A reliable computerized litho-morphometric model for development of 3D maps of Topographic Aggravation Factor (TAF): the cases of East Mountain (Utah, USA) and Port au Prince (Haiti)

Abstract

A reliability analysis was performed of a model capable of computing Topographic Aggravation Factors (TAF) for real topographic features using a digital elevation model. This model is a module in the SiSeRHMap hybrid model that, by a metamodeling process, computes frequency depending maps (multispectral) of acceleration response taking into account the topographic effect. The model is described by a structure comparable to a series–parallel circuit problem that solves for the response of each given x, y, z map point by scaling the 1D seismic response by the TAF in the frequency domain (each a component of the series circuit). The TAF is dependent on two coupled factors (the parallel components): (1) the 3D shape of the surface and (2) the stiffness of an “equivalent uniform relief”. Reliability analyses were performed on two different areas each characterized by complex topographic features. The first case modelled the East Mountain area (Utah, USA), where a detailed topographic effects study was conducted. A comparison between the TAFs developed in this study and the estimated Median Reference Method and Standard Spectral Ratio results calculated from the recorded ground motions indicated good agreement between the numerical and experimental results. The second case performed a comparison-parametric analysis of two nearby topographic features located in Port-au-Prince, Haiti. For this case, the complete SiSeRHMap model was applied by utilizing stratigraphic and topographic modules. The results clearly confirm the role of the 3D-topographic surface in the seismic site response and the reliability of SiSeRHMap in predicting it.