GPS measurements from the Ladakh Himalaya, India: Preliminary tests of plate-like or continuous deformation in Tibet

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 fl uid than like a plate.

Intensity, Magnitude, Location, and Attenuation in India for Felt Earthquakes since 1762

“…The surprising proximity of the 1803 and 1991 earthquakes is suggestive that one may be a recurrence of the other. In 188 years, the present day convergence rate would result in a slip deficit of greater than 3 m, more than sufficient to drive an M 6.8 earthquake (Jade et al, 2004). The 1819 Allah Bund Earthquake…”

“…Thus, according to our intensity analysis, the 1833 and 1866 earthquakes both appear to have ruptured similar locations in the Nepal Himalaya with similar magnitudes. In this case, unlike the 1803/1991 earthquake pair, the slip in the second event would not have developed over the course of 33 years with a geodetic convergence rate of 18 mm=yr (Jade et al, 2004). *Columns a, b, c, and d refer to the variables in equation (1).…”

Crustal–lithospheric structure and continental extrusion of Tibet

“…The depth is consistent with the earthquake rupturing the base of the crust, and is consistent with the compressional state of stress beneath the Karakoram today, but similar to the deep earthquakes beneath Nepal-southern Tibet, it is likely that elevated temperatures in the middle crust preclude earthquakes beneath the Karakoram. Jade et al (2004) suggested that active right-lateral slip along the Karakoram Fault could be no more than 3.4 mm a À1 based on GPS measurements.…”

Present‐day crustal thinning in the southern and northern Tibetan Plateau revealed by GPS measurements

“…The data set of He et al [2013] contains 16 campaign-mode sites located in a localized dense network across central segment of Altyn Tagh Fault from the Tarim Basin to northern Tibet and measured twice in the period of 2009-2011. In addition, we show published velocities for surrounding regions (Figure 1): from the Nepal Himalaya [e.g., Banerjee et al, 2008;Bettinelli et al, 2006;Bilham et al, 1997;Feldl and Bilham, 2006], northwest Himalaya [Banerjee and Bürgmann, 2002], Pamir-Hindu Kush [Ischuk et al, 2013;Mohadjer et al, 2010], Kashmir and Ladakh Himalaya [e.g., Jade et al, 2004;Schiffman et al, 2013], eastern Himalaya, Naga Hills, and Shillong Plateau [Devachandra et al, 2014;Vernant et al, 2014].…”

“…East-west extension in southern Tibet is part of an active strain rate field that includes overthrusting of the Himalaya onto India in a direction perpendicular to the local strike of the range; the rigidity of the Indian plate and the curvature of the range require such extension of southern Tibet [e.g., Armijo et al, 1986;Copley and McKenzie, 2007;Jade et al, 2004;Chen, 1982, 1983;Molnar and Lyon-Caen, 1989;Styron et al, 2011]. Moreover, because gradients in horizontal normal stresses should, in general, lie parallel to gradients in gravitational potential energy [e.g., England and Jackson, 1989;England and McKenzie, 1982], the radial overthrusting at the Himalaya is a likely consequence of any rheological structure or vertical distribution of flow, whether that flow occurs without shear on horizontal planes as in a thin viscous sheet [e.g., England and Molnar, 1997], as channel flow [e.g., Clark and Royden, 2000;Royden, 1996], or as a gravity current [Copley, 2012;Copley and McKenzie, 2007].…”