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Integration of Site Effects into Probabilistic Seismic Hazard Assessment.Integration of site effects into probabilistic seismic hazard methods.

Abstract : The overall goal of this research work is of provide recommendations on how to integrate site effects into Probabilistic Seismic Hazard Assessment, better known as PSHA, a well-known and widely used methodology. Globally used to estimate seismic hazard and risk at regional and local scales. We therefore review the methods available in the literature to obtain the seismic hazard curve at the surface of a soft soil site, starting with the simplest and most generic methods (partially probabilistic), up to the full site-specific methods (partially and fully probabilistic), requiring an excellent site-specific characterization, rarely available except exceptional cases such as the case of Euroseistest site. It is precisely on the example of this site that are compared a number of these methods, as well as a new one. And it is precisely at the Euroseistest that we performed an example of application of the different methods as well as a new one that we propose as a result of this work.The specificity and difficulty of these "site-specific" PSHA studies comes from the non-linear nature of the response of the soft sites, as well as from the fact that the reference rock controlling this response is often very rigid. The "rock to hard rock adjustment" and "convolution" aspects of the rock seismic hazard, together with the amplification function or the transfer function (empirical or numerical) of a site are therefore the subject of particular attention in these studies. comparative studies. A general framework is presented on how to simultaneously take into account the site-specific characteristics, such as the complete or reduced random variability ("single station sigma"), host-to -target adjustments and the linear / nonlinear behavior of a site, where we explain all the followed steps, the different corrections performed, the benefits and difficulties that we found in the process and the ways we sort them and discussing them when the answer was not straight forward.This comparative study is divided into two parts: the first deals with non-site-specific methods and site-specific hybrid methods (probabilistic evaluation of rock hazard and deterministic of the site response). The second deals with two approaches taking into account the convolution of rock hazard and the site response in a probabilistically way. One of the major results of the first is the increase of the epistemic uncertainty on the soft site hazard compared to the rock hazard, due to acumulation of uncertainties associated to each step. Another major common result to both studies is the very important impact of non-linearity on soft sites, as well as the complexity on how to account for them: the variability associated with the use of different non-linear simulation codes appears to be greater than the method-to-method variability associated with the two different full convolution probabilistic methods. We emphasize on the importance of improving the way in which the site effects are included into probabilistic seismic hazard methods, PSHA. And we also emphasize on the importance of instrumenting active sites with soft sediments, such as the Euroseistest, to test and validate numerical models.Finally, a summary of the results, the general conclusions, discussion of key methodological issues, and perspectives for improvement and future work are presented.Keywords: Site Effects, Epistemic Uncertainty, PSHA, single station sigma, host to target adjustments, linear and nonlinear site effects, soil site response.
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https://tel.archives-ouvertes.fr/tel-01825052
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Submitted on : Thursday, June 28, 2018 - 9:00:13 AM
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Claudia Aristizabal. Integration of Site Effects into Probabilistic Seismic Hazard Assessment.Integration of site effects into probabilistic seismic hazard methods.. Earth Sciences. Université Grenoble Alpes, 2018. English. ⟨NNT : 2018GREAU011⟩. ⟨tel-01825052⟩

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