Effects of arbitrary shaped surface topographies on earthquake ground motion using boundary element method in time domain



In this paper, the direct boundary element method in time domain is used for the calculation of local amplifications of seismic waves by real 3-dimensional surface topographies. The presented method is effective for modelling surface irregularities with arbitrary shapes under complex incident wave forms. A real topography with particular importance in Iran, Urmia Hill, which represents a complex surface irregularity with sloping boundaries, is considered as a study case and its seismic behaviour, particularly sloping boundary effects, is studied under SH and SVincident waves with various azimuths and angles of incidence. This method can equally be used for P or mixed P-S incidences. The boundary is modelled using quadrilateral (8-node) elements, and synthetic displacement time history based on the deterministic approach is used for excitation of the model. The results show that the areas located at the end of slopes experience more excitations in some cases, while greater amplifications occur in the nearby flat areas in some other incidences. The amplification pattern is shown to be completely dependent on the wave type and the direction of sloped boundaries with respect to the angle and azimuth of incidence.