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This paper presents a methodology to evaluate life safety risk of coastal communities vulnerable to seismic and tsunami hazards. The work explicitly incorporates two important aspects in tsunami evacuation modeling: (1) the effect of earthquake-induced damage to buildings on building egress time, (2) the effect of earthquake-induced debris on horizontal evacuation time. The city of Seaside, Oregon, is selected as a testbed community. The hazard is based on a megathrust earthquake and tsunami from the Cascadia Subduction Zone that was defined in a previous study. The built environment consists of buildings and the transportation network for the city. Fragility analysis is used to estimate the seismic damage to buildings and resulting debris that covers portions of the road network. The horizontal evacuation time is determined based on the shortest path to shelters, including the increased travel time due to the earthquake-generated debris. The effects of different mitigation strategies are quantified. Results indicate the fatality and life safety risk of a near-field tsunami increases by 4.2–8.3 times when the effects of building egress and earthquake-induced debris are considered. The choice of population layer affects the life safety risk and thus the maximum risk is obtained when daytime populations are considered. Use of mitigation strategies result in a significant decrease in the number of fatalities. For hazards with recurrence intervals larger than 500- to 1000-years, the seismic retrofit is comparable to vertical evacuation and an effective strategy in reducing fatalities and associated risks. Implementing all mitigation strategies reduces the life safety risk by 90%. [ABSTRACT FROM AUTHOR]

This paper presents a methodology to evaluate the direct and general equilibrium losses for a testbed community subjected to a megathrust earthquake and tsunami hazard originating in the Cascadia Subduction Zone. The testbed community studied consists of buildings for all residential and commercial sectors in the economy. A fragility analysis and functionality model are applied to estimate the direct damage and losses of these buildings at the parcel level. The process relies on Monte Carlo simulations (MCS) that propagate uncertainties from the hazards through to the damage and loss models. A computable general equilibrium (CGE) model is used to assess aggregated general equilibrium losses to the community. As an important mitigation strategy, seismic retrofit reduces the direct loss to building functionality and general equilibrium losses. Results show that the vulnerability of economic sectors depends on the hazard type, hazard intensity, economic zone, and building type, and the risks vary with the recurrence interval. The highest risks are associated with 500-year and 1,000-year mean recurrence intervals for joint seismic–tsunami hazards, respectively. Results from assessing different design alternatives show that whereas retrofitting all buildings to the highest code level considered results in the lowest losses, retrofitting only commercial buildings can be an efficient retrofit option for enhancing community resilience when controlling for costs. Last, a sensitivity analysis shows that losses and associated risks are sensitive to the definition of building functionality, which highlights the necessity for a common definition of building functionality when performing vulnerability analyses. [ABSTRACT FROM AUTHOR]

This paper presents a framework to evaluate the regional and local resilience of infrastructure networks following disruptions from natural hazards. Herein, the regional resilience of a network relates to the accessibility of a community within a larger network, whereas the local resilience concerns the ability of a network to provide its intended service within the boundaries of a community. Using this framework, a methodology is developed to demonstrate its application to a road and highway transportation network disrupted by ground shaking and inundation under a Cascadia Subduction Zone earthquake and tsunami scenario. The regional network extents encompass the entire coast of the US state of Oregon. Embedded within this regional network are 18 local networks associated with coastal communities. Regional and local connectivity indexes are defined to identify the initial damage and then track the postdisaster recovery of the transportation network, i.e., evaluate the network resilience. The study results identify the attributes that lead to a regionally or locally resilient network and highlight the importance of considering local infrastructure networks embedded within larger regional networks. It is shown that without regional considerations, the time to recover may be severely underpredicted. The methodology is further used as a decision support tool to demonstrate how mitigation options impact the transportation network's resilience. The importance of strategically considering mitigation options is emphasized as some communities see significant reductions in time to recover, whereas others see little to no improvement. [ABSTRACT FROM AUTHOR]

Tsunamis are low-probability high-consequence events, usually caused by an earthquake in the ocean and can result in high casualty rates and billions of dollars in damage. Tsunamis can be divided into two main categories: near-field and far-field tsunamis, based on the location of their origin with respect to the site of interest. To perform risk assessment of communities subjected to tsunamis, the current approach would be to use empirical data from historical events, making the data site specific. Recently, researchers have developed approaches to estimate the risk of structures subjected to far-field earthquake generated tsunamis using a simulated tsunami force on a structure numerically. However, for near-field tsunamis, ground motions caused by the earthquake will reach the structure earlier than the tsunami, damaging the structure, which can substantially impair its structural performance in the following tsunami. The multi-hazard case of tsunami following earthquake is discussed herein and a physics-based approach to estimate the risk of structures subjected to them is presented. An illustrative example is presented to elaborate the methodology for a steel building. Successive nonlinear analyses are used to develop fragility functions based on joint earthquake-tsunami intensity measures (spectral acceleration-flow depth-flow velocity). These functions are used in combination with hazard analysis of a specific location to obtain loss estimates. Three different approaches were used for this process and the results showed that the use of the joint three intensity-measure fragilities is essential for the accuracy when estimating damage or structural loss and neglecting their interaction results in substantial errors. [ABSTRACT FROM AUTHOR]

