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1.
Southwest Yunnan, located in the southern segment of the north-south seismic belt, is one of the regions with strong tectonic movement and seismic activity in China. Study on the characteristics of tectonic setting and deep geophysical field in the region is an important issue in basic science. In 2013, we conducted a 600-km-long Menghai-Gengma-Lushui profile of deep seismic wide-angle reflection/refraction and high-resolution seismic refraction in Southwest Yunnan. In this paper, we use 6 groups of clear intracrustal P-wave phases picked from the seismic record sections of 11 shots to build a velocity structure model of basement and 2D crustal P-wave of the region by using finite difference inversion and ray travel time forward fitting technology. The results show that, from south to north, the crust gradually thickens along the profile and its basement shows a significant lateral heterogeneity. In the vicinity of the Nanting River fault, the basement structure shows the character of alternate depressions and uplifts, and the shallowest basement is about 1.0 km. In the vicinity of Tengchong and Lancang, the basement is about 5.0 km deep. The velocity of the middle and lower crust in the region generally increases with the increasing of depth. At the block boundary and beneath the fault tectonic belt, the velocity contours show apparent irregularity and the P-wave velocity changes sharply. In this region, the Moho gradually deepens from south to north with relatively large lateral undulations. The shallowest point of the Moho is located near Menghai at a depth of about 32.0 km. The deepest point of the Moho is located near Tengchong at a depth of about 40.5 km. Between Gengma and Yongde, the Moho shows significantly fast uplifting and depressing with an amplitude of about 4.0 km. Beneath the Nanting River fault, Longling-Ruili fault, Dayingjiang fault and Tengchong volcano, the basement velocity structure, 2D crustal P-wave velocity structure, distribution of average profile velocity and intracrustal interface spreading also show significant changes from the basement to the top of the Moho, indicating that the crustal velocity and medium physical properties beneath the fault tectonic belt are apparently different from the crustal materials on its both sides, which suggests that these faults should be in a certain scale and may extend to the lower crust or the top of the upper mantle. The earthquakes in the region mainly occurred at a depth of 10–20 km, and the seismic activity is related to the intracrustal medium velocity difference and fault belt distribution. The results can serve as the important data of the crust-mantle structure for the analysis of the deep tectonic setting, earthquake precise positioning, seismogenic structure modeling of the seismic activities in Southwest Yunnan, as well as the important reference for the evaluation of seismic hazard and the planning of earthquake disaster mitigation of this region.  相似文献   

2.
As a result of the left-lateral strike-slipping of the Altyn Tagh fault in Neotectonic period, a contra-rotational structure, namely the Zhaobishan vortex structure, has developed at the juncture of the main Altyn Tagh fault and the northern fringe fault of the Qilian Mountains.Preliminary analysis on the deformation and evolution of the Zhaobishan vortex structure. In combination with the previous data, suggests that the tectonic transform between the Altyn Tagh fault and the northern fringe fault of the Qilian Mountains attributes to the deformation of the rotational structure. The existence of a series of rotational structures along the Altyn Tagh fault and on the northeastern edge of the Qinghai-Xizang(Tibet) plateau indicate that as the substance in the northern Qinghal-Xizang (Tibet) plateau moves clockwise around the eastern tectonic knot of the Himalayas, rotational structures become the principal mode on the northern marginal zone of the Plateau of transforming and absorbing tectonic deformation.  相似文献   

3.
In this paper,according to the geological structure and the data on seismicity in the Shanxi seismic belt,the tectonic stress field of this belt is numerically imitated by using the finite element method,and by analyzing synthetically the characteristics of seismogeoiogical structure,seismicity and tectonic stress field,the trend of the coming macroseism in the Shanxi seismic belt can be roughly assessed.The main estimate is as follows.From 1993 to 2015,a strong earthquake with Ms=6.2±0.4 may occur in the Shanxi seismic belt,and there are 3 possible locations for earthquake occurrence,if we arrange according to the order of possibility of earthquake occurrence,the location of a coming earthquake would be(1)the region between Huoxian and Hongdong;(2)the region surrounded by Datong,Huairen,Yingxian and Hunyuan,and(3)the region surrounded by eastern Lingqiu to both ends of the Laiyuan fault.  相似文献   

