[1] Recent studies of the northeastern part of the Tibetan Plateau have called attention to two emerging views of how the Tibetan Plateau has grown. First, deformation in northern Tibet began essentially at the time of collision with India, not 10-20 Myr later as might be expected if the locus of activity migrated northward as India penetrated the rest of Eurasia. Thus, the north-south dimensions of the Tibetan Plateau were set mainly by differences in lithospheric strength, with strong lithosphere beneath India and the Tarim and Qaidam basins steadily encroaching on one another as the region between them, the present-day Tibetan Plateau, deformed, and its north-south dimension became narrower. Second, abundant evidence calls for acceleration of deformation, including the formation of new faults, in northeastern Tibet since~15 Ma and a less precisely dated change in orientation of crustal shortening since~20 Ma. This reorientation of crustal shortening and roughly concurrent outward growth of high terrain, which swings from NNE-SSW in northern Tibet to more NE-SW and even ENE-WSW in the easternmost part of northeastern Tibet, are likely to be, in part, a consequence of crustal thickening within the high Tibetan Plateau reaching a limit, and the locus of continued shortening then migrating to the northeastern and eastern flanks. These changes in rates and orientation also could result from removal of some or all mantle lithosphere and increased gravitational potential energy per unit area and from a weakening of crustal material so that it could flow in response to pressure gradients set by evolving differences in elevation.

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[1] Based on field investigations, aerial-photo morphological analysis, topographic profiling, and optically stimulated luminescence (OSL) dating of alluvial surfaces, we estimate vertical components of the slip rate along the South Heli Shan thrust fault, which lies on the northern margin of the Hexi Corridor and the northeastern edge of the Tibetan Plateau. The fault consists of three segments with scarp heights ranging from less than 1 m to more than 16 m. OSL dating indicates that most of the alluvial fans cut by fault scarps formed during the transition from the last glacial stage to the present interglacial stage from 19 to~9 ka along southern Heli Shan and from~27 ka to~22 ka along its northern margin. In addition, remnants of older alluvial fan have been abandoned after~67 ka. Scarp heights increase from west to east and reach a maximum of more than 16 m near the eastern end. Using three approaches, we calculate late Quaternary slip rates for each of the three fault segments along the southern margin and the fault on the northern flank. These approaches yield maximum vertical slip rates from 0.18 to 0.2 mm/a for the western segment, 0.3 to 0.43 mm/a for the central segment, 0.36 to 0.53 mm/a for the eastern segment, and 0.21 mm/a for the Wutongjing Fault, which lies on the north side of the Heli Shan. For a range of likely fault dips, these correspond to 0.1-0.2 mm/a of average horizontal shortening for the western segment, and increase to 0.4-0.5 mm/a across the eastern segment of the southern Heli Shan Fault. Combining the height of the eastern parts of the Heli Shan (Daqing Peak) above the Hei He (a major river that incised the western end of the range) and the vertical component of the slip rate of the eastern segment, we suggest that the Heli Shan was uplifted by motion on the South Heli Shan Fault beginning sometime between 1 and 4 Ma, most likely since~2 Ma. This age suggests that the Tibetan Plateau continues to grow northeastward across the Hexi Corridor.

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Significance The Songpan-Ganzi terrane lies in the central-east of the Tibetan Plateau, which was considered a stable block in some tectonic models. Its deformation mode is of crucial importance for understanding the evolutionary history and seismic hazard of the plateau. The recent Maduo earthquake occurred inside the terrane. We resolve a bilateral rupture process with distinct super- and subshear rupture modes for this event. We also find that pervasive folding structures that are aligned by shear deformation in the current Songpan-Ganzi terrane are responsible for the seismic wave anisotropy and shear strain orientation in its upper crust. Its deformation mode can be classified as distributed simple shear, which receives shear loads from side walls and produces internal earthquakes.

GPS measurements from sites within the Tibetan Plateau show not only east‐southeast‐west‐northwest extension but also, more importantly, horizontal dilation throughout the interior of the plateau. Assuming conservation of volume, vertical (thinning) strain rates equal horizontal dilation rates, and they, 8.9 ± 0.8 nanostrain a−1 and 7.4 ± 1.2 nanostrain a−1 in northern and southern Tibet, and 12.0 ± 3.2 nanostrain a−1 in its southwestern part, suggest no measureable difference. Principal extensional strain rates also are similar in magnitude and orientation. If crustal thinning began at 10–15 Ma and the current rates of horizontal dilation applied both to the entire crust and to that period, the crust should have thinned by 5.5–8.5 km. If isostatic equilibrium applied, the mean elevation of the plateau would have dropped ~1 km. The similar rates for northern, southern, and southwestern Tibet suggest that the processes dictating crustal extension, normal faulting, and crustal thinning in the three regions differ little from one another.

We constrain the slip rate for the frontal thrust of the Qilian Shan (north-eastern Tibet) by combining structural investigations, satellite imagery, topographic profiling, and 10 Be exposure dating. We surveyed two terrace levels, and from each, we took 6-7 samples in profiles dug to depths of 2 m. These constrain inheritance and determine the precise ages of abandonment of the terraces: 29.9 ± 7.8 ka for the upper terrace and 16.3 ± 4.4 ka for the lower one. Topographic profiles with a determination of burial of the footwall by sediment yield offsets of the surfaces of 96.4 ± 4.4 and 40.1 ± 2.8 m. The average vertical rate is 2.8 ± 1.3 mm a )1 with a horizontal slip rate of 2.5 mm a )1 . This rate is higher than those determined farther north on similar structures, but is consistent with the GPS velocity field, and accounts for roughly half of the geodetic shortening across the Qilian Shan.

Reconstruction of the along‐fault slip distribution provides an insight into the long‐term rupture patterns of a fault, thereby enabling more accurate assessment of its future behavior. The increasing wealth of high‐resolution topographic data, such as Light Detection and Ranging and photogrammetric digital elevation models, allows us to better constrain the slip distribution, thus greatly improving our understanding of fault behavior. The South Heli Shan Fault is a major active fault on the northeastern margin of the Tibetan Plateau. In this study, we built a 2 m resolution digital elevation model of the South Heli Shan Fault based on high‐resolution GeoEye‐1 stereo satellite imagery and then measured 302 vertical displacements along the fault, which increased the measurement density of previous field surveys by a factor of nearly 5. The cumulative displacements show an asymmetric distribution along the fault, comprising three major segments. An increasing trend from west to east indicates that the fault has likely propagated westward over its lifetime. The topographic relief of Heli Shan shows an asymmetry similar to the measured cumulative slip distribution, suggesting that the uplift of Heli Shan may result mainly from the long‐term activity of the South Heli Shan Fault. Furthermore, the cumulative displacements divide into discrete clusters along the fault, indicating that the fault has ruptured in several large earthquakes. By constraining the slip‐length distribution of each rupture, we found that the events do not support a characteristic recurrence model for the fault.