Terrane‐controlled crustal shear wave splitting in Taiwan

Abstract

Taiwan is the result of arc‐continent collision associated with the convergence of the Philippine Sea plate with the eastern Eurasian plate continental margin. The locus of deformation is found in eastern Taiwan in the form of mountain building (Central Range) with underlying thickened lithosphere. Rapid tectonic exhumation in the Central Range has uncovered low‐to‐high‐grade metamorphic rocks marked by steep cleavage. We carried out a crustal seismic anisotropy study across Taiwan, producing a database of over 27,000 local earthquake shear wave splitting measurements. Additionally, we carried out rock physics measurements of metamorphic outcrop samples to quantify shear wave rock anisotropy. We produced a map of station‐averaged splitting measurements across Taiwan. Patterns of fast shear wave directions correlate with tectonic terranes produced by plate convergence. Deformation‐related mineral‐preferred orientation in the metamorphic rocks produces a significant amount of the crustal anisotropy in the Taiwan collision zone.

Stress‐ and Structure‐Induced Anisotropy in Southern California From Two Decades of Shear Wave Splitting Measurements

“…This suggests that fast directions can be controlled by local‐scale geological blocks. A similar observation was reported by Okaya et al () showing that patterns of fast directions correlate with tectonic terranes across the Southern Central Range in Taiwan. They inferred that minerals in metamorphic rocks might form preferred alignment due to crustal deformation.…”

SKS Splitting and the Scale of Vertical Coherence of the Taiwan Mountain Belt

“…Figure shows that the theoretically predicted ϕ is orogen‐parallel at about 20° with δ t roughly 0.2 s for most Ω. This agrees with the general results of Okaya et al () who measured local shear wave splitting to obtain δ t of 0.1–0.5 s and ϕ more or less orogen‐parallel along the mountain range (the Hsuehshan Range and the Central Range). Kuo et al () using local intraslab events observed δ t < 0.1 s in northern Taiwan, also suggesting little net anisotropy along the path traveling through the lithosphere.…”

“…Near the surface, cracks and active faults aligned by tectonic stress are major detectable fabrics (e.g., Chang et al, ; Chen et al, ). A few kilometers into the upper crust, cracks closed and subvertical foliation/cleavage planes and terrain boundary faults developed during the arc‐continent collision dominate, producing orogen‐parallel anisotropy (Huang et al, ; Okaya et al, ). The lower crust, or the crust of the underthrusted EP lithosphere, likely undergoes subduction‐induced shear that yields convergence‐parallel anisotropy (Huang et al, ).…”

Probing crustal anisotropy by receiver functions at the deep continental drilling site KTB in Southern Germany

“…; Okaya et al . ). We want to draw special attention on receiver function studies, which have observed the pattern of the converted Ps waves for several anisotropic scenarios (e.g.…”

“…Effects of seismic anisotropy within the crust have been often observed in body and surface waves (e.g. Ozacar and Zandt 2004;Sherrington, Zandt and Frederiksen 2004;Bostock and Christensen 2012;Bianchi et al 2016;Okaya et al 2016). We want to draw special attention on receiver function studies, which have observed the pattern of the converted Ps waves for several anisotropic scenarios (e.g.…”