Abstract. A quantitative definition for the land–sea (coastal) transitional area is
proposed here for wave-driven areas, based on the variability and isotropy of met-ocean
processes. Wind velocity and significant wave height fields are examined for
geostatistical anisotropy along four cross-shore transects on the Catalan coast
(north-western Mediterranean), illustrating a case of significant changes along the
shelf. The variation in the geostatistical anisotropy as a function of distance from the
coast and water depth has been analysed through heat maps and scatter plots. The results
show how the anisotropy of wind velocity and significant wave height decrease towards the
offshore region, suggesting an objective definition for the coastal fringe width. The
more viable estimator turns out to be the distance at which the significant wave height
anisotropy is equal to the 90th percentile of variance in the anisotropies within a
100 km distance from the coast. Such a definition, when applied to the Spanish
Mediterranean coast, determines a fringe width of 2–4 km. Regarding the probabilistic
characterization, the inverse of wind velocity anisotropy can be fitted to a log-normal
distribution function, while the significant wave height anisotropy can be fitted to a
log-logistic distribution function. The joint probability structure of the two
anisotropies can be best described by a Gaussian copula, where the dependence parameter
denotes a mild to moderate dependence between both anisotropies, reflecting a certain
decoupling between wind velocity and significant wave height near the coast. This
wind–wave dependence remains stronger in the central bay-like part of the study area,
where the wave field is being more actively generated by the overlaying wind. Such a
pattern controls the spatial variation in the coastal fringe width.
Ground Movement Analysis Based on Stochastic Medium Theory
