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The margins of the Tibetan Plateau are the most recent evolving part of the orogen, where distributed fault systems accumulate intraplate crustal deformation induced by the Indo-Asian collision, and many great earthquakes occur. Understanding the paleoearthquake history of the faults along the Tibetan margins will increase our knowledge of the process of outward growth of the Tibetan Plateau, seismic hazard assessments, and intraplate earthquake patterns. However, until now, few paleoseismic studies were conducted along the northern Tibetan margin, which hampers our understanding of fault activity and seismic hazards posed to the densely populated cities in the region. In this study, we excavated paleoseismic trenches across the Fodongmiao-Hongyazi fault (FHF) along the northern Tibetan margin. Five Holocene events were documented from five trenches based on OSL and radiocarbon-14 dating of trench horizons and careful analysis of stratigraphy and fault structures. These events are FE5 (9.6–7.7 ka), FE4 (7.6–7.0 ka), FE3 (4.4–3.5 ka), FE2 (3.2–1.8 ka), and the 1609 M 71/ 4 Hongyapu earthquake. The average recurrence interval of the five events is ~2.0 ka. Additionally, combined with morphotectonic features and trench observations, the 1609 Hongyapu earthquake most likely caused the whole fault to rupture with a length of ~95 km. Its moment magnitude was estimated to be 7.2 ± 0.2 based on empirical statistical relationships between the magnitude, surface rupture length, and coseismic offset. • Five events were revealed on the FHF along the northern Tibetan margin since the Holocene. • The earthquake recurrence interval is about 2.0 ka. • The 1609 M 71/ 4 Hongyapu Earthquake ruptured the ~95-km-long FHF. [ABSTRACT FROM AUTHOR]

[Display omitted] • New GPS data in the Eastern Himalayan Syntaxis. • The strike-slip rates of the western and middle segments of the Jiali fault are low. • The eastern segment of the Jiali fault no longer accommodates strike-slip motion. • Decrease in the slip rate of the Jiali fault coincides with new faults emergence. • The eastern segment of the Jiali fault seems to rotate clockwise. Large strike-slip faults play an important role in slip partitioning of the oblique convergence between the Indian plate and the Eurasian plate. The Karakorum-Jiali fault zone (KJFZ) is regarded as the southernmost major fault in the strike-slip faults system of the Tibetan plateau. The significance of the Jiali fault as the southern boundary of the eastward extrusion of the Tibetan plateau remains subject to debate due to the wide disagreements in its strike-slip rate. There is also a huge mismatch between its previously predicted low slip rate and the accommodation of the most significant compression in the frontal Eastern Himalayan Syntaxis. New GPS measurements suggest that the dextral strike-slip rate of the western segment, the middle segment, and the western part of the eastern segment of the Jiali fault is 5.0 ± 0.5 mm/yr, 2.4 ± 0.8 mm/yr, and 3.8 ± 0.9 mm/yr, respectively. As for the eastern segment of the Jiali fault, based on a two-dimensional elastic dislocation model, we search for the optimal solutions of the strike-slip rates along its two branch faults. They no longer accommodate strike-slip motion. But the diffuse active fault zone between the Mishimi and Puqu fault, inferred by the distribution of small earthquakes and systematic geologic mapping, may accommodate the strike slip motion with an estimated rate less than 5 mm/yr. Thus, it is predicted to have taken place the eastern segment. The eastern segment of the Jiali fault appears to have horizontally rotated clockwise around the Namche-Barwa Syntaxis. [ABSTRACT FROM AUTHOR]

