eprintid: 1377 rev_number: 14 eprint_status: archive userid: 2 dir: disk0/00/00/13/77 datestamp: 2015-02-17 07:45:33 lastmod: 2017-02-08 12:21:32 status_changed: 2015-04-27 12:10:47 type: article metadata_visibility: show creators_name: Bommer, Julian J. creators_name: Abrahamson, Norman A. corp_creators: Civil & Environmental Engineering Department Imperial College London, UK corp_creators: Geosciences Department Pacific Gas & Electricity, USA title: Why Do Modern Probabilistic Seismic-Hazard Analyses Often Lead to Increased Hazard Estimates? ispublished: pub subjects: MP3_3 divisions: EPOS-P full_text_status: none keywords: PSHA abstract: The basic elements of probabilistic seismic-hazard analysis (PSHA)were established almost four decades ago and PSHA has now become the most widely used approach for estimating seismic-design loads. Although the use of PSHA is widespread, considerable confusion remains regarding the details of how the calculations should be performed. This situation is largely a result of the way the discipline of PSHA evolved through a series of articles, reports, and software packages. This article demonstrates that the feature of PSHA about which there is perhaps the greatest degree of misunderstanding is the treatment of the aleatory variability in groundmotion prediction equations, which exerts a very pronounced influence on the calculated hazard. Probabilistic hazard studies performed in recent years have frequently resulted in appreciably higher design ground motions than had been obtained in previous assessments carried out in the 1970s and 1980s, often sparking controversial debate. Although several factors may contribute to the higher estimates of seismic hazard in modern studies, the main reason for these increases is that in the earlier studies the ground-motion variability was either completely neglected or treated in a way that artificially reduced its influence on the hazard estimates. date: 2006-12 date_type: published publication: Bulletin of the Seismological Society of America volume: 96 number: 6 publisher: Seismological Society of America pagerange: 1967-1977 id_number: doi:10.1785/0120060043 refereed: TRUE issn: 0037-1106 official_url: http://dx.doi.org/10.1785/0120060043 access_IS-EPOS: limited owner: Publisher citation: Bommer, Julian J. and Abrahamson, Norman A. (2006) Why Do Modern Probabilistic Seismic-Hazard Analyses Often Lead to Increased Hazard Estimates? Bulletin of the Seismological Society of America, 96 (6). pp. 1967-1977. DOI: https://doi.org/10.1785/0120060043