The damage caused by tsunamis to coastal communities is often not only the result of the flowing water itself, but also of transported debris. Although there have been efforts to characterize forces from single-debris impacts, a more general scenario of multiple-debris impacts has not been studied experimentally. To address this need, experimental studies were performed, considering the effect of debris orientation and the number of debris field components on peak impact and damming forces on coastal structures. These forces are evaluated both qualitatively and quantitatively to provide insight into the nature of these impacts. For a few selected cases, a number of trials were conducted and an initial statistical study of the debris field collision phenomena performed. Observed forces and results are presented in terms of normalized quantities using analytical equations commonly used to calculate impact or drag forces. The lessons from this work provide an initial data set that can be used to guide further experimental and numerical studies on debris-laden tsunami flows. [ABSTRACT FROM AUTHOR]

Large earthquakes and tsunamis can damage or lead to the collapse of lifeline bridges, resulting in human and socioeconomic losses as well as prolonged recovery times. Although many simulation models are available for the individual effects of earthquake and tsunami hazards on bridges, there are limited modeling approaches for predicting damage from sequential earthquake and tsunami hazards. A bridge modeling approach, which includes soil-foundation-structure interaction effects, is developed within the finite-element framework OpenSees to quantify sequential earthquake and tsunami-induced damage. Multihazard interaction diagrams that relate earthquake and tsunami intensity measures to bridge system damage show that the residual effects of earthquake loading on the bridge system reduce resistance to subsequent tsunami loading. [ABSTRACT FROM AUTHOR]

Probabilistic Tsunami Hazard Analysis (PTHA) can be used to evaluate and quantify tsunami hazards for planning of integrated community-level preparedness, including mitigation of casualties and dollar losses, and to study resilient solutions for coastal communities. PTHA can provide several outputs such as the intensity measures (IMs) of the hazard quantified as a function of the recurrence interval of a tsunami event. In this paper, PTHA is developed using a logic tree approach based on numerical modeling for tsunami generated along the Cascadia Subduction Zone. The PTHA is applied to a community on the US Pacific Northwest Coast located in Newport, Oregon. Results of the PTHA are provided for five IMs: inundation depth, flow speed, specific momentum flux, arrival time, and duration of inundation. The first three IMs are predictors of tsunami impact on the natural and built environment, and the last two are useful for tsunami evacuation and immediate response planning. Results for the five IMs are presented as annual exceedance probability for sites within the community along several transects with varying bathymetric and topographic features. Community-level characteristics of spatial distribution of each IM for three recurrence intervals (500, 1000, 2500 year) are provided. Results highlight the different pattern of IMs between land and river transects, and significant magnitude variation of IMs due to complex bathymetry and topographic conditions at the various recurrence intervals. IMs show relatively higher magnitudes near the coastline, at the low elevation regions, and at the harbor channel. In addition, results indicate a positive correlation between inundation depth and other IMs near the coastline, but a weaker correlation at inland locations. Values of the Froude number ranged 0.1-1.0 over the inland inundation area. In general, the results in this study highlight the spatial differences in IMs and suggest the need to include multiple IMs for resilience planning for a coastal community subjected to tsunami hazards. [ABSTRACT FROM AUTHOR]

Tsunamis affect coastal regions around the world, resulting in fatalities and catastrophic damage to communities. Fragility functions form the basis of most risk and resilience analyses at the individual structure level, thereby allowing physical infrastructure components to be included at the community level. For tsunami loading, the vast majority of fragilities that have been developed are based on postevent observations in the field, which are usually specific to the site of the event. In this paper, a methodology to generate physics-based tsunami fragility functions is proposed, using vector intensity measures, such as tsunami flow depth and flow velocity and several combinations thereof. The proposed methodology relies on Monte Carlo Simulation for consideration of material uncertainties and includes epistemic uncertainties in the tsunami force calculation. The ability of different tsunami intensity measures (flow depth, flow velocity, and momentum flux), which are common in the literature, to predict the response of structures are investigated, and a new intensity measure (kinematic moment of momentum flux) that represents overturning moment of a structure for tsunami fragility curves is proposed. The methodology is illustrated using an application example consisting of a steel moment frame structure and fragility functions based on the kinematic moment of momentum flux are presented and shown to be a better predictor with less epistemic uncertainty. [ABSTRACT FROM AUTHOR]

