Seismic wave simulation in the presence of real volcano topography

We use a finite-difference method on a 3-D staggered grid to simulate seismic wave propagation in the presence of strong topographic variations. An application to Merapi volcano, Indonesia, is presented. In order to focus on the effect of topography on the seismic wave field, calculations are performed for a rather simple model with an isotropic point source and a homogeneous subsurface medium. Despite this simplicity of the model a complex wave field evolves. Results of the computation are shown in synthetic seismograms, snapshots of the wave field and in a particle motion analysis. Waves reflected and converted at the free surface can be identified. The first P-wave arrivals show linear polarization whereas at later times the wave field is a superposition of shear and Rayleigh waves resulting in a more complicated particle motion pattern. The effect of volcano topography on seismic waves can be clearly demonstrated. We confirm that the finite-difference method we use is apt for numerical modeling in volcano seismology.