A kappa Model for Mainland France

作者:Douglas John*; Gehl Pierre; Bonilla Luis Fabian; Gelis Celine
来源:Pure and Applied Geophysics, 2010, 167(11): 1303-1315.
DOI:10.1007/s00024-010-0146-5

摘要

An important parameter for the characterization of strong ground motion at high-frequencies (> 1 Hz) is kappa, kappa, which models a linear decay of the acceleration spectrum, a(f), in log-linear space (i.e. a(f) = A (0) exp(- pi kappa f) for f > f (E) where f is frequency, f (E) is a low frequency limit and A (0) controls the amplitude of the spectrum). kappa is a key input parameter in the stochastic method for the simulation of strong ground motion, which is particularly useful for areas with insufficient strong-motion data to enable the derivation of robust empirical ground motion prediction equations, such as mainland France. Numerous studies using strong-motion data from western North America (WNA) (an active tectonic region where surface rock is predominantly soft) and eastern North America (ENA) (a stable continental region where surface rock is predominantly very hard) have demonstrated that kappa varies with region and surface geology, with WNA rock sites having a kappa of about 0.04 s and ENA rock sites having a kappa of about 0.006 s. Lower kappa s are one reason why high-frequency strong ground motions in stable regions are generally higher than in active regions for the same magnitude and distance. Few, if any, estimates of kappa s for French sites have been published. Therefore, the purpose of this study is to estimate kappa using data recorded by the French national strong-motion network (RAP) for various sites in different regions of mainland France. For each record, a value of kappa is estimated by following the procedure developed by Anderson and Hough (Bull Seismol Soc Am 74:1969-1993, 1984): this method is based on the analysis of the S-wave spectrum, which has to be performed manually, thus leading to some uncertainties. For the three French regions where most records are available (the Pyrenees, the Alps and the Ctes-d'Azur), a regional kappa model is developed using weighted regression on the local geology (soil or rock) and source-to-site distance. It is found that the studied regions have a mean kappa between the values found for WNA and ENA. For example, for the Alps region a kappa value of 0.0254 s is found for rock sites, an estimate reasonably consistent with previous studies.

  • 出版日期2010-11