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1.
2-D crustal structure and velocity ratio are obtained by processing S-wave data from two wide-angle reflec-tion/refraction profiles in and around Jiashi in northeastern Pamir,with the result of P-wave data taken into con-sideration.The result shows that:1)Average crustal velocity ratio is obviously higher in Tarim block than in West Kunlun Mts.and Tianshan fold zone,which reflects its crustal physical property of “hardness“and stability.The relatively low but normal velocity ratio(Poisson‘s ratio)of the lower crust indicates that the “downward thrusting“ of Tarim basin is the main feature of crustal movement in this area.2)The rock layer in the upper crust of Tian-shan fold zone is relatively“soft“,which makes it prone to rupture and stress energy release.This is the primary tectonic factor for the concentration of small earthquakes in this area.3)Jiashi is located right over the apex or the inflection point of the updoming lower crustal interface C and the crust-mantle boundary,which is the deep struc-tural background for the occurrence of strong earthquakes.The alternate variation of vp/vs near the block bounda-ries and the complicated configuration of the interfaces in the upper and middle part of the upper crust form a par-ticular structural environment for the Jiashi strong earthquake swarm.vp/vs is comparatively high and shear modulus is low at the focal region,which may be the main reason for the low stress drop of the Jiashi strong earthquake swarm.  相似文献   

2.
By processing S-wave data from the Fanshi-Huai'an-Taipusiqi DSS profile,which is a three-component,wide-angle reflection/refraction profile,and in the light of the results from P-wave interpretation,two-dimensional(2-D)structures of the crust and upper mantle are presented,including S-wave velocity Vs and the physical parameter of medium-Poisson's ratio a.Taking other geological and geophysical information into account,and with reference to the results from petrophysical experiments at home and abroad,we carried out interpretation and inference with respect to deep crustal structure,tectonics,and lithologic characters.It has been concluded that in the upper and middle crust,a values are mostly not greater than 0.25,and rocks,which generally assume brittle,are mainly composed of granite; the rocks in the lower layer of the upper crust between Yangyuan-Huai'an containing inorganic CO2 itself releases carbon; for the rocks in the lower crust and crust-mantle transitional zone,which are comparatively plasti  相似文献   

3.
In this article,we analyze the characters of SV-component receiver function of teleseismic body waves and its advantages in mapping the S-wave velocity structure of crust in detail.Similar to radial receiver function,SV-component receiver function can be obtained by directly deconvolving the P-component from the SV-component of teleseismic recordings.Our analyses indicate that the change of amplitude of SV-component receiver function against the change of epicentral distance is less than that of radial receiver function.Moreover,the waveform of SV-component receiver function is simpler than the radial receiver function and gives prominence to the PS converted phases that are the most sensitive to the shear wave velocity structure in the inversion.The synthetic tests show that the convergence of SV-component receiver function inversion is faster than tnat of the radial receiver function inversion.As an example,we investigate the S-wave velocity structure beneath HIA sta-tion by using the SV-component receiver function inversion method.  相似文献   

4.
Receiver function of body wave under the 23 stations in Yunnan was extracted from 3-component broadband digital recording of teleseismic event. Thus, the S-wave velocity structure and distribution characteristics of Poisson's ratio in crust of Yunnan are obtained by inversion. The results show that the crustal thickness is gradually thinned from north to south. The crustal thickness in Zhongdian of northwest reaches as many as 62.0 km and the one in Jinghong of further south end is only 30.2 km. What should be especially noted is that there exists a Moho upheaval running in NS in the Chuxiong region and a Moho concave is generally parallel to it in Dongchuan. In addition, there exists an obvious transversal inhomogeneity for the S-wave velocity structure in upper mantle and crust in the Yunnan region. The low velocity layer exists not only in 10.0-15.0 km in upper crust in some regions, but also in 30.0-40.0 km in lower crust. Generally, the Poisson's ratio is on the high side, however it has a better co  相似文献   

