活动断层研究

地震发生在活动断层上，而断层活动并非都一定发震，为进行地震危险性分析，确定未来可能发生地震的地段和强度，因此把活动断层分成地震破裂段进行研究，分析断层活动在时间上、空间上的不均匀性是十分重要的。     

用高分辨率地震技术研究活动断层

基于重大工程前期区域工程地质勘查的需要,在华北平原北部XY地区进行了一次高分辨率P波三维地震和S波二维地震描述、刻画地下活断层的试验研究,取得了本地区浅、中、深不同深度的地震成果。其中F1断层是该区一条重要控制断层,其重、磁、电资料虽有微弱显示,但位置不准确,难以对其活动性进行评价。经过本次综合勘探后,落实了该断层的存在,并发现该断层在工区范围内的中部分裂成F1-1及F1两条断层,F1-1、F1断层在平面上呈北东向“Y”字型展布,断距在纵、横向都呈现显著的分段特征,其断距最小90m,最大可达300m。该次勘探所获纵波反射主频达120～150Hz,活动断层地震成象十分清楚。可见高分辨率三维地震与超浅层横波反射地震相结合,可有效评价活动断层,为防震减灾工程研究提供可靠信息。     

青藏高原东北缘地震断层的研究

青藏高原东北缘新构造运动强烈,地震活动频繁。调查资料表明,伴随每次大地震的发生,都将产生规模不等的地震断层。本文研究了该区地震断层的分布规律、类型以及与先存断裂的关系等,同时对研究区不同地段的地壳稳定性进行了初步评价。      

活动逆断层错动引起的隧道响应分析

地震发生时,活动断层错动常常会导致上覆土层的变形破裂,进而对土层中的隧道结构造成严重破坏。本文运用有限元方法模拟60°活动逆断层错动下的覆土-隧道体系的破坏过程,探究隧道结构响应规律。结果表明,对于下盘隧道,靠近断裂带时承受巨大的弯矩和剪力,当隧道与断层保持一定安全距离后,所受弯矩、剪力迅速减小。为了保证使用安全,下盘隧道需要与断层保持30 m以上的安全距离。对于上盘隧道,在断层错动下受到很小的弯矩、剪力,但是会产生很大的位移。进一步研究揭示了土层参数（弹性模量、剪胀角）对隧道响应的影响。对于弹性模量取值较大的土层,土层发生贯通破裂时的断层错动量较小,隧道承受较小的峰值荷载。对于剪胀角取值较大的土层,破裂带倾角较小,隧道承受较大的峰值荷载。     

基岩逆断层错动引起的上覆土体变形预测

基岩逆断层错动引起上覆土体变形会导致地表及地下建筑的破坏,相应的变形预测模型仍较为缺乏,相关因素的影响规律尚未掌握。本文通过补余误差方程来表征逆断层错动引起的上覆土体变形,建立可预测不排水条件下上覆土体的变形理论计算模型,并通过离心机实验数据、数值模拟数据加以验证。对比分析结果表明,补余误差方程能表征基岩逆断层错动所引起的地表及地表以下土体变形。参数分析结果表明:基岩错动量的幅值对地表不均匀隆起区域范围的影响并不显著;形状参数的增加会使得地表不均匀隆起区域趋向集中;断层倾角的增加会使得地表不均匀隆起区域向断层上盘一侧偏移。     

大陆构造变形与地震活动——以青藏高原为例

大陆内部构造变形和地震活动往往突显出复杂的、区域性的特征,很难用板块构造理论来解释。青藏高原是大陆构造变形的典型实例,具有不同构造变形的分区特征,不仅表现在物质组成、地形地貌和断裂组合等方面的不同,而且还表现出不同的地震活动特征。东昆仑断裂带以北的青藏高原北部地块,主要发育一系列挤压环境下的盆岭构造,表现为以连续变形为特征的上地壳挤压缩短变形;高原中北部巴颜喀拉地块,具有整体向东运动的特点,变形主要集中在其边缘,表现为刚性块体运动特征。在东部,由于稳定的四川盆地(扬子地块)的阻挡,位于龙日坝和龙门山断裂带之间相对坚硬的龙门山地区受到东西向强烈挤压,西部边界为伸展变形;在高原中央腹地羌塘地块西部,由于上地壳物质在向东挤出的驱动下不断变形,沿一系列小型正断层和走滑断层以伸展变形为主,表现为弥散型变形特征。相比之下,羌塘地块的东部向东-南东方向挤出,在大型走滑断层之间形成一个刚性块体;高原南部地块以东西向伸展的南北向裂谷系为主要变形特征,高原南缘以南北向挤压的大型逆冲断裂系为特征。历史地震和仪器记录的大地震(M≥8)只发生在高原东北和东南部的大型走滑带,以及东部和南部边缘的大型逆冲断裂上,沿...     

