Full-Waveform Modelling of Seismic Wave Propagation and Scattering within Extrusive Basalt Sequences
Abstract
Imaging beneath and estimating the thickness of basalt layers using controlled source seismology remains a significant challenge. Highly heterogeneous basalt flows interbedded with sediments results in complex scattering and attenuation of the seismic wavefield during conventional reflection surveys. Wide-angle refraction data has often been used to aide velocity model development in such geological settings. However, modelling and inversion of wide-angle data often makes use of ray-tracing algorithms (e.g. first-arrival tomography) which does not account for the heterogeneity of the geology and results in oversimplified models being developed. Using heterogeneous models of basalt sequences, developed from wireline logs and field analogues, we use 2D elastic finite difference modelling to understand the effect of different properties of basalt sequence on the first arrival refracted seismic waves. We show that refractions from a basalt sequence cannot be considered as a single arrival. The layering of high velocity basalt flows with lower velocity sediments has a dominant control on these refractions with the observed arrivals being composed by the interference of energy propagating in the higher velocity layers. Further we find that the first arrival only propagates throughout the top of the sequence so the belief that these data can be used to constrain the thickness of these sequences is unfounded. Rough interfaces of lava flows have a lesser effect on the refractions, but have a more significant influence on the reflected arrivals.The results of this project has implications for exploration of volcanic margins and other research where estimation of the thickness of volcanic layers is significant.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2017
- Bibcode:
- 2017AGUFM.S13A0632S
- Keywords:
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- 7219 Seismic monitoring and test-ban treaty verification;
- SEISMOLOGY;
- 7260 Theory;
- SEISMOLOGY;
- 7270 Tomography;
- SEISMOLOGY;
- 7290 Computational seismology;
- SEISMOLOGY