| Title | Azimuthal anisotropy in Bayesian surface wave tomography: application to northern Cascadia and Haida Gwaii, British Columbia |
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| Author | Gosselin, J M; Audet, P; Schaeffer, A J ; Darbyshire, F A; Estève, C |
| Source | Geophysical Journal International vol. 224, issue 3, 2020 p. 1724-1741, https://doi.org/10.1093/gji/ggaa561 |
| Image |  |
| Year | 2020 |
| Alt Series | Natural Resources Canada, Contribution Series 20200680 |
| Publisher | Oxford University Press |
| Document | serial |
| Lang. | English |
| Media | paper; on-line; digital |
| File format | pdf; html |
| Province | British Columbia |
| Area | Haida Gwaii; Cascadia; Canada |
| Lat/Long WENS | -140.0000 -118.0000 63.0000 40.0000 |
| Subjects | Science and Technology; tectonics; anisotropy; surface wave studies; seismic waves; seismology |
| Illustrations | location maps; diagrams; graphs |
| Released | 2020 11 20 |
| Abstract | Surface wave tomography is a valuable tool for constraining azimuthal anisotropy at regional scales. However, sparse and uneven coverage of dispersion measurements make meaningful uncertainty estimation
challenging, especially when applying subjective model regularization. This paper considers azimuthal anisotropy constrained by measurements of surface wave dispersion data within a Bayesian trans-dimensional (trans-d) tomographic inversion. A
recently proposed alternative model parametrization for trans-d inversion is implemented in order to produce more realistic models than previous studies considering trans-d surface wave tomography. The reversible-jump Markov chain Monte Carlo
sampling technique is used to numerically estimate the posterior probability density of the model parameters. Isotropic and azimuthally anisotropic components of surface wave group velocity maps (and their associated uncertainties) are estimated
while avoiding model regularization and allowing model complexity to be determined by the data information content. Furthermore, data errors are treated as unknown, and solved for within the inversion. The inversion method is applied to measurements
of surface wave dispersion from regional earthquakes recorded over northern Cascadia and Haida Gwaii, a region of complex active tectonics but highly heterogeneous station coverage. Results for isotropic group velocity are consistent with previous
studies that considered the southern part of the study region over Cascadia. Azimuthal anisotropic fast-axis directions are generally margin-parallel between Vancouver Island and Haida Gwaii, with a small change in direction and magnitude along the
margin which may be attributed to the changing tectonic regime (from subduction to transform tectonics). Estimated errors on the dispersion data (solved for within the inversion) reveal a correlation between surface wave period and the dependence of
data errors on travel path length. This paper demonstrates the value of considering azimuthal anisotropy within Bayesian tomographic inversions. Furthermore, this work provides structural context for future studies of tectonic structure and dynamics
of northern Cascadia and Haida Gwaii, with the aim of improving our understanding of seismic and tsunami hazards. |
| GEOSCAN ID | 327965 |
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