Probabilistic Seismic Hazard Analysis Methodology Research Articles

Probabilistic Tsunami Hazard Assessment for a Site in Eastern Canada

Unlike probabilistic seismic hazard analysis (PSHA), there is not a well-established methodology for probabilistic tsunami hazard analysis (PTHA). The PTHA methodology presented is similar to the widely used PSHA methodology for ground motion, and incorporates both aleatory and epistemic uncertainty in calculating the probability of exceeding runup and drawdown values produced by tsunamigenic sources. Evaluating tsunami hazard is more difficult in locations such as the eastern coastline of Canada because of low tsunami recurrence rates and few historical examples. In this study, we evaluated the hazard from local and far-field earthquake and landslide tsunamigenic sources at a site on the Bay of Fundy in New Brunswick, Canada. These sources included local faults, the Puerto Rico subduction zone, fault sources in the Azores-Gibraltar plate boundary region, and landslides on the Canadian continental slope and in the Canary Islands. Using a new PTHA methodology that is closely linked to well-established PSHA methodology combined with tide stage probability, we calculated that the return period for a wave runup exceeding the tidal range of +4 m level above mean sea level (highest astronomical tide) is approximately 14,500 years.

Peak Acceleration Uncertainty Analysis of Seismic Hazard Assessment

The macroseismic intensity is a subjective indicator of ground motion intensity. Convex analysis method and China Probabilistic Seismic Hazard Analysis methodology are combined to derive peak acceleration for Ningbo city, China. The peak acceleration interval obtained by using the convex set theory-based seismic hazard analysis methodology is compared with that calculated by using China Probabilistic Seismic Hazard Analysis methodology. The sensitivity analysis indicates that the interval of peak acceleration is most sensitive to the annual occurrence rate. Furthermore, the correlation of uncertain variables cannot be neglected for peak acceleration prediction.

Convex set theory-based seismic hazard analysis of low seismicity area

Historical seismic data and seismogenic information are quite scarce for the low seismicity region, and modeling the parameters uncertainties based on probabilistic model is suspicious. The convex set theory-based seismic hazard analysis approach is proposed. The uncertainties of b value, the annual occurrence rate v and the upper bound magnitude M u are described by the envelop bound convex model and the ellipsoidal bound convex model. Convex analysis method and China probabilistic seismic hazard analysis methodology are combined to perform a bound seismic hazard analysis for Ningbo city, China. The seismic intensity interval obtained using the bound seismic hazard analysis is compared with that calculated using China probabilistic seismic hazard analysis methodology. The sensitivity analysis indicates that the interval of seismic intensity is most sensitive to the annual occurrence rate v. Furthermore, the different convex models have little effect on the interval of seismic intensity.

PROBABILISTIC SEISMIC HAZARD ANALYSIS FOR NUCLEAR POWER PLANTS - CURRENT PRACTICE FROM A EUROPEAN PERSPECTIVE

The paper discusses the methodology and the use of probabilistic seismic hazard analysis (PSHA) for nuclear power plants from a European perspective. The increasing importance of risk-informed approaches in the nuclear oversight process observed in many countries has contributed to increasing attention to PSHA methods. Nevertheless significant differences with respect to the methodology of PSHA are observed in Europe. The paper gives an overview on actual projects and discusses the differences in the PSHA-methodology applied in different European countries. These differences are largely related to different approaches used for the treatment of uncertainties and to the use of experts. The development of a probabilistic scenario-based approach is identified as a meaningful alternative to the development of uniform hazard spectra or uniform confidence spectra.

Probabilistic seismic hazard in the San Francisco Bay area based on a simplified viscoelastic cycle model of fault interactions