4.
Based on the seismic station data sets from Sichuan and Yunnan provinces, we employed a multi-step seismic location method (Hypo2000 + Velest + HypoDD) to precisely locate the 7,787 earthquakes that occurred during 2010-2015 along the eastern boundaries of the Sichuan-Yunnan rhombic block, namely from southern Dawu to the Qiaojia segment. The final results show that location precision is greatly advanced and epicenter distribution exhibits good consistency with the linear distribution of the seismic faults. Earthquake distribution is quite intensive at the intersection region in the southern segment of the Xianshuihe fault, the Anninghe fault zone, the Xiaojinhe fault zone and the Daliangshan fault zone to the east. The depth profile of seismicity shows a clear stepwise activity along the active seismic fault zones. The profile crossing the faults of the Xianshuihe, Anninghe, and Daliangshan presents a complex interaction among faults near the multiple faults intersection region, Shimian, where the earthquakes are obviously divided into two groups in depth. Earthquakes are very rare at the depth of 15km-20km, which is consistent with the region of the plastic rheology between 14km-19km calculated by Zhu Ailan et al.,(2005).  相似文献   

5.
For the first time on the Chinese mainland, long-range wide-angle seismic reflection/refraction profiling technology has been applied to seismic wave phases from different depths and with different attributes within the various blocks of the North China Craton to characterize the structure of the crust and upper mantle lithosphere. By comparative analysis of the seismic wave phase characteristics in each block across a 1500-km-long east-west profile, we have identified conventional Pg, Pci, PmP and Pn phases in the crust, made a clear contrast between PL1 and PL2 waves belonging to two groups of lithospheric-scale phases, and produced a model of crust-mantle velocity structures and tectonic characteristics after one- and two-dimensional calculations and processing. The results show that the thickness of the crust and lithosphere gradually deepens from east to west along the profile. However, at the reflection/refraction interface, seismic waves in each group show obvious localized changes in each block. Also, the depth to the crystalline basement changes greatly, from as much as 7.8 km in the North China fault basin to only about 2 km beneath the Jiaodong Peninsula and Taihang-Lüliang area. The Moho morphology as a whole ranges from shallow in the east to deep in the west, with the deepest point in the Ordos Block at 47 km; in contrast, the North China Plain Block is uplifting. The L1 interface of the lithosphere is observed only to the west of Taihang Mountains, at a relatively slowly changing depth of about 80 km. The L2 interface varies from 75 to 160 km and shows a sharp deepening to the west of Taihang Mountains, forming a mutation belt.  相似文献   

6.
This paper introduces the basic parameters, focal mechanism solutions and earthquake sequence characteristics of the Kalpin MS5.3 earthquake sequence of December 1, 2013, and analyzed seismic activity before the earthquake, the adjacent tectonic features and the precursory anomaly at fixed points within a range of 200km. Research indicates:(1) The earthquake occurred on Kalpin fault, the source rupture type is thrust faulting with sinistral strike-slip component. (2) The earthquake sequence is mainshock-aftershock type, with the aftershock distribution attenuating quickly and trending NE. (3) Abnormal seismic activity before the earthquake was characterized by seismically nesting quiescence of MS2.0-4.0 earthquakes, seismic quiescence of MS4.0 earthquakes and seismic belts of MS3.0 earthquakes in the Kalpin block, abnormal enhancement zone of moderate earthquakes on Puchang fault and seismological parameters. (4) Anomalies of precursory observation data at fixed stations are mainly characterized by mutation. Apart from the borehole tiltmeter in Halajun, the spatial distribution of other abnormal precursors showed a phenomenon of migration from the near field to far field and from the epicenter to the peripheries.  相似文献   

