Degree of Coupling in 3D Multilayer Continental Lithospheric Buckling: Implications for Tectonic Underpressure

The interplay between lithospheric strength contrast and tectonic compression by relative plate motion drives buckling instability. Analysis of lithospheric buckling with plate tectonic history is essential for inferring lithospheric strength. Based on 3D viscoelastic numerical modeling, we investigated the shape, symmetry, and coupling of layers under complex stress environments (i.e., compression/extension velocity conditions) depending on different strength structures in the lithospheric multilayer models. Our models included two strong and sandwiched weak layers in a low strength matrix, simulating the simplified strength envelopes of the continental lithosphere. Additional extensional or compressional boundary conditions were applied perpendicular to the main compression. The strength and thickness of the layers determine the degree of coupling of the layers. We found that the boundary conditions dominate the overall geometry and symmetry. The boundary conditions with the extension produced a smaller cylindrical buckling structure than the uniaxial compression models. In the biaxial compression models, the relative amount of shortening along both axes determines the axis of symmetry. The sandwiched weak layer with a larger thickness and lower strength decoupled the buckling structures in terms of wavelength and amplitude, providing insight into the decoupled lithospheric buckling beneath the Tibetan Plateau. The simultaneous deformation of the two strong layers caused a spatial dynamic pressure difference in the weak layer, which may lead to buckling-induced intraplate volcanism.