We construct a viscoelastic cycle model of plate boundary deformation that includes the effect of time‐dependent interseismic strain accumulation, coseismic strain release, and viscoelastic relaxation of the substrate beneath the seismogenic crust. For a given fault system, time‐averaged stress changes at any point (not on a fault) are constrained to zero; that is, kinematic consistency is enforced for the fault system. The dates of last rupture, mean recurrence times, and the slip distributions of the (assumed) repeating ruptures are key inputs into the viscoelastic cycle model. This simple formulation allows construction of stress evolution at all points in the plate boundary zone for purposes of probabilistic seismic hazard analysis (PSHA). Stress evolution is combined with a Coulomb failure stress threshold at representative points on the fault segments to estimate the times of their respective future ruptures. In our PSHA we consider uncertainties in a four‐dimensional parameter space: the rupture peridocities, slip distributions, time of last earthquake (for prehistoric ruptures) and Coulomb failure stress thresholds. We apply this methodology to the San Francisco Bay region using a recently determined fault chronology of area faults. Assuming single‐segment rupture scenarios, we find that future rupture probabilities of area faults in the coming decades are the highest for the southern Hayward, Rodgers Creek, and northern Calaveras faults. This conclusion is qualitatively similar to that of Working Group on California Earthquake Probabilities, but the probabilities derived here are significantly higher. Given that fault rupture probabilities are highly model‐dependent, no single model should be used to assess to time‐dependent rupture probabilities. We suggest that several models, including the present one, be used in a comprehensive PSHA methodology, as was done by Working Group on California Earthquake Probabilities.

Comment on "Why Do Modern Probabilistic Seismic-Hazard Analyses Often Lead to Increased Hazard Estimates?" by Julian J. Bommer and Norman A. Abrahamson

This comment discusses some heuristic biases with respect to the correct treatment of uncertainty in probabilistic seismic-hazard analysis (PSHA) observed in the recent article titled “Why Do Modern Probabilistic Seismic-Hazard Analyses Often Lead to Increased Hazard Estimates” by Julian J. Bommer and Norman Abrahamson. I show that the distinction between aleatory variability and epistemic uncertainty in seismic-hazard analysis represents a think model rather than an objective property of earthquake occurrence. It is demonstrated that the separation between epistemic uncertainty and aleatory variability is model dependent. I show that a correct application of this think model does not lead to an increase of hazard estimates, because the total uncertainty to be incorporated into a PSHA model is bounded by the uncertainty observed in the real world. Ground-motion variability cannot be statistically treated as an inherent property of earthquake occurrence. Its statistical measures are model dependent. A refined definition of the terms epistemic uncertainty and aleatory variability is suggested. Furthermore, the paper addresses the observation that the methodology of traditional PSHA may lead to a violation of the energy conservation principle. Finally, a summary of some of the most problematic areas of current PSHA methodology is given.

Probabilistic Seismic Hazard Assessment Methodology for Distributed Seismicity

This study deals with probabilistic seismic hazard analysis (PSHA) based on earthquakes that cannot be assigned to specific geologic structures (distributed seismicity). To calculate seismic hazard from distributed seismicity, the PSHA methodology is extended in numerous ways. A simple quantitative seismotectonic model enables statistical incorporation of certain seismotectonic knowledge and the application of attenuation relationships that are based on fault distance. The influence of a large historic earthquake on seismic hazard is taken into account with an energy-based seismic activity rate, obtained by spatial distribution of the released seismic energy. It will be shown that for at least a rough seismic hazard assessment, the type of geometrical seismicity modeling is not a deciding factor. To illustrate this, the classical seismic source zone approach and the improved spatially smoothed seismicity approach are studied in detail to determine their common and distinctive components. Except the geometry of modeling the seismic activity, there is no essential difference between the two approaches. Seismic activity in Slovenia can be treated as distributed seismicity. For this reason, the presented methodology is applied to the calculation of seismic hazard maps of Slovenia as a case study. Manuscript received 22 August 2002.

A Methodology for Probabilistic Fault Displacement Hazard Analysis (PFDHA)

We present a methodology for conducting a site-specific probabilistic analysis of fault displacement hazard. Two approaches are outlined. The first relates the occurrence of fault displacement at or near the ground surface to the occurrence of earthquakes in the same manner as is done in a standard probabilistic seismic hazard analysis (PSHA) for ground shaking. The methodology for this approach is taken directly from PSHA methodology with the ground-motion attenuation function replaced by a fault displacement attenuation function. In the second approach, the rate of displacement events and the distribution for fault displacement are derived directly from the characteristics of the faults or geologic features at the site of interest. The methodology for probabilistic fault displacement hazard analysis (PFDHA) was developed for a normal faulting environment and the probability distributions we present may have general application in similar tectonic regions. In addition, the general methodology is applicable to any region and we indicate the type of data needed to apply the methodology elsewhere.