7.
The interaction zone between southern Tianshan and northern Tarim is located at the northeast side of Pamir. It is a region with high seismicity. We constructed a seismotectonic model for the west part of this zone from geological profiles, deep crust seismic detection and earthquake focal mechanisms data. Based on the synthesized geological features, deep crust structure, and earthquake focal mechanisms, we think that the main regional tectonic feature is that the Tianshan tecto-lithostratigraphic unit overthrusts on the Tarim block. The Tianshan tectonic system includes the Maidan fault and thrust sheets in front of the fault; The Tarim tectonic system includes the underground northern Tarim margin fault, conjugate faults in basement and overthrust fault in shallow. The northern Tarim margin fault is a high angle fault deep in the Tarim crust, adjusting different trending deformation between Tianshan and Tarim. It is a major active fault that can generate large earthquakes. The other faults, such as the Tianshan overthrust system and the Tarim basement faults in this area may generate moderately strong earthquakes with different styles.  相似文献   

8.
The cycle process of the tidal force niche for the Ludian M_S6.5 earthquake occurring in Ludian County, Yunnan Province, China on August 3, 2014 was calculated. The earthquake occurred near the middle point phase. It indicates that the type of seismogenic fault that the tide force acted on belongs to the thrust fault. According to the tidal niche cycle,the abnormal OLR( Outgoing Long-wave Radiation) change was analyzed based on NOAA satellite data around the whole land area of China before and after the earthquake.The result shows that the OLR changed evidently with tide force change. Temporally,the change went through the evolution process of initial OLR rise → strengthening → abnormal peaking → attenuation → returning to normal; and spatially,the abnormal area wound its way along the Zhaotong-Ludian fault and went through a scattered → conversion →scattered process. This process is similar to the change process of rock breaking under stress loading. The results indicate that the tidal force of a celestial body could trigger an earthquake when the tectonic stress reaches its critical breaking point and the OLR anomaly is proportional to the seismic tectonic stress change. It is of great use to combine OLR and tidal force in earthquake precursory observation.  相似文献   

9.
Introduction An earthquake could be caused by the failure of focal material or fast slip on the pre-existed faults under the tectonic stress based on the understanding of the occurrence process of earth-quakes in which the stress change could play a key role. Therefore to examine the stress change is beneficial to understanding the physic process actually occurring in the source region deeply. The apparent stress is defined as the product of seismic efficiency and the average stress on the foc…  相似文献   

10.
Taking the Huaihe to the Nvshanhu segment of the Tanlu (Tancheng-Lujiang) fault zone as the main research target to explore whether there has been new activity since the late Quaternary, and based on the interpretation of remote sensing images and repeated surface investigations, we excavated trenches at the sections where the tectonic landform is significant, identified and recorded the deformation patterns of the fault and analyzed the activity behavior. Samples of new activity and deformation were collected and oriented slices were ground based on the samples'' original state to make the micro structural analysis and demonstration. All of the above research shows very clear linear tectonic geomorphology along the fault, three trenches across the fault zone all revealed new deformation traces since late Quaternary. The latest stratum dislocated by the fault is the late Quaternary and Holocene. The main slip mode is stick slip, as represented typically by fault scarps, wedge accumulation, the faults and the filled cracks and so on. In general, it shows the characteristics of brittle high-speed deformation and belongs to the prehistoric earthquake ruins. The above understanding was confirmed partially by microscopic analysis. In addition, the similarities and differences and the possible reasons for the characteristics of the latest activities of the Tancheng-Lujiang fault zone in the north and south of the Huaihe River regions are also discussed in this paper.  相似文献   

11.
用地震活动性参数（地震频度Ｎ，地震能量Ｅ和地震ｂ值）的二维空间等值线计算机扫描技术，系统地追踪了１９８３年菏泽５．９级地震前后三项地震活动性参数的空间动态演化情况。结果表明，菏泽５．９级地震前１－４年，河北平原断陷南部地区特别是其东界聊考断裂带地震活动异常增强，地震频度增高，地震能量释放加速而地震ｂ值降低；地震活动增强区的长度约２００余公里，未来主震发生于地震活动增强区的边缘；震后约一年左右震中周  相似文献   

