Understanding the formation of the North Qilian Shan in the NE Tibetan Plateau provides insights into the growth mechanisms of the northern region of the plateau across time. Detrital zircon fission-track (ZFT) analyses of river sediments can provide a comprehensive understanding of the exhumation history during prolonged orogenesis. Here, we applied the detrital thermochronology approach to the Qilian Shan orogenic belt. This work presents the first single-grain detrital ZFT data from river-bed sediments of the upper Hei River catchment in North Qilian Shan. The single ZFT ages are widely distributed between about 1200 Ma and about 40 Ma. These data record the protracted history of the Qilian Shan region from the Neoproterozoic evolution of Rodinia and late Paleozoic amalgamation of Central Asia to the accretion of the Gondwanian blocks during the Meso-Cenozoic era. Strong post-magmatic cooling events occurred in North Qilian Shan at 1200~1000 Ma, corresponding to the assembly of the Rodinia supercontinent. The age population at 800 Ma documents the oceanic spreading in the late Neoproterozoic dismantling of Rodinia. ZFT ages ranging from about 750 Ma to 550 Ma (with age peaks at 723 Ma and 588 Ma) are consistent with the timing of the opening and spreading of the Qilian Ocean. The age peaks at 523 Ma and 450 Ma mark the progressive closure of that ocean ending with the collision of the Qilian block with the Alxa block—North China craton in the Devonian. The Qilian Ocean finally closed in Late Devonian (age peak at 375 Ma). In the late Paleozoic (275 Ma), the subduction of the Paleotethys Ocean led to extensive magmatic activity in the North Qilian Shan. During the Lower Cretaceous (145 Ma), the accretion of the Lhasa block to the south (and potentially the closure of the Mongol-Okhotsk Ocean to the northeast) triggered a renewed tectonic activity in the Qilian Shan. Finally, a poorly defined early Eocene exhumation event (50 Ma) suggests that the NE Tibetan Plateau started to deform nearly synchronously with the onset of the India-Asia collision. This study demonstrates the usefulness of combining modern-river detrital thermo-/geochronological ages and bedrock geochronological ages to understand large-scale orogenic evolution processes.

Active faults are generally defined as faults that have moved in the past and will continue to be active in the future. They are expected to cause deformation and potential disasters if they are localized close to human activities. The definition and classification of active faults are important bases for evaluating the risk. This paper summarizes and compares the history, status, and progress of their definition and classification schemes used in representative countries and regions, as well as in some relevant standards, in active fault mapping, in the construction of spatial databases, and in some other aspects. It is concluded that the current geodynamic setting, existing technical means, geological operability, application purpose, and social acceptability of active faulting hazard in a specific area comprehensively determine the selection of the definition and classification. The key parameter in defining active faults is the time limit. It usually involves four time scales, i.e., Neotectonic (post-Neogene), Quaternary, Late Quaternary, and Holocene. The definition using a short time scale, such as Late Quaternary and Holocene, is usually suitable for the plate boundary zone, which has a high strain rate, but active faults in the intraplate deformation region and stable continental region should be defined with a long time scale, such as the Quaternary and Neotectonics. In addition, the magnitude standard can determine the activity intensity of active faults, which most generally includes three classes, namely, M ≥ 5.0 damaging earthquakes, M ≥ 6.0 strong earthquakes, and M ≥ 6.5 earthquakes that may produce surface displacement or deformation. The M ≥ 5.0 earthquake is generally applicable to regional earthquake prevention and risk mitigation in many countries or regions, but the M ≥ 6.5 earthquake magnitude benchmark is generally used as the standard in rules or regulations regarding active fault avoidance. The most common classification schemes in many countries or regions are based on fault activity, which is reflected mainly by the fault slip rate and fault recurrence interval (FRI), as well as by the last activation time. However, when determining the specific quantitative parameters of the different activity levels of faults, it is necessary to comprehensively consider the differences in activity and ages of the faults in the study region, as well as the amount and validity of existing data for the purpose of classifying different active levels of faults effectively.

The seismic effects in Nyalam, Gyirong, Tingri and Dinggye counties along the southern border of Tibet were investigated during 2–8 May 2015, a week after the great Nepal earthquake along the Main Himalaya Thrust. The intensity was VIII in the region and reached IX at two towns on the Nepal border, resulting in the destruction of 2700 buildings, seriously damaging over 40 000 others, while killing 27 people and injuring 856 in this sparsely populated region. The main geologic effects in this steep rugged region are collapses, landslides, rockfalls, and ground fissures, many of which are reactivations of older land slips. These did great damage to the buildings, roads, and bridges in the region. Most of the effects are along four incised valleys which are controlled by N-trending rifts and contain rivers that pass through the Himalaya Mountains and flow into Nepal; at least two of the larger aftershocks occurred along the normal faults. And, the damage is not related to the faulting of N-trending rifts but rather is distributed along the intensity of Nepal earthquake. Areas weakened by the earthquake pose post-seismic hazards. Another main characteristic of damage is the recurrence of the old landslide and rockfalls. In addition, there is an increased seismic hazard along active N-trending grabens in southern Tibet due to the shift in stress resulting from the thrust movement that caused the Nepal earthquake. NW-trending right-lateral strike-slip faults also may be susceptible to movement. The results of the findings are incorporated in some principle recommendations for the repair and reconstruction after the earthquake.

High-resolution topographic and stratigraphic datasets have been increasing applied in active fault investigation and seismic hazard assessment. There is a need for the comprehensive analysis of active faults on the basis of the correlating geomorphologic features and stratigraphic data. The integration of TLS and GPR was adopted to characterize the 3D geometry of the fault on the Maoyaba segment of Litang fault. The TLS was used to obtain the high-resolution topographic data for establishing the 3D surficial model of the fault. The 2D 250 MHz and 500 MHz GPR profiles were carried out to image the shallow geometry of the fault along four survey lines. In addition, the 3D GPR survey was performed by ten 2D 500 MHz GPR profiles with 1 m spacing. From the 2D and 3D GPR results, a wedge-shaped deformation zone of the electromagnetic wave was clearly found on the GPR profiles, and it was considered to be the main fault zone with a small graben structure. Three faults were identified on the main fault zone, and fault F₁ and F₃ were the boundary faults, while the fault F₂ was the secondary fault. The subsurface geometry of the fault on the GPR interpreted results is consistent with the geomorphologic features of the TLS-derived data, and it indicates that the Maoyaba fault is a typical, normal fault. For reducing the environmental disruption and economic losses, GPR was the most optimal method for detecting the subsurface structures of active faults in the Litang fault with a non-destructive and cost-effective fashion. The 3D surface and subsurface geometry of the fault was interpreted from the integrated data of TLS and GPR. The fusion data also offers the chance for the subsurface structures of active faults on the GPR profiles to be better understood with its corresponding superficial features. The study results demonstrate that the integration of TLS and GPR has the capability to obtain the high-resolution micro geomorphology and shallow geometry of active faults on the Maoyaba segment of the Litang fault, and it also provides a future prospect for the integration of TLS and GPR, and is valuable for active fault investigation and seismic hazard assessment, especially in the Qinghai-Tibet Plateau area.