An integrated north–south paleo-Dadu-Anning River: New insights from bulk major and trace element analyses of the Xigeda Formation

The Xianshuihe-Anninghe fault extends SE–S and constitutes the southeastern margin of the Tibetan Plateau.However,the Dadu River which is associated with the fault does not flow following the path,but makes a 90ºturn within a distance of 1 km at Shimian,heading east,and joins the Yangtze River,finally flowing into the East China Sea.Adjacent to the abrupt turn,a low and wide pass near the Daqiao reservoir at Mianning separates the N–S course of the Dadu River from the headwater of the Anning River which then flows south into the Yunnan Province along the Anninghe fault.Therefore,many previous studies assumed southward flow of the paleo-Dadu River from the Shimian to the Anning River.However,evidences for the capture of the integrated N–S paleo-Dadu-Anning River,its timing,and causes are still insufficient.This study explored the paleo-drainage pattern of the Dadu and Anning Rivers based on bulk mineral and geochemical analyses of the large quantities of fluvial/lacustrine sediments along the trunk of the Dadu and Anning Rivers.Similar with sands in the modern Dadu River,the Xigeda sediments also exhibit a granitoid affinity with the bulk major mineral compositions of quartz(>50%),anorthite(about 10%),orthoclase(about 5%),muscovite(about 5%),and clinochlore(about 4%).Correspondingly,bulk major elements show high SiO_(2),with all samples>60%,and some of them>70%,low TiO_(2)(≤0.75%),P_(2)O_(5)(≤0.55%),FeO*(≤5%),and relatively high CaO(1.02%–8.51%),Na_(2)O(1.60%–2.52%),and K_(2)O(2.17%–2.71%),with a uniform REE patterns.Therefore,synthesizing all these results indicate that these lacustrine sediments have similar material sources,which are mainly derived from its course in the Songpan-Ganzi flysch block,implying that the paleo-Dadu originally flowed southward into the Anning River and provided materials to the Xigeda ancient lake.The rearrangement of the paleo-Dadu River appears to be closely related to the locally focused uplift driven by strong activities of the XianshuiheXiaojiang fault system.

Offshore Fault Geometrics in the Pearl River Estuary,Southeastern China:Evidence from Seismic Reflection Data

The Pearl River Estuary(PRE) is located at the onshore-offshore transition zone between South China and South China Sea Basin, and it is of great significant value in discussing tectonic relationships between South China block and South China Sea block and seismic activities along the offshore active faults in PRE. However, the researches on geometric characteristics of offshore faults in this area are extremely lacking. To investigate the offshore fault distribution and their geometric features in the PRE in greater detail, we acquired thirteen seismic reflection profiles in 2015. Combining the analysis of the seismic reflection and free-air gravity anomaly data, this paper revealed the location, continuity, and geometry of the littoral fault zone and other offshore faults in PRE. The littoral fault zone is composed of the major Dangan Islands fault and several parallel, high-angle, normal faults, which mainly trend northeast to northeast-to-east and dip to the southeast with large displacements. The fault zone is divided into three different segments by the northwest-trending faults. Moreover, the basement depth around Dangan Islands is very shallow, while it suddenly increases along the islands westward and southward. These has resulted in the islands and neighboring areas becoming the places where the stress accumulates easily. The seismogenic pattern of this area is closely related to the comprehensive effect of intersecting faults together with the low velocity layer.

The Cenozoic activities of Yangjiang-Yitongdong Fault: insights from analysis of the tectonic characteristics and evolution processes in western Zhujiang(Pearl) River Mouth Basin