12.
The Helan Mountains and Yinchuan Basin(HM-YB) are located at the northern end of the North-South tectonic belt,and form an intraplate tectonic deformation zone in the western margin of the North China Craton(NCC).The HM-YB has a complicated history of formation and evolution,and is tectonically active at the present day.It has played a dominant role in the complex geological structure and modern earthquake activities of the region.A 135-km-long deep seismic reflection profile across the HM-YB was acquired in early 2014,which provides detailed information of the lithospheric structure and faulting characteristics from near-surface to various depths in the region.The results show that the Moho gradually deepens from east to west in the depth range of 40-48 km along the profile.Significant differences are present in the crustal structure of different tectonic units,including in the distribution of seismic velocities,depths of intra-crustal discontinuities and undulation pattern of the Moho.The deep seismic reflection profile further reveals distinct structural characteristics on the opposite sides of the Helan Mountains.To the east,The Yellow River fault,the eastern piedmont fault of the Helan Mountains,as well as multiple buried faults within the Yinchuan Basin are all normal faults and still active since the Quaternary.These faults have controlled the Cenozoic sedimentation of the basin,and display a "negative-flower" structure in the profile.To the west,the Bayanhaote fault and the western piedmont fault of the Helan Mountains are east-dipping thrust faults,which caused folding,thrusting,and structural deformation in the Mesozoic stratum of the Helan Mountains uplift zone.A deep-penetrating fault is identified in the western side of the Yinchuan Basin.It has a steep inclination cutting through the middle-lower crust and the Moho,and may be connected to the two groups of faults in the upper crust.This set of deep and shallow fault system consists of both strike-slip,thrust,and normal faults formed over different eras,and provides the key tectonic conditions for the basin-mountains coupling,crustal deformation and crust-mantle interactions in the region.The other important phenomenon revealed from the results of deep seismic reflection profiling is the presence of a strong upper mantle reflection(UMR) at a depth of 82-92 km beneath the HM-YB,indicating the existence of a rapid velocity variation or a velocity discontinuity in that depth range.This is possibly a sign of vertical structural inhomogeneity in the upper mantle of the region.The seismic results presented here provide new clues and observational bases for further study of the deep structure,structural differences among various blocks and the tectonic relationship between deep and shallow processes in the western NCC.  相似文献   

13.
The Dongsha submarine canyon is a large canyon belonging to a group of canyons on the northeastern South China Sea margin. Investigation of the Dongsha canyon is important for understanding the origin of this canyon group as well as the transport mechanism of sediments on the margin, and the evolution of the Taixinan foreland basin and the associated Taiwan orogenic belt. In this study, the morphology, sedimentary characteristics, and origin of the Dongsha canyon were investigated by integrating high-resolution multi-channel seismic reflection profiles and high-precision multibeam bathymetric data. This is a slope-confined canyon that originates in the upper slope east of the Dongsha Islands, extends downslope in the SEE direction, and finally merges with the South Taiwan Shoal canyon at a water depth of 3000 m. The total length and average width of the canyon are around 190 and 10 km, respectively. Eleven seismic sequence boundaries within the canyon fills were identified and interpreted as incision surfaces of the canyon. In the canyon fills, four types of seismic facies were defined: parallel onlap fill, chaotic fill, mounded divergent facies, and migrated wavy facies. The parallel onlap fill facies is interpreted as alternating coarser turbidites or other gravity-flow deposits and fine hemipelagic sediments filling the canyon valley. The chaotic fill facies is presumed to be debrites and/or basal lag deposits filling the thalwegs. The mounded divergent and migrated wavy seismic facies can be explained as canyon levees consisting mainly of overspilled fine turbidites and sediment waves on the levees or on the canyon-mouth submarine fans. Age correlation between the sequence boundaries and the ODP Site 1144 data suggests that the Dongsha canyon was initiated at approximately 0.9 Ma in the middle Pleistocene. Mapping of the canyon indicates that the canyon originated at the upstream portion of the middle reach of the modern canyon, and has been continuously expanding both upstream and downstream by retrogressive erosion, incision, and deposition of turbidity currents and other gravity transport processes. The ages of the sequence boundaries representing major canyon incision events are in good agreement with those of global sea-level lowstands, indicating that sea-level changes may have played an important role in the canyon's development. The Dongsha canyon developed in a region with an active tectonic background characterized by the Taiwan uplifting and the development of the Taixinan foreland basin. However, no evidence suggests that the canyon formation is directly associated with local or regional faulting and magmatic activities. Turbidity currents and other gravity transport processes(including submarine slides and slumps) may have had an important influence on the formation and evolution of the canyon.  相似文献   

