The Xianshuihe Fault Zone (XSHF) frequently experiences strong earthquakes owing to its high slip rate; particularly, the Kangding segment within the XSHF is structurally complex. To conduct an accurate regional seismic hazard analysis of XSHF, it is necessary to understand the slip rates of the branch faults of the Kangding segment. In this study, we aimed to determine the slip rates of the Yalahe Fault (YLHF) and the northwestern segment of the Zheduotang Fault (ZDTF), which are both parts of the Kangding segment. We using LaDiCaoz_v2 software, and 10Be cosmogenic nuclide dating techniques. Our analysis showed slip rates of 3.5 +/- 0.3 mm yr-1 and 2.3 +/- 0.2 mm yr-1 since 12.7 ka and 7.8 ka for the YLHF, implying a decreasing slip rate trend post the Holocene period. Furthermore, we obtained slip rates of 1.9 +/- 0.3 mm yr-1 since 42.7 ka and 1.8 +/- 0.2 mm yr-1 since 15.7 ka for the northwest segment of the ZDTF. Notably, these slip rates are significantly lower than those observed for the southeastern ZDTF. Furthermore, in the late Quaternary, the combined slip rate for the XSHF reached a maximum of 9.9-15.5 mm yr-1. We also observed that the Anninghe Fault inherited 48.2 % of slip rate from XSHF. These findings provide a comprehensive overview of slip rate partitioning among branch faults in the Kangding segment, offering novel insights into the seismic behavior of the XSHF and improving regional seismic hazard assessment.

On September 5, 2022, a M6. 8 earthquake occurred in Luding county, Sichuan Province. The epicenter is located at the southeastern end of the Xianshuihe fault. The preliminary results of field geological investigation show that no obvious surface rupture caused in this earthquake. We obtain the static horizontal coseismic displacements within 90 km of the epicenter at 31 survey-mode and continuously operated GNSS stations. The deformation pattern measured by GNSS is agreement with the left-lateral strike slip faulting mechanism. The maximum horizontal coseismic displacement observed by GNSS reaches 23 cm, and the GNSS stations within 50 km of the epicenter records coseismic offsets generally over 1 cm. The optimal coseismic slip model derived from GNSS data shows that the surface rupture mainly concentrated between Moxi town to Tianwan township. The coseismic slip concentrates at depths of 2 similar to 8 km, with the maximum slip of 1. 96 m. The estimated seismic moment is 9. 25 X 10(18) N " m, corresponding to M(w)6. 6. The earthquake has enhanced the Coulomb stress on the fault planes around the periphery of the source rupture area, and a large fraction of aftershocks occurred in the region where Coulomb stress increased. Considering the interseismic coupling ratio, historical earthquake ruptures and Coulomb stress variations, it is worth paying more attentions on seismic hazards of Anninghe fault, Daliangshan fault and Kangding Moxi segment of the Xianshuihe fault in near future.

The restraining and releasing bend region, encompassing the South Qianning, Kangding, and North Moxi segments, occupies a distinctive position within the Xianshuihe fault zone and plays a pivotal role in the analysis of seismic hazards. Our study focused on paleoearthquake research on the Qianning segment of the Xianshuihe fault zone through the integration of tectonic geomorphology, trench excavations, and radiocarbon dating methodologies. Three events, designated as ET1-ET3, have been found, occurring at 635-519, 823-672, and 3515-1482 yr B.P., respectively. A chronological framework for earthquake events has been established since the Holocene. The coefficient of variation (CoV) (0.75 reveals a weakly periodic recurrence model governing the activity of the Qianning segment. Moreover, both the Qianning and Kangding segments exhibit heightened susceptibility to cascading ruptures within the context of a single earthquake. The integration of shallow and deep data reveals a noteworthy transformation in the fault structure, transitioning from a solitary deep structure within the Qianning segment to a flower structure in the Kangding segment. This structural evolution is attributed to the migration of activity from the Yalahe Fault to the Selaha Fault and Zheduotang Fault, resulting in the short-cutting process within the Xianshuihe Fault Zone.

