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1.
Based on GPS velocity during 1999-2007, GPS baseline time series on large scale during 1999-2008 and cross-fault leveling data during 1985-2008, the paper makes some analysis and discussion to study and summarize the movement, tectonic deformation and strain accumulation evolution characteristics of the Longmenshan fault and the surrounding area before the MS8.0 Wenchuan earthquake, as well as the possible physical mechanism late in the seismic cycle of the Wenchuan earthquake. Multiple results indicate that:GPS velocity profiles show that obvious continuous deformation across the eastern Qinghai-Tibetan Plateau before the earthquake was distributed across a zone at least 500km wide, while there was little deformation in Sichuan Basin and Longmenshan fault zone, which means that the eastern Qinghai-Tibetan Plateau provides energy accumulation for locked Longmenshan fault zone continuously. GPS strain rates show that the east-west compression deformation was larger in the northwest of the mid-northern segment of the Longmenshan fault zone, and deformation amplitude decreased gradually from far field to near fault zone, and there was little deformation in fault zone. The east-west compression deformation was significant surrounding the southwestern segment of the Longmenshan fault zone, and strain accumulation rate was larger than that of mid-northern segment. Fault locking indicates nearly whole Longmenshan fault was locked before the earthquake except the source of the earthquake which was weakly locked, and a 20km width patch in southwestern segment between 12km to 22.5km depth was in creeping state. GPS baseline time series in northeast direction on large scale became compressive generally from 2005 in the North-South Seismic Belt, which reflects that relative compression deformation enhances. The cross-fault leveling data show that annual vertical change rate and deformation trend accumulation rate in the Longmenshan fault zone were little, which indicates that vertical activity near the fault was very weak and the fault was tightly locked. According to analyses of GPS and cross-fault leveling data before the Wenchuan earthquake, we consider that the Longmenshan fault is tightly locked from the surface to the deep, and the horizontal and vertical deformation are weak surrounding the fault in relatively small-scale crustal deformation. The process of weak deformation may be slow, and weak deformation area may be larger when large earthquake is coming. Continuous and slow compression deformation across eastern Qinghai-Tibetan Plateau before the earthquake provides dynamic support for strain accumulation in the Longmenshan fault zone in relative large-scale crustal deformation.  相似文献   

2.
Based on the GPS velocity field data of 1999-2007 and 2011-2013,we used the least squares configuration method and GPS velocity profile results to synthetically analyze the dynamic evolution characteristics of crustal deformation in the Yunnan area before and after the Wenchuan earthquake. The dynamic evolution of GPS velocity field shows that the direction is gradually changed from the south in the southern part of the Sichuan-Yunnan block to the south-west in the southern Yunnan block and there is a clear relative motion characteristic near the block boundary fault zone. Compared with the GPS velocity of 1999-2007, the results of 2011-2013 also reflect segmental deformation characteristics of the block boundary fault zone. Southeast movement shows a significant increase, which may be related to crustal deformation adjustment after the Wenchuan earthquake. The dynamic evolution of strain parameters shows a pattern of "extension in the middle and compression at both ends" in the whole area and the distribution of deformation (shear, extension or compression) is closely related to the background motion and deformation characteristics of the main fault zone. Compared with the results of the period of 1999-2007, the extensional deformation zone of 2011-2013 is expanded eastward and southward. The compressional deformation of the eastern boundary (the Xiaojiang fault zone) of the Sichuan-Yunnan block is no longer significant, which is mainly concentrated in the northern section of the Xiaojiang fault zone and may be related to the post-seismic deformation adjustment of the Wenchuan earthquake. The GPS velocity profile results show that the left-lateral slip velocity of the Xiaojiang fault zone reduced gradually from north to south (10mm/a-5mm/a), and the width of the northern section is wider. The right-lateral slip rate of the Honghe fault zone is about 4mm/a, and the deformation width is wider. The dynamic results show that the Wenchuan earthquake has little effect on the deformation modes of these two fault zones.  相似文献   

3.
Using the GPS velocity data from 27 stations around the Eastern Kunlun fault as constraints,we first invert the slip velocities of the Eastern Kunlun fault,the north boundary fault of the Qaidam basin,the Mani-Yushu fault and the Margai Caka fault before the Kekexili MS8.1 earthquake with a 3-D elastic half-space dislocation model. The deformation field calculated from the slip movement of these faults can be considered the deformation background field of the earthquake. Based on the deformation background field with tectonic implications,we have obtained the strain field and earthquake moment accumulation field. The results show that there are two obvious high moment accumulation rate regions,one of which is the Dongdatan-Xidatan segment of the Eastern Kunlun fault where the M_S8.1 earthquake occurred in 2001.  相似文献   

4.
Systematic differences in the duration and frequency content of ground motions from the hanging wall and footwall during the 2008 Wenchuan earthquake are investigated,focusing on the influence of these differences on structural input energy based on the elastic and inelastic energy responses of structures.A comparison of the input energy spectra between the hanging wall and the footwall reveal that the structural input energy on the hanging wall is not amplified due to the short duration and low peak ground velocity to acceleration ratio(V/A).However,the larger demand of structural input energy on the footwall in the range of medium and long periods is observed and the demand increases up to 50% relative to the average level of structural input energy for rupture distances larger than 30 km.The importance of considering the footwall effect on structural input energy when comparing ground motions in the range of medium and long periods is recognized.  相似文献   

