Asia kinematics

Kinematics and dynamics of continental deformation

Supported by various grants from NSF's Theoretical and Experimental Geophysics Program

Collaborators (recent past and present)

• Rebecca Bendick, University of Montana, Missoula
• Roger Bilham and Kali Wallace, CIRES and Department of Geological Sciences, University of Colorado
• Erik Brown, University of Minnesota in Duluth
• Roland Bürgmann, University of California, Berkeley
• Philip England, Oxford University
• George Hilley, Stanford University
• Anatoli Ischuk, Nikolai Ischuk, Jakhongir Nizomov, and Umed Saidulloev, Institute of Earthquake Engineering and Seismology of the Academia of Sciences of the Republic of Tajikistan
• Sridevi Jade and Vinod Gaur, Centre for Mathematical Modelling and Computer Simulation, Bangalore India
• Asif Khan, University of Peshawar
• Aleksandr Novikov, Gennady G. Schelochkov, and Petr Yeremeyev, Research Station, Russian Academy of Sciences, Bishkek, Kyrgyzstan
• Shen Zhengkang and Zhang Peizhen, Institute of Geology, China Seismology Administration, Beijing China
• Aleksandr V. Zubovich, Central Asian Institute for Applied Geo-Sciences (CAIAG), Bishkek, Kyrgyzstan

"The upper crust is just a bunch of crumbs sticking together" from Rick Sibson who got it from a stall in a men’s lavatory at the Mayfair Station of the London Underground.

We continually update evidence for rates of deformation in Asia in order to construct a field of deformation for that region. We are testing the idea that continental deformation is best described by continuous deformation of a viscous fluid, if with blocks of crust on top of that deforming fluid. If this idea is correct, then rates of deformation respond to a smoothly varying stress field across Asia and to a smoothly varying viscosity field. This work has involved the compilation of rates of slip on major faults and the computation of an internally compatible (in the sense of Saint Venant) strain-rate field [England and Molnar, 1997a, 2005]. We also work with GPS velocities, such those from the Chinese CMONOC array (Figure 1) [Zhang et al., 2004], data obtained in collaboration with Indian [e.g., Jade et al., 2004] and Pakistani colleagues, and in a project just starting with colleagues from Tajikistan and Kyrgyzstan.

A result that differs from what others report is that velocity fields that we deduce from Quaternary faulting and from GPS measurements differ little, both on the scale of Asia as a whole [England and Molnar, 2005], and in specific regions, like the Tien Shan [Abdrakhmatov et al., 1996; Thompson et al., 2002] and for Karakorum fault in western Tibet [Brown et al., 2002, 2005; Jade et al., 2004]. In doing this, we challenge some published rates; for instance, Zhang Peizhen and I find no convincing evidence for a slip rate on the Altyn Tagh fault in excess of ~10 mm/yr.

Among results from this work, we found that the strain-rate field that we obtain matches that predicted by the equation of equilibrium for a thin viscous sheet in a gravity field, and hence the idea that we can describe deformation in terms of a continuum pass this test [England and Molnar, 1997b]. The velocity field that we calculate from Quaternary faulting agrees with the GPS velocity fields, suggesting that rates obtained for several year periods do not differ from those appropriate for thousands to tens of thousands of years [England and Molnar, 2005]. The velocity field near a major strike-slip fault in Tibet implies that the crust of Tibet must include a low-viscosity zone in the middle to lower crust, but the viscosity is not unusually low [Hilley et al., 2005]

We have been working separately in India and Pakistan, on separate studies.

In India we seek constraints on India’s movement with respect to other plates and on internal deformation within India itself. Analysis of GPS data from Ladakh in northwestern India [Jade et al., 2004] suggests that the rate that India underthrusts the Himalaya is constant along the range (a result consistent with Tibet behaving like a humongous piece of ripe camembert cheese flowing onto the Indian plate). Preliminary results show that the Indian subcontinent deforms internally at a measurable rate described easily as a few mm/yr of north-south shortening across the subcontinent.

In Pakistan Nicole Feldl, while a student here in Colorado, and our Pakistani colleagues installed a network of GPS control points to study the thrusting of the Potwar Plateau and Salt Range onto the Indian Shield in northern Pakistan. Our main goal is to determine whether such thrusting occur aseismically by steady creep within the salt layers or in earthquakes. Becky Bendick and Roger Bilham have analyzed these data and have preliminary results.