The complexity of strike-slip fault segmentation affects the initiation, propagation, and termination of earthquake ruptures and the earthquake magnitude. Studying the fault geometry, kinematics, and segmentation provides fundamental knowledge for mitigating earthquake hazards along faults. The Zemuhe, Daliangshan, and Xiaojiang Faults intersect along the eastern boundary of the Tibetan Plateau in the area from Ningnan in Sichuan Province to Qiaojia in Yunnan Province. Although few large earthquakes have occurred on these faults, the relationships between the intersections of these three faults and earthquake rupture behavior in this region are poorly constrained. The interpretation of aerial photographs and detailed field surveys revealed the geometric pattern and fault kinematics in the area of intersection. The distribution patterns and focal depths near the faults were obtained via analysis of seismic data in the area of intersection. The northern segment of the Xiaojiang Fault deviates approximately 25° northwest of Qiaojia, forming a conspicuous bend. The Xiaojiang Fault continues to extend southeast of the Ningnan Basin, where it intersects with the southern segment of the Zemuhe Fault, forming a pull-apart basin approximately 4.5 km wide. The bend and Ningnan pull-apart basin mark the segmented boundary between the Zemuhe Fault and the Xiaojiang Fault, which may prevent the propagation of large earthquake ruptures along the eastern boundary fault. Moreover, the lack of obvious geometric complexity between the Daliangshan Fault and Xiaojiang Fault might hinder the prevention of earthquake rupture propagation. Additionally, our results suggest that different earthquake prevention and disaster reduction measures should be taken for different cities in the region.

The ongoing Cenozoic Indo-Asia continental collision not only formed the highly elevated Tibetan Plateau but also reactivated the crustal deformation in adjacent Paleozoic-Mesozoic orogens. This includes the renewed phase of deformation in the Qinling Orogen, northeast of the Tibetan Plateau, which was formed initially by Paleozoic closure of the Paleo-Tethys and subsequent early Triassic continental collision between the North and South China blocks. Debates continue as to when and how the reactivation initiated. To investigate this question, this study reports a vertical profile of apatite and zircon (U???Th)/He thermochronometric ages from the Guangtoushan Granite to estimate the exhumation history of the central Qinling Orogen, where previous models for the growth of the Tibetan Plateau inferred late Cenozoic northeastward growth of the Tibetan Plateau by outward flow of the lower crust from the plateau interior. Age-elevation relationship and thermal history modelling suggest two phases of relatively rapid exhumation during the early Cretaceous (-130???110 Ma) and the latest Cretaceous ??? early Paleocene (-70???50 Ma), respectively. The early Cretaceous exhumation coincided with the time of the Lhasa-Qiangtang collision, whose far field effects have been widely reported in regions of the central-northern Tibetan Plateau. In the southern and central Qinling, our finding of an early Paleocene (-70???50 Ma) increase in exhumation rate followed by minimal exhumation during the late Cenozoic suggests negligible impact of the lower crust flow from the expanding Tibetan Plateau on the rock exhumation of the Qinling. Instead, our study suggests instant strain migrations from the Lhasa-Qiangtang and Indo-Asia collision zones to the northeast margin of the Tibetan Plateau during the early Cretaceous and the early Paleocene, respectively, supporting the models highlighting the importance of rigid blocks in facilitating intracontinental strain migration.

