the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Methods for evaluating the significance and importance of differences amongst probabilistic seismic hazard results for engineering and risk analyses: A review and insights
Helen Crowley
Vitor Silva
Warner Marzocchi
Laurentiu Danciu
Rui Pinho
Abstract. When new seismic hazard models are published it is natural to compare them to existing models for the same location. This type of comparison routinely indicates differences between the assessed hazards in the various models. The question that then arises is whether these differences are scientifically significant, given the large epistemic uncertainties inherent in all seismic hazard models, or practically important, given the use of hazard models as inputs to risk and engineering calculations. A difference that exceeds a given threshold could mean that building codes may need updating, risk models for insurance purposes may need to be revised, or emergency management procedures revisited. In the current literature there is little guidance on what constitutes a significant or important difference, which can lead to lengthy discussions amongst hazard analysts and end users. This study reviews proposals in the literature on this topic and examines how applicable these proposals are for several sites considering various seismic hazards models for each site, including the two European Seismic Hazard Models of 2013 and 2020. The implications of differences in hazard for risk and engineering purposes are also examined to understand how important such differences are for potential end users of seismic hazard models. Based on this, we discuss the relevance of such methods to determine the scientific significance and practical importance of differences between seismic hazard models and identify some open questions. Finally, we make some recommendations for the future.
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John Douglas et al.
Status: open (extended)
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RC1: 'Comment on egusphere-2023-991', Anonymous Referee #1, 10 Jul 2023
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The paper reviews the methods for establishing whether the differences amongst PSHA results, based on different hazard models, can be deemed significant or important. Significant has a clear scientific meaning in the statistical context, important much less so.
Despite more could be perhaps expected from the knowledgeable authors, most exercises performed in of the paper are trivial and why they need a journal paper remains a question after the review.
The main issue with this is that it provides a limited innovative contribution. More specifically, Section 2 recalls the methods available in literature for evaluating whether the differences between PSHA results are important or significant. Such methods are then applied in some exercises presented in Section 3. However, the objective of Section 3 is not clear, apart from comparing site-specific hazard curves from some known PSHA models.
Another comment pertains to lines 63-75. The usefulness of the discussion about contouring is questionable. It is quite obvious that contouring is used (only) for representation purposes, and that this may hide differences between PSHA results, at the same site, based on different hazard models. In fact, the ground motion intensity to be used for seismic design is taken from the PSHA numerical results, which are generally provided to users. This reviewer suggests reducing/removing this part.
Section 4 proposes a new method for evaluating whether changes on PSHA results at one site, due to different hazard models, can be deemed important. The implementation of such method needs fragility functions and therefore it seems to depend on the building stock that is considered at the site (this is explained in Section 4.2). Indeed, the procedure allows one to establish whether “small changes on the seismic hazard can lead to important differences on risk metrics” (lines 467-468). There is an apparent ambiguity, which can be summarized in the following question: does the study investigates the “importance” of the difference between hazard or risk results? This reviewer finds that this should be clearly stated in the abstract and introduction.
The next comment is partly related to the previous one. In fact, it is not clear why the effect of the difference amongst PSHA models should be explored considering (only) risk (as it appears from the paper) rather than hazard results. Is there a specific reason?
Lines 415-420 discuss that the differences between the five considered hazard models are not important because the average annual probability of collapse (AAPC) for mid-rise RC buildings in Beznau, designed according to the different PSHA models, is always below a pre-determined threshold. In the proposed exercise, authors assume the AAPC threshold equal to 2x10-4, a typical considered value. However, the metric and the threshold value for establishing importance/non-importance of difference between results are completely arbitrary.
Lines 436-437: For the European hazard, there is only one city where the hazard change from ESHM13 to ESHM20 can be deemed important, shown in red in the table”. There is no red edit in the tables. Do authors mean the bold edit in Table 4?
Citation: https://doi.org/10.5194/egusphere-2023-991-RC1
John Douglas et al.
John Douglas et al.
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