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1.
Introduction It is well known that the occurrence of moderate and strong earthquakes and the distribution of seismically active belts are most directly related to deep crustal faults. Therefore, studying geometrical spreading and physical state of medium of deep crustal faults has always been a major subject in earthquake science. It is not only of great significance to the understanding of deep structural background and seismogenic mechanism of strong earthquakes, but also of great help to se…  相似文献   

2.
This paper studies the computation method of two-step inversion of interface and velocity in a region. The 3-D interface is described by a segmented incomplete polynomial; while the reconstruction of 3-D velocity is accomplished by the principle of least squares in functional space. The computation is carried out in two steps. The first step is to inverse the shape of 3-D interface; while the second step is to do 3-D velocity inversion by distributing the remaining residual errors of travel time in accordance with their weights. The data of seismic sounding in the Tangshan-Luanxian seismic region are processed, from which the 3-D structural form in depth of the Tangshan seismic region and the 3-D velocity distribution in the crust below the Tangshan-Luanxian seismic region are obtained. The result shows that the deep 3-D structure in the Tangshan seismic region trends NE on the whole and the structure sandwiched between the NE-trending Fengtai-Yejituo fault and the NE-trending Tangshan fault is an uplifted zone of the Moho. In the 3-D velocity structure of middle-lower crust below that region, there is an obvious belt of low-velocity anomaly to exist along the NE-trending Tangshan fault, the position of which tallies with that of the Tangshan seismicity belt. The larger block of low-velocity anomaly near Shaheyi corresponds to a denser earthquake distribution. In that region, there is an NW-trending belt of high-velocity anomaly, probably a buried fault zone. The lower crust below the epicentral region of the Tangshan M S=7.8 earthquake is a place where the NE-trending belt of low-velocity anomaly meets the NW-trending belt of high-velocity anomaly. The two sets of structures had played an important role in controlling the preparation and occurrence of the M S=7.8 Tangshan earthquake. Contribution RCEG97006, Research Center of Exploration Geophysics, China Seismological Bureau, China. This project is supported by the Chinese Joint Seismological Science Foundation.  相似文献   

3.
Ｆｅａｔｕｒｅｓｏｆｉｓｏｓｔａｔｉｃｇｒａｖｉｔｙａｎｏｍａｌｙａｎｄｓｅｉｓ┐ｍｉｃａｃｔｉｖｉｔｙｉｎｔｈｅＣｅｎｔｒａｌＡｓｉａｎｒｅｇｉｏｎＳＨＥＮＧ－ＭＩＮＧＦＡＮＧ１）（方盛明）ＲＵＩＦＥＮＧ２）（冯锐）ＣＨＡＮＧ－ＺＨＥＮＧＴＩＡＮ...  相似文献   

4.
The observation of the fault-zone trapped waves was conducted using a seismic line with dense receivers across surface rupture zone of the M=8.1 Kunlun Mountain earthquake. The fault zone trapped waves were separated from seismograms by numerical filtering and spectral analyzing. The results show that: a) Both explosion and earthquake sources can excite fault-zone trapped waves, as long as they locate in or near the fault zone; b) Most energy of the fault-zone trapped waves concentrates in the fault zone and the amplitudes strongly decay with the distance from observation point to the fault zone; c) Dominant frequencies of the fault-zone trapped waves are related to the width of the fault zone and the velocity of the media in it. The wider the fault zone or the lower the velocity is, the lower the dominant frequencies are; d) For fault zone trapped waves, there exist dispersions; e) Based on the fault zone trapped waves observed in Kunlun Mountain Pass region, the width of the rupture plane is deduced to be about 300 m and is greater than that on the surface. Foundation item: Joint Earthquake Science Foundation of China (201001). Contribution No. RCEG200305, Research Center of Exploration Geophysics, China Earthquake Administration.  相似文献   