Based on the multi-data of the global ionospheric map (GIM), ionospheric total electron content (TEC) inversed from GPS observations, the critical frequency of the F2 layer (fOF2) from the ionosonde, electron density (Ne), electron temperature (Te), and He+ and O+ densities detected by the China Seismo-Electromagnetic Satellite (CSES), the temporal and spatial characteristics of ionospheric multi-parameter perturbations were analyzed around the Maerkang Ms6.0 earthquake swarm on 9 June 2022. The results showed that the seismo-ionospheric disturbances were observed during 2–4 June around the epicenter under quiet solar-geomagnetic conditions. All parameters we studied were characterized by synchronous changes and negative anomalies, with a better consistency between ionospheric ground-based and satellite observations. The negative ionospheric anomalies for all parameters appeared 5–7 days before the Maerkang Ms6.0 earthquake swarm can be considered as significant signals of upcoming main shock. The seismo-ionospheric coupling mechanism may be a combination of two coupling channels: an overlapped DC electric field and an acoustic gravity wave, as described by the lithosphere–atmosphere–ionosphere coupling (LAIC). In addition, in order to make the investigations still more convincing, we completed a statistical analysis for the ionospheric anomalies of earthquakes over Ms6.0 in the study area (20°~40° N, 92°~112° E) from 1 January 2019 to 1 July 2022. The nine seismic events reveal that most strong earthquakes are preceded by obvious synchronous anomalies from ground-based and satellite ionospheric observations. The anomalous disturbances generally appear 1–15 days before the earthquakes, and the continuity and reliability of ground-based ionospheric anomaly detection are relatively high. Based on the integrated ionospheric satellite–ground observations, a cross-validation analysis can effectively improve the confidence level of anomaly identification and reduce the frequency of false anomalies.

The Yalahe Fault (YLHF) is a sub-strand of the Xianshuihe Fault Zone (XSHF) that plays an important role in understanding the structural deformation pattern of the Kangding segment and analyzing the seismic hazards in this area. However, little is known regarding the recurrence patterns and characteristics of large earthquakes along the YLHF. We reveal six recent paleoearthquake events on the YLHF using tectonic geomorphology, trench excavations, and radiocarbon dating. The six events, E6-E1, are constrained to have occurred during (from oldest to youngest, respectively) 20,975-20,749, 18,981-18,817, 10,437-10,252, 7168-6269, 3465-2490 yr BP, and after 1380 +/- 60 CE. The most recent event may correspond to the 1700 CE similar to M 7 earthquake. The average recurrence interval was 3365 yr in the Holocene, and the coefficient of variation was 0.13, indicating that the YLHF follows a quasiperiodic recurrence model. The YLHF may experience cascading ruptures with two adjacent faults (Selaha and Zheduotang). The range of activity was located north of Huiyuan Temple and south of Jingai. Deformed strata show that the YLHF is kinematically characterized by transtension. In addition, the YLHF accumulated parts of the slip rate of the single-stranded XSHF. Therefore, the YLHF plays a significant role in the tectonic deformation of the XSHF in the Kangding segment with a high seismic hazard.

AbstractThe Zheduotang fault (ZDTF) is located in the Kangding section of the Xianshuihe fault zone (XSHF). While the ZDTF plays an essential role in understanding the structural deformation pattern of the Kangding section. Little information is known about the paleoearthquake offsets and slip behavior of the ZDTF. It is therefore essential to analyze the seismic hazards in this area. Using UAV-based photogrammetry, high-resolution satellite images, and field observations, we mapped the surface trace of the fault in detail and measured the horizontal and vertical offsets geomorphological landforms along the fault. The binned cumulative offset probability density (COPD) distribution was calculated to analyze single-event and multievent cumulative offsets. We found that the ZDTF has scarps along its entire ~46 km length, and the offset distributions of its northwestern (NW) and southeastern (SE) sections feature different characteristics. The SE section follows a uniform slip model based on the relationship between cumulative and coseismic offsets. We estimated the maximum potential earthquake magnitudes of the NW section and SE section to be M6.6 and M7.0, respectively, from the measured offsets and empirical formulas. Finally, we discussed the seismic hazard of the ZDTF based on our findings and paleoearthquake data. The NW section is at risk of large earthquakes recurring in the future, whereas the SE section has a low risk of a >M7.0 earthquake recurring in the next 100 years. If these two sections rupture at the same event in the future, the maximum potential magnitude of the ZDTF is M7.2.