14.
Introduction The development and application of Interferometric Synthetic Aperture Radar (InSAR) have a close relationship with the sensors development of Synthetic Aperture Radar (SAR). The conception of SAR is proposed comparatively to the real aperture radar antenna. It is well known that the longer the antenna is, the higher the observation resolution will be. Just limited by the length of the antenna, the resolution of real aperture radar is generally very low and cannot meet the r…  相似文献   

15.
太行山南缘盘谷寺断裂新构造运动特征对分析太行山地区构造地貌演化，乃至研判我国东部新构造活动形势具有重要意义。基于Landsat 8 OLI遥感影像数据和ASTER GDEM数据，对盘谷寺断裂线性构造进行初步解释，分析冲沟发育、坡向坡度等构造地貌特征，通过构建遥感影像与高程数据相叠加的三维地貌模型，进一步优化断裂构造地貌视觉效果。研究结果表明，盘谷寺断裂为1条平面呈舒缓波状、近东西走向的南倾正断层。在断裂下盘，由西向东依次发育了密集的平行状侵蚀沟、断层三角面和低矮的侵蚀残丘等多种构造地貌类型，反映了断裂不同部位垂向运动的差异性。构造运动导致断层两盘地表坡向和坡度的明显变化，综合剖面分析结果，认为断裂在新构造期活动强度由西向东逐渐减弱。  相似文献   

16.
南北地震带北段强震破裂空段的地震危险性研究   总被引：3，自引：1，他引：2       下载免费PDF全文
综合活动构造与重要活动断裂带的历史及现今强震震源区或破裂分布等资料,南北地震带北段存在长期缺少MSge;7.0地震的破裂空段．为了考察这些空段的地震危险性,首先采用Burgers体黏弹介质模型,计算周围有记载以来的历史强震在空段引起的库仑应力动态演化;其次结合背景地震发生率,采用Dieterich模型分析历史强震对空段地震活动的影响,讨论了空段所在区域的地震发生概率．结果显示,南北地震带北段强震破裂空段的地震危险性程度自高到低依次是:东昆仑活动断裂带东段的若尔盖——九寨沟段、六盘山断裂带中南段空段、香山——天景山段裂中南段同心空段、天祝——大靖空段、西秦岭北缘断裂带中西段、西秦岭北缘断裂带东段．该结果可为南北地震带北段的地震危险性估计提供参考．   相似文献   

