Yanxiu Shao

Understanding how connected fault segments may rupture sequentially or simultaneously to produce large earthquakes is a fundamental problem in earthquake physics and seismic hazard assessment. Addressing this issue requires integrated constraints on fault geometry, slip behavior, and rupture history across interconnected fault systems. The Subei triple junction along the eastern section of the Altyn Tagh fault, which connects thrust (Danghe Nan Shan thrust) and strike-slip fault segments (Altyn Tagh and Yema-Daxue Shan faults), is an ideal site for investigating such cascading rupture processes. In this study, we excavated three new paleoseismic trenches around the Subei junction, including two across the Danghe Nan Shan thrust and one across the Altyn Tagh fault. Detailed stratigraphic logging, identification of abundant paleoseismic indicators, and dense optical stimulated luminescence (OSL) dating constrain the timing of late Quaternary surface-rupturing earthquakes. Our results indicate that three to four surface-rupturing events occurred at these sites during the Holocene, with overlapping age ranges among the different fault segments. By integrating our new paleoseismic constraints with previously studies, we identify at least one Holocene earthquake that likely involved synchronous rupture of the Altyn Tagh fault, the Yema–Daxue Shan fault, and the Danghe Nan Shan thrust. Multicycle dynamic rupture modeling incorporating fault geometry and long-term slip rates further support such cascading ruptures across the strike-slip and thrust fault network. These results provide rare field-based evidence that large earthquakes on the eastern section of Altyn Tagh fault may involve multiple fault segment ruptures. Our findings highlight the importance of considering fault interactions and cascading rupture scenarios when assessing seismic hazard in complex continental fault systems.

Slip-rate decrease along the eastern Altyn Tagh fault has long been interpreted as due to strain transfer from the strike-slip fault to the sequential thrust splays of the Qilian Shan. While the 2D kinematics of such strain transfer is now becoming well documented thanks to numerous field studies as well as an increase in geodetic and InSAR data, how the structures connect, interact during large rupturing events and evolve on the long-term is not well known. We focus on the Danghe Nan Shan thrust, a major splay of the Altyn Tagh fault (ATF), at one of these complex fault junctions. Near Subei, the western Danghe Nan Shan thrust comprises two left-stepping faults outlined by fault scarps in front of folded and uplifted alluvial fans and terraces. Age constraints of the accumulated slip of four terraces standing 7–60 m above the present stream bed yield shortening and vertical uplift rates of 0.5 ± 0.1 and 1.1 ± 0.3 mm/yr, respectively, over the last 130 ka on one of the thrust. Overall, about 1-1.4 mm/yr uplift and shortening rates are determined, in agreement with late Miocene long-term exhumation rate estimates. We emphasize the need for precise long-term slip rate determination and understanding the three-dimensional structures of fault connections to evaluate strain transfer between faults and related seismic hazard on these complex fault systems.

The mechanisms of stress transfer across continental plate interiors during continent-continent collision, as well as the timing and the style of far-field fault system responses, remain poorly constrained. The collision between the Indian subcontinent and what is now Tibet began in the Eocene and has involved still on-going north-south convergence throughout southern Tibet and the Himalayas, providing an exceptional natural laboratory for studying continental collision processes.The Altyn Tagh Fault (ATF), a >1600-km-long lithospheric-scale strike-slip fault marking the northern boundary of the Tibetan Plateau, is a key structure for investigating how deformation propagated following the India-Asia collision. However, the timing of its (sinistral?) initiation remains uncertain, with proposed ages ranging from the Mesozoic to the Miocene. These uncertainties largely reflect the involved structural complexities and the difficulty of directly dating the fault's protracted brittle activity. To address this long-standing problem and to better understand the ATF’s evolution and its role in the Plateau build-up, we conducted detailed structural investigations of two significant outcrops in the Old Aksay region (Gansu province). These exposures preserve a complex fault internal architecture containing numerous Brittle Structural Facies (BSFs), that is, distinct rock domains defined by characteristic fault rocks, mineralogy, textures, and kinematics. Repeated faulting at those outcrops localized deformation into weaker zones, creating thick foliated gouge layers, and along discrete slip surfaces, while lithons from earlier slip events were locally preserved. Their juxtaposition records the temporal and spatial evolution of the ATF, including its deformation mechanisms, physical conditions during initial faulting and subsequent reactivations. We combined multiscalar structural analysis with multi-grain-size K-Ar dating of synkinematic illite separated from BSFs at both outcrops.The results reveal a protracted, episodic faulting history from the Early Cretaceous (~115 Ma) to the Quaternary (~0.6 Ma), documenting at least five reactivation events. The earliest record at ~115 Ma suggests the ATF existed from before collision as a lithospheric weakness inherited from Mesozoic intracontinental deformation. Crucially, we identify an Early Eocene event (~56 Ma) that provides the first direct geochronological evidence for brittle deformation nearly synchronous with the initial India-Asia collision farther south, supporting models of rapid stress transfer to the northernmost plateau margin. A Late Oligocene reactivation at ~26 Ma coincides with rapid, widespread Miocene exhumation and sedimentation across northeastern Tibet. Late Pliocene (~3 Ma) and Middle Pleistocene (~0.6 Ma) events record continuing slip and deformation localization during progressive Plateau expansion.This intricate >100 Myr archive demonstrates that long-lived lithospheric weaknesses can preserve deformation spanning multiple tectonic regimes. Beyond providing a robust temporal framework for the tectonic evolution of the northern Tibetan Plateau, our results highlight the efficiency of far-field stress transfer through rigid lithosphere even over very large distances, and establish a powerful methodological protocol for integrating geochronological records and structural investigations in intracontinental orogens worldwide.

