Zhonghai Wu

The Jiali Fault Zone is one of the key active tectonic structures along the southeastern margin of the Tibetan Plateau and has been widely regarded as the southern boundary structure accommodating the lateral extrusion and eastward escape of the Qiangtang and Sichuan–Yunnan blocks. Assessing its Quaternary activity is important for understanding the tectonic evolution and deformation partitioning of southeastern Tibet. This study focuses on the Yi ong–Zayu segment of the Jiali Fault Zone, using high-resolution stereo imagery from the GF-7 satellite. The ERDAS dense image matching method was applied to generate a dense point cloud and a 0.8 m high-resolution digital surface model. Combining regional remote sensing image interpretation with field surveys, we characterize the geomorphic expression and Quaternary deformation of the Yi ong–Zayu segment. The results show no significant surface displacement along the fault. The alluvial fans are largely preserved, and there are no continuous, co-directional offsets along the tributary channels or river systems. In particular, clear evidence for Quaternary right-lateral strike-slip displacement is absent. Instead, localized normal faults with NW–SE to approximately E–W strikes occur in limited areas. This study focuses on the Yi ong–Zayu segment of the Jiali Fault Zone, using high-resolution stereo imagery from the GF-7 satellite. The ERDAS dense image matching method was applied to generate a dense point cloud and a 0.8 m high-resolution digital surface model. Combining regional remote sensing image interpretation with field surveys, we characterize the geomorphic expression and Qua-ternary deformation of the Yi ong–Zayu segment. The results show no significant surface displacement along the fault. The alluvial fans are largely preserved, and there are no continuous, co-directional offsets along the tributary channels or river systems. In particular, clear evidence for Quaternary right-lateral strike-slip displacement is absent. Instead, localized normal faults with NW–SE to approximately E–W strikes occur in limited areas. These findings indicate that the Yi ong–Zayu segment experienced limited Quaternary deformation and has not functioned as a major boundary strike-slip fault since the Quaternary. Instead, it has been influenced by the rotational extrusion of the southeastern Tibetan Plateau, exhibiting characteristics of regional extensional tectonic activity. The present-day deformation is consistent with a rotation–extrusion model, in which crustal material undergoes clockwise rotation around the eastern Himalayan syntaxis and gradually transfers southeastward toward the Sichuan–Yunnan region due to the obstruction of the rigid Sichuan Basin.

Sand liquefaction is a major secondary hazard following strong earthquakes, often causing lateral spreading, surface settlement, and sand volcanoes that lead to significant structural damage and economic losses. This study investigates sand liquefaction phenomena induced by the MW 7.1 Dingri earthquake in Tibet on January 7, 2025, aiming to reveal its spatial distribution and dynamic evolution. Using field surveys, drone imagery, remote sensing interpretation, and drilling data, the study identifies three main liquefaction zones: the southern Pengqu River valley, the area near Dingmu Co Lake, and the southeastern side of Kongmo Co Lake. Groundwater depths in the affected basin ranged from 5.6 to 9.0 meters, closely aligning with local river and lake water levels. Surface damage was dominated by lateral spreading and sand volcanoes. Field evidence and stress analysis suggest a multi-phase evolution: under tectonic stress and gravity, tensile fractures form; seismic vibration triggers liquefaction, with pore fluid and sand being expelled through fractures. On gentle slopes, lateral spreading occurs as surface blocks slide and collide, generating additional fractures through compression, from which sand volcanoes erupt—often aligned linearly. This research offers critical insights into the mechanics of earthquake-induced sand liquefaction on the Tibetan Plateau and provides a foundation for future hazard assessment and mitigation efforts in seismically active, high-altitude regions.

