Abstract:
Observations of relative motion in a geodetic network in Ladakh, India, and across southern Tibet indicate slow shear on the Karakorum fault, rapid east-west extension across the whole of southern Tibet, and constant arc-normal convergence between India and southern Tibet along the Himalayan arc. Measurements of ten campaign-style and six permanent sites with global positioning system (GPS) precise geodesy provide these bounds on the style and rates of the large-scale deformation in the Tibet-Himalaya region. Divergence between sites at Leh, Ladakh, India, and Shiquanhe, western Tibet, as well as slow relative motion among sites within the Ladakh network, limit right-lateral slip parallel to the Karakorum fault to only 3.4 ± 5 mm/yr. This low rate concurs with a recent estimate of 3–4 mm/yr for Late Holocene time, but disagrees with the much higher rate of 30–35 mm/yr that has been used to argue for plate-like behavior of the Tibetan Plateau. Convergence between Ladakh and the Indian subcontinent at 18.8 ± 3 mm/yr at 224° ± 17° (1σ) differs little from estimates of convergence across the central segment of the Himalaya. Finally, lengthening of the baseline between Leh, Ladakh, and Lhasa (in southeastern Tibet) at 17.8 ± 1 mm/yr or between Leh and Bayi (farther to the southeast) at 18 ± 3 mm/yr, is consistent with an extrapolation of rates of east-west extension of the Tibetan Plateau based both on shorter GPS baselines (e.g., Lhasa-Simikot) and on diverging slip vectors of earthquakes in the Himalaya. We interpret these results to indicate that Tibet behaves more like a fluid than like a plate.