The Yangjiang-Yitongdong Fault (YJF) is an important NW-trending regional fault, which divides the Zhujiang (Pearl) River Mouth Basin (ZRMB) into western and eastern segments. In Cenozoic, the northern continental margin of the South China Sea (SCS) underwent continental rifting, breakup, seafloor spreading and thermal subsidence processes, and the Cenozoic activities of YJF is one part of this series of complex processes. Two long NW-trending multichannel seismic profiles located on both sides of the YJF extending from the continental shelf to Continent-Ocean Boundary (COB) were used to study the tectonic and sedimentary characteristics of western ZRMB. Using the 2D-Move software and back-stripping method, we constructed the balance cross-section model and calculated the fault activity rate. Through the comprehensive consideration of tectonic position, tectonic evolution history, featured structure, and stress analysis, we deduced the activity history of the YJF in Cenozoic. The results showed that the YJF can be divided into two segments by the central uplift belt. From 65 Ma to 32 Ma, the YJF was in sinistral motion as a whole, inherited the preexisting sinistral motion of Mesozoic YJF, in which, the southern part of YJF was mainly in extension activity, controlling the formation and evolution of Yunkai Low Uplift, coupled with slight sinistral motion. From 32 Ma to 23.8 Ma, the sinistral motion in northern part of YJF continued, while the sinistral motion in southern part began to stop or shifted to a slightly dextral motion. After 23.8 Ma, the dextral motion in southern part of YJF continued, while the sinistral motion in northern part of YJF gradually stopped, or shifted to the slightly dextral motion. The shift of the YJF strike-slip direction may be related to the magmatic underplating in continent-ocean transition, southeastern ZRMB. According to the analysis of tectonic activity intensity and rift sedimentary structure, the activities of YJF in Cenozoic played a regulating role in the rift extension process of ZRMB.

Dynamic Analysis of Deformational Structures of the Xianniishan Fault Zone in the Three Gorges of the Yangtze River

Field investigation and laboratory work reveal that inhomogeneity of the deformation of the Xiannushan fault is mainly characterized by lateral zonation, longitudinal segmentation and downward stratification. Based on these results, a 3-D deformational structure model of the fault was established and its geometrical and kinematic characteristics in two main deformational stages i.e. the main Yanshanian and Himalayan were discussed. The directions of principal and the differential stresses in these two stages were determined by using conjugate joints, striations of fault planes and microstructures of the fault zone. The direction of σI is N-S in direction with differential stresses of 150-250 MPa in the Yanshanian, and N70E with a differential stress ranging from 80-120 MPa in the Himalayan.

The neotectonic deformation and earthquake activity in Zhuanglang river active fault zone of Lanzhou

Lanzhou Institute of Seismology, China Seismological Bureau, Lanzhou 730000, China 2) Institute of Geology, China Seismological Bureau, Beijing 100029,

Main active faults and seismic activity along the Yangtze River Economic Belt:Based on remote sensing geological survey

The Yangtze River Economic Belt(YREB)spans three terrain steps in China and features diverse topography that is characterized by significant differences in geological structure and presentday crustal deformation.Active faults and seismic activity are important geological factors for the planning and development of the YREB.In this paper,the spatial distribution and activity of 165 active faults that exist along the YREB have been compiled from previous findings,using both remote-sensing data and geological survey results.The crustal stability of seven particularly noteworthy typical active fault zones and their potential effects on the crustal stability of the urban agglomerations are analyzed.The main active fault zones in the western YREB,together with the neighboring regional active faults,make up an arc fault block region comprising primarily of Sichuan-Yunnan and a“Sichuan-Yunnan arc rotational-shear active tectonic system”strong deformation region that features rotation,shear and extensional deformation.The active faults in the central-eastern YREB,with seven NE-NNE and seven NW-NWW active faults(the“7-longitudinal,7-horizontal”pattern),macroscopically make up a“chessboard tectonic system”medium-weak deformation region in the geomechanical tectonic system.They are also the main geological constraints for the crustal stability of the YREB.

Slip Rate of Yema River–Daxue Mountain Fault since the Late Pleistocene and Its Implications on the Deformation of the Northeastern Margin of the Tibetan Plateau

The slip rate of Yema River–Daxue Mountain fault in the western segment of Qilian Mountains was determined by the dated offset of river risers or gullies. Results indicate that the left-lateral fault slip rate is 2.82 ± 0.20 mm/a at Dazangdele site,2.00 ± 0.24 mm/a at Shibandun site,and 0.50 ± 0.36 and 2.80 ± 0.33 mm/a at two sites in Zhazihu. The ideal average slip rate of the whole fault is 2.81 ± 0.32 mm/a. The lower slip rate confirms part of the displacement of Altyn Tagh fault was transformed into an uplifting of the strap mountains in the western segment of Qilian Mountains,whereas another part transformed into sinistral displacement of Haiyuan fault. This study illustrates that the slip of large strike-slip faults in the northeastern margin of the plateau transforms into crust thickening at the tip of the fault without large-scale propagation to the outer parts of the plateau.