青藏高原中段活动断层运动速度及驱动机理

在大比例尺活动断层勘测调查基础上,通过测定典型断层位移和活动时代,计算重要活动断层运动速度,分析青藏高原中段地壳水平运动规律。发现青藏高原中段晚更新世～全新世发育大量iW-iWW一近EW向活动断裂,其中昆仑山活动断裂、可可西里南缘活动断裂、通天河活动断裂、崩错活动断裂、念青唐古拉山东麓活动断裂和雅鲁藏布江活动断裂水平运动速度达6～10mm／a,风火山活动断裂、乌丽活动断裂和雁石坪活动断裂水平运动速度达3～4mm／a,唐古拉山活动断裂与格仁错活动断裂水平运动速度约2mm／a。自晚更新世以来,青藏高原中段存在显著的地壳东向运动,相对于柴达木地块的地壳东向运动速度自南北两侧向中部逐步增大,至唐古拉山地区达最大值约40mm／a。青藏高原中段断裂活动、地壳运动与近SN向构造挤压及地壳内部东向水平剪切存在动力学成因联系。     

川滇地区重力场特征与地壳变形研究

对川滇地区重力场特征进行了研究,获得了研究区内地壳厚度分布及变形特征。总体上,研究区内地壳厚度从西北向东南逐渐减小。川滇菱形块体中内部出现了广泛的地壳增厚现象,并可能一直延伸至菱形块体的最南端。丽江-小金河断裂带在重力场特征上表现为龙门山断裂带向西南的延伸,其东侧主体构造走向等特征与扬子地块一致,推测丽江-小金河断裂带与龙门山断裂、红河断裂带一起构成了扬子地块的西边界。滇西地区布格重力一阶导数与现今地壳变形格局总体一致,主体构造方向为北北西-近南北向,代表了“新”构造主体构造线的方向;上延至45km后,主体构造上转变为以近东西向为主。     

青藏高原东北缘现今构造变动与地震活动特征

笔者利用青藏高原东北缘20世纪70年代以来的精密水准网和跨断层流动形变网监测资料和近10a来高精度GPS观测结果,结合地质构造和地震活动,研究和探讨了该区现今构造变动和强震活动的一些特征和初步机理。结果表明：①研究区现今构造变动具有空间分布的不均一性和随时间演化的非平稳性,其总体趋势呈现为新构造时期以来的继承性;②构造变动过程中的快速隆升异常区和与之相伴生的高梯度变形带、以及显著地断层活动异常,是较强地震孕育的标志,地震往往发生在具有较高应变积累的区域附近;③印度板块对青藏高原的强烈挤压是该区构造变动与地震活动的主动力环境;构造变动和地震与块体活动及区域构造应力场变化密切相关。     

Present-day Block Movement and Fault Activity on the Eastern Margin of the Tibetan Plateau

The geology and tectonics in the eastern margin of Tibetan Plateau are complex. The main tectonic framework is composed of blocks and faults. Using discontinuous global positioning system survey data for 2008–2014, the velocity field for the Eurasia reference framework was obtained. Based on the velocity field, the present-day velocities of the blocks and boundary faults were estimated. The results reveal that the movement rates of the Chuan-Qing, South China, Chuan-Dian and Indo-China blocks are(17.02±0.60) mm/a,(8.77±1.51) mm/a,(13.85±1.31) mm/a and(6.84 ± 0.74) mm/a, respectively, and their movement directions are 99.5°, 120.3°, 142.9° and 153.3°, respectively. All blocks exhibit clockwise rotation. The displacement rates of the Xianshuihe, Longmenshan, Anninghe, Zemuhe, Xiaojiang and Red River faults are(7.30±1.25–8.30±1.26) mm/a,(10.07±0.97–11.79±0.89) mm/a,(0.96±0.74–2.98±1.73) mm/a,(2.03±0.49–3.20±0.73) mm/a,(3.45±0.40–6.02±0.50) mm/a and(6.23±0.56) mm/a, respectively. The Xianshuihe, Anninghe, Zemuhe and Xiaojiang faults show leftlateral strike-slip movement, while the Longmenshan and Red River faults show right-lateral strikeslip. These characteristics of the blocks and faults are related to the particular tectonic location and dynamic mechanism.     

Crustal Motion Characteristics in the Eastern Margin of the Tibetan Plateau and Adjacent Regions after the Wenchuan Earthquake

The Wenchuan earthquake has altered the crustal motion characteristics in the eastern margin of the Tibetan Plateau and adjacent regions.Using discontinuous GPS survey data for 2008–2012, the velocity field for the Eurasia reference framework has been obtained, and the general trend of contemporary crustal motion after the occurrence of the Wenchuan earthquake has been studied.In addition, using the velocity field, the block movement velocity has been estimated by least-squares fitting.Furthermore, the properties and displacement rates of main faults have been obtained from the differences in velocity vectors of the blocks on both sides of the faults.The results reveal that there are no obvious changes in the general characteristics of crustal motion in this area after the Wenchuan earthquake.The earthquake mainly changed the rate of the movement of the Chuan-Qing block and caused variation in the movement direction of the South China block.The effect of the earthquake on faults is mainly reflected in variations in fault displacement velocity; there is no fundamental change in the properties of fault activity.The displacement rates of the Xianshuihe fault decreased by 3–4 mm/a, the Longmenshan fault increased by 9–10 mm/a, and the northern segment of the Anninghe fault increased by approximately 9 mm/a.Furthermore, the displacement rates of the Minjiang, Xueshan, Huya, Longquanshan, and Xinjin faults increased by 2–3 mm/a.This implies that the effects of the Wenchuan earthquake on crustal movement can mainly be observed in the Chuan-Qing, South China, and N-Chuan-Dian blocks and their internal faults, as well as the Xianshuihe and Longmenshan faults and the northern section of the Anninghe fault.The reason for this is that the Wenchuan earthquake disturbed the kinematic and dynamic balance in the region.     

