<p>The Taiwan foreland basin consists of a thick sedimentary layer overlying the crust of the underthrusting Eurasian continent. To investigate whether deformation differs between the sedimentary cover and the basement, we applied a two-layer modeling approach to a set of local shear wave splitting measurements. The inversion for two-layer anisotropy is based on Bayesian inference with a Markov Chain Monte Carlo sampling algorithm. Using a shortest-distance least-squares scheme, the inversion identifies an upper-layer fast polarization direction <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="44195_2025_108_Article_IEq1.gif" Format="GIF" Height="17" Rendition="HTML" Resolution="72" Type="Linedraw" Width="16" /> </InlineMediaObject> <EquationSource Format="TEX">\(\phi\)</EquationSource> </InlineEquation> most likely centered at an azimuth of 121°, closely aligning with the geodetically derived maximum horizontal contraction directions. The lower-layer <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="44195_2025_108_Article_IEq2.gif" Format="GIF" Height="17" Rendition="HTML" Resolution="72" Type="Linedraw" Width="16" /> </InlineMediaObject> <EquationSource Format="TEX">\(\:\phi\:\)</EquationSource> </InlineEquation> is centered at 74°, coinciding with the strike of extensional fault systems preserved in the pre-Miocene basement. Bivariate analyses of model parameters confirm that <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="44195_2025_108_Article_IEq3.gif" Format="GIF" Height="17" Rendition="HTML" Resolution="72" Type="Linedraw" Width="16" /> </InlineMediaObject> <EquationSource Format="TEX">\(\phi \)</EquationSource> </InlineEquation> is well resolved in both layers, despite a potential strong inter-layer tradeoff. We interpret the upper-layer anisotropy as stress-induced caused by the plate convergence and the lower-layer anisotropy as structure-induced associated with faults inherited from past rifting of the continental margin. The combined effects of present-day deformation and pre-existing continental margin structures shape the foreland architecture before it continues to underthrust the Taiwan orogenic wedge.                  </p>

Bayesian inversion for the crustal anisotropy of the Taiwan foreland basin: syn- and pre-orogenic deformation

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2025年7月4日

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Cheng-Chien Peng,
Ban-Yuan Kuo,
Ting-Li Chen,
Kenn-Ming Yang

摘要

The Taiwan foreland basin consists of a thick sedimentary layer overlying the crust of the underthrusting Eurasian continent. To investigate whether deformation differs between the sedimentary cover and the basement, we applied a two-layer modeling approach to a set of local shear wave splitting measurements. The inversion for two-layer anisotropy is based on Bayesian inference with a Markov Chain Monte Carlo sampling algorithm. Using a shortest-distance least-squares scheme, the inversion identifies an upper-layer fast polarization direction \(\phi\) most likely centered at an azimuth of 121°, closely aligning with the geodetically derived maximum horizontal contraction directions. The lower-layer \(\:\phi\:\) is centered at 74°, coinciding with the strike of extensional fault systems preserved in the pre-Miocene basement. Bivariate analyses of model parameters confirm that \(\phi \) is well resolved in both layers, despite a potential strong inter-layer tradeoff. We interpret the upper-layer anisotropy as stress-induced caused by the plate convergence and the lower-layer anisotropy as structure-induced associated with faults inherited from past rifting of the continental margin. The combined effects of present-day deformation and pre-existing continental margin structures shape the foreland architecture before it continues to underthrust the Taiwan orogenic wedge.