The Holocene Activity Evidence of the Yema River-Daxue Mountain Fault in Western Qilian Mountain

Altyn Tagh fault controls the deformation characteristics of the northern margin of the Qinghai-Tibet Plateau.The sinistral slip rate of the eastern segment of the fault reduces gradually where the reduction transforms into the deformation within Qilian Mountain,forming a series of thrust faults and strike-slip faults.Among them,the Yema River-Daxue Mountain fault is one of the important structural transform faults in the study area.Based on the differences of the geometrical characteristics and activities,the fault is divided into four segments,the Yema River segment,the Shibandun segment,the Liushapo segment and the Baishitougou segment,among which the former three are Holocene active faults,and the Baishitougou segment belongs to late Pleistocene fault.The excavated trenches imply a total of 6paleoearthquake events,and at least 4 events have occurred during Holocene,whose occurrence times are 8300±700 yr BP,6605±140 yr BP,4540±350 yr BP,2098±47 yr BP,respectively.The recurrence interval is 2600±600 yr BP that is close to the lapsed time of the last one,2098±47 yr BP,which suggests that the Yema River-Daxue Mountain fault is in a high risk of major earthquakes in the future.The vertical coseismic displacements of the four Holocene paleoearthquake events are 100 cm,42 cm,40 cm and 50 cm,respectively,the horizontal coseismic displacements are 5 m,4.5–5.5 m,5–8 m and 4–5.5 m,separately,and then the reference magnitude of the paleoearthquake events is conjectured to be M7.6±0.1.

The characteristics of Quaternary activity of faults in the sea area near the Yangtze River mouth

By shallow seismic prospecting, it is showed that the faults in the sea area near the Yangtze River mouth are mainly the NE and NW-trending faults. The main activity time of fault is Pliocene to Early Pleistocene, and the latest activity is up to Middle Pleistocene. The maximum of fault is generally several tens meters with the throw decreased upward. The dislocation near the bottom of Middle Pleistocene is 12～13 m. The average vertical displacement rate is on a level of 10-3 mm/a.

K-Ar Dating of Fault Gouges from the Red River Fault Zone of Vietnam

Constraining the timing of fault zone formation is fundamentally important in terms of geotectonics to understand structural evolution and brittle fault processes.This paper presents the first authigenic illite K-Ar age data from fault gouge samples collected from the Red River Shear Zone at Lao Cai province,Vietnam.The fault gouge samples were separated into three grain-size fractions(<0.1 μm,0.1-0.4 μm and 0.4-1.0 μm).The results show that the K-Ar age values decrease from coarser to finer grain fractions(24.1 to 19.2 Ma),suggesting enrichment in finer fraction of morerecently grown authigenic illites.The timing of the fault movement are the lower intercept ages at 0%detrital illite(19.2 ± 0.92 Ma and 19.4 ± 0.49 Ma).In combination with previous geochronological data,this result indicates that the metamorphism of the Day Nui Con Voi(DNCV) metamorphic complex took place before ca.26.8 Ma.At about 26.8 Ma-25 Ma,the fault strongly acted to cause the rapid exhumation of the rocks along the Red River-Ailoa Shan Fault Zone(RR-ASFZ).During brittle deformation,the DNCV slowly uplifted,implying weak movement of the fault.This brittle deformation might have lasted for ca.5 Ma.

