Seismic Pressures in Offshore Areas: Numerical Results

Norberto Flores-Guzmán Enrique Olivera-Villaseñor Andriy Kryvko Alejandro Rodríguez-Castellanos Francisco Sánchez-Sesma About the authors

Abstract

The purpose of this study is to obtain numerical estimations of seismic pressures in offshore areas considering the effect of seabed configurations and soil materials. To this end, the Boundary Element Method is used to irradiate waves, so that force densities can be obtained for each boundary element. From this hypothesis, Huygens´ Principle is implemented since the diffracted waves are constructed at the boundary from which they are radiated. Application of boundary conditions allows us to determine a system of integral equations of Fredholm type of second kind and zero order. Various models were analyzed, the first one is used to validate the proposed formulation. Other models of ideal seabed configurations are developed to estimate the seismic pressure profiles at several locations. The influence of P- and SV-wave incidence was also highlighted. In general terms, it was found that soil materials with high wave propagation velocities generate low pressure fields. The difference between the maximum pressure values obtained for a soil material with shear wave velocity of β = 3000 m/s is approximately 9 times lower than those obtained for a material with β = 90 m/s, for the P-wave incidence, and 2.5 times for the case of SV-waves. These results are relevant because the seabed material has direct implications on the field pressure obtained. A relevant finding is that the highest seismic wave pressure due to an offshore earthquake is almost always located at the seafloor.

Keywords:
Offshore structures; seismic pressures; oil industry; earthquake; elastic waves; Boundary Element Method

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