Identifying the locations of potential landslide areas is fundamental for disaster prevention and mitigation. Considering the close relationship between landslides and geomorphic evolution, a new approach is proposed to predict which areas are prone to landslides based on the analysis of topographic features in the area affected by the 2014 Ludian, Yunnan, China, Ms6.5 earthquake. In our method, the expected slope angle (ES), which is related to the local relief in a grid cell, is defined to describe the terrain features within grid cells. Based on the relationship between the expected slope angle and the average slope, the cells in the study region can be classified into 3 different terrains. Our study shows that large landslides triggered by the Ludian earthquake are prone to occur in regions where the expected slope angle and average slope angle show obvious differences, which means that the region has sharp changes in relief and slope. In comparison with the coseismic landslides triggered by the 2017 Jiuzhaigou, Sichuan, China, Ms7.0 earthquakes, preliminary analyses infer that the distribution of coseismic landslides follows the general mass transportation features of a special region and that their occurrences are the kind of simultaneous adjustment of excess geomorphicity of hill slopes to a steady state.

The 8 August 2017 Jiuzhaigou, China, earthquake (Ms 7.0) occurred within Jiuzhaigou County, northern Aba Prefecture, Sichuan province, China. The earthquake generated 4834 coseismic landslides with individual areas >7.8 m2 over a 600 km2 region. Both the quantity of landslides and the areas that were affected by landslides are similar to those typical for earthquakes of similar magnitude in the eastern Tibetan Plateau, suggesting that the regional geologic structure significantly effects seismic attenuation. Instead of correlating geological and topographic factors with the co-seismic landslide distribution pattern, this study focuses on analyzing the seismic landslide susceptibility, which comes from a calculation of critical acceleration values using a simplified Newmark block model analysis. Results show that seismic landslide susceptibility plays an important role in the co-seismic landslide pattern. Based on the seismic landslide susceptibility, it becomes feasible to provide a quick evaluation of earthquake-triggered landslides when combined with a peak ground acceleration map for an event. Moreover, the correlation between the characteristics of seismic landslide susceptibility and previously observed landslides suggest that an unmapped extension of the Huya fault was the source fault of the Jiuzhaigou earthquake.

On 8 August 2017 an earthquake (MS7.0) occurred within Jiuzhaigou County, Northern Aba Prefecture, Sichuan Province, China, triggering 4834 landslides with an individual area greater than 7.8 m2 over a more than 400 km2 region. Instead of correlating geological and topographic factors with the coseismic landslide distribution pattern, this study has attempted to reveal the control from seismic landslide susceptibility mapping, which relies on the calculation of critical acceleration values using a simplified Newmark block model. We calculated the average critical acceleration for each cell of the gridded study area (1 km×1 km), which represented the seismic landslide susceptibility of the cell. An index of the potential landslide area generation rate was defined, i.e., the possible landsliding area in each grid cell. In combination with PGA (peak ground acceleration) distribution, we calculated such indexes for each cell to predict the possible landslide hazard under seismic ground shaking. Results show that seismic landslide susceptibility plays an important role in determining the coseismic landslide pattern. The places with high seismic landslide susceptibility tends to host many landslides. Additionally, the areas with high potential landslide area generation rates have high real landslide occurrence rates, consistent with dominant small-medium scale landslides by this earthquake. This approach can aid assessment of seismic landslide hazards at a preliminary stage. Additionally, it forms a foundation for further research, such as the rapid evaluation of post-earthquake landslides and identifying highly impacted areas to help decision makers prioritize disaster relief efforts.

NW向的鲜水河断裂带乾宁—康定段由3条分支断裂组成,自东向西分别为雅拉河断裂、色拉哈断裂和折多塘断裂,这3条断裂自全新世以来均有明显的活动.雅拉河断裂、色拉哈断裂和折多塘断裂南段分别发生过1700年7级、1725年7级和1955年7.5级地震.1:50000的鲜水河活动断裂带地质图(1995)及现有相关研究结果表明,折多塘断裂全新世活动段南起折多塘村附近,向N至康定机场附近,全长约30km,该段也是1955年7.5级地震地表破裂带展布的位置,而康定机场以北的西北段没有全新世活动的报道.文中通过影像解译,结合野外地质调查,发现折多塘断裂西北段全新世活动的新证据.经实地调查与探槽开挖等工作核实,该活动段自SE起于康定机场北侧,向NW延伸到多日阿嘎莫村,呈NW向展布,NW端邻近色拉哈断裂北段.文中结果表明折多塘断裂在全新世的活动范围较前人的研究成果向NW延伸了15km.该发现为完善鲜水河断裂带乾宁—康定段的折多塘断裂、色拉哈断裂以及雅拉河断裂这3支活动断裂的平面几何图像提供了一些依据,对深入认识鲜水河断裂带康定段在各分支断裂上的应变分配、强震破裂模式等方面具有重要意义.

