Tsunami hazard warning and risk prediction based on inaccurate earthquake source parameters

This study investigates the issues related to underestimation of the earthquake source parameters in the context of tsunami early warning and tsunami risk assessment. The magnitude of a very large event may be underestimated significantly during the early stage of the disaster, resulting in the issuance of incorrect tsunami warnings. Tsunamigenic events in the Tohoku region of Japan, where the 2011 tsunami occurred, are focused on as a case study to illustrate the significance of the problems. The effects of biases in the estimated earthquake magnitude on tsunami loss are investigated using a rigorous probabilistic tsunami loss calculation tool that can be applied to a range of earthquake magnitudes by accounting for uncertainties of earthquake source parameters (e.g., geometry, mean slip, and spatial slip distribution). The quantitative tsunami loss results provide valuable insights regarding the importance of deriving accurate seismic information as well as the potential biases of the anticipated tsunami consequences. Finally, the usefulness of rigorous tsunami risk assessment is discussed in defining critical hazard scenarios based on the potential consequences due to tsunami disasters

Use of offshore wind farms to increase seismic resilience of Nuclear Power Plants

One of the challenges faced by the engineering profession is to meet the energy requirement of an increasingly prosperous world. Nuclear power was considered as a reliable option until the Fukushima Daiichi Nuclear Power Plant (NPP) disaster which eroded the public confidence. This short paper shows that offshore wind turbines (due to its shape and form, i.e. heavy rotating mass resting at the top of a tall tower) have long natural vibration periods (>3.0 s) and are less susceptible to earthquake dynamics. The performance of near-shore wind turbines structures during the 2011 Tohoku earthquake is reviewed. It has been observed that they performed well. As NPPs are often sited close to the sea, it is proposed that a small wind farm capable of supplying emergency backup power along with a NPP can be a better safety system (robust and resilient system) in avoiding cascading failures and catastrophic consequences

Seismic performance evaluation framework considering maximum and residual inter-story drift ratios:application to non-code conforming reinforced concrete buildings in Victoria, BC, Canada

This paper presents a seismic performance evaluation framework using two engineering demand parameters, i.e. maximum and residual inter-story drift ratios, and with consideration of mainshock-aftershock (MSAS) earthquake sequences. The evaluation is undertaken within a performance-based earthquake engineering framework in which seismic demand limits are defined with respect to the earthquake return period. A set of 2-, 4-, 8-, and 12-story non-ductile reinforced concrete buildings, located in Victoria, British Colombia, Canada, is considered as a case study. Using 50 mainshock and MSAS earthquake records (two horizontal components per record), incremental dynamic analysis is performed, and the joint probability distribution of maximum and residual inter-story drift ratios is modeled using a novel copula technique. The results are assessed both for collapse and non-collapse limit states. From the results, it can be shown that the collapse assessment of 4- to 12-story buildings is not sensitive to the consideration of MSAS seismic input, whereas for the 2-story building, a 13% difference in the median collapse capacity is caused by the MSAS. For unconditional probability of unsatisfactory seismic performance, which accounts for both collapse and non-collapse limit states, the life safety performance objective is achieved, but it fails to satisfy the collapse prevention performance objective. The results highlight the need for the consideration of seismic retrofitting for the non-ductile reinforced concrete structures

Multi-variate seismic demand modelling using copulas:application to non-ductile reinforced concrete frame in Victoria, Canada

AbstractJoint probabilistic characteristics of key structural demand variables due to intense ground shaking are important for quantitative seismic loss estimation. Current damage–loss models require inputs of multiple seismic demand parameters, such as maximum/residual inter-storey drift ratio (ISDR) and peak floor acceleration (PFA). This study extends current seismic demand estimation methods based on incremental dynamic analysis (IDA) by characterising dependence among different engineering demand parameters (EDP) using copulas explicitly. The developed method is applied to a 4-storey non-ductile reinforced concrete (RC) frame in Victoria, British Columbia, Canada. The developed multi-variate seismic demand model is integrated with a storey-based damage–loss model to assess the economic consequences due to different earthquake loss generation modes (i.e. non-collapse repairs, collapse, and demolition). Results obtained from this study indicate that the effects of multi-variate seismic demand modelling on the expected seismic loss ratios are significant. The critical information is the limit state threshold for demolition. In addition, consideration of a realistic dependence structure of maximum and residual inter-storey drift ratios can be important for seismic loss estimation as well as for multi-criteria seismic performance evaluation

