Preliminary analysis of crustal shear‐wave splitting in the Sanjiang lateral collision zone of the southeast margin of the Tibetan Plateau and its tectonic implications

Abstract

The collision of the Indian and Eurasian plates, to the east of the eastern Himalayan syntaxes, forms the Sanjiang lateral collision zone in the southeast margin of the Tibetan Plateau, where there are intense crustal deformation, active faults, earthquakes, as well as a metallogenic belt. Given the lack of adequate seismic data, shear‐wave splitting in this area has not been studied. With seismic data from a temporary seismic linear array, as well as permanent seismic stations, this paper adopts the identification on microseismic event to pick more events and obtains shear‐wave splitting parameters from local earthquakes. From the west to the east, the study area can be divided into three subzones. The “fast” polarization (i.e. the polarization of the fast shear wave) varies gradually from NNW to NS to NNE in these three subzones. The time delay of the slow shear wave (i.e. the time difference between the two split shear waves) also increases in the same direction, indicating the presence of seismic anisotropy above 25 km in the crust. Both shear‐wave splitting parameters are closely related to stress, faults and tectonics. The scatter and the “dual” (i.e. two) dominant orientations of the fast polarizations at several stations indicate strong distortions caused by nearby faults or deep tectonics. The anisotropic parameters are found to be related to some degree to the metallogenic belt. It is worth to further analyse the link between the anisotropic pattern and the metallogenic area, which suggests that shear‐wave splitting could be applied to study metallogeny. This paper demonstrates that the identification on microseismic event is a useful tool in detecting shear‐wave splitting details and exploring its tectonic implications.

Crustal Structure of the Chuan‐Dian Block Revealed by Deep Seismic Sounding and its Implications for the Outward Expansion of the East Tibetan Plateau

“…Li et al (2018) thought that the distribution of LVZs was closely related to the activation of blocks and fault zones (eg., Songpan-Ganze block, XJF), whereas Zhao et al (2008) believed that the LVZs acted as a decollement decoupling the deformation between the upper and lower crust. Although intense study of the Tibetan Plateau has led to a consensus that the LVZs are developed in the middle-lower crust of the Tibetan Plateau (Nelson and Zhao,1996;Wei et al, 2001;Nábělek et al, 2009;Zhang et al, 2011;Teng et al, 2013;Gao et al, 2019), the crustal flow model is still debated.…”

On the Origin of Seismic Anisotropy in the Shallow Crust of the Northern Volcanic Zone, Iceland

“…Seismic anisotropy, the directional dependence of seismic wave‐speed, has been observed in the crust across a range of environments (Boness & Zoback, 2006; Gao et al., 2019; Illsley‐Kemp et al., 2018; Johnson et al., 2011; Kaviris et al., 2020). The nature of anisotropy can be broadly classified as either effective (i.e., a long‐wavelength, bulk property of an otherwise heterogeneous medium) or intrinsic, arising from the anisotropic elastic structure at the crystal lattice level.…”

Delay Time (δt) and Polarization Direction (φ) Analysis Based on Shear Wave Splitting (SWS) Method

“…Shear Wave Splitting analysis has been widely used to study seismic to identify the anisotropy inside the earth [10], [11]. Shear Wave Splitting (SWS) is a secondary (S) wave phenomenon, which has been polarized while entering an anisotropy medium [12]. When the S wave gets into the anisotropy medium, the wave's polarization will split in two perpendicularly, known as Sfast and Sslow [9].…”