EARTHQUAKE FOCAL MECHANISM AND ITS TECTONIC SIGNIFICANCE ALONG THE TWO SIDES OF THE RED RIVER FAULT ZONE

The Red River Fault Zone is a gigantic slide-slip fault zone extending up to 1000km from Tibet to SouthChina Sea. It has been divided into the north, central and south segments according to the difference of thegeometry, kinetics, and seismicity on the land, but according to the contacted relationship between the old pre-Cenozoic block in Indochina Peninsula and the South China block, the Red River Fault Zone was divided into two parts extending from land to ocean, the north and south segments. Since the Tertiary, the Red River Fault Zone suffered first the sinistral movement and then the dextral movement. The activities of the north and the south segments were different. Based on the analysis of earthquakes and focal mechanism solutions,earthquakes with the focus depths of 0-33km are distributed over the whole region and more deep earthquakes are distributed on the northeastern sides of the Red River fault. Types of faulting activities are the thrust in the northwest, the normal in the north and the strike-slip in the south, with the odd type, viz. the transition type, in the other region. These show the Red River Fault Zone and its adjacent region suffered the extruding force in NNW direction and the normal stress in NEE direction and it makes the fault in the region extrude-thrust,horizontal strike-slip and extensional normal movement.

Preliminary Study on Cenozoic Group and Fault Activity in the Sea Area Near the Yangtze River Mouth

By shallow seismic prospecting, the Cenozoic Group in the sea area near the Yangtze River Mouth can be divided into five seismic sequences. They correspond to the Quaternary, Pliocene, Upper Miocene, Lower Miocene and Eocene respectively. The Quaternary System covers all the detecting area. The Tertiary System overlaps and thins out from NE to SW. The sedimentary basement mainly consists of volcanic rock (J 3) and acidic rock (r 3 5). Paleogene or Late Cretaceous basins are not found there. The faults that have been detected are all normal faults. They can be divided into three groups (NE, NW, near EW) by their trend. The NE and NW trending faults are predominant, and agree with aeromagnetic anomaly. Their length and displacement are larger than that of the EW trending faults. The activity of the NE trending faults is different in different segments. The SW segment is a Quaternary fault, the middle segment is a Neogene fault, The NE is Paleogene. But the segment of the NW trending fault is not obvious. The average vertical displacement rate is about 0 015mm/a.

Large-Scale Dextral Strike-Slip Movement and Associated Tectonic Deformation Along the Red-River Fault Zone

Field investigation has revealed that the large-scale dextral strike-slip movement and the associated tectonic deformation along the Red River fault zone have the following features: geometrically, the Red River fault zone can be divided into three deformation regions, namely, the north, central and south regions. The north region lies on the eastern side of the Northwest Yunnan extensional taphrogenic belt, which is characterized by the 3 sets of rift-depression basins striking NNW, NNE and near N-S since the Pliocene time, and on its western side is the Lanping-Yunlong compressive deformation belt of the Paleogene to Neogene; the deformation in the central region is characterized by dextral strike-slip or shearing. The east Yunnan Miocene compressive deformation belt lies on the eastern side of the fault in the south, and the Tengtiaohe tensile fault depression belt is located on its west. In terms of tectonic geomorphology, the aforementioned deformation is represented by basin-range tectonics in the north, linear faulted valley-basins in the central part and compressive (or tensional) basins in the south. Among them, the great variance in elevation of the planation surfaces on both sides of the Cangshan-Erhai fault suggests prominent normal faulting along the Red River fault since the Pliocene. From the viewpoint of spatial-temporal evolution, the main active portion of the fault was the southern segment in the Paleogene-Miocene-Pliocene, which is represented by “tearing” from south to north. The main active portion of the fault has migrated to the northern segment since the Pliocene, especially in the late Quaternary, which is characterized by extensional slip from north to southeast. The size of the deformation region and the magnitude of deformation show that the eastern plate of the Red River fault has been an active plate of the relative movement of blocks.

雅鲁藏布江断裂带东段现今地应力测量与断层活动性分析

为获取位于雅鲁藏布江断裂带东段加查县新建水电站工程场区的地应力状态,探讨雅鲁藏布江断裂带东段活动性,采用自主研发的新一代水压致裂地应力测试技术,实测获取了工程场区的地应力状态,并在收集雅鲁藏布江断裂带沿线地应力数据基础上,结合摩尔-库仑破裂准则,对其断层活动性进行了探讨。结果表明:(1)在工程厂区内122.75~418.75 m深度,实测最大水平主应力SH介于6.07~37.62MPa之间,最小水平主应力Sh介于3.13~20.33MPa之间,最大水平主应力优势方向为北北东向;(2)主应力关系总体表现为SH>Sh>Sv(Sv为垂向主应力),应力结构有利于逆断层的孕育和活动;(3)实测及收集的大部分数据应力莫尔圆与摩擦系数为0.6的破坏临界线相交,表明整体上雅鲁藏布江断裂带东段发生滑动失稳的风险较高,其中西侧贡嘎至朗县一带风险高于东侧林芝地区。

