On the Use of Fractal Surfaces to Understand Seismic Wave Propagation in Layered Basalt Sequences

Abstract

The aim of this study is to better understand how a layered basalt sequence affects the propagation of a seismic wave, which has implications for sub-basalt seismic imaging. This is achieved by the construction of detailed, realistic models of basalt sequences, using data derived directly from outcrop analogues. Field data on the surface roughness of basaltic lava flows were captured using terrestrial laser scanning and satellite remote sensing. The fractal properties of the surface roughness were derived, and it can be shown that the lava flow surface is fractal over length scales up to approximately 2 km. The fractal properties were then used to construct synthetic lava flow surfaces using a von Karman power spectrum, and the resulting surfaces were then stacked to create a synthetic lava flow sequence. P-wave velocity data were then added, and the resulting model was used to generate synthetic seismic data. The resulting stacked section shows that the ability to resolve the internal structure of the lava flows is quickly lost due to scattering and attenuation by the basalt pile. A further result from generating wide-angle data is that the appearance of a lower-velocity layer below the basalt sequence may be caused by destructive interference within the basalt itself.