The Gulang-Zhongwei Fault is a northeast splay of the Haiyuan fault (east of 102°E) accommodating mostly left-lateral slip and some thrusting. Its slip history and kinematics are critical for understanding the mechanisms of slip partitioning along the oblique convergence at the margin of the plateau. Up to now, a consensus on its slip rate remains elusive; previous investigations have yielded divergent estimates ranging from

The lack of research on the slip behavior of the NW-trending faults in the central Tibetan Plateau constrains our understanding of the deformation models for this region. The Ba Co Fault, located in the central Tibetan Plateau, is a NW–SE-trending right-lateral strike-slip fault. Its eastern section has been active in the Holocene and plays an important accommodating role in the northward compression and east–west extension of the Tibetan Plateau. This study presents a detailed analysis of the geomorphic features of the eastern section of the Ba Co Fault in the Ngari Prefecture of Tibet, precisely measuring the newly discovered surface rupture zone on its eastern side and preliminarily discussing the activity of the fault based on the optically stimulated luminescence (OSL) dating results. The results reveal that the eastern segment of the Ba Co Fault displays geomorphic evidence of offset, including displaced Holocene alluvial–fluvial fans at the mountain front and partially offset ridges. A series of pressure ridges, trenches, counter-slope scarps, and shutter ridge ponds have developed along the fault trace. Some gullies exhibit a cumulative dextral displacement of approximately 16–52 m. The newly discovered co-seismic surface rupture zone extends for a total length of ~21 km, with a width ranging from 30 to 102 m. Pressure ridges within the rupture zone reach heights of 0.3–5.5 m, while trenches exhibit depths of 0.6–15 m. Optically stimulated luminescence (OSL) dating constrains the timing of the surface-rupturing earthquake to after 5.73 ± 0.17 ka. The eastern segment of the Ba Co Fault experienced a NW-trending compressional deformation regime during the Holocene, manifesting as a transpressional dextral strike-slip fault. Magnitude estimation indicates that this segment possesses the potential to generate earthquakes of M ≥ 6. The regional tectonic analysis indicates that the activity of the eastern section of the Ba Co Fault is related to the shear model of the conjugate strike-slip fault zone in the central Tibetan Plateau and may play a boundary role between different shear zones.

《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。

Geometric complexities play an important role in the nucleation, propagation, and termination of strike-slip earthquake ruptures. The 2021 Mw7.4 Maduo earthquake rupture initiated at a large releasing stepover with a complex fault intersection. In the epicentral region, we conducted detailed mapping and classification of the surface ruptures and slip measurements associated with the earthquake, combining high-resolution uncrewed aerial vehicle (UAV) images and optical image correlation with field investigations. Our findings indicate that the coseismic ruptures present discontinuous patterns mixed with numerous lateral spreadings due to strong ground shaking. The discontinuous surface ruptures are uncharacteristic in slip to account for the large and clear displacements of offset landforms in the epicentral region. Within the releasing stepovers, the deformation zone revealed from the optical image correlation map indicates that a fault may cut diagonally across the pull-apart basin at depth. The left-lateral horizontal coseismic displacements from field measurements are typically ≤0.6 m, significantly lower than the 1–2.7 m measured from the optical image correlation map. Such a discrepancy indicates a significant proportion of off-fault deformation or the possibility that the rupture stopped at a shallow depth during its initiation phase instead of extending to the surface. The fault network and multi-fault junctions west and south of the epicenter suggest a possible complex path, which retarded the westward propagation at the initial phase of rupture growth. A hampered initiation might enhance the seismic ground motion and the complex ground deformation features at the surface, including widespread shaking-related fissures.