The Chenghai Fault Zone is a major active intrablock structure within the Sichuan–Yunnan Block at the southeastern margin of the Tibetan Plateau and exhibits pronounced along-strike kinematic segmentation. However, the Quaternary left-lateral slip rate of its central Qina segment remains poorly constrained. Here, we integrate field investigations, remote-sensing geomorphic mapping, UAV photogrammetry, and U-series dating to investigate the fault-offset Qiaonan paleolandslide along the Jinjiang Fault. The Qina segment consists mainly of the NNE-striking Qina and Jinjiang faults, which together form an overall left-stepping fault system dominated by left-lateral strike-slip motion. Geomorphic restoration of well-preserved landslide margins using high-resolution UAV-derived orthophotos and digital surface models indicates a cumulative left-lateral displacement of approximately 100 m. Independent DEM-based restoration yields a horizontal displacement of ~97 m, providing a consistent estimate of the fault offset. U-series dating of secondary carbonate cement within the landslide deposit yields a ^230Th–U age of 257.7 ± 3.2 ka. Because the dated carbonate precipitated after landslide emplacement, this age provides only a minimum-age constraint on the paleolandslide. Consequently, the calculated apparent left-lateral slip rate of ~0.39–0.47 mm/yr should be regarded as an upper-bound estimate rather than a precisely determined slip rate for the Jinjiang Fault. The Jinjiang Fault also left-laterally offsets the Jinsha River by ~3.04–3.25 km. Assuming that this displacement began to accumulate with the initiation of the Dali faulted-basin system at ca. 7.6 Ma, the corresponding long-term average slip rate is ~0.40–0.43 mm/yr. However, this estimate depends on an assumed fault-initiation age and therefore represents an end-member long-term average. When considered together with previous interpretations of possible fault-activity migration within the Chenghai Fault Zone, the Quaternary upper-bound rate is compatible with, but does not demonstrate, a reduction in the left-lateral strike-slip component during the Late Cenozoic. Such temporal variations may reflect changes in deformation partitioning among intrablock faults within the Dali faulted-basin system, although this interpretation remains tentative and requires additional chronological and slip-rate constraints. Our results demonstrate the potential of fault-offset paleolandslides to provide valuable geomorphic and chronological constraints on the Quaternary behavior of slowly slipping intrablock faults, while highlighting the importance of independent chronological control for resolving long-term variations in fault slip.

Sand liquefaction is a major secondary hazard following strong earthquakes, often causing lateral spreading, surface settlement, and sand volcanoes that lead to significant structural damage and economic losses. This study investigates sand liquefaction phenomena induced by the MW 7.1 Dingri earthquake in Tibet on January 7, 2025, aiming to reveal its spatial distribution and dynamic evolution. Using field surveys, drone imagery, remote sensing interpretation, and drilling data, the study identifies three main liquefaction zones: the southern Pengqu River valley, the area near Dingmu Co Lake, and the southeastern side of Kongmo Co Lake. Groundwater depths in the affected basin ranged from 5.6 to 9.0 meters, closely aligning with local river and lake water levels. Surface damage was dominated by lateral spreading and sand volcanoes. Field evidence and stress analysis suggest a multi-phase evolution: under tectonic stress and gravity, tensile fractures form; seismic vibration triggers liquefaction, with pore fluid and sand being expelled through fractures. On gentle slopes, lateral spreading occurs as surface blocks slide and collide, generating additional fractures through compression, from which sand volcanoes erupt—often aligned linearly. This research offers critical insights into the mechanics of earthquake-induced sand liquefaction on the Tibetan Plateau and provides a foundation for future hazard assessment and mitigation efforts in seismically active, high-altitude regions.

How the southeastern margin of the Tibetan Plateau accommodates east- to southeastward extrusion of plateau material remains a long-standing and debated issue. The Chenghai Fault Zone, a major left-lateral strike-slip fault within the Dali–Lijiang fault system, plays an important role in accommodating Late Cenozoic crustal extrusion in this region. Here we focus on the Zhoucheng–Qingshui Fault, the western branch of the Chenghai Fault Zone, and document its geometry and kinematics through integrated remote-sensing interpretation, 1:50,000-scale active tectonic mapping, optically stimulated luminescence dating, and measurements of displaced geomorphic markers. We further evaluate fault activity migration and estimate cumulative displacement and slip rates for the Zhoucheng–Qingshui Fault and other branches of the Chenghai Fault Zone. Our results suggest possible redistribution of fault activity between the western and eastern branches of the Chenghai Fault Zone. The Zhoucheng–Qingshui Fault was strongly active before the Middle Pleistocene, but its activity has markedly weakened since the Late Pleistocene. Although this fault preserves larger cumulative displacement than the main Chenghai Fault strand, the Binchuan and Shangcang–Yupeng faults in the southeastern part of the fault zone currently show stronger activity. This contrast implies possible eastward migration of activity in the southern segment, whereas the northern segment appears to show an opposite migration polarity. We propose that this pattern reflects internal strain redistribution within the Chenghai Fault Zone. Clockwise rotation of crustal blocks along the southeastern Tibetan Plateau may have generated contrasting releasing and restraining domains, promoting strain localization within releasing domains. This migration pattern suggests that crustal extrusion in southeastern Tibet is strongly modulated by block rotation.