Since the Ms 7.0 earthquake occurred in Lushan on April 20, 2013, five years after the Wenchuan Ms 8.0 earthquake, the seismogenic potential of southern Longmen Shan has been a considerable concern. Comparative studies of active faults and deep structures of the Lushan and Wenchuan earthquakes are important to evaluate Longmen Shan potential. Terrace measurements, geophysical surveys and borehole drilling reveal that late Quaternary fault activity in the southern segment of the Longmen Shan thrust belt is weaker than that along the central segment, Magnetotelluric data across the southern segment of the Longmen Shan thrust belt show that the central fault and the front-range fault are the electrical boundaries of the crust and that the Longmen Shan thrust belt is a high-resistivity body. The Lushan earthquake occurred at the boundary zone between the high and low-resistivity bodies, and the crustal structure of the southern Longmen Shan thrust belt matches the multiunit combination seismogenic model, indicating a potential large earthquake in Longmen Shan. Compared to conditions along the central segment, the low-resistivity layer of the upper and lower crust on the western side of the Songpan-Ganzi block develops along the Xianshuihe fault, which may reduce the strain accumulated from the Songpan-Ganzi block to the southern Longmen Shan thrust belt. This interpretation suggests that the main crustal shortening is accommodated by foreland thin fold structures, whereas the structural deformation accommodated by the thrust belt accounts for only a small proportion; thus, the seismogenic potential of southern Longmen Shan is weaker than that of the central segment.

The Mw 6.1 2014 Ludian, Yunnan, China earthquake triggered numerous coseismic landslides that do not appear to be associated with any previously known seismogenic fault. Traditional models of triggering for seismically generated landslides do not provide a reasonable explanation for the landslide pattern observed here. Here the Newmark method is applied to a grid to calculate the minimum accelerations required for slope failures throughout the affected region. The results demonstrate that for much of the study area, the distribution of failure prone slopes is similar to the actual pattern of coseismic landslides, however there are some areas where the model predicts considerably fewer failures than occurred. We suggest that this is a result of the complex source faults that generated the Ludian earthquake, which produced a half -conjugate rupture on nearly EW- and NNW trending faults at depth. The rupture directed much of its seismic moment southeast of the epicenter, increasing ground shaking and the number of resulting landslides.

According to history and instruments,south Longmenshan fault,which is considered a seismogenic structure,has experienced three strong shocks.,the 1327 Tianquan,the 1970 Dayi,and the 2013 Lushan earthquakes.These earthquakes triggered rockfall and landslides.We survey the typical landslide and the historical earthquake landslides along the Dachuan-Shuangshi fault across the earthquake area and find the distribution range and transport distances triggered by historical earthquakes greater than the Lushan earthquake.The density,volume and particle size triggered by the historical earthquake reduces from southwest to northeast along the fault.Results from the rock fall of the historical earthquakes and the Lushan earthquake,based on relative chronological tests of buried object and epigenetic lichen,and the formula of sensible radius and epicenter,show that the ground vibration is more heavily triggered by the Tianquan earthquake in 1327.Vibrations from the 1327 earthquake may have triggered the Tianquan county "Dayanbeng" and Shuangshi town "Shaijingshu".The historical earthquake epicenter may be located in the southwest section of the Dachuan-Shuangshi fault,near Tianquan county Xiangshuixi town.The intensity from the epicenter is greater than 9,and the magnitude of the paleo-earthquake may be great than or equal to the Lushan earthquake.