5.
Based on the results from seismogeological study,aeromagnetic inversion and deepseismic sounding(DSS),it is found that the M≥8.0 earthquakes in North China have three common deep structural characteristics,i.e,they all took place above the ultra-crustal deep faults or on the edges of the tectonic blocks with higher intensity,and there are low-velocity,low-density and high-conductive layers deep in the epicentral regions.The origins of the earth-quakes are also discussed and the two possibilities of seismogenesis are proposed,i.e,tectonic movement and intracrustal explosion.  相似文献   

6.
In the estimation of seismic tendency, using Gutenberg-Richter’sb-value and using Hurst exponent are two commonly used methods. Based on the fractal geometry of earthquake time series, we point out that these two methods correlate to each other. In the perspective of fractional Brownian motion (FBM), an earthquake sequence withb>3/4 and that withb<3/4 have different dynamic properties. Foundation item: The MOST Project G1998040705. Contribution No. 01FE2010, Institute of Geophysics, China Seismological Bureau.  相似文献   

7.
Ray equation migration of wide-angle reflections in 2-D medium is one kind of Kirchhoff prestack depth migration method. Based on ray theory, this method can be used extensively in 2-D inhomogeneous medium, and shows its advantage in wide-angle reflection study. After calculating ray fields, we can get the wave fields of sources and receivers by interpolation, and the intensity (or amplitude) A p corresponding to the depth point P at travel-time t P =t SP +t PR can be found in seismograms. Ray equation migration is completed by transforming A P according to the specific relation, migrating it to the depth point, then calculating the ray fields of lots of sources and receivers in the same way and finally stacking the outcomes. Numerical calculation has yielded satisfactory results. Data processing of the Zhuangmu-Yuexi-Huangmei-Zhanggondu profile passing through the Dabie orogenic zone provides a structural form of M-discontinuity along the profile. The result shows that the high pressure metamorphic rock zone of South Dabie rock mass is related to the uplifting of M-discontinuity here. "Mountain root" exists under North Dabie rock mass, which conforms with gravity isostasy theory. The Xiaotian-Mozitan fault is a suture zone as a result of the collision of North China plate with Yangtze plate, and extends through M-discontinuity. The abyssal fault near Liu’an is the extended eastern section of the Luonan-Minggang fault, which is also confirmed here. Contribution No. RCEG 96012, Research Center of Exploration Geophysics, SSB, China. This project was supported by the National Natural Science Foundation of China and the Chinese Joint Seismological Science Foundation.  相似文献   

8.
In the light of the single scattering model of coda originating from local earthquakes, and based on the aftershock coda registered respectively at the 4 short period stations installed near the foci shortly after theM7.6 Lancang andM7.2 Gengma earthquakes, this paper has tentatively calculated the rate of amplitude attenuation and theQ c-value of the coda in the Lancang and Gengma areas using a newly-founded synthetic determination method. Result of the study shows the rate of coda amplitude attenuation demonstrates remarkable regional differences respectively in the southern and northern areas. The southern area presents a faster attenuation (Q c=114), whereas the northern area shows a slower attenuation (Q c=231). The paper also discusses the reasons causing such differences. Result of the study also suggests a fairly good linear relation between the coda source factorA o(f) and the seismic moment and the magnitude. Using the earthquake scaling law, the following formulas can be derived: lgM 0=lgA 0(f)+17.6,M D=0.67lgA 0(f)+1.21 and logM 0=1.5M D+15.79. In addition, the rates of amplitude attenuationβ s andβ m are respectively calculated using the single scattering and multiple scattering models, and the ratioβ s/βm=1.20−1.50 is found for the results respectively from the two models. Finally, the mean free pathL of the S-wave scattering in the southern and northern areas are determined to be 54 km and 122 km respectively by the relations which can distinguish between the inherentQ i and scatteringQ s, testify to this areas having lowQ-values correspond to stronger scatterings. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,14, 71–82, 1992. This study is partly supported by the Seismological Science Foundation of the State Seismological Bureau of China, and the present English version of the paper is translated from its Chinese original by Wenyi Xia, Seismological Bureau of Yunnan Province.  相似文献   

9.
    