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.     

Palynological Evidence of Late Pleistocene Soft-sediment Deformation Event in the Northeastern Margin of the Tibetan Plateau

The northeastern margin of the Tibetan Plateau is the youngest part of the Tibetan Plateau where tectonic activity is intense and climate change is complex. In this study, combined with field investigations, we explored accelerator mass spectrometry 14C and optically stimulated luminescence dating and palynological analysis of the sedimentary sequence in the Qingshuihe Basin to explain the origin of soft-sediment deformation layer. Dating and palynological results from the Sanchahe section in th...     

青藏高原莫霍面形态的重力模拟及其对探讨高原隆升机制的意义

青藏高原是印度板块板欧亚板块碰撞形成的巨大变形带，岩石圈地幔的变形特征对高原的隆或意义重大。本文分析了远震ＰＫＰ走时残差沿高原中部剖面的变化，发现莫霍面的断错在整个高原是普遍存在的；利用人工地震资料作为约束，用重力资料对莫霍面的形态进行了反演模拟，认为岩石圈地幔的断错和叠覆可能是青藏高原隆升的重要机制；最后讨论了板块中部热和密度不均匀性以及地幔流动对青藏高原岩石圈变形的影响。     

Deep Seismogenic Environment in the Southern Section of the Longmenshan Fault Zone on the Eastern Margin of the Tibetan Plateau and Lushan Ms 7.0 Earthquake

The 2,026 earthquake events registered by the Sichuan regional digital seismic network and mobile seismic array after the April 20 th,2013 Lushan earthquake and 28,188 pieces of data were selected to determine direct P waves arrival times. We applied the tomographic method to inverse the characteristics of the velocity structure for the three-dimensional(3D) P wave in the mid-upper crust of the seismic source region of the Lushan earthquake. The imaging results were combined with the apparent magnetization inversion and magnetotelluric(MT) sounding retest data to comprehensively study the causes of the deep seismogenic environment in the southern section of the Longmenshan fault zone and explore the formation of the Lushan earthquake. Research has shown that there are obvious differences in velocity structure and magnetic distribution between the southern and northern sections of the Longmenshan fault zone. The epicenter of the Lushan earthquake is located near the boundary of the high and low-velocity anomalies and favorable for a high-velocity section. Moreover,at the epicenter of the Lushan earthquake located on the magnetic dome boundary of Ya’an,the development of high velocity and magnetic solid medium favors the accumulation and release of strain energy. Lowvelocity anomalies are distributed underneath the are of seismogenic origin,The inversion results of the MT retest data after the April 20 th Lushan earthquake also indicate that there a high-conductor anomaly occurs under the area of seismogenic origin of the Lushan earthquake,Therefore,we speculated that the presence of a high-conductivity anomaly and low-velocity anomaly underneath the seismogenic body of the Lushan earthquake could be related to the existence of fluids. The role of fluids caused the weakening of the seismogenic layer inside the mid-upper crust and resulted in a seismogenic fault that was prone to rupture and played a triggering role in the Lushan earthquake.     

Last Deglacial Soft−Sediment Deformation at Shawan on the Eastern Tibetan Plateau and Implications for Deformation Processes and Seismic Magnitudes

The eastern margin of the Tibetan Plateau is characterized by frequent earthquakes; however, research of paleo?earthquakes in the area has been limited, owing to the alpine topography and strong erosion. Detailed investigations of soft?sediment deformation (SSD) structures are valuable for understanding the trigger mechanisms, deformation processes, and the magnitudes of earthquakes that generate such structures, and help us to understand tectonic activity in the region. To assess tectonic activity during the late Quaternary, we studied a well?exposed sequence of Shawan lacustrine sediments, 7.0 m thick, near Lake Diexi in the upper reaches of the Minjiang River. Deformation is recorded by both ductile structures (load casts, flame structures, pseudonodules, ball?and?pillow structures, and liquefied convolute structures) and brittle structures (liquefied breccia, and microfaults). Taking into account the geodynamic setting of the area and its known tectonic activity, these SSD structures can be interpreted in terms of seismic shocks. The types and forms of the structures, the maximum liquefaction distances, and the thicknesses of the horizons with SSD structures in the Shawan section indicate that they record six strong earthquakes of magnitude 6–7 and one with magnitude >7. A recent study showed that the Songpinggou fault is the seismogenic structure of the 1933 Ms7.5 Diexi earthquake. The Shawan section is located close to the junction of the Songpinggou and Minjiang faults, and records seven earthquakes with magnitudes of ~7. We infer, therefore, that the SSD structures in the Shawan section document deglacial activity along the Songpinggou fault.