Three‐dimensional P wave azimuthal anisotropy in the lithosphere beneath China

Abstract

Seismic anisotropy in the upper mantle beneath East Asia has been studied extensively using shear wave (SKS) splitting measurements, which have provided important information on mantle dynamics in this region. However, SKS measurements have poor vertical resolution, and so their interpretations are usually not unique. In this work we use a large number of traveltime data from 34,036 local earthquakes recorded by 1563 seismic stations to determine the first model of 3-D P wave azimuthal anisotropy in the lithosphere beneath China. Our results show that the fast velocity directions (FVDs) are generally correlated with the surface geologic features, such as the strikes of the orogens, active faults, and tectonic boundaries. The FVDs in the upper crust are normal to the maximal horizontal stress (σ H ) in regions with extensive compression such as the Tibetan Plateau, whereas they are subparallel to σ H in strike-slip shear zones such as the western and eastern Himalayan syntax. The comparison of the FVDs of P wave anisotropy with SKS splitting measurements indicates that beneath the Tibetan Plateau the seismic anisotropy in the lithosphere contributes significantly to the SKS splitting observations. In contrast, in east China the P wave FVDs in the lithosphere are different from the SKS splitting measurements, suggesting that the SKS splitting is mainly caused by the anisotropy in the deeper mantle such as the asthenosphere and the mantle transition zone under east China. These novel results provide important new information on the lithospheric deformation and mantle dynamics in East Asia.

Seismic anisotropy tomography: New insight into subduction dynamics

“…A 3-D model of Vp azimuthal anisotropy in the lithosphere beneath the entire Mainland China was determined using local-earthquake arrival-time data (Huang et al, 2014) (Fig. 8).…”

“…The major causes of seismic anisotropy are lattice-preferred orientation (LPO) and shape-preferred orientation (SPO) of the materials constituting the Earth. In the crust, orientations of local and regional structure and tectonics can cause seismic anisotropy, such as fault systems (e.g., Zhang and Schwartz, 1994;Bokelmann, 1995;Huang et al, 2014;Koulakov et al, 2015). In the mantle, seismic anisotropy may reflect convection flows and is usually interpreted by LPO of olivine crystals (e.g., Karato and Wu, 1993;Fouch and Rondenay, 2006;Wang and Zhao, 2008;Long, 2013;.…”

Multiscale Seismic Tomography

“…The effects may become more serious and complex for a large-aperture seismic network, such as the USArray (e.g., and ChinaArray (e.g., Huang et al 2014). This amount of effects is certainly greater than the picking error of the observed teleseismic P-wave arrivals (~ 0.1 s).…”

Seismic tomography and anisotropy of the Helan‐Liupan tectonic belt: Insight into lower crustal flow and seismotectonics

“…The seismic velocity structure of the crust and uppermost mantle has been assumed to be isotropic in the above mentioned previous studies. However, seismic anisotropy has been revealed in many regions of the world, providing critical information on the past and present deformations in the crust and upper mantle [e.g., Fouch and Rondenay , ; Huang et al , , , ; Wang and Zhao , , ; Wei et al , , ; Zhao et al , ; Koulakov et al , ; Zhao et al , ]. Previous seismic anisotropy results obtained by shear wave splitting measurements indicate that the northeastern Tibetan Plateau exhibits a vertically coherent deformation in the lithosphere [e.g., J. Li et al , ; Flesch et al , ], which is inconsistent with the lower crustal ductile flow model.…”