Slip rates of the Altyn Tagh, Kunlun and Karakorum faults (Tibet) from 3D mechanical modeling (original) (raw)
2008, Earth and Planetary Science Letters
We use 3-D mechanical modeling representing faults as planar surfaces with frictional properties that obey Coulomb-failure process to explore the long-term slip rates of the Altyn Tagh fault and Kunlun faults in the north Tibetan plateau. Crustal rheology is simplified as an elastoplastic upper crust and a viscoelastic lower crust. Far-field GPS velocities and late Quaternary fault slip rates are used to constrain the model results. Rheological tests show that effective fault friction lower than 0.1-0.08 leads to high slip rates that fit with geologically and geodetically determined slip rates of the Kunlun fault (10-11.7 ± 1.5 mm/yr). Meanwhile, the modeled Altyn Tagh fault reaches slip rates~13.7 mm/yr to~17.8 mm/yr in its central portion, between ranges of the geological slip rates. Associated with high slip rates, our model predicts that central Tibet (~84°E-95°E) from the Altyn Tagh fault to the north of the Himalayan arc accommodates north-south shortening and east-west extension rates of~10-12 mm/yr and~8-10 mm/yr, respectively. We also question the widely accepted idea that interseismic strain is driven at the base of the seismogenic zone by a screw dislocation. If this assumption fails, the presented model implies that interseismic strain around large strikeslip faults could be distributed in a much broader way if the lithosphere deforms as a thin elastic plate rather than an elastic half-space with an embedded dislocation. If this distributed deformation is ignored, and the instantaneous surface deformation field modeled as that resulting from slip on a dislocation below a specified depth embedded in an elastic half-space, the estimated slip rate will inevitably be lower than the true long-term slip rate. This appears to explain why geodetic slip rates proposed for the Altyn Tagh fault (5-10 mm/yr) are lower than some of the geological slip rates.
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2004
The dextral Karakoram fault zone, that bounds the southwestern margin of Tibet, is widely regarded as one of the major strike-slip faults that accommodates the eastward extrusion of the thickened crust of Tibet. In northern Ladakh, the Karakoram fault bounds the Pangong transpressional zone, with the active fault trace following the eastern margin of the range. Exhumation within this zone reveals mylonites that have absorbed much of the deformation along the fault. Two sets of dikes are evident within the main fault strand that bounds the transpressional zone. Whilst one dike set is concordant with the dominant foliation and shows mylonitic fabric, the youngest dike set are less deformed and cross-cut the shear zone fabric. Using U-Pb ID-TIMS data from five shear zone samples deformed by differing degrees, we infer that fault initiation occurred between 15.68F0.52 and 13.73F0.28 Ma. Since absolute offset is difficult to determine we couple these age constraints with suggested minimum and maximum offsets of the Baltoro-type granites. The offset range of 40-150 km reveals that the Karakoram fault has a longterm average slip-rate in the range 2.7-10.2 mm/year, the lower rate being compatible with GPS, InSAR and cosmogenic data for the fault. The small range of offset and low slip-rates do not support rapid, large-scale extrusion of Tibet along lithosphericscale faults and strengthens the argument that Tibet does not behave in a rigid, plate-like, manner.
Nailing down the slip rate of the Altyn Tagh fault
Geophysical Research Letters, 2013
1] Previous estimates of the geodetic and geologic slip rates of the 1500 km long Altyn Tagh fault bordering the northern edge of the Tibetan plateau vary by a factor of five. Proposed reasons for these discrepancies include poor GPS geometry, interpretative errors in terrace morphology, and changes in fault slip rate over time. Here we present results from a new dense GPS array orthogonal to the fault at~86.2°E that indicates a velocity of 9.0 À3.2 / +4.4 mm/yr, in close agreement with geomorphologic estimates at the same location. Our estimated geodetic slip rate is consistent with recent geological slip rates based on terrace offsets. The resulting mean combined geological and geodetic slip rate (9.0 ± 4.0 mm/yr) is remarkably uniform for the central 800 km of the Altyn Tagh fault, significantly lower than early kinematic estimates and consistent with deformation elsewhere in Tibet and central Asia.
The Influence of Gravity on the Displacement Field Produced by Fault Slip
Geophysical Research Letters, 2017
We calculated surface displacements produced by a synthetic megathrust earthquake using two spherical, layered, elastic dislocation models which differ only in that one model accounts for the coupling between elasticity and gravity and the other does not. We show that including gravity perturbs the displacement field differently in the near‐, medium‐, and far‐fields. As a result, slip inversions based on an Earth model without gravity cannot simultaneously fit the near‐, medium‐ and far‐field displacements generated using a forward model including gravity. This suggests that the spatially systematic misfits between observations and dislocation predictions seen in the literature arise, at least in part, because these studies are based on models that neglect gravity. Although the magnitude of the far‐field displacements is small compared to those of the near‐field, our slip inversions show the most improvement when we both up‐weight the far‐field observations and use a physically cons...
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