Ground-Motion Prediction Models for Arias Intensity and Cumulative Absolute Velocity for Japanese Earthquakes Considering Single-Station Sigma and Within-Event Spatial Correlation

Arias intensity (I-A) and cumulative absolute velocity (CAV) are ground-motion measures that have been found to be well suited to application in a number of problems in earthquake engineering. Both measures reflect multiple characteristics of the ground motion (e.g., amplitude and duration), despite being scalar measures. In this study, new ground-motion prediction models for the average horizontal component of I-A and CAV are developed, using an extended database of strong-motion records from Japan, including the 2011 Tohoku event. The models are valid for magnitude greater than 5.0, rupture distance less than 300 km, and focal depth less than 150 km. The models are novel because they take account of ground-motion data from the 2011 Tohoku earthquake while incorporating other important features such as event type and regional anelastic attenuation. The residuals from the ground-motion modeling are analyzed in detail to gain further insights into the uncertainties related to the developed median prediction equations for I-A and CAV. The site-to-site standard deviations are computed and spatial correlation analysis is carried out for I-A and CAV, considering both within-event residuals and within-event single-site residuals for individual events as well as for the combined dataset

Probabilistic earthquake-tsunami multi-hazard analysis:application to the Tohoku region, Japan

This study develops a novel simulation-based procedure for the estimation of the likelihood that seismic intensity (in terms of spectral acceleration) and tsunami inundation (in terms of wave height), at a particular location, will exceed given hazard levels. The procedure accounts for a common physical rupture process for shaking and tsunami. Numerous realizations of stochastic slip distributions of earthquakes having different magnitudes are generated using scaling relationships of source parameters for subduction zones and then using a stochastic synthesis method of earthquake slip distribution. Probabilistic characterization of earthquake and tsunami intensity parameters is carried out by evaluating spatially correlated strong motion intensity through the adoption of ground motion prediction equations as a function of magnitude and shortest distance from the rupture plane and by solving nonlinear shallow water equations for tsunami wave propagation and inundation. The minimum number of simulations required to obtain stable estimates of seismic and tsunami intensity measures is investigated through a statistical bootstrap analysis. The main output of the proposed procedure is the earthquake-tsunami hazard curves representing, for each mean annual rate of occurrence, the corresponding seismic and inundation tsunami intensity measures. This simulation-based procedure facilitates the earthquake-tsunami hazard deaggregation with respect to magnitude and distance. Results are particularly useful for multi-hazard mapping purposes and the developed framework can be further extended to probabilistic earthquake-tsunami risk assessment

Assessing infrequent large earthquakes using geomorphology and geodesy in the Malawi Rift

In regions with large, mature fault systems, a characteristic earthquake model may be more appropriate for modelling earthquake occurrence than extrapolating from a short history of small, instrumentally observed earthquakes using the Gutenberg–Richter scaling law. We illustrate how the geomorphology and geodesy of the Malawi Rift, a region with large seismogenic thicknesses, long fault scarps, and slow strain rates, can be used to assess hazard probability levels for large infrequent earthquakes. We estimate potential earthquake size using fault length and recurrence intervals from plate motion velocities and generate a synthetic catalogue of events. Since it is not possible to determine from the geomorphological information if a future rupture will be continuous (7.4 ≤ M W ≤ 8.3 with recurrence intervals of 1,000–4,300 years) or segmented (6.7 ≤ M W ≤ 7.7 with 300–1,900 years), we consider both alternatives separately and also produce a mixed catalogue. We carry out a probabilistic seismic hazard assessment to produce regional- and site-specific hazard estimates. At all return periods and vibration periods, inclusion of fault-derived parameters increases the predicted spectral acceleration above the level predicted from the instrumental catalogue alone, with the most significant changes being in close proximity to the fault systems and the effect being more significant at longer vibration periods. Importantly, the results indicate that standard probabilistic seismic hazard analysis (PSHA) methods using short instrumental records alone tend to underestimate the seismic hazard, especially for the most damaging, extreme magnitude events. For many developing countries in Africa and elsewhere, which are experiencing rapid economic growth and urbanisation, seismic hazard assessments incorporating characteristic earthquake models are critical