Problems with logic trees in earthquake hazard evaluation

doi:10.1016/0013-7952(94)00060-F

Engineering Geology

Volume 39, Issues 1–2, May 1995, Pages 1-3

https://doi.org/10.1016/0013-7952(94)00060-F Get rights and content

Abstract

Logic trees make sense when used in earthquake risk analysis where costs are compared for specific outcomes. However logic trees fail in earthquake hazard analysis when they are used to develop earthquake ground motions for applications in engineering. The failure stems from a misguided attempt to assign numbers for degrees of belief which are personal and indefinable, almost like love or taste, and for which there are neither tests nor measurements. The result is a complicated jumble of egocentric impressions. In contrast, the need in engineering is to have values that are based as much as possible on evidence.

References (4)

E.I. Krinitzsky
Earthquake probability in engineering — Part 1: The use and misuse of expert opinion
Eng. Geol.
(1993)
E.L. Krinitzsky
Earthquake probability in engineering — Part 2: Earthquake recurrence and limitations of Gutenberg-Richter b-values for the engineering of critical structures
Eng. Geol.
(1993)

There are more references available in the full text version of this article.

Cited by (27)

Seismic hazard assessment from the perspective of disaster prevention
2022, Earthquakes and Sustainable Infrastructure: Neodeterministic (NDSHA) Approach Guarantees Prevention Rather than Cure
Hazard, risks, and prediction
2022, Earthquakes and Sustainable Infrastructure: Neodeterministic (NDSHA) Approach Guarantees Prevention Rather than Cure
Nowadays, in a Big Data World, Science can disclose natural hazards, assess risks, and deliver the state-of-the-art knowledge of looming disasters (in advance catastrophes) along with useful recommendations on the level of risks for decision-making in regard to engineering design, insurance, and emergency management. Science cannot remove, yet, people’s favor for illusion regarding reality, as well as political denial, ignorance, and negligence among decision-makers. The general conclusion is confirmed by application and testing against earthquake reality the innovative methodology of neodeterministic seismic hazard assessment (NDSHA). NDSHA results are based on reliable seismic evidence, pattern recognition of earthquake-prone areas, implications of the uniﬁed scaling law for earthquakes, and exhaustive scenario-based modeling of ground shaking.
Prediction models and seismic hazard assessment: A case study from Taiwan
2019, Soil Dynamics and Earthquake Engineering
Citation Excerpt :
It was found that PSHA predictions were quite deviated from our instrumental data/observation [52], while DSHA might underestimate seismic hazard without considering the aleatory uncertainty of a GMPE model [54]. Others include proper/improper use of logic-tree analysis in seismic hazard analysis, and the issue with the assessment’s transparency and repeatability, among others [57,58]. The comments summarized here should provide a more complete review on seismic hazard analysis, while it is beyond the scope of this study to justify each of them.
Proposed in the late 1980s, cumulative absolute velocity (CAV) is a new intensity measure for earthquake ground motion characterizations, followed by studies and applications such as CAV ground motion prediction equations (GMPEs). In this study, two new CAV GMPEs were developed with 24,667 strong-motion records from Taiwan, and the first CAV seismic hazard assessment for Taipei (the most important city in Taiwan) was then conducted using the local CAV models. It shows that the annual rate for the study area to encounter a ground motion with CAV >0.97 g-sec is 0.002 per year, corresponding to a 10% occurrence probability in 50 years. By contrast, the deterministic scenario-based analysis shows that the CAV seismic hazard is about 0.60 g-sec for the study area. Future studies are worth conducting to develop more sophisticated, local CAV GPMEs and to explore more applications of such CAV prediction models, such as the developments of PGA-CAV joint probability distributions for conducting PGA-CAV joint seismic hazard assessments.
Seismic hazard analyses for Taipei city including deaggregation, design spectra, and time history with excel applications
2013, Computers and Geosciences
Citation Excerpt :
By Krinitzsky's definition (1995, 2003), such 70% to 30% weighting, for example, is a meaningless number because it cannot be supported scientifically. Take the recent PSHA study for Taiwan as an example, Wang et al. (2012a) pointed out that the intention of using logic-tree analysis is understandable, but without any support to the weights, that logic-tree analysis is indeed egocentric (Krinitzsky, 1995), and not being traceable (Klugel, 2008). With two sides of equally logical opinions, we are in a neutral position toward the use of logic-tree on one condition: When the logic-tree calculation is part of a PSHA, its detail needs to be supported to some degree.