Based on the long period surface wave data recorded by the China Digital Seismograph Network (CDSN), theQ R of fundamental mode Rayleigh wave with periods from 10 s to 146 s is determined for the eastern Sino-Korean paraplatform in this paper. TheQ β models of the crust and upper mantle are respectively obtained for the 4 paths, with the aid of stochastic inverse method. It shows that in the eastern Sino-Korean paraplatform, the average crustalQ β is about 200, and that there exists a weak attenuation layer in the middle crust (about 10–20 km deep) which is possibly related to earthquake-prone layer. A strong attenuation layer (lowQ) of 70 km thick extensively exists in the uppermost mantle, with the buried depth about 80 km. The averageQ R of fundamental mode Rayleigh wave is between the value of stable tectonic region and that of active tectonic region, and much close to the latter. Contribution No. 96A0001, Institute of Geophysics, SSB, China. Funded by the Chinese Joint Seismological Science Foundation.  相似文献   

10.
Ruichang-Yangxin earthquake is another moderate earthquake in Yangxin-Jiujiang area since 2005 Jiujiang-Ruichang M5.7 earthquake. In order to more understand the seismic activities in this area, we study the moment tensor solution and the seismogenic structure of the Ruichang-Yangxin earthquake. Precise earthquake relocation shows that the mainshock occurred on the southwestern part of the NE-trending fault and aftershocks are distributed not only along the NE-trending fault but also along its conjugated NW-trending fault. By comprehensive analysis on the earthquake distribution, characteristics of isoseismal curve, focal mechanism, and regional structure characteristics, it is inferred that this earthquake is caused by the NE-trending Tanlu fault. In addition, it has close relationship with the conjugated NW-trending fault as well. Many researches have shown that the junction area is the earthquake-prone area, and should be paid more attention to. And our study also proves this viewpoint.  相似文献   

11.
WANG  Jian 《地震学报(英文版)》2004,17(4):381-388
In this paper, we calculated the seismic pattern of instrumental recorded small and moderate earthquakes near the epicenter of the 1303 Hongtong M=8 earthquake, Shanxi Province. According to the spatial distribution of small and moderate earthquakes, 6 seismic dense zones are delineated. Temporal distribution of ML≥2 earthquakes since 1970 in each seismic dense zone has been analyzed. Based on temporal distribution characteristics and historical earthquake activity, three types of seismicities are proposed. The relationship between seismic types and crustal medium is analyzed. The mechanism of three types is discussed. Finity of strong earthquake recurrence is proposed. Seismic hazard in mid-long term and diversity of earthquake disaster in Shanxi seismic belt are discussed.  相似文献   

12.
    
A brief account of the development of the research on mining earthquakes and the general situation of the Mentougou Coal Mine medium-scale experiment field for earthquake prediction and the project of monitor and prediction is given. The differences of waveforms between mining earthquakes and natural earthquakes is discussed. The magnitude-frequency distribution of the 79 000 mining earthquakes of overM l 1. 0 from 1984 to 1995 is summarized. Finally, taking PH and PV, the principal compressive stress components of the focal mechanism of the mining earthquakes, as the criteria, analyses the stress background of the 12 large mining earthquakes. Contribution No. 95C0002, Institute of Geophysics, SSB, China. This study is sponsored by the Chinese Joint Seismological Science Foundation.  相似文献   

13.
High frequency fall-off of source spectra using Q -free spectra estimation   总被引：1，自引：0，他引：1  
ＩｎｔｒｏｄｕｃｔｉｏｎＴｈｅｅａｒｔｈｑｕａｋｅｓｏｕｒｃｅｓｐｅｃｔｒａｓｔｕｄｉｅｓｍａｙｂｅｔｒａｃｅｄｂａｃｋｔｏｌａｔｅ１９６０ｓ（Ａｋｉ,１９６７;Ｂｒｕｎｅ,１９７０;Ｈａｎｋｓ,１９７９）．Ｆｏｒｉｔｓｉｍｐｏｒｔａｎｃｅｉｎｓｔｒ...  相似文献   

