Towards the non-ergodic ground motion models of Turkey: Assessment of systematic site, source and path effects

Önder, Fatih Mehmet
Ground Motion Models (GMMs) and their standard deviations (σ) are the most significant contributors of the median ground motions and their variability that are estimated in Probabilistic Seismic Hazard Analysis (PSHA). Most of the GMMs used in the current practice were derived from the datasets that include recordings from multiple sites attenuating from different seismic sources; therefore, the standard deviation of these GMMs includes the spatial and temporal variability of ground motions based on the ergodic assumption. In the last decade, several attempts were made to decompose the sigma of GMMs into different components such as site-to-site, path-to-path and source-to-source variability in regions with well-established ground motion datasets. The primary objective of this study is to evaluate the systematic site, source and path effects in the Turkish strong motion dataset in order to provide the necessary tools to develop a fully non-ergodic GMM for Turkey. To this end, the updated Turkish Strong Motion Database (N-TSMD, Akbaş et al., 2022) that contains 23019 recordings from 743 earthquakes recorded at 904 stations is utilized. The site terms (δS2S) and the related standard deviations (φ_(ss,s)) for the state-of-the-art NGA-West2 GMMs are calculated for each station in the N-TSMD and ≈15% reduction in total sigma is achieved, which is consistent with the previous studies in literature for other regions. Spatial distribution of calculated site terms are assessed to identify regional differences and underlying reasons such as basin effects and uncertainities in shear wave velocity profile. In addition to the systematic site effects, repeatable source effects mapped into the event terms are also investigated, which may result in a further reduction in total sigma for selected regions. Finally, the site and source corrected within-event terms (δWS_es) are examined for systematic path effects on a site-specific basis to observe any remaining bias.


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Citation Formats
F. M. Önder, “Towards the non-ergodic ground motion models of Turkey: Assessment of systematic site, source and path effects,” M.S. - Master of Science, Middle East Technical University, 2022.