Volcano topography, structure and intrinsic attenuation: Their relative influences on a simulated 3D visco-elastic wavefield

摘要

The seismic wavefield recorded on volcanoes can be significantly influenced by path effects. Scattering from the topography and internal volcanic structure can play a dominant role in the recorded seismograms. Intrinsic attenuation is also thought to play an important role in the characteristics of volcano seismic signals. We use 3D numerical modelling of wave propagation in elastic and visco-elastic media including complex velocity models and topography to investigate the scattering and attenuation characteristics of synthetic seismograms. We generate 5 distinct volcano models and simulate wave propagation through these models using shallow and deep double-couple broadband sources. We then analyse 129 synthetic seismograms calculated on the free surface. The synthetic seismograms resemble VT-A and VT-B events. The scattering effect of the topography alone is capable of producing complex seismograms. The introduction of an internal velocity structure increases the duration of these seismograms while the introduction of intrinsic attenuation decreases the duration but not the complexity. We fitted our synthetic seismograms to the diffusion in a half-space model to quantify the scattering and attenuation coefficients. The scattering quality factor measured on all 129 stations for all 5 volcano models was similar. Therefore, we deduce that the topography appears to be the dominant scatterer. The intrinsic attenuation quality factor for each of the specific models cannot be accurately recovered using the diffusion in a half-space model. The measured quality factor is not only sensitive to the attenuation properties but also to the structural properties. In all cases the scattering is more dominant than the intrinsic attenuation.