Nailing down the slip rate of the Altyn Tagh fault (original) (raw)
Related papers
Geology, 2009
For more than two decades the slip rate along the active, left-slip Altyn Tagh fault of northwestern Tibet has been disputed, with millennial rates reported to be as much as three times faster than those determined geodetically. This problem is signifi cant because the total offset, plate-boundary length, and age of the Altyn Tagh fault make it the most important single structure accommodating India-Asia convergence north of the Himalayas. Here we show that the central Altyn Tagh fault slipped at only 14-9 mm/a over the past 4-6 ka by tightly bracketing the age of a displaced fl uvial terrace riser at Yuemake ). This result contradicts previous latest Quaternary rates and is consistent with those derived from geodetic, paleoseismic, and geologic measurements, and thus resolves the long-standing dispute over the latest Quaternary slip rate along the longest active strike-slip fault in Tibet.
Crustal deformation along the Altyn Tagh fault system, western China, from GPS
Journal of Geophysical Research, 2001
We collected GPS data from the southern Tarim basin, the Qaidam basin, and the western Kunlun Shan region between 1993 and 1998 to determine crustal deformation along the Altyn Tagh fault system at the northern margin of the Tibetan plateau. We conclude from these data that the Altyn Tagh is a left-lateral strike slip fault with a current slip rate of ˜9 mm/yr, in sharp contrast with geological estimates of 20-30 mm/yr. This contrast poses an enigma: because the GPS data cover a wider region than the geologic data, they might be expected to reveal somewhat more slip. We also find that the Tarim and Qaidam basins behave as rigid blocks within the uncertainty of our measurements, rotating clockwise at a rate of ˜11 and ˜4.5 nrad/yr, respectively, with respect to the Eurasia plate. The rotation of the Tarim basin causes convergence across the Tian Shan, increasing progressively westward from ˜6 mm/yr at 87°E to ˜18 mm/yr at 77°E. Our data and other GPS data suggest that the Indo-Asia collision is mainly accommodated by crustal shortening along the main Himalayan thrust system (˜53%) and the Tian Shan contractional belt (˜19%). Eastward extrusion of the Tibetan plateau along the Altyn Tagh and Kunlun faults accommodates only ˜23% of the Indo-Asia convergence.
Geodetic Observations of Shallow Creep on the Laohushan‐Haiyuan Fault, Northeastern Tibet
Journal of Geophysical Research: Solid Earth, 2021
We investigated the spatial distribution of aseismic creep on the Laohushan‐Haiyuan fault using Global Positioning System (GPS) data (1999–2017) and Interferometric Synthetic Aperture Radar (InSAR) data (2003–2010). Comparisons among GPS, InSAR line‐of‐sight (LOS) rates, and leveling show that neither leveling nor GPS vertical velocities can fit the vertical signal mapped into the LOS, implying either complicated vertical crustal deformation in northeastern Tibet and/or complex error structures in the InSAR data. Thus, we combined horizontal GPS with high‐pass filtered InSAR data to produce a continuous LOS rate map crossing the fault. Our geodetic data reveal three creep sections along the fault. Both the restored LOS data and decomposed ascending and descending InSAR data highlight the fact that vertical motion can cause an overestimation of creep rate; we obtained a refined creep rate of 2.5 ± 0.4 mm/a on the Laohushan fault. We further identified a 10 km‐long, ∼3–5 mm/a creep se...
Slip rates of the Altyn Tagh, Kunlun and Karakorum faults (Tibet) from 3D mechanical modeling
Earth and Planetary Science Letters, 2008
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.
