Assessment of ground motion variability and its effects on seismic hazard analysis: a case study for iceland |
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Authors: | Teraphan Ornthammarath John Douglas Ragnar Sigbj?rnsson Carlo Giovanni Lai |
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Institution: | (1) ARN/RIS, BRGM, 3 avenue C. Guillemin, BP 36009, Orl?ans Cedex 2, 45060, France |
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Abstract: | Probabilistic seismic hazard analysis (PSHA) generally relies on the basic assumption that ground motion prediction equations
(GMPEs) developed for other similar tectonic regions can be adopted in the considered area. This implies that observed ground
motion and its variability at considered sites could be modelled by the selected GMPEs. Until now ground-motion variability
has been taken into account in PSHA by integrating over the standard deviation reported in GMPEs, which significantly affects
estimated ground motions, especially at very low probabilities of exceedance. To provide insight on this issue, ground-motion
variability in the South Iceland Seismic Zone (SISZ), where many ground-motion records are available, is assessed. Three statistical
methods are applied to separate the aleatory variability into source (inter-event), site (inter-site) and residual (intra-event
and intra-site) components. Furthermore, the current PSHA procedure that makes the ergodic assumption of equality between
spatially and temporal variability is examined. In contrast to the ergodic assumption, several recent studies show that the
observed ground-motion variability at an individual location is lower than that implied by the standard deviation of a GMPE.
This could imply a mishandling of aleatory uncertainty in PSHA by ignoring spatial variability and by mixing aleatory and
epistemic uncertainties in the computation of sigma. Station correction coefficients are introduced in order to capture site
effects at different stations. The introduction of the non-ergodic assumption in PSHA leads to larger epistemic uncertainty,
although this is not the same as traditional epistemic uncertainty modelled using different GMPEs. The epistemic uncertainty
due to the site correction coefficients (i.e. mean residuals) could be better constrained for future events if more information
regarding the characteristics of these seismic sources and path dependence could be obtained. |
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