14.
Conclusions The sequence of the November 29, 1999 Xiuyan, Liaoning, earthquake withM S=5.4 is relocated, and its rupture process is analyzed. Results are as follows: The rupture extended mainly before the January 12, 2000,M S=5.1 earthquake. There are two phases of rupture extending: The first phase was before the November 29, 1999,M S=5.4 earthquake, epicenters were situated within a small region with a dimension of about 5 km, and the focal depth increased. It shows that the rupture mainly extended from shallow part to deep in the vertical direction. The second phase was between theM S=5.4 earthquake and theM S=5.1 earthquake, earthquakes migrated along southeast, the focal depth decreased. It indicates that the rupture extended along southeast and from deep to shallow part. Foundation item: The Project of “Mechanism and Prediction of the Strong Continental Earthquake” (95-13-05-04). Contribution No. 01FE2017, Institute of Geophysics, China Seismological Bureau.  相似文献   

15.
The geography information system of the 1303 Hongton M=8 earthquake has been established. Using the spatial analysis function of GIS, the spatial distribution characteristics of damage and isoseismal of the earthquake are studies. By comparing with the standard earthquake intensity attenuation relationship, the abnormal damage distribution of the earthquake is found, so the relationship of the abnormal distribution with tectonics, site condition and basin are analyzed. In this paper, the influence on the ground motion generated by earthquake source and the underground structures near source also are studied. The influence on seismic zonation, anti-earthquake design, earthquake prediction and earthquake emergency responding produced by the abnormal density distribution are discussed. Foundation item: National important fundamental research “The Basic Research of Important Project in Damage Environment” and The important project “The Seismic Hazard Assessment Research and Anti-earthquake Structure Research” from China Earthquake Administration during the 10th Five-year Plan. Contribution No. 04FE1008, Institute of Geophysics, China Earthquake Administration.  相似文献   

16.
Characteristics of present-day tectonic movement in the northeastern margin of Qinghai-Xizang plateau (Tibetan) are studied based on earthquake data. Evidence of earthquake activity shows that junctures between blocks in this area consist of complicated deformation zones. Between the Gansu-Qinghai block and Alxa block there is a broad compressive deformation zone, which turns essentially to be a network-like deformation region to the southeast. The Liupanshan region, where the Gansu-Qinghai block contacts the Ordos block, is suffering from NE-SW compressive deformation. Junction zone between the Ordos and Alxa block is a shear zone with sections of variable trend. The northwestern and southeastern marginal region of the Ordos is under NNW-SSE extension. The above characteristics of present-day tectonic deformation of the northeastern Qinghai-Xizang plateau may be attributed to the northeastward squeezing of the plateau and the resistance of the Ordos block, as well as the southeastward extrusion of the plateau materials. Foundation item: State Natural Science Foundation of China (49732090) and the Development Program on National Key Basic Researches under the Project Mechanism and Prediction of Continental Strong Earthquakes (95-13-02-05). Contribution No. 00FE2003, Institute of Geophysics, China Seismological Bureau.  相似文献   

17.
Following a new train of thinking, this paper has explored first the potential information in the ground resistivity data observed by the existing geoelectric observation system, investigated and proposed a new dimensionless geoelectric precursor factor, the degree of ground resistivity anisotropy, S, and studied the characteristics of dynamic evolution pattern of S during the seismogenic process. The results show that, during the seismogenic process, the degree of ground resistivity anisotropy (S) displays a process of 'normal' →'abnormal strengthening (amplitude, range)' →abnormal weakening' → 'earthquake occurrence'→ 'normal'. The earthquake would occur at the time when the S value has entered the late stage of strengthening and turns to weaken and in the gradient belt on the margin of S anomaly region. The dynamic evolution pattern of S reflects the changes of the tectonic stress field during the seismogenic process. Therefore, it would be possible to trace the process of earthquake generation and occurrence from the dynamic evolution pattern of S so as to service earthquake prediction.  相似文献   