(a) Blocks distributed surround the Tibetan Plateau. (b) Active tectonics in the northeastern Tibetan Plateau. The black rectangle within the inset shows the study area. The thick grey line shows the block boundary. Blue arrows show the global positioning system (GPS) velocity with respect to the Eurasian Plate, and the green arrows represent the GPS velocity with respect to GAB. (c) Deformation rates of these faults and folds in the compressional stepover of the eastern ATF. JTF: Jinta Fault, HLF: Helishan Fault, LSF: Longshoushan Fault, NQLF: North Qilian Shan Fault, SS: sinistral strike-slip rate, Sh: shortening rate, V: vertical rate, HLX Fo.: Hongliuxia thrustfold belt, HSG Anti.: Huoshaogou Anticline, NKTF: North Kuantanshan Fault, LJM Anti.: Laojunmiao Anticline, and BYF: Baiyang Fault. [Display omitted] • Shortening rate of the Hongliuxia region was 0.7 ± 0.2 mm/yr in Late Pleistocene. • Hongliuxia region showed more N–S shortening than the W–E strike-slip. • Stepover was formed between the eastern Altyn Tagh fault and Jinta-Nanshan fault. The Altyn Tagh Fault (ATF) and the North Qilian Shan Fault, as the northern margin of the Tibetan Plateau, have always been the focus of attention while developing a propagation model of the plateau. However, rocks in the North Qilian Shan Fault are intensely deformed and understanding the deformation history is difficult. The ATF and North Qilian Shan Fault have propagated into the Hexi Corridor and led to a series of new faults and folds. Based on simple kinematics and insignificant deformations of these new faults and folds, the geological process can be easily understood. The Hongliuxia region, which represents a positive flower structure in the easternmost part of the ATF, is the binding transformation site between the ATF and North Qilian Shan Fault. In this study, the kinematics of the Hongliuxia region was determined based on structural profiling and fault surveys. The shortening rate (0.7 ± 0.2 mm/yr) was estimated from the deformation and 10Be exposure age of fluvial terraces. We found that the ATF might be connected to the Jinta-Nanshan Fault by a compressional stepover on the northern part of the Yumen Basin, which transforms into a series of compressional ridges, including the Hongliuxia thrustfold belt, Huoshaogou Anticline, and North Heishan Fault. We infer that the ATF and the Longshoushan Fault, which serve as boundary faults, might be linked by multiple compressional stepovers. The gradual changes of the striking angles by compressional stepovers indicated the transformation from strike-slip to compressional structures and these changes caused the two boundary faults (ATF and Longshoushan Fault) to jointly undergo crustal deformation associated with the northward propagation of the Tibetan Plateau. This study can advance our understanding of the relationship between ATF and the Qilian Shan thrust fault system. [ABSTRACT FROM AUTHOR]

The ongoing convergence between India and Eurasia apparently is accommodated not merely by crustal shortening in Tibet, instead also by motions along strike slip faults which are usually boundaries between tectonic blocks, especially in the Tibetan Plateau. Quantification of this strike slip faulting is fundamental for understanding the collision between India and Eurasia. Here, we use a variety of geomorphic observations to place constraints on the late Quaternary kinematics and slip rates of the Ganzi–Yushu fault, one of the significant strike-slip faults in eastern Tibet. The Ganzi–Yushu fault is an active, dominantly left-lateral strike-slip structure that can be traced continuously for up to 500 km along the northern boundary of the clockwise-rotating southeastern block of the Tibetan Plateau. We analyse geomorphic evidence for deformation, and calculate the late Quaternary slip rates at four sites along the eastern portion of the fault trace. The latest Quaternary apparent throw rates are variable along strike but are typically ~ 1 mm/a. Rates of strike-slip displacement are likely to be an order of magnitude higher, 8–11 mm/a. Trenching at two locations suggests that the active fault behaviour is dominated by strike-slip faulting and reveals several earthquake events with refined information of timing. The 2010 M w 6.9 Yushu earthquake, which occurred on the northwestern segment of the Ganzi–Yushu fault zone, provides additional evidence for fault activity. These observations agree with GPS-derived estimates, and show that late Quaternary slip rates on the Ganzi–Yushu fault are comparable to those on other major active strike-slip faults in the eastern Tibetan Plateau. [ABSTRACT FROM AUTHOR]