5.
Pn arrival time data are collected from the bulletins of both national and regional seismological network in China-These data are tomographically inverted to map the lateral variation and anisotropy of Pn velocity in the northeast-ern marginal region of Qinghai-Xizang plateau.The average Pn velocity in this region is 8.09km/s,being a little higher than the average for whole China,Higher velocity is found in tectonically stable Qaidam basin,while lower velocity is seen in and around tectonically active Shanxi graben.The region where the 1920 Haiyuan great earth-quake occurred shows a slightly low Pn velocity.A noticeable result is that,differing from the tectonically com-pressive Tianshan region.where Pn velocity is low,the Qilianshan region,where the Neotectonic deformation is also primarily compressive,shows high Pn velocity,In the uppermost mantle beneath the Ordos plateau Pn veloc-ity is inhomogeneous,varying from higher velocity in southwestern part to lower one in northeastern part.This may be attributed to possible movement of the Ordos block,as there are strong earthquakes all around the block.  相似文献   

6.
Crustal structure beneath the Songpan—Garze orogenic belt   总被引：2，自引：0，他引：2  
The Benzilan-Tangke deepseismic sounding profile in the western Sichuan region passes through the Song-pan-Garze orogenic belt with trend of NNE.Based on the travel times and the related amplitudes of phases in the record sections,the 2-D P-wave crustal structure was ascertained in this paper.The velocity structure has quite strong lateral variation along the profile.The crust is divided into 5layers,where the first,second and third layer belong to the upper crust,the forth and fifth layer belong to the lower crust.The low velocity anomaly zone gener-ally exists in the central part of the upper crust on the profile,and it integrates into the overlying low velocity basement in the area to the north of Ma‘erkang.The crustal structure in the section can be divided into 4parts:in the south of Garze-litang fault,between Garze-Litang fault and Xianshuihe fault,between Xianshuihe fault and Longriba fault and in the north of Longriba fault,which are basically coincided with the regional tectonics division.The crustal thickness decreases from southwest to northeast along the profile,that is ,from62km in the region of the Jinshajiang River to 52km in the region of the Yellow River.The Moho discontinuity does not obviously change across the Xianshuihe fault basesd on the PmP phase analysis.The crustal average velocity along the profile is lower,about 6.30 km/s.The Benzilan-Tangke profile reveals that the crust in the study area is orogenic.The Xianshuihe fault belt is located in the central part of the profile,and the velocity is positive anomaly on the upper crust,and negative anomaly on the lower crust and upper mantle.It is considered as a deep tectonhic setting in favor of strong earthquake‘s accumulation and occurrence.  相似文献   

7.
A teleseismic profile consisting of 26 stations was deployed along 30°N latitude in the eastern Tibetan Plateau. By use of the inversion of P-wave receiver function, the S-wave velocity structures at depth from surface to 80 km beneath the profile have been determined. The inversion results reveal that there is significant lateral variation of the crustal structure between the tectonic blocks on the profile. From Linzhi north of the eastern Himalayan Syntaxis, the crust is gradually thickened in NE direction; the crustal thickness reaches to the maximum value (~72 km) at the Bangong-Nujiang suture, and then decreased to 65 km in the Qiangtang block, to 57―64 km in the Bayan Har block, and to 40―45 km in the Sichuan Basin. The eastern segment of the teleseismic profile (to the east of Batang) coincides geographically with the Zhubalong-Zizhong deep seismic sounding profile carried out in 2000, and the S-wave velocity structure determined from receiver functions is consistent with the P-wave velocity structure obtained by deep seismic sounding in respect of the depths of Moho and major crustal interfaces. In the Qiangtang and the Bayan Har blocks, the lower velocity layer is widespread in the lower crust (at depth of 30―60 km) along the profile, while there is a normal velocity distribution in lower crust in the Sichuan Basin. On an average, the crustal velocity ratio (Poisson ratio) in tectonic blocks on the profile is 1.73 (σ = 0.247) in the Lhasa block, 1.78 (σ = 0.269) in the Banggong-Nujiang suture, 1.80 (σ = 0.275) in the Qiangtang block, 1.86 (σ = 0.294) in the Bayan Har blocks, and 1.77 (σ = 0.265) in the Yangtze block, respectively. The Qiangtang and the Bayan Har blocks are characterized by lower S-wave velocity anomaly in lower crust, complicated Moho transition, and higher crustal Poisson ratio, indicating that there is a hot and weak medium in lower crust. These are considered as the deep environment of lower crustal flow in the eastern Tibetan Plateau. Flowage of the ductile material in lower crust may be attributable to the variation of the gravitational potential energy in upper crust from higher on the plateau to lower off plateau.  相似文献   