Finally, we (Becky Bendick, Anatoli Ischuk, Nikolai Ischuk, Jakhongir Nizomov, Aleksandr Novikov, Umed Saidulloev, Gennady Schelochkov, Aleksandr V. Zubovich, Petr Yeremeyev, and I) have installed the beginnings of a GPS network in Tajikistan and adjacent Kyrgyzstan. The network includes 4 continuously recording stations, and so far 25 campaign sites. Initial measurements will be made in the autumn of 2007. Our goals include examining possible continental subduction beneath the Pamir, quantifying movements within the Tajik Depression, and assessing the extent to which the Pamir behaves as a rigid block or a large piece of Camembert cheese, slightly smaller than Tibet.

Figure 1. Global positioning system (GPS) velocities (mm/yr) for control points in and around the Tibetan Plateau with respect to stable Eurasia, plotted on shaded relief map using oblique Mercator projection about the present-day axis of rotation for India with respect to Eurasia. Ellipses denote 1s errors. Blue polygons show locations of GPS velocity profiles in other figures in the paper by Zhang et al. [2004]. Dashed yellow polygons show regions that we used to calculate dilatational strain rates (again, see Zhang et al. [2004]). Yellow numbers 1-7 represent regions of Himalaya, Altyn Tagh, Qilian Shan, Qaidam Basin, Longmen Shan, Tibet, and Sichuan and Yunnan, respectively.

References

Abdrakhmatov, K. Ye., S. A. Aldazhanov, B. H. Hager, M. W. Hamburger, T. A. Herring, K. B. Kalabaev, V. I. Makarov, P. Molnar, S. V. Panasyuk, M. T. Prilepin, R. E. Reilinger, I. S. Sadybakasov, B. J. Souter, Yu. A. Trapeznikov, V. Ye. Tsurkov, and A. V. Zubovich, Relatively recent construction of the Tien Shan inferred from GPS measurements of present-day crustal deformation rates, Nature, 384, 450-453, 1996.

Brown, E. T., R. Bendick, D. L. Bourlès, V. K. Gaur, P. Molnar, G. M. Raisbeck, and F. Yiou (2002), Slip rates of the Karakorum fault, Ladakh, India, determined using cosmic ray exposure dating of debris flows and moraines, J. Geophys. Res., 107, 10.1029/2000JB000100, 2002.

Brown, E. T., P. Molnar, and D. L. Bourlès (2005), Technical comment on "Slip-rate measurements on the Karakorum Fault may imply secular variations in fault motion," Science, 309, 1326b.

England, P., and P. Molnar (1997), The field of crustal velocity in Asia calculated from Quaternary rates of slip on faults, Geophys. J. Int., 130, 551-582.

England, P., and P. Molnar, Active deformation of Asia: from kinematics to dynamics, Science, 278, 647-650, 1997.

England, P., and P. Molnar (2005), Late Quaternary to decadal velocity fields in Asia, J. Geophys. Res., 110, B12401, doi:10.1029/2004JB003541.

Hilley, G. E., R. Bürgmann, P.-Z. Zhang, and P. Molnar (2005), Bayesian inference of plastosphere viscosities near the Kunlun Fault, northern Tibet, Geophys. Res. Lett., 32, L01302, doi:10.1029/ 2004GL021658.

Jade, S., B. C. Bhatt, R. Bendick, V. K. Gaur, P. Molnar, M. B. Anand, and D. Kumar (2004), GPS measurements from the Ladakh Himalaya, India: Preliminary tests of plate-like or continuous deformation in Tibet, Geol. Soc. Amer. Bull., 116, 1385-1391.

Thompson, S. C., R. J. Weldon, C. M. Rubin, K. Abdrakhmatov, P. Molnar, and G. W. Berger (2002), Late Quaternary slip rates across the central Tien Shan, Kyrgyzstan, central Asia, J. Geophys. Res., 107, 10.1029/2001JB000596.

Zhang, P.-Z., Z.-k. Shen, M. Wang, W.-j. Gan, R. Bürgmann, P. Molnar, Q. Wang, Z.-j. Niu, J.-z. Sun, J.-c. Wu, Sun Hanrong, and You Xinzhao (2004), Continuous deformation of the Tibetan Plateau from global positioning system data, Geology, 32, 809-812.