Site Specific Seismic Hazard Assessment – Propagation of Site Properties Uncertainties

Research output: ThesisMaster's Thesis

Abstract

The prediction of ground motion triggered by a seismic scenario is an essential tool for seismic hazard assessment. In the nuclear safety domain, each step must be carefully studied, constrained and uncertainties should be considered. One of these steps is related to the influence of superficial geological layers on the incoming ground motion (called site effects), previously emitted by a fault
and then traveling through the crust. One way to incorporate information related to superficial layers consists on applying Ground Motion Prediction Equations (GMPE) using a limited number of parameters (mainly Vs30 corresponding to the average velocity in the 30 upper meters). However, this approach cannot totally take into account site specificities since it corresponds to an average assessment of the considered parameters. Site effects can be included by using adapted sitespecific models. In this work, numerical simulations are used to include detailed 1D site properties from surface to the bedrock and to propagate related uncertainties for the seismic hazard assessment on a particular site in the Rhone Valley. We first detail the numerical methodology workflow first based on computing the input motion at depth through the definition of a ground
motion computed on an outcropping reference rock with a GMPE and the use of an associated velocity and density profile. In a second step, by using depth ground motion and detailed 1D site properties, ground motion is calculated at the free surface. Sources of uncertainties are identified and detailed, followed by several sensitivity tests that are performed to identify parameters that
trigger large site to rock amplification and to quantify the impact of their uncertainties. It is shown that uncertainties regarding the method used to compute amplification, the bedrock shear wave velocity, the reference rock velocity profile, its density and the soil column properties can induce
variabilities in the estimation of the site specific seismic hazard. Moreover, seismic hazard assessment using this methodology is barely insensitive to very thin superficial layers properties and amplification factors variations in the Fourier domain is often higher than the response spectra ones in our results. Finally, uncertainties are propagated through a logic tree of 1000 branches to
estimate the site-specific seismic hazard on the particular site using 1D models from the geophysical prospections measurements. The resulted response spectra are then compared to the Berge-Thierry (2003) GMPE for sediment conditions.
Original languageEnglish
Supervisors/Advisors
  • Cornou, Cecile, Supervisor, External person
  • Provost, Ludmila, Supervisor, External person
Award date24 Jul 2018
Place of PublicationGrenoble
Publication statusUnpublished - 2018

Keywords

  • GMPEs
  • seismic hazard assessment
  • sensitivity analysis
  • site specific
  • seismology
  • Numerical simulation
  • python
  • geophysics
  • input motion
  • Vs profiles

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