2014年8月3日发生于云南省东北部鲁甸县的MS 6.5地震触发了显著的同震滑坡并造成了严重地面破坏和人员伤亡.与已有地震诱发滑坡事件相比,鲁甸地震同震滑坡的空间分布较为特殊:与震中和已知断裂的关系都不明显,滑坡密度最大的区域并不在震中附近区域,且通常用于判断滑坡空间分布范围的地震动峰值加速度(PGA)也不能解释这样的分布格局.与以往研究地震滑坡与地质构造、地形地貌等影响因素相互间的关系不同,文中着重讨论地震滑坡敏感性对地震滑坡的控制作用.基于Newmark刚体滑块模型,文中计算了鲁甸地震滑坡影响区的坡体临界加速度值,并用来衡量地震滑坡敏感性程度:临界加速度值小,表明地震滑坡敏感性程度高,滑坡需要的外力较小,坡体在地震动作用下容易失稳;反之,坡体就越稳定.结果表明,鲁甸震区地震滑坡敏感性程度较高的地区主要沿牛栏江及其支流沙坝河、龙泉河两岸分布,震中及其北部地区的地震滑坡敏感性程度较低.对比研究区坡体地震滑坡敏感性分布与实际滑坡分布,可以看出二者之间具有较高的一致性:地震滑坡敏感性程度较高的区域往往是发生大量滑坡的地区.进一步,文中讨论了根据地震滑坡敏感性判断同震滑坡格局的优势,认为地震滑坡敏感性对同震滑坡的分布起到了控制作用;同时,区域性地震滑坡敏感性的研究不仅有助于理解同震滑坡分布格局,还可以为震源构造的研究提供依据,并且可以作为震后滑坡快速评估及地震滑坡危险性区划的基础.

公路边的滑坡崩塌在中国西南地区是常见的一类地质灾害.道路的开挖一方面改变了边坡原有的地表形态,形成了新的较陡的边坡,如果缺乏保护措施,新的陡坡很容易失稳,从而形成以滚石或浅层滑坡为主的边坡破坏.另一方面,道路开挖有可能会改变原有坡体的结构,降低坡体的安全系数,引起较大规模的滑坡,造成更为严重的灾害.因此,坡体开挖的位置对其稳定程度会产生一定的影响.文中以岩质边坡为例,在建立边坡模型的基础上,采用二维极限平衡数值模拟方法,分析了道路开挖位置对整体边坡稳定性的影响;同时,对加载地震作用的边坡稳定性也进行了模拟分析.研究结果表明,对于有潜在滑动面的坡体,在不同位置进行开挖对坡体稳定性的影响是不同的:在坡脚处或接近滑动面滑出位置开挖道路,将减小阻滑力而导致整体稳定性降低;在接近坡顶处开挖道路则会因卸载坡体物质而提高整体稳定性.合理的开挖位置与坡体坡度有密切关系,在不降低整体安全系数的情况下,坡度较陡的坡体,其开挖位置相应要高一些.无论坡体角度大小,地震作用能够显著降低边坡的稳定性.

Rapid assessment of the distribution of earthquake-triggered landslides is an important component of effective disaster mitigation. The effort should be based on both seismic landslide susceptibility and the ground shaking intensity, which is usually measured by peak ground acceleration (PGA). In this paper, we address this issue by analyzing data from the Mw6.1 2014 Ludian, China earthquake. The Newmark method of rigid-block modeling was applied to calculate the critical acceleration of slopes in the study area, which serve as measurement of slope stability under seismic load. The assessment of earthquake-triggered landslide hazard was conducted by comparing these critical accelerations with the distribution of known PGA values. The study area was classified into zones of five levels of landslide hazard: high, moderate high, moderate, light, and very light. Comparison shows that the resulting landslide hazard zones agree with the actual distribution of earthquake-triggered landslides. Nearly 70% of landslides are located in areas of high and moderately high hazard, which occupy only 17% of the study region. This paper demonstrates that using PGA, combined with the analysis of seismic landslide susceptibility, allows a reliable assessment of earthquake-triggered landslides hazards. This easy-operation mapping method is expected to be helpful in emergency preparedness planning, as well as in seismic landslide hazard zoning.