17.
Studying the geologic architecture of the Xiong’an New Area will provide important basis for the evaluation of crustal stability, urban planning and infrastructural projects in this region, and it is also of great significance in exploring the occurrence of oil and gas, geothermal, hot dry rock and other resources. The stratigraphic system of the study area is established by using latest high quality seismic reflection and deep borehole data. Characteristics of the major faults developed in the study area are finely depicted with the method of structural analysis. Tectonic evolution of Xiong’an and adjacent areas is reconstructed by using balanced geological cross-section technique. The tectonic activity of the study area is discussed on the basis of the development of secondary faults and the distribution of active earthquakes across the region. This study demonstrates that Xiong’an New Area is located at the transfer zone of the central and northern Jizhong Depression. There are three regional unconformities developed in this area, by which four structural layers are sub-divided. Controlled by the Taihang Mountain piedmont fault, the Daxing fault, the Rongcheng fault and the Niudong fault, the structural framework of the study area is characterized by intervening highs with sags. This structural pattern has an important controlling over the reservoir characteristics, hydrocarbon accumulation and the distribution of geothermal resources and hot dry rock within this region. Rifting in this area began in the early Paleogene, exhibiting typical episodic character and became inactive in Neogene. The development feature of secondary faults along with the distribution of active earthquakes indicate that Xiong’an New Area has been in a relatively stable tectonic setting since the Neogene, while the Baxian Sag and other structural units to the east of it have obviously been in a rather active environment.  相似文献   

18.
近断层竖向地震动P-Δ效应研究   总被引：1，自引：1，他引：0  
竖向效应是近断层地震动的主要特点，竖向地震动对工程结构形成的P-Δ效应是造成结构破坏的主要原因。本文以单自由度体系为研究对象，选取汶川地震的近断层强震数据进行研究，分析竖向地震动所产生P-Δ效应的放大作用特征。分析结果表明汶川地震中，相比于中远场区域，近断层区域内竖向地震动作用所产生的P-Δ效应具有明显的放大作用，且近断层内这种放大作用具有普遍性；当自振周期一定时，不同台站获得地震动的放大系数离散性较小，主要分布于均值附近；其分析结果符合地震动的一般规律，分析结果合理。在此基础上建立了以均值为代表值的放大系数谱，可以与抗震设计反应谱结合使用，从而为活断层附近区域内的结构抗震设计问题提供定量化参考依据。  相似文献   

19.
The extensional model of the South China Sea(SCS)has been widely studied,but remains under debate.Based on the latest high-quality multi-channel seismic data,bathymetric data,and other obtained seismic profiles,the asymmetric characteristics between the conjugate margins of the SCS are revealed and extensional model of the SCS margin is discussed further.Spatial variation of morphology,basement structure,and marginal faults are discovered among the SCS margin profiles.As for the NS-trending variation,the basement of northern margin displays in the shape of step downwards to the sea,while the basement of southern margin is composed of wide rotated and tilted blocks,without any obvious bathymetric change.The variation also exists in the development of marginal faults between the conjugate margins,and detachment fault system is identified on the southern margin.Along the southern margin from east to west,the Eastern and Southwestern Basins developed different structural units.Based on the tectonic contrast of the conjugate margins,differential extensional model is proposed to explain the spatial variation of the SCS structure,which introduces detachment faults controlling the evolution of the SCS.The upper crust above the detachment fault was deformed by simple shear,while the lower crust and upper mantle below the detachment fault was deformed by pure shear.Because of the different lateral transfer between the upper brittle faulting and the lower ductile extensional regions,there developed marginal plateau(Liyue basin)and outer rise(Zhenghe massif)on the lower plate margin of the Eastern Basin and the Southwestern Basin,respectively.The evolution of the present SCS may be influenced by the diachronous close of the paleo-SCS.  相似文献   

20.
根据青藏块体东北缘地区的跨断层流动水准测量资料,分别从断层形变异常的空间分布特征,不同断裂带上断层形变平均活动速率的分布和断层形变群体性异常在时间上的分布三个方面进行了统计、对比、分析和研究。结果显示,自2002年以来青藏块体东北缘地区的断层形变异常的主体区域逐步由西向东迁移,地震活动也具由西向东迁移的现象;断层平均活动速率也是东部区偏高。但是,断层形变群体异常在时间上的分布显示目前该区域断层形变异常活动的数量和强度均不十分显著,短期内发生强震的可能性不大。本文提出的方法及初步结论对该区域日常地震预测及震情跟踪工作有一定的参考价值。  相似文献   

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