18.
The seismogenic fault and the dynamic mechanism of the Ning’er, Yunnan Province MS6.4 earthquake of June 3, 2007 are studied on the basis of the observation data of the surface fissures, sand blow and water eruption, land-slide and collapse associated with the earthquake, incorporating with the data of geologic structures, focal mecha-nism solutions and aftershock distribution for the earthquake area. The observation of the surface fissures reveals that the Banhai segment of the NW-trending Ning’er fault is dominated by right-lateral strike-slip, while the NNE-trending fault is dominated by left-lateral strike-slip. The seismo-geologic hazards are concentrated mainly within a 330°-extending zone of 13.5 km in length and 4 km in width. The major axis of the isoseismal is also oriented in 330° direction, and the major axis of the seismic intensity VIII area is 13.5 km long. The focal mechanism solutions indicate that the NW-trending nodal plane of the Ning’er MS6.4 earthquake is dominated by right-lateral slip, while the NE-trending nodal plane is dominated by left-lateral slip. The preferred distribution orientation of the aftershocks of MS≥2 is 330°, and the focal depths are within the range of 3~12 km, predominantly within 3~10 km. The distribution of the aftershocks is consistent with the distribution zone of the seismo-geologic hazards. All the above-mentioned data indicate that the Banhai segment of the Ning’er fault is the seismogenic fault of this earthquake. Moreover, the driving force of the Ning’er earthquake is discussed in the light of the active block theory. It is believed that the northward pushing of the Indian plate has caused the eastward slipping of the Qinghai-Tibetan Plateau, which has been transformed into the southeastern-southernward squeezing of the southwest Yunnan region. As a result, the NW-trending faults in the vicinity of the Ning’er area are dominated by right-lateral strike-slip, while the NE-trending faults are dominated by left-lateral strike-slip. This tectonic  相似文献   

19.
IntroductionThenortheasternregionofQinghai-Xizangplateauisthejunctionregionofthethreeblocks,ie.,Qinghai-Xizang,AIxaandordosblock.TianandDing(l998)studiedtheclockwisetypequasi-trijunctionaroundHaiyuan-YinchuaninnortheasternregionofQinghai-Xizangplateau.Thethreet6ctonicbranchesofthequasi4rjunctionareQiIianshanfaultzone,Yinchuan-Jedai-Linhe(YJL)fractureddepressionbasinandLiupanshanfaultzone.TheQilianshanfaultzoneshowssin-istraIandcompressionalmovement,themovementofYJLbasinisofdextraland…  相似文献   

20.
The deep seismic reflection data on profile HY2 are reprocessed by the method of simultaneous inversion of velocity distribution and interface position. By the travel-time inversion with the data of the diving wave Pg and fault plane reflection wave, we determine the geometric form and velocity of Haiyuan fault zone interior and surrounding rock down to 10 km depth. The measured data show that the amplitudes have strong attenuation in the range of stake number 37–39 km, suggesting the fault zone has considerable width in the crustal interior. The results of this paper indicate that to the north of the fault zone the crystalline basement interface upheaves gradually from southwest to northeast and becomes shallow gradually towards northeast, and that to the south of the fault zone, within the basin between Xihua and Nanhua mountains, the folded basement becomes shallow gradually towards southwest. The obliquity of the fault zone is about 70° above the 3 km depth, about 60° in the range of the 3–10 km depths. From the results of this paper and other various citations, we believe that Haiyuan fault zone is in steep state from the Earth’s surface to the depth of 10 km. Foundation item: Joint Seismological Science Foundation of China (201001) and State Key Basic Research Development and Programming Project (95-13-02-02). Contribution No. RCEG200308, Exploration Geophysical Center, China Earthquake Administration.  相似文献   

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