8.
Since S-wave velocity of the subsurface is an important parameter in near surface applications,many studies have been conducted for its estimation.Among the various methods that use surface waves or body waves,Rayleigh wave inversion is the most popular.In practice,the densities and P-wave velocities of different layers are usually assumed to be known to avoid ill-posed problems,as they have less influence on the dispersion curves.However,improper assignment of these two groups of parameters leads to inaccurate estimation of the S-wave velocity profile.In order to address this problem,the all-parameters Rayleigh wave inversion strategy is proposed in which the S-wave velocities,layer thicknesses,densities and P-wave velocities of different layers are included as the unknown parameters for inversion.Meanwhile,the transitional Markov Chain Monte Carlo(TMCMC)algorithm is applied for the implementation of all-parameters Rayleigh wave inversion.One simulated example and two real-test applications are demonstrated to verify the capability of the proposed method in the estimation of the S-wave velocity profile,the densities and the P-wave velocities.Furthermore,it is verified that the proposed method achieved more accurate S-wave velocity profile estimation than the traditional approach.  相似文献   

9.
1-D and 2-D calculation and interpretation are carried out with the DSS data from the western section of Heze-Changzhi profile and the southern section of Zhengzhou-Jinan profile. 2-D velocity structure is determined in Tangyin graben and its adjacent area. The result shows that velocity structure of the crust and upper mantle is obviously different in vertical and lateral directions. Crustal thickness varies apparently in this area, and there are local low velocity blocks in the interior crust. The swelling M-discontinuity corresponds to Tangyin graben and Moho depth at the highest swelling position is 31 km. Toward the east, its depth gradually increases to 32 km in Xunxian swelling; toward the west, M-discontinuity becomes a steep zone at the piedmont uplift of Taihang Mountain and reaches 40 km at depth near Changzhi. Through analyzing the relationship between historical earthquakes and deep structure in North China, we infer that seismic risk exists in Tangyin graben and its adjacent area.  相似文献   

10.
Through the analysis and 2-D inversion for the 5 profiles in Haiyuan arcuate tectonic region (105°～107°E,36°～37.5°N) in the northeastern margin of Qinghai-Xizang Plateau, we have obtained the electric structure within a range of 160 km in width (east-west) and 60 km in depth in the studied area. The results show that the crustal electric structure can be divided into 6 sections, corresponding respectively to Xiji basin (Ⅰ), Xihuashan-Nanhuashan uplift (Ⅱ), Xingrenbu-Haiyuan basin (Ⅲ), Zhongwei-Qingshuihe basin (Ⅳ), Zhongning-Hongsibu basin (Ⅴ) and west-margin zone of Ordos (Ⅵ) from the southwest to the northeast. The crustal electric structure is characterized by a broom-shaped pattern, which scatters to the northwest and shrinks to the southeast. The structures in the top part of Haiyuan arcuate tectonic region are complete and large, however, they diminish from the arc top to the northwest and southeast ends. In the depth from 0 km to 10 km, the resistivity is high in the sections Ⅱ and Ⅵ, but relatively low in the other four sections, showing a similar pattern of basin depression. The electrical basement in the section Ⅲ is the deepest, displaying a "dustpan" shape that is deep in the southwest and shallow in the northeast. A series of discontinuous zones with high conductivity exist in the middle-lower crust in Haiyuan arcuate tectonic region, which is possibly related to the moderate and strong earthquakes in the region. The resistivity distribution in the focal area of the 1920 Haiyuan earthquake is significantly heterogeneous with an obviously high conductivity zone near the hypocenter regime.  相似文献   