Highway bridges are one of the most vulnerable constituents of transportation networks when exposed to one or more natural hazards, such as earthquakes, hurricanes, tsunamis, and riverine floods. To facilitate and enhance prehazard and posthazard event mitigation and emergency response strategies of transportation systems and entire communities, probabilistic risk and resilience assessment methodologies have attracted increased attention recently. In this context, fragility and restoration models for highway bridges subjected to a range of hazards are essential tools for efficient and accurate quantification of risk and resilience. This paper provides a comprehensive review of state-of-the-art fragility and restoration models for typical highway bridge classes that are applicable for implementation in multihazard risk and resilience analyses of regional portfolios or transportation networks in the United States. An overview of key gaps in the literature is also presented to guide future research. [ABSTRACT FROM AUTHOR]

Annual exceedance probabilities of the maximum tsunami inundation depth, hMax, and momentum flux, MMax, conditional on a full-rupture event of the Cascadia Subduction Zone (CSZ) were used to estimate the probability of building damage using a fragility analysis at Seaside, Oregon. Tax lot data, Google Street View, and field reconnaissance surveys were used to classify the buildings in Seaside and to correlate building typologies with existing fragility curves according to the construction material, number of stories, and building seismic design level based on the date of construction. A fragility analysis was used to estimate the damage probability of buildings for 500-, 1000-, and 2500-year exceedance probabilities conditioned on a full-rupture CSZ event. Finally, the sensitivity of building damage was estimated for both the aleatory and epistemic uncertainties involved in the process of damage estimation. Probable damage estimates from the fragility curves based on hMax and on MMax both generally show higher damage probability for structures that are wooden and closer to the shoreline than those that are reinforced concrete (RC) and further landward of the shoreline. However, a relatively high and somewhat unrealistic damage probability was found at the river and creek region from the fragility curve analysis using hMax. Within 500 m from the shoreline, wood structure damage shows 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 modeling of the tsunami inundation (friction), the building classification (material and date of construction), and the type of fragility curves (depth or momentum flux type curves). Further from the shoreline, the wood structures showed similar aleatory and epistemic uncertainties, qualitatively similar to the RC structure sensitivity closer to the shoreline. [ABSTRACT FROM AUTHOR]

• Decision support framework for quantifying and improving infrastructure resilience. • Framework considers multiple hazards and interdependence between infrastructure. • Framework also includes decision support options and community expectations. • Resilience = P (robustenss ∩ rapidity) and is quantified using a Bayesian network. • Framework is applied to Seaside, Oregon, for seismic ground shaking and tsunami hazards. A probabilistic decision support framework is developed in this study for community resilience planning under multiple hazards using performance goals based guidelines such as the Oregon Resilience Plan and the National Institute of Standards and Technology Community Resilience Planning Guide. Herein, resilience of community infrastructure systems is defined as the joint probability of achieving robustness and rapidity based performance goals, which is quantified using Bayesian networks. The framework assesses the effects of decision support options such as selection of hazards, resilience goals, and mitigation (ex-ante) and response (ex-post) strategies to identify measures that can improve infrastructure performance to meet community defined resilience goals. This framework is applied for resilience assessment of building, transportation, water, and electric power infrastructure systems in Seaside, Oregon, under combined earthquake ground shaking and tsunami inundation hazards corresponding to different return periods. Uncertainties in damage, restoration, and economic losses are explicitly considered and propagated in the framework using Monte Carlo simulation (MCS). The MCS results are then used to inform the Bayesian network, which evaluates the joint resilience of infrastructure systems in Seaside. Results highlight the impact of considering different performance goals, introduction of ex-ante and ex-post measures, and interdependencies between various infrastructure systems on infrastructure resilience. [ABSTRACT FROM AUTHOR]

Tsunamis are rare destructive phenomena caused by the sudden displacement of a large amount of water in the ocean and can result in enormous losses to coastal communities. The resilience of coastal communities to tsunamis can be improved through the use of risk-informed decision making tools. Performance-Based Engineering (PBE) approaches have been developed for different natural hazards including earthquake, fire, hurricane, and wind to perform probabilistic risk assessment for structures. In this study, a probabilistic Performance-Based Tsunami Engineering (PBTE) framework based on the total probability theorem is proposed for the risk assessment of structures subject to tsunamis. The proposed framework can be disaggregated into the different basic analysis phases of hazard analysis, foundation and structure characterization, interaction analysis, structural analysis, damage analysis, and loss analysis. An application example consisting of the risk assessment of a three-story steel moment frame structure was performed using the proposed framework. The probability of exceedance of the total replacement cost including structural, nonstructural, and content losses were computed. [ABSTRACT FROM AUTHOR]