مروری بر ادبیات فنی رفتار لرزه‌ای غیرخطی دره‌ های آبرفتی دو بعدی

پاسخ لرزه‌ای دره‌های آبرفتی به‌شدت تحت تاثیر هندسه و مشخصات مکانیکی دره و لایه‌های رسوبی داخل آن است. امواج لرزه‌ای که از منبع به سایت وارد می‌شوند، ممکن است به علت اختلاف سرعت حرکت موج در بین لایه‌های مختلف، به‌شدت دچار بزرگنمایی شوند. یکی از دلایل اصلی برای ارائه‌ی تحلیل‌های پاسخ ساختگاه، تفاوت در پاسخ لرزه‌ای سازه‌هایی است که با فرکانس‌های متفاوت بر روی زمین قرار دارند. مطالعات زیادی درزمینه‌ی تحلیل رفتار لرزه‌ای عوارض توپوگرافی صورت گرفته است که عمدتاً به‌صورت خطی یا خطی معادل بوده است‌ و تحلیل‌های غیرخطی سهم اندکی از این پژوهش‌ها را شامل می‌شوند. در این مقاله به بررسی مطالعات عددی انجام‌شده بر روی رفتار لرزه‌ای غیرخطی دره‌های آبرفتی تحت اثر امواج مهاجم پرداخته ‌شده است. نتایج موجود در ادبیات فنی آورده شده و اثر پارامترهای مختلف و نحوه‌ی تاثیر آنها بر روی پاسخ لرزه‌ای دره‌های آبرفتی بررسی ‌شده است. همچنین تفاوت میان روش‌های مختلف موجود در ادبیات فنی و نتایج به‌دست‌آمده مشخص گردیده است و در نهایت به جمع‌بندی تاثیرات و میزان اهمیت هرکدام از این پارامترها پرداخته‌ شده است.

a literature review on nonlinear seismic behavior of two-dimensional alluvial valleys

alluvial valleys are one of the most important topographic features in many seismically active regions of theworld. these features can have a significant impact on the seismic response of the sites located inside or near them.the seismic response of alluvial valleys is strongly influenced by the geometric shape of the valley, the mechanicalproperties of the sedimentary layers that fill the valley, and the type of seismic waves that enter from the earthquakesource. the seismic waves that reach the site from the source may undergo amplification or deamplification due tothe changes in wave velocity among different layers, reflection, refraction, and interference. this phenomenon cancause differences in the seismic response of structures that are located on the ground with different frequencies, andconsequently increase the risk of damage to the structures. therefore, the analysis of site response in alluvial valleysis of great importance.in this paper, the numerical studies performed on the nonlinear seismic behavior of alluvial valleys under theeffect of incident waves are investigated. in these studies, different methods such as finite element method,boundary element method, finite difference method, and hybrid method are used. also, the effect of variousparameters such as the geometric shape of the valley, the thickness and mechanical properties of the sedimentarylayers, the type and intensity of the incident waves, the behavioral models of the materials, and the degree ofnonlinearity of them on the seismic response of alluvial valleys are studied. the results obtained from these studiesare compared with the existing results in the technical literature and the differences and similarities of them aredetermined.in these studies, the nonlinear seismic behavior of two-dimensional and one-dimensional alluvial valleys is alsoinvestigated. the nonlinear effects on the seismic response of alluvial valleys are studied by considering differentbehavioral models such as linear models, bounded models, mechanical models, and hysteresis models. the resultsshow that the nonlinear seismic behavior of two-dimensional and one-dimensional alluvial valleys can havesignificant differences with the linear seismic behavior of them. for example, the nonlinear seismic response of twodimensionaland one-dimensional alluvial valleys may have less amplification or deamplification than the linearseismic response of them. also, the nonlinear seismic response of two-dimensional and one-dimensional alluvialvalleys may be strongly affected by the type and intensity of the incident waves, the behavioral model of thematerials, and the degree of nonlinearity of them. so, it is important to note that the results of nonlinear site responseanalysis are highly dependent on the specific parameters used in the analysis, such as the shear-wave velocity, massdensity, and damping ratio. therefore, these parameters should be chosen carefully, and the analysis results shouldbe checked with field measurements or other methods.finally, the main summary of the effects and importance of each of these parameters for the analysis of siteresponse in alluvial valleys is presented. also, the difference between the various methods available in the literatureand their results have been identified.