HR: 0800h
AN: T11C-1276    [Abstracts]
TI: Three-dimensional Mechanical Modeling of the GPS Velocity Field around the Northeastern Tibet and Surrounding Region
AU: * He, J
EM: jkhe@mail.igcas.ac.cn
AF: Jiankun He, Institute of Geology and Geophysics, Chinese Academy of Sciences, Chaoyang District,, Beijing, 100029 China
AU: Li, Y
EM: liyx@public.tpt.tj.cn
AF: Yanxing Li, First Crustal Deformation Monitoring Center, China Seismological Bureau, Tianjing, 300180 China
AU: Teng, C
AF: Jiankun He, Institute of Geology and Geophysics, Chinese Academy of Sciences, Chaoyang District,, Beijing, 100029 China
AB: The northeastern Tibet and surrounding region is an intense active tectonic area with great potential of strong earthquakes. Active tectonics is featured mainly by left-lateral transpressive deformation along the Qilian Shan and right-lateral transtensional deformation between the Alashan and the Ordos blocks out of the Tibet. This region gives a good example to investigate how the strain rate is partitioning around the plateau edge and how the remainder strain rate of Tibetan deformation is propagating towards the interior of the Eurasia plate with relative to the Indian-Eurasia convergence. In this study, we use three-dimensional mechanical models incorporated the main active faults as Coulomb-type friction zones to simulate the surface velocity field as dense GPS data shown. We simplify the rheological structure of lithosphere as a frictional upper crust underlying with the viscoelastic lower crust with available heat flow. Topographic loading on the model surface and hydrostatic pressure on the model base are added. The models are solved with Adeli finite element code, and modeled velocities are checked using the chi-square merit function with dense GPS data. We test the model with fault friction ranged from 0.4 to 0.01 on different major fault systems. Results show: (1) with a relatively high fault friction ~0.4-0.2, the northeastern Tibet and surrounding region could behave like diffusive deformation, but the modeled velocities and the strain rate seem unable to fit the GPS data and the seismic data, respectively. (2) To best fit the GPS data, a relatively low fault friction ~0.05-0.02 is needed. At this condition, the deformation is localized mainly around the Qilian Shan in northeastern Tibet and between the Alashan and the Ordos blocks out of the Tibet, consistent with the active tectonics and the strong earthquake distribution. (3) Changes of the fault friction out of the Tibet seem to affect the modeled velocity quite small, suggesting that the northeastern Tibetan boundary might be more sensitive to cause the present-day deformation as the dense GPS indicated. Fifteen model experiments give some first-order results. We conclude: (1) The northeastern Tibetan boundary may presently represent as a mechanically weakness zone at least in the upper crust relative to its surrounding regions. (2) This weakness boundary absorbs a significant amount of crust deformation relative to the Indian-Eurasia convergence from oblique thrusting on its western segment to nearly pure strike slipping on its eastern segment. (3) Slip partitioning from oblique thrusting to purely strike slipping from west to east associated with the unique fault geometry of the northeastern Tibetan edge may play an important role on active extension between the Alashan and the Ordos blocks. (4) The present-day surface motion of the northeastern Tibet and surrounding region reflects the active tectonics more likely as rigid-block deformation, especially out of the northeastern Tibetan plateau.
DE: 8020 Mechanics
DE: 8107 Continental neotectonics
DE: 8158 Plate motions--present and recent (3040)
DE: 8159 Rheology--crust and lithosphere
DE: 1208 Crustal movements--intraplate (8110)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting