First Multi-Scale, Finite-Frequency Tomography Illuminates 3-D Anatomy of the Tibetan Plateau
First Multi-Scale, Finite-Frequency Tomography Illuminates 3-D Anatomy of the Tibetan Plateau A map showing color-coded topography of the Himalayan-Tibetan collision zone. Finite-frequency travel-times recorded by 108 broadband stations (green triangles) are used to obtain multi-scaled, tomographic images for a large volume beneath western Tibet (box outlined by dashed lines). Blue solid lines indicate locations of profiles along which cross-sections of δlnVP and δlnVS are shown in Figure 3b and 3c. Blue dashed lines mark profiles across the Lunggar and the Yadong-Gulu rifts where profiles of electric resistivity are inferred from magnetotelluric (MT) measurements (at locations shown as purple open circles) and being directly compared with our results of δlnVS in Figure 3d. For reference, positions of other temporary seismic stations, located to the east of our region of study and whose data were used to construct the tomographic profile of Tilmann et al. [2003], are also plotted (brown dashed line and orange inverted triangles). Other features not explained in the legend are: Young or active normal faults (red curves, Taylor and Yin [2009]); major geologic boundaries (solid curves), including (from north to south) JRS, the Jinsha River Suture; BNS, the Bangong-Nujiang Suture; IYS, the Indus-Yarlung Suture; STD, the South Tibet Detachment System; MCT, the Main Central Thrust; and MBT, the Main Boundary Thrust.
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With a new multi-scale parameterization, 3-D images from finite-frequency seismic tomography, including the very first images beneath central Tibet from S-waves, reveal that regions of low electric resistivity in the crust, previously observed along active rifts in southern Tibet, correlate well with regions of low P- and S-wave speeds (V). However, such regions are not interconnected, indicating that a prevailing south-directed, channel-like crustal flow seems inactive or this popular geodynamic model needs modification. In the upper mantle, there is no clear indication of regional down-welling between depths of 100 to 400 km. Instead, a strong, lateral boundary between high and low V extends up to 33°N, marking the northern limit of sub-horizontally advancing Indian lithospheric mantle.
</p><p>References
</p><p>Hung, S.-H., W.-P. Chen, L.-Y. Chiao and T.-L. Tseng, First multi-scale, finite-frequency tomography illuminates 3-D anatomy of the Tibetan plateau, Geophys. Res. Lett., 37, doi:10.1029/2009GL041875 (with on-line supplements), 2010.
</p><p>Acknowledgements: We thank S.-L. Chung for helpful discussions, L. Zhao, an anonymous referee, and the Editor for their comments that help improve the manuscript. This work was supported by National Science Council of Taiwan grants 96-2119-M-002-016 and 97-2745-M- 002-011 (S.-H.H.) and U.S. National Science Foundation grants EAR99-09362 (“Hi-CLIMB”), EAR05-51995, and EAR06-35419 (W.-P.C.)</p>