11.
玛沁-靖边剖面S波资料研究与探讨   总被引：8，自引：3，他引：8       下载免费PDF全文
对玛沁——靖边剖面深地震测深S波资料处理解释，获得本区S波二维地壳速度结构和波速比结构．结果表明，该区S波二维速度结构和波速比结构，沿剖面存在着明显的差异．剖面西段和海原地区下方呈现S波速度偏低，而波速比偏高的结构特征；剖面中段和东段的S波速度和波速比正常．根据S波速度结构和波速比结构的横向变化特征，讨论了两大异常区岩性的变化．推测海原大地震孕育发生不仅与构造活动有关，而且与该区的岩石性质有关．   相似文献   

12.
收集了首都圈数字化地震遥测台网58个井下摆2003-2008年记录的102次M≥3.0地震的数据.通过鉴别直达波及对应地表反射波的波形,发现两者到时差与震中矩和方位角无关.基于斯涅尔定律,分析获得了这些台站上方厚约300 m浅地表土层P波和S波平均速度结构以及波速比.结果表明,首都圈区域近地表P波和S波平均速度分别约为...  相似文献   

13.
崔辉辉  周元泽 《地震学报》2016,38(5):659-670
本文基于中国数字地震台网记录的发生于日本北海道地区的一次中源地震的三重震相资料研究了日本海俯冲区地幔转换带的速度结构．结果表明,该区域P波速度结构与S波速度结构的一致性整体上较强．冷的西太平洋俯冲板块导致410 km间断面出现了10 km的抬升,660 km间断面出现了25 km的下沉;410 km和660 km间断面之上均存在与俯冲板块相关的高速层;660 km间断面下方存在厚度为65 km的低速异常．纵横波波速比vP/vS值在210—400 km深度范围内偏低,约为1.827,体现出海洋板块低泊松比的特征;在560—685 km深度范围内,该值偏高,约为1.831,可能预示地幔转换带底部含有一定量的水．   相似文献   

14.
IntroductionBetween January and April of 1997, 7 earthquakes with M(6.0 occurred successively in Jiashi, Xinjiang. The continual occurrence of strong earthquakes within such a small area and in such a short period of time is exceptional for intraplate earthquakes. The Jiashi earthquake swarm took place on the northeast side of the Pamirs, where the Tarim basin, South Tianshan and West Karakoram meet (HU, et al, 1989). This is also a place where a number of active faults develop, so it is…  相似文献   

15.
利用1980年1月-2008年12月宁夏地震台网记录的中小地震事件直达波到时数据,采用单台多震和达法,对吴忠-灵武地区该时段内MS ≥ 5.0地震发生前波速比变化进行回溯性分析,并对该区未来短期内震情趋势进行研判,所得结果表明：①吴忠-灵武地区MS ≥ 5.0地震前波速比存在正常→降低→上升(恢复)→发震的异常变化过程;②研究区台站出现波速比异常,其空间分布对发震位置具有一定指示意义,即发震位置可能位于波速比下降台站或存在异常台站所连线的多边形边缘或内部;③据近期扫描结果,海原地震台波速比异常较显著,需密切关注宁夏南部及邻区地球物理观测资料的变化。  相似文献   