塔里木盆地塔河油田逆冲背斜区奥陶系古暗河系统发育特征

塔里木盆地塔河油田古暗河系统研究尚处于初始阶段,主要从暗河的深浅分布、结构样式等特征开展暗河洞穴的划分,较少从构造、断裂、古地貌、地下水位等地质方面综合分析复杂暗河系统的空间发育规律,致使暗河的主次从属关系、空间叠置样式、原始连通关系难以厘清,从而制约了塔河油田开发后期的综合治理研究。为了明确塔河油田主体区逆冲背斜区奥陶系古暗河系统发育特征,利用构造断裂解析、古地貌恢复、地震属性刻画、纵断剖面解读等方法进行了S67井区古暗河的类型识别、系统划分和地质成因研究,尤其首次识别并剖析了潜流回流暗河。结果表明,S67井区处于塔河主体区岩溶台原南缘的低地势区,发育幅差较小的峰丛洼地、溶丘洼地,地表水系下切深度较浅;逆冲背斜为低角度逆冲推覆构造样式,逆冲背斜之上的网格状断裂为多层状暗河系统提供有利溶蚀通道。研究区奥陶系发育相对独立的、树枝状结构的地下水位暗河系统和潜流带暗河系统,地下水位型暗河可分为主干型、支流型和废弃型,潜流回流暗河可分为上升型、对称型。控制逆冲背斜区古暗河发育的主要因素有古地貌、地下水位、逆冲背斜构造和次级断裂网络等。

塔里木盆地塔河北部“过溶蚀残留型”断溶体发育特征及其成因

为了研究塔里木盆地塔河北部强剥蚀区海西早期古岩溶洞穴发育特征,用古地貌恢复、岩溶水系统分析、测井-岩心洞穴识别和地震属性刻画等方法进行了YQ5井区的洞穴类型样式识别、缝洞结构刻画和洞穴成因演化研究。研究结果表明:YQ5井区在塔河油田Ⅱ号和Ⅲ号古岩溶台地北部的地势平缓区,总体为多期次岩溶叠加改造后的残留地貌,主要发育幅差较小的溶峰洼地、溶丘洼地和溶丘平原,南部发育NE向展布的峰丛垄脊沟谷。与塔河油田主体区及斜坡区不同,YQ5井区地下和地表水系的流向与地貌趋势不一致,岩溶水系统遭受构造作用破坏,导致补给、径流和排泄的岩溶水循环过程不完整。YQ5井区主要发育暗河型洞穴和“过溶蚀残留型”断溶体。暗河型洞穴充填较为严重,洞穴的有效储集空间受到破坏,影响油气开发效果。岩溶台地的构造抬升造成区域侵蚀基准面的下降,顺走滑断裂的垂向侵蚀作用有利于“过溶蚀残留型”断溶体的持续发育和保存,油气开发效果好。“过溶蚀残留型”断溶体的发育主控因素为走滑断裂、地层剥蚀强度和负向地貌。与塔河古岩溶台地演化过程一致,YQ5井区的岩溶演化经历深切曲流期、岩溶改造期和下渗断溶期3个阶段。暗河型洞穴被持续改造破坏,断溶体则持续建造。

基于GNSS的红河断裂中段现今变形特征

采用红河断裂带中段加密布设的GNSS连续站观测资料以及前人发布的速度场结果,获取红河断裂带中段及邻区现今地壳运动速度场。根据川滇地区活动断裂分布建立研究区三维有限元模型,以红河断裂带中段及邻区GNSS速度场为约束,获得红河断裂带中段不同段落的现今滑动速率和区域应变率场。结果表明,红河断裂带弥渡-元江段右旋走滑速率为1.2±0.6 mm/a,挤压速率为0.6±0.5 mm/a;红河断裂带元江-元阳段右旋走滑速率为1.8±0.7 mm/a,挤压速率为1.5±0.6 mm/a。应变率结果显示,红河断裂带中段及邻区以剪切变形为主,最大剪应变率高值区位于小江断裂带附近,最大幅度约为62×10^(-9)/a,红河断裂剪切变形相对较弱;面应变率显示,红河断裂元江-元阳段挤压变形较为显著,挤压应变率值约为10×10^(-9)/a,该段落处于强闭锁状态,未来地震危险性值得关注。