Given the difficulty of earthquake forecast, Probabilistic Seismic Hazard Analysis (PSHA) has been a method to best estimate site-specific ground motion or response spectra in earthquake engineering and engineering seismology. In this paper, the first in-depth PSHA study for Taipei, the economic center of Taiwan with a six-million population, was carried out. Unlike the very recent PSHA study for Taiwan, this study includes the follow-up hazard deaggregation, response spectra, and the earthquake motion recommendations. Hazard deaggregation results show that moderate-size and near-source earthquakes are the most probable scenario for this city. Moreover, similar to the findings in a few recent studies, the earthquake risk for Taipei should be relatively high and considering this city's importance, the high risk should not be overlooked and a potential revision of the local technical reference would be needed. In addition to the case study, some innovative Excel applications to PSHA are introduced in this paper. Such spreadsheet applications are applicable to geosciences research as those developed for data reduction or quantitative analysis with Excel's user-friendly nature and wide accessibility.
Seismic Hazard Analysis - Quo vadis?
2008, Earth-Science Reviews
Citation Excerpt :
There are many other known problems associated with the PSHA methodology. These issues have been documented in numerous papers published in scientific journals of high reputation as for example, Krinitzsky (1993a,b), Krinitzsky (1995a,b), Hofmann (1996), Molchan et al. (1997), Krinitzsky (1998), Brune (1999), Anderson and Brune (1999), Panza and Romanelli (2001), Krinitzsky (2002), Klügel et al. (2006). This request seems to be a trivial one from the perspective of modern quality management.
The paper is dedicated to the review of methods of seismic hazard analysis currently in use, analyzing the strengths and weaknesses of different approaches. The review is performed from the perspective of a user of the results of seismic hazard analysis for different applications such as the design of critical and general (non-critical) civil infrastructures, technical and financial risk analysis. A set of criteria is developed for and applied to an objective assessment of the capabilities of different analysis methods. It is demonstrated that traditional probabilistic seismic hazard analysis (PSHA) methods have significant deficiencies, thus limiting their practical applications. These deficiencies have their roots in the use of inadequate probabilistic models and insufficient understanding of modern concepts of risk analysis, as have been revealed in some recent large scale studies. These deficiencies result in the lack of ability of a correct treatment of dependencies between physical parameters and finally, in an incorrect treatment of uncertainties. As a consequence, results of PSHA studies have been found to be unrealistic in comparison with empirical information from the real world. The attempt to compensate these problems by a systematic use of expert elicitation has, so far, not resulted in any improvement of the situation. It is also shown that scenario-earthquakes developed by disaggregation from the results of a traditional PSHA may not be conservative with respect to energy conservation and should not be used for the design of critical infrastructures without validation. Because the assessment of technical as well as of financial risks associated with potential damages of earthquakes need a risk analysis, current method is based on a probabilistic approach with its unsolved deficiencies.
Traditional deterministic or scenario-based seismic hazard analysis methods provide a reliable and in general robust design basis for applications such as the design of critical infrastructures, especially with systematic sensitivity analyses based on validated phenomenological models. Deterministic seismic hazard analysis incorporates uncertainties in the safety factors. These factors are derived from experience as well as from expert judgment. Deterministic methods associated with high safety factors may lead to too conservative results, especially if applied for generally short-lived civil structures. Scenarios used in deterministic seismic hazard analysis have a clear physical basis. They are related to seismic sources discovered by geological, geomorphologic, geodetic and seismological investigations or derived from historical references. Scenario-based methods can be expanded for risk analysis applications with an extended data analysis providing the frequency of seismic events. Such an extension provides a better informed risk model that is suitable for risk-informed decision making.
How to obtain earthquake ground motions for engineering design
2002, Engineering Geology
The earthquake ground motions that ultimately are selected for engineering design depend chiefly on the criticality of a site or structure and the engineering analyses that are to be performed. Several key steps are necessary in this selection process: They are (1) a reconnaissance to understand the hazards and obtain preliminary earthquake ground motions; (2) decisions on the application of deterministic or probabilistic methods; (3) selection of appropriate motions for requirements in design; (4) consideration of thresholds at which motions become significant for engineering; and (5) decisions on specifying appropriate earthquake ground motions for sizes of earthquakes, distances from sources, the structures, sites, and testing to be done. This paper presents five tables that show steps for evaluating these factors and for enabling the investigator to specify earthquake ground motions appropriate for engineering design.

View all citing articles on Scopus

View full text

Problems with logic trees in earthquake hazard evaluation

Abstract

Eng. Geol.

Eng. Geol.