Island Arc, 2011
The question of whether millennial-scale geological slip rates are consistent with decade-scale geodetic slip rates is of great importance in evaluating the nature of continental deformation within the Tibetan Plateau. We determined the time-averaged slip rate of the Sulu He segment of the Altyn Tagh Fault, near Changma in Gansu Province, China, based on geomorphic analysis, remote sensing data, and cosmogenic 10 Be surface-exposure age dating. Quaternary alluvial fan deposits in the study area (Qf1, Qf2, Qf3) are displaced by left-lateral movement along the Altyn Tagh Fault. Because of the large accumulated displacement of these fans, some of them have become disconnected from the fan apexes that are directly linked to the debris-source areas in the piedmont of the Qilian Shan to the south. The total minimum offsets are estimated to be about 429 Ϯ 41 m for Qf1, about 130 Ϯ 10 m for Qf2, and 32 Ϯ 1 m for Qf3. The 10 Be surface-exposure ages obtained for Qf1 and Qf2 are 100-112 ka and 31-43 ka, respectively. Accordingly, the slip rate since the period of Qf1 and Qf2 depositions is calculated to have been about 3.7 mm/yr.
Geosphere
High-resolution topographic or imagery data effectively reveal geomorphic offsets along faults that can be used to deduce slipper event of recurrent rupture events. Documentation of patterns of geomorphic offsets is scarce on faults that undergo both creep and coseismic rupture. In this paper, we used newly acquired high-resolution light detection and ranging (LiDAR) data to compile geomorphic offsets along the Laohu Shan section of the Haiyuan fault, in the northern Tibetan Plateau, where interferometric synthetic aperture radar (InSAR) data suggest creep presently occurs over a 35-km-long stretch at a rate comparable to the long-term geological slip rate, despite evidence for past coseismic fault rupture. Numerous offset gullies identified using the LiDAR data yield a range of offsets from less than 2 m up to 50 m. These offsets have well-separated probability density peaks at 2-3 m, ~7 m, and ~14 m, with increments of 2-3 m, 4-6 m, and 5-7 m. The sequence of paleoseismic events along the Laohu Shan section indicates that the gullies with offsets of 2-3 m are likely related to surface rupture of the historical 1888 Jingtai earthquake, plus subsequent creep. Offset increments of 4-6 m and 5-7 m may represent coseismic slip in past paleoseismic events plus creep during the interseismic period. The creeping Laohu Shan section preserves numerous discrete cumulative offsets, with an offset clustering pattern indistinguishable from that on a locked fault with recurrent earthquake ruptures. Association of offset increments with known paleoseismic events yields a slip rate of 3-5 mm/yr during the past 200 years, roughly similar to the ~5 mm/yr creep rate. If the ratio of surface creep rate to the total fault slip rate has been continuous, then seismic moment release by brittle ruptures, and thus seismic hazard, would be much reduced on the Laohu Shan section of the Haiyuan fault. Alternatively, the current high creep rate may be a transient phenomenon, perhaps after slip following the 2000 Jingtai Mw 5.6 earthquake or in response to the adjacent 1920 M ~8 Haiyuan earthquake rupture that terminated immediately to the east.
