Error inflation in Probabilistic Seismic Hazard Analysis

Modern earthquake ground motion hazard mapping in California began following the 1971 San Fernando earthquake in the Los Angeles metropolitan area of southern California. Earthquake hazard assessment followed a traditional approach, later called Deterministic Seismic Hazard Analysis (DSHA) in order to distinguish it from the newer Probabilistic Seismic Hazard Analysis (PSHA). In DSHA, seismic hazard in the event of the Maximum Credible Earthquake (MCE) magnitude from each of the known seismogenic faults within and near the state are assessed. The likely occurrence of the MCE has been assumed qualitatively by using late Quaternary and younger faults that are presumed to be seismogenic, but not when or within what time intervals MCE may occur. MCE is the largest or upper-bound potential earthquake in moment magnitude, and it supersedes and automatically considers all other possible earthquakes on that fault. That moment magnitude is used for estimating ground motions by applying it to empirical attenuation relationships, and for calculating ground motions as in neo-DSHA (ZUCCOLO et al., 2008). The first deterministic California earthquake hazard map was published in 1974 by the California Division of Mines and Geology (CDMG) which has been called the California Geological Survey (CGS) since 2002, using the best available fault information and ground motion attenuation relationships at that time. The California Department of Transportation (Caltrans) later assumed responsibility for printing the refined and updated peak acceleration contour maps which were heavily utilized by geologists, seismologists, and engineers for many years. Some engineers involved in the siting process of large important projects, for example, dams and nuclear power plants, continued to challenge the map(s). The second edition map was completed in 1985 incorporating more faults, improving MCE's estimation method, and using new ground motion attenuation relationships from the latest published results at that time. CDMG eventually published the second edition map in 1992 following the Governor's Board of Inquiry on the 1989 Loma Prieta earthquake and at the demand of Caltrans. The third edition map was published by Caltrans in 1996 utilizing GIS technology to manage data that includes a simplified three-dimension geometry of faults and to facilitate efficient corrections and revisions of data and the map.The spatial relationship of fault hazards with highways, bridges or any other attribute can be efficiently managed and analyzed now in GIS at Caltrans. There has been great confidence in using DSHA in bridge engineering and other applications in California, and it can be confidently applied in any other earthquake-prone region. Earthquake hazards defined by DSHA are: (1) transparent and stable with robust MCE moment magnitudes; (2) flexible in their application to design considerations; (3) can easily incorporate advances in ground motion simulations; and (4) economical. DSHA and neo-DSHA have the same approach and applicability. The accuracy ...

Section: Nuclear Power Plant Siting Regulationsmentioning

confidence: 99%

History of Modern Earthquake Hazard Mapping and Assessment in California Using a Deterministic or Scenario Approach

Mualchin

2010

“…The huge quantity of attenuation relations existing in the literature attests to the difficulty inherent in choosing an attenuation relation to be used in the computation, which is strongly dependent on the data sets used for its calibration. Moreover, the mathematical model of PSHA is inaccurate since ''it was assumed that all uncertainty of the problem is concentrated in the uncertainty term of the attenuation equation and all other parameters in the model are not random'' (KLÜ GEL, 2007b). This introduces a systematic error into the calculation process that can invalidate the hazard estimate.…”

Section: Introductionmentioning

confidence: 99%

Neo-Deterministic and Probabilistic Seismic Hazard Assessments: a Comparison over the Italian Territory

Zuccolo

Vaccari

Peresan

et al. 2010

Estimates of seismic hazard obtained using the neodeterministic approach (NDSHA) and the probabilistic approach (PSHA) are compared for the Italian territory. The NDSHA provides values larger than those given by the PSHA in areas where large earthquakes are observed and in areas identified as prone to large earthquakes, but lower values in low-seismicity areas. These differences suggest the adoption of the flexible, robust and physically sound NDSHA approach to overcome the proven shortcomings of PSHA, thus allowing for a reliable seismic hazard estimation, especially for those areas characterized by a prolonged quiescence, i.e. in tectonically active sites where events of only moderate size have occurred in historical times.

“…Alternative approaches for reducing uncertainty are aimed at providing a more consistent classification of uncertainties and at reducing the uncertainties analytically by improved consideration of dependency between the different physical parameters of a PSHA model (KLÜ GEL et al, 2006;KLÜ GEL 2007b) or by reducing the effects of the ergodic assumption (ATKINSON 2006). Nevertheless, there are some fundamental problems associated with the traditional PSHA method which are rooted deeper in the mathematical concept and the modelling assumptions of the method itself.…”

Section: Introductionmentioning

confidence: 99%

Uncertainty Analysis and Expert Judgment in Seismic Hazard Analysis

Klügel¹

2010

Self Cite

The large uncertainty associated with the prediction of future earthquakes is usually regarded as the main reason for increased hazard estimates which have resulted from some recent large scale probabilistic seismic hazard analysis studies (e.g. the PEGASOS study in Switzerland and the Yucca Mountain study in the USA). It is frequently overlooked that such increased hazard estimates are characteristic for a single specific method of probabilistic seismic hazard analysis (PSHA): the traditional (CornellMcGuire) PSHA method which has found its highest level of sophistication in the SSHAC probability method. Based on a review of the SSHAC probability model and its application in the PEGASOS project, it is shown that the surprising results of recent PSHA studies can be explained to a large extent by the uncertainty model used in traditional PSHA, which deviates from the state of the art in mathematics and risk analysis. This uncertainty model, the Ang-Tang uncertainty model, mixes concepts of decision theory with probabilistic hazard assessment methods leading to an overestimation of uncertainty in comparison to empirical evidence. Although expert knowledge can be a valuable source of scientific information, its incorporation into the SSHAC probability method does not resolve the issue of inflating uncertainties in PSHA results. Other, more data driven, PSHA approaches in use in some European countries are less vulnerable to this effect. The most valuable alternative to traditional PSHA is the direct probabilistic scenariobased approach, which is closely linked with emerging neo-deterministic methods based on waveform modelling.