GNSS约束的红河断裂带现今三维闭锁耦合程度及时空演变特征研究

为研究红河断裂带近年来活动状态的演变特征,并分析该区域地震危险性,基于1999~2007年、1999~2017年2期GNSS速度场数据,采用负位错块体模型反演红河断裂带的闭锁程度与滑动亏损空间动态分布。结果表明,红河断裂带的闭锁程度具有两端强、中间弱的特点。红河断裂带北段和南段局部断层闭锁深度为20 km,闭锁程度较高;中段为浅层闭锁,闭锁深度为5 km。在滑动亏损方面,北段为2.5~5 mm/a,积蓄能量速度较快;中段为0.4~1.8 mm/a,南段为1.5~2 mm/a,中、南两段较为平稳。在2008年以后,红河断裂带整体闭锁特点不变,南、北两段深度闭锁状态开始向中间扩散,红河断裂带整体闭锁程度加深,同时滑动亏损速率有所增加,断层北段地震风险继续增大,而断层南段活动状态变得不稳定。

青海喇家遗址极可能由地震导致的砂土液化泥流造成:“12·18”积石山地震的启示

形成于3900年前的青海省民和县喇家遗址,号称“东方庞贝”,是一处举世闻名的灾难遗址,但其成因争论由来已久、悬而未决。学者提出的多种“洪水成因”之说,已深入民众之心,但这次灾难事件真的和洪水有关么?2023年12月18日甘肃积石山县的6.2级地震的震中距喇家遗址仅16 km,不仅使喇家遗址博物馆损坏严重,而且触发的泥流在离遗址仅5 km处的民和县中川乡金田村和草滩村,造成了民房和村民被直接掩埋的灭顶之灾,可能是喇家灾难遗址形成过程的重现,成为对比研究喇家遗址成因的重要实证材料。通过对此次地震灾害的野外实地调查和综合研究,或许能解开喇家遗址成因之谜。积石山地震使黄土之下古河床砾石层中地下水沿地表破裂喷出上涌,进而造成黄土液化并顺冲沟快速往下游流动形成泥流,流经草滩村、金田村时泥流遇阻,漫出冲沟将部分房屋冲毁甚至导致村民被掩埋。特殊的地层结构及富集的地下水,在地震的触发之下造成砂土液化并形成泥流,是造成中川乡地震灾害的重要原因。现场调查表明,草滩村一家五口被掩埋的悲剧,并非典型的“砂涌”造成,更无“洪水”的痕迹,而是地震的次生泥流灾害所致。将今论古,结合喇家遗址的文化遗存保存状况及沉积物特征进一步推断,喇家遗址的形成可能与强降雨形成的山间洪流无关,更不是由所谓的“大洪水”造成的。3900年前的古地震及其造成的砂土液化和快速流动的泥流,极可能是造成喇家遗址瞬时灾难的主要成因。

基于PLC的自动测流机器人系统设计

针对当前河道测流存在的效率和自动化程度较低、测量模式单一等问题,提出了一套基于可编程逻辑控制器(PLC)的河道自动测流机器人系统设计与实现方案。该机器人系统由运动系统、采集系统、人机交互以及远程通信四大模块组成。首先,设计了自动测流机器人系统的硬件结构,实现了自动测流机器人在河流轨道上运动、铅鱼收放等功能。然后,开发了基于PLC的测控系统,设计了PLC梯形图和硬件连接方案,实现了自动测流机器人运动控制。最后,自动测流机器人系统通过RS-485通信协议将多传感器采集的数据传输到操控屏,结合4G远程技术,实现了采集数据和操作指令的远程传输。通过现场模拟的采集测试,该机器人系统可实现自动测流、远程操控、故障自检等功能,并提供多种测量模式,满足河道测流的使用需求。该系统的设计为开展智能化河流数据采集的研究奠定了基础。