Uncertainty In Seismic Hazard Research Articles

Risk-targeted hazard for seismic design in New Zealand considering individual and societal risk targets

The promotion of risk-targeted hazard as the basis of seismic design internationally has increased over the past decade. Risk-targeted hazard estimates are derived through convolution of hazard curves with representative fragility functions and provide a means to target uniform risk across a region. Using risk targets also enables performance objectives of building codes that are consistent with other life risks and can include societal input into the expected performance of structures. Current design procedures using a uniform-hazard spectrum are unable to provide equal risk across the country due to variation in the shapes of hazard curves in different locations and uncertainty in structural response. In this article a framework is proposed, which can be used with national seismic hazard models, to produce risk-targeted hazard spectra for seismic design. This study extends the risk-targeted hazard framework through full quantification of epistemic uncertainty in seismic hazard and includes multiple risk targets for individual and societal risk at the building and city scales. The article describes a framework that can be used to adjust current seismic design force levels in New Zealand standards to target uniform seismic risk for buildings considering both the performance of individual buildings and the performance of cities.

Seismicity Simulation and a Forecast Model Based on Monte Carlo Simulation Techniques and Performance of Distribution Models

In seismic hazard studies, simulation techniques are exploited relatively less compared to other statistical methods. The main purposes of their use were merely scientific: either to reduce uncertainty in seismic hazard or to test the consistency of a forecast. Its limited exploitation in the field does not mean that the method could not be exploited further. Given sufficient data and with the right models, a full-scale simulation is possible, which in fact becomes a forecast with future timing, location and magnitude of future events are simulated.Within this context, the main purpose of this study is to layout a method to create a full scale simulation with all the parameters namely the time, location and magnitude of an earthquake is simulated. For that purpose, in addition to the main parameters defining past seismic patterns, namely the temporal, spatial, magnitude distributions, the combined spatio-magnitude distribution is also modeled. As another improvement compared to the current procedures, occurrence date is assigned to the simulated event according to the inter-event time distribution, which enhances the simulation procedure. The eventual temporal distribution and the associated earthquake rates are checked with the original earthquake rate for its consistency. In the end, a simulation procedure, which can also be used as a forecast model is developed to improve the existing procedures further.

Consideration and Propagation of Ground Motion Selection Epistemic Uncertainties to Seismic Performance Metrics

This paper investigates various approaches to propagate the effect of epistemic uncertainty in seismic hazard and ground motion selection to seismic performance metrics. Specifically, three approaches with different levels of rigor are presented for establishing the conditional distribution of intensity measures considered for ground motion selection, selecting ground motion ensembles, and performing nonlinear response history analyses (RHAs) to probabilistically characterize seismic response. The mean and distribution of the seismic demand hazard is used as the principal means to compare the various results. An example application illustrates that, for seismic demand levels significantly below the collapse limit, epistemic uncertainty in seismic response resulting from ground motion selection can generally be considered as small relative to the uncertainty in the seismic hazard itself. In contrast, uncertainty resulting from ground motion selection appreciably increases the uncertainty in the seismic demand hazard for near-collapse demand levels.

A seismic hazard uncertainty analysis for the New Madrid seismic zone

A review of the scientific issues relevant to characterizing earthquake sources in the New Madrid seismic zone has led to the development of a logic tree of possible alternative parameters. A variability analysis, using Monte Carlo sampling of this consensus logic tree, is presented and discussed. The analysis shows that for 2%-exceedence-in-50-year hazard, the best-estimate seismic hazard map is similar to previously published seismic hazard maps for the area. For peak ground acceleration (PGA) and spectral acceleration at 0.2 and 1.0s (0.2 and 1.0sSa), the coefficient of variation (COV) representing the knowledge-based uncertainty in seismic hazard can exceed 0.6 over the New Madrid seismic zone and diminishes to about 0.1 away from areas of seismic activity. Sensitivity analyses show that the largest contributor to PGA, 0.2 and 1.0sSa seismic hazard variability is the uncertainty in the location of future 1811–1812 New Madrid sized earthquakes. This is followed by the variability due to the choice of ground motion attenuation relation, the magnitude for the 1811–1812 New Madrid earthquakes, and the recurrence interval for M>6.5 events. Seismic hazard is not very sensitive to the variability in seismogenic width and length.