Possible layered lithospheric anisotropy around Longmenshan Faults by teleseismic S wave splitting and receiver functions

Abstract

This study conducts an in-depth analysis of seismic anisotropy around the Longmenshan Faults. Utilizing a dataset of about 7710 earthquake catalogs from July 2007 to March 2023, we applied S wave splitting and receiver function methods to examine Pms and XKS waveforms collected from 12 fixed broadband stations across Gansu and Sichuan provinces. Our analysis revealed significant variations in seismic anisotropy between the crust and lithosphere, marked by distinct fast wave directions and delay times. These characteristics point to the possibility for layered anisotropy within the region. A two-layer anisotropy inversion analysis at key stations further delineated the differential anisotropic behaviors between the crust and the upper mantle, underscoring the impact of local geological structures and mantle dynamics. Crucially, our study posits the existence of layered anisotropy around the Longmenshan Fault Zone, a finding that significantly advances our comprehension of the region’s seismic anisotropy and adds a vital dimension to our understanding of its subsurface structural intricacies and tectonic evolution.

Lithospheric deformation revealed by teleseismic phases SKS PKS and SKKS splitting in the NE margin of the Tibetan plateau

“…Along the Haiyuan fault to Yinchuan graben, although the direction of the FPD is consistent, there is a large delay time in all of them. The FPD in the Longmenshan fault zone takes on a distinctive NE direction and has shown this feature from within the Tibetan plateau block, it also exhibits a deflection along the strike of the Longmenshan fault zone, which gradually deflects to the ENE direction (Wang and Gao, 2024), with the delay time decreasing from west to east, a deviation that stands in contrast to the findings of Liu et al (2020). However, in the absence of anisotropy results from other nearby stations, the origin and prevalence of this directional change remains elusive, and it is impossible to tell whether it is a localized phenomenon or a general feature of the region.…”