9:30 AM - 9:45 AM
[S21-3-04] Shear-wave Splitting in the Crust and its Tectonic Implications
Shear-wave will split into two independent components with almost orthogonal polarizations, when it propagates through anisotropic media. The polarization of fast shear wave (PFS) is parallel to the strike of the cracks, as well as the direction of maximum horizontal compressive stress. Therefore the polarization of fast shear wave can be adopted to study stress in the crust. Stress can influence crack density and aspect ratio of cracks in the crust. The time-delay of slow shear-wave suggests the anisotropic degree and stress status. However in many typical tectonic zones, the crustal anisotropy, especially the PFS, is strongly changed by local tectonics, such as faults.
In North China zone, seismic anisotropy from shear-wave splitting in the crust show strong relationship to faults. PFS on the fault is always parallel to the strike-slip faults. However in the zone away from faults, PFS turns to parallel to direction of maximum horizontal compressive stress.
In northeastern margin zone of Tibetan Plateau, PFS suggests the influence both from stress field and from strike of tectonics/faults. However, in southeastern margin zone of Tibetan Plateau, PFS clearly indicates consistent to crustal deformation, as well as corresponding to GPS data. In both zones, seismic anisotropies in the crust are quite different with those in the upper mantle.
In zone of typical thrust fault, Longmenshan faults, where Wenchuan 8.0 magnitude earthquake occurred in 2008, we found the crustal anisotropy almost is not changed by the thrust faults. PFS is only parallel to direction of maximum horizontal compressive stress. But it shows the influence from faults in the zone away from pure thrust fault. The anisotropic pattern in the crust is different in the upper mantle.
In this study, we discuss shear-wave splitting of local seismic wave and analyze seismic anisotropy in the crust and its tectonic implications. Furthermore we compare seismic anisotropy in the crust and in the mantle.
In North China zone, seismic anisotropy from shear-wave splitting in the crust show strong relationship to faults. PFS on the fault is always parallel to the strike-slip faults. However in the zone away from faults, PFS turns to parallel to direction of maximum horizontal compressive stress.
In northeastern margin zone of Tibetan Plateau, PFS suggests the influence both from stress field and from strike of tectonics/faults. However, in southeastern margin zone of Tibetan Plateau, PFS clearly indicates consistent to crustal deformation, as well as corresponding to GPS data. In both zones, seismic anisotropies in the crust are quite different with those in the upper mantle.
In zone of typical thrust fault, Longmenshan faults, where Wenchuan 8.0 magnitude earthquake occurred in 2008, we found the crustal anisotropy almost is not changed by the thrust faults. PFS is only parallel to direction of maximum horizontal compressive stress. But it shows the influence from faults in the zone away from pure thrust fault. The anisotropic pattern in the crust is different in the upper mantle.
In this study, we discuss shear-wave splitting of local seismic wave and analyze seismic anisotropy in the crust and its tectonic implications. Furthermore we compare seismic anisotropy in the crust and in the mantle.