max], (3) the maximum momentum flux, M[subscript Max], (4) the initial arrival time exceeding a 1 m inundation depth, T[subscript A], and (5) the duration exceeding a 1 m inundation depth, T[subscript h], 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 M[subscript Max]. It is observed at the shoreline that MMax increases by an order of magnitude from the 500-year to the 1,000-year event, while h[subscript Max] 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 (< 10 min) is observed at the higher ground level (z > 3 m) while a longer Th (~100 min) is observed near the river and creek.
For the tsunami damage assessment, the annual exceedance of the IMs, h[subscript Max] and M[subscript Max] are used to estimate building damage using a fragility curve analysis. Tax lot data, Google Street View, and field reconnaissance surveys are used to classify the buildings at a community scale and match with existing fragility curves according to construction material, floor level and build year. The fragility analysis is used to estimate the damage probability of buildings for a 1,000-year event conditioned on a full-rupture CSZ event. The sensitivity of building damage to the both the aleatory and epistemic uncertainty involved in the process of damage estimation are presented. Fragility curves based on depth and based on momentum flux both generally show higher damage probability for structures that are wooden and closer to the shoreline than those that are reinforced concreted (RC) and landward of the shoreline. However, a relatively high damage probability was found at the river and creek region from the fragility curve analysis using h[subscript Max]. Within 500 m from the shoreline, wood structure damage shows a significant sensitivity to the aleatory uncertainty of the tsunami generation from the CSZ event. On the other hand, RC structure damage showed equal sensitivity to the aleatory uncertainty of the tsunami generation as well as the epistemic uncertainties due to the numerical modelling of the tsunami inundation (friction), the building classification (material and build year), and the type of fragility curves (depth or momentum type curves). Further from the shoreline, the wood structures showed similar uncertainties to the aleatory and epistemic uncertainties.