17:15 〜 18:45
[SSS09-P01] Seismic radial anisotropy in southeastern Tibetan Plateau and its implications for regional geodynamic evolution
キーワード：southeastern Tibetan Plateau, seismic radial anisotropy, shear wave velocity, crustal deformation
The southeastern Tibetan Plateau is characterized by intricate crustal tectonic features, encompassing recent seismic megathrust events. Prior research has postulated the presence of two distinct north-south (N-S) oriented channlized flows of viscous material within the crust. Recent investigations have unveiled a noteworthy northeast-southwest (NE-SW) belt-shaped geological structure in the western Sichuan region, exhibiting relatively high seismic velocities and anomalous radial anisotropy (Vsv < Vsh), possibly indicative of a Moho ramp. The juxtaposition of this NE-SW structural zone with one of the postulated crustal channel flows has generated interest in the interaction and potential influence of this geological feature on earthquake focal mechanisms and regional crustal strain distribution. In this study, we have significantly refined regional crustal models for shear wave velocity and radial anisotropy through ambeint noise tomography, utilizing Rayleigh and Love wave disperison data from a dense seismic array. This high-resolution model has enabled us to explore the association between the NE-SW belt-shaped negative radial anisotropy and channelized viscous flows. Additionally, our research has unveiled a region of generalized negative radial anisotropy within the western Chuan-Dian fragment at dephts of 30-40 km, suggestive of historical compression. Drawing upon various geophysical and geological evidence, we present a geodynamic evolution model, which proposes a sequence of events: Permian plume activity, norhtward east Himalyayn syntaxis advancing causing NEE-SWW compression, shift to N-S shorting, strain accumulation, depth-dependent deformation, and a shift in strain concentration. The geodynamic model offers valuable insights into the regional distribution of crustal strain and the underlying mechanisms of large seismic events.