Journal of Geophysical Research, 2005
1] Millennial slip rates have been determined for the Altyn Tagh fault (ATF) at three sites near Aksay ($94°E) in northeastern Tibet by dating fluvial channels and terrace riser offsets with radiocarbon and 10 Be-26 Al surface exposure dating. Up to nine main surfaces are defined on the basis of morphology, elevation, and dating. The abandonment age of some surfaces is constrained by radiocarbon dating, which typically coincides with the youngest cosmogenic ages for a particular surface. Older surface exposure ages are taken to represent the duration of terrace emplacement. Cumulative offsets range from 20 to 260 m and fall in distinct groups, indicative of climatically modulated regional landscape formation. Most samples are younger than 14kaandpostdatetheLastGlacialMaximum.TheendoftheearlyHoloceneoptimummarkstheboundarybetweentheagesofthetwomainterracelevelsat5−6ka.AtthislongitudetheATFisdividedintoanorthernandsouthernbranch.ThenorthernATFshouldthusyieldaminimumratefortheATFsystem.Sliprateestimatesusingtheabandonmentageoftheoverlyinglevelforfillterracesorchannelsandtheemplacementoftheunderlyinglevelforstrathterracesgive30consistentresults,yieldinganaverageHolocenerateof17.8±3.6mm/yr.Itis14 ka and postdate the Last Glacial Maximum. The end of the early Holocene optimum marks the boundary between the ages of the two main terrace levels at 5-6 ka. At this longitude the ATF is divided into a northern and southern branch. The northern ATF should thus yield a minimum rate for the ATF system. Slip rate estimates using the abandonment age of the overlying level for fill terraces or channels and the emplacement of the underlying level for strath terraces give 30 consistent results, yielding an average Holocene rate of 17.8 ± 3.6 mm/yr. It is 14kaandpostdatetheLastGlacialMaximum.TheendoftheearlyHoloceneoptimummarkstheboundarybetweentheagesofthetwomainterracelevelsat5−6ka.AtthislongitudetheATFisdividedintoanorthernandsouthernbranch.ThenorthernATFshouldthusyieldaminimumratefortheATFsystem.Sliprateestimatesusingtheabandonmentageoftheoverlyinglevelforfillterracesorchannelsandtheemplacementoftheunderlyinglevelforstrathterracesgive30consistentresults,yieldinganaverageHolocenerateof17.8±3.6mm/yr.Itis9 mm/yr less than the long-term rate obtained near Tura at $87°E (26.9 ± 6.9 mm/yr), in keeping with the inference of an eastward decreasing rate on the ATF, due to increased thrusting to the south. However, it remains twice the rate determined by GPS studies. Citation: Mériaux, A.-S., et al. (2005), The Aksay segment of the northern Altyn Tagh fault: Tectonic geomorphology, landscape evolution, and Holocene slip rate,
Reconciliation of the Early Slip History of the Altyn Tagh Fault, Northern Tibetan
Open Journal of Geology
Whether the Altyn Tagh fault (ATF) had been extended beyond its current northeastern tip and linked with strike-slip faults in East Asia is a key to understanding the timing and mechanisms of crustal deformation in the northern Tibetan Plateau. We present Late Cretaceous dextral movement affected by Okhotomorsk Block-East Asia collision and a larger sinistral offset since Late Eocene along the ATF based on the provenance analysis of western Jiuxi Basin. Moreover, currently available estimates of offset based on displaced Paleozoic and Jurassic rocks could not represent the maximum offset due to late Cretaceous dextral offset.
Characterizing the 700 km wide system of active faults on the Shan Plateau, southeast of the eastern Himalayan syntaxis, is critical to understanding the geodynamics and seismic hazard of the large region that straddles neighboring China, Myanmar, Thailand, Laos, and Vietnam. Here we evaluate the fault styles and slip rates over multi-timescales, reanalyze previously published short-term Global Positioning System (GPS) velocities, and evaluate slip-rate gradients to interpret the regional kinematics and geodynamics that drive the crustal motion. Relative to the Sunda plate, GPS velocities across the Shan Plateau define a broad arcuate tongue-like crustal motion with a progressively northwestward increase in sinistral shear over a distance of ~700 km followed by a decrease over the final ~100 km to the syntaxis. The cumulative GPS slip rate across the entire sinistral-slip fault system on the Shan Plateau is ~12 mm/year. Our observations of the fault geometry, slip rates, and arcuate southwesterly directed tongue-like patterns of GPS velocities across the region suggest that the fault kinematics is characterized by a regional southwestward distributed shear across the Shan Plateau, compared to more block-like rotation and indentation north of the Red River fault. The fault geometry, kinematics, and regional GPS velocities are difficult to reconcile with regional bookshelf faulting between the Red River and Sagaing faults or localized lower crustal channel flows beneath this region. The crustal motion and fault kinematics can be driven by a combination of basal traction of a clockwise, southwestward asthenospheric flow around the eastern Himalayan syntaxis and gravitation or shear-driven indentation from north of the Shan Plateau.