16.
Extensive geophysical research has been carried out in southeast Tibet due to the complex geological structure and high seismicity. The study of the Moho interface can provide useful information for the geophysical research. SWChinaCVM-1.0 is the first version of a regional community velocity model for the Sichuan-Yunnan region and aims to provide a reference for seismological research in the region. Based on this model, a high-precision community Moho interface model can be obtained using common conversion point (CCP) stacking, to further expand the applicability of SWChinaCVM-1.0. Before CCP stacking, it is necessary to check the fit of the practical and theoretical travel times of the Ps phase and its multiples under the constraints of the model. Using this method, referred to as Hκ0 stacking, we determined the Moho interface. However, the multiples were poorly fitted with the theoretical travel times at many stations, and the crustal thickness obtained was inconsistent with previous findings. Therefore, we speculate that the SWChinaCVM-1.0 model has some limitations that render it incompatible with the CCP stacking method. To further verify this hypothesis, we performed H-κ stacking using the vP-vS model, vP model, vS model, and the regional average velocity vP0 and compared the results with those of Hκ0 stacking. The results of the comparison indicate that the SWChinaCVM-1.0 model requires improvements. In addition, by analyzing the SWChinaCVM-1.0 inversion process, we found that the vS model was more reliable than the vP model. Finally, we adopted the crustal thickness obtained using H-κ stacking based on the vS model as the initial version of a community Moho interface model for the Sichuan-Yunnan region (SWChinaCVM-MOHO-1.0).  相似文献   

17.
在陆地气枪主动源技术系统不断发展的基础上，使用地震层析成像和计算机图像处理技术，把地震波物理参数(地震波速度和vP/vS)演化过程以气象云图的形式表现出来，达到“看图识天气”的目的。利用地震波速“地下云图”的结果开展地震孕育过程和机理研究，深入了解强震发生前后震源区地震波速度和波速比的时空演化表征，总结提取具有普适性的地震学前兆参数及其指标，对进一步提高地震预测预报效能有着重要科学意义。  相似文献   

18.
The Hi-CLIMB seismic array is located in the central-western Tibetan Plateau. The H-κ-c method (Li JT et al., 2019) was applied to receiver function data on the HiCLIMB, which corrects the back-azimuthal variations in the arrival times of Ps and crustal multiples caused by crustal anisotropy and dipping interfaces before performing H-κstacking. Compared to the traditional H-κ method, the H-κstacking results after harmonic corrections showed considerable improvements, including greatly reduced errors, significantly less scattered H (crustal thickness) and κ (crustal vP/vS ratio) values, and clearer patterns of H and κ in different Tibetan blocks. This demonstrates that the H-κ-c method works well even for regions with complex crustal structures, such as the Tibetan Plateau, when there are helpful references from nearby stations or other constraints. The variation in crustal thickness agrees with previous studies but tends to be relatively shallower beneath most of the plateau. Two regions with particularly high crustal vP/vS were observed, namely, one in the northern Himalaya block and beneath the YarlungZangbo suture, and the other in the Qiangtang block. Their correlation with mid-crust low S velocities from previous studies suggests the possible presence of fluid or partial melt in the two regions, which may have implications for the crustal flow model. In contrast, the Lhasa block had relatively lower crustal vP/vS and relatively higher crustal S velocity within the plateau, which is interpreted to be mechanically stronger than the Himalaya and Qiangtang blocks, and without mid-crust partial melt.  相似文献   

19.
东北地区660km间断面附近波速结构研究   总被引：6，自引：1，他引：5       下载免费PDF全文
叶玲玲  李娟 《地震学报》2012,34(2):137-146
我国东北地区位于西北太平洋和达-贝尼奥夫俯冲带前缘,其深部速度结构对理解板块俯冲行为以及地幔物质的交换有重要意义.利用区域三重震相模拟方法,对中国地震观测台网记录到的两个深源地震P波和SH波波形数据,进行了相对到时和波形的拟合,获得了我国东北地区660 km间断面附近波速结构.结果表明,研究区域下方的间断面没有发生明显...  相似文献   

20.
INTRODUCTIONXIJI－Halyuan－Zhon驯el region Is a well－known eaythquake－prone one In China．From 876 to1989,IOrty－five earthquakes with M。34．7 occurred In and around the。glon(Ma Xingyuan,et al,1989)．Seismic activity In this area Is evidently cha。cterized by large matlnltude and high frequency．The 1920 Haiyuan earthquake(M＝8．5)happened nght In this region,which caused a seriousdisaster and had a wide－ranging effect seldom seen worldwide．For the years,lots of…  相似文献   

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