In southern Tibet, tectonic extension has created north–south rift systems that host hydrothermal zones with episodic silica sinter and travertine deposition. Earlier researchers usually attributed these deposits to hydrothermal activity driven by regional tectonics. However, the timing of deposition and its possible climatic controls remain poorly constrained. In this study, we dated six samples from the Targejia geothermal field and the Xiakangjian hot spring area using electron spin resonance (ESR), and evaluated ESR signal stability, dose response, and irradiation effects to assess age reliability. The new ages range from 209 to 49 kyr. When combined with 108 published ages, they indicate repeated sinter and travertine formation over the past 720 kyr. The dated deposits are concentrated in several intervals, especially during the last 100 kyr, and some age clusters occur near warm and humid stages. These patterns suggest that tectonics controlled where hydrothermal systems developed, whereas climate-related changes in recharge, meltwater supply, permafrost thaw, and water–rock interaction may have affected when deposition was more active. Because the compiled ages come from different methods and have uneven uncertainties, this climate link remains provisional and needs testing with additional samples dated by consistent protocols.

《地球科学》(ISSN 1000-2383;CN42-1874/P) (原刊名《地球科学——中国地质大学学报》ISSN 1000-2383;CN42-1233/P)，创刊于1957年，是由教育部主管、中国地质大学主办的综合性地学学术理论期刊，月刊，2015年改名为《地球科学》,她以反映中国地质大学教学与科研最新的、高水平的基础地质、应用地质、资源与环境地质及地学工程技术研究成果为主要任务。

《地球科学》(ISSN 1000-2383;CN42-1874/P) (原刊名《地球科学——中国地质大学学报》ISSN 1000-2383;CN42-1233/P)，创刊于1957年，是由教育部主管、中国地质大学主办的综合性地学学术理论期刊，月刊，2015年改名为《地球科学》,她以反映中国地质大学教学与科研最新的、高水平的基础地质、应用地质、资源与环境地质及地学工程技术研究成果为主要任务。

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.

Although geomorphic evidence and shallow geometry of active faults are significant for the understanding and assessing of fault activity and seismic hazards, it is challenging to acquire high-resolution topographic data and shallow geometry of the Yushu fault by conventional methods. Here, we present a case study to reconstruct the detailed surficial and subsurface geometry of the Yushu fault using terrestrial laser scanning (TLS), multi-frequency ground penetrating radar (GPR) and trenching. TLS was suitable for measuring the high-resolution three-dimensional (3D) topographic data of the fault. GPR surveys with different frequency antennas (25 MHz, 100 MHz, 250 MHz and 500 MHz) were conducted to image the shallow geometry of active faults at different depths and spatial resolutions. The typical groove landscape, parallel to surface traces of the fault, was clearly observed on the TLS-derived data. A ~40 m width narrow fault system and three faults were identified on the different frequency GPR profiles. Furthermore, faults F₁ and F₂ were supposed to be boundary faults but were sinistral-lateral strike-slip faults with a normal component, while fault F₃ was inferred as the secondary fault. The western trench section, despite the limited investigation depth (~2 m), was well consistent with the 500 MHz GPR result, especially in the location of fault F₂. Finally, a 3D surficial and subsurface model was established from the TLS-derived data and GPR data offering multi-sensor and multi-view spatial data to characterize and understand the fault’s kinematics and characteristics. In addition, the shallow geometry of the fault on the GPR results would be better interpreted with the help of the corresponding surficial data. The study results demonstrate that a combination of TLS, multi-frequency GPRs and trenching can be successfully used for reconstructing a detailed surficial and subsurface geometry of the Yushu fault. It will play an increasing role in comprehensive understanding and assessing fault behavior and seismic hazards, especially on the Tibetan Plateau and the adjacent area.