5.
The results from interpretation of the aerophotos and in-situ seismogeological researches show that there are some obvious late-Quaternary activities along the Moxi-Mianning segment of the Xianshuihe-Anninghe fault zone, with the characteristics of sinistral-slip movement accompanied by some significant vertical slip components. Since late-Quaternary, the average horizontal slip rate of the segment at the south of Moxi along the Xianshuihe fault is 6.0～9.9mm/a and 4.7～5.3mm/a along the segment at the north of Mianning of the Anninghe fault. The results from the investigation of coseismic dislocation and ground rupture show that the ground rupture caused by 1876 Kangding-Luding earthquake with M 7 3/ 4 can extend to the south of Tianwan. The segment at the north of Mianning of the Anninghe fault has a background for producing M7.5 earthquake and the geological record of the last strong earthquake must be the proofs of the 1327 earthquake with M>6.0 with poor historical records.  相似文献   

6.
The Crust-Mantle Structure in Zhangbei-Shangyi Earthquake Area   总被引：4，自引：0，他引：4  
The seismic data obtained from the wide angle reflection and refraction profiles that pass through Zhangjiakou area of Hebei Province were interpreted. Some conclusions drawn from the result are as follows: (1) The nearly EW-trending Zhangbei-Chongli crustal fault zone and WNW-trending Zhangjiakou-Bohai Sea deep crustal fault zone meet in the Zhangbei earthquake (Ms = 6.2) area; (2) At the intersection, the two deep crustal fault zones that stretch to the Moho and the discontinuities of interfaces within the crust form the path for large area basalt eruption in Hannuoba; (3) In the earthquake area, the local velocity reversal in the middle-upper crust and abnormal low velocity zone in the lower crust imply that the magmatic activity there is still fairly violent; and (4) The recent activity of Zhangjiakou-Bohai Sea deep crustal fault zone may be the main cause of the Zhangbei earthquake.  相似文献   

7.
A continuous GPS array across the southern segment of the Longmenshan fault zone recorded the deformation during the process of the Lushan MS7.0 earthquake that occurred on April 20, 2013. Such data can provide meaningful information regarding the dynamic evolution of crustal deformation in the seismogenic zone. Our studies have shown that the occurrence of the Wenchuan earthquake led to the loading of compressive and sinistral shearing strain on the southern segment of the Maoxian-Wenchuan fault, whereby the extrusion strain accumulated at a greater rate than before the Wenchuan earthquake. The strain time series in the seismogenic zone revealed that the principal compression strain rates decreased from west to east in the direction of N30°–45°W. Furthermore, the area to the east of Beichuan-Yingxiu fault behaved as a zone of compressive deformation with obvious sinistral shearing deformation. The surface strain and the first shearing strain time series decreased with time, while the area to the west of the Beichuan-Yingxiu fault behaved as a zone of dextral shear deformation that increased with time. Furthermore, the regional deformation field before the Lushan earthquake showed that the rate of extrusion strain accumulation in the southern segment of the Longmenshan fault zone was obviously larger than before the Wenchuan earthquake. Moreover, the sinistral shearing strain accumulated in the area of the southern segment of the Maoxian-Wenchuan fault. Based on the above analysis, we consider that the eastward movement of the Bayan Har block increased considerably following the Wenchuan earthquake, which enhanced the accumulation of compression strain in the southern segment of the Longmenshan fault zone.  相似文献   

8.
Great earthquakes often occur along or near active fault belts. Thus, monitoring and research on fault deformation are quite important. Methods such as short-leveling, short- baseline and integrated monitoring profile across fault belts have been used to monitor fault activities for many years. GNSS observations are mainly used to obtain the horizontal velocity field in large areas and to study the activities and deformation of major blocks. GNSS technology has been used to monitor and study the deformation of faults from a different aspects, In this paper, some applications and new explorations of GNSS are discussed. They are： （1） Research and monitoring of strike-slip activities of faults with GNSS. （2） Research and monitoring of vertical activities of faults with GNSS. （3） Investigating the laws of deformation of blocks on the sides of fault zone and setting up strain models to deduce the activities and deformation of faults with respective models and compare the deduced results with the actual measurements across fault. It is concluded that a larger discrepancy between the deduced and the observed deformation indicates a stronger interaction between the blocks, which can be important for predicting the location of a strong earthquake and assessing seismic hazard, as well as the seismicity trend.  相似文献   

9.
Based on the finite element numerical algorithm,the coseismic displacements of the Wenchuan MS8.0 earthquake are calculated with the rupture slip vectors derived by Ji and Hayes as well as Nishimura and Yaji.Except in a narrow strip around the rupture zone,the coseismic displacements are consistent with those from GPS observation and InSAR interpretation.Numerical results show that rupture slip vectors and elastic properties have profound influences on the surface coseismic deformation.Results from models with different elastic parameters indicate that:①in homogeneous elastic medium,the surface displacements are weakly dependent on Poisson's ratio and independent of the elastic modulus;②in horizontally homogeneous medium with a weak zone at its middle,the thickness of the weak zone plays a significant role on calculating the surface displacements;③in horizontally and vertically heterogeneous medium,the surface displacements depend on both Poisson's ratio and elastic modulus.Calculations of coseismic deformation should take account of the spatial variation of the elastic properties.The misfit of the numerical results with that from the GPS observations in the narrow strip around the rupture zone suggests that a much more complicated rupture model of the Wenchuan earthquake needs to be established in future study.  相似文献   

10.
The regional seismotectonic environment for the Zhangbei- Shangyi earthquake is described, and in combination with the distribution of macroscopic seismic intensity, source mechanism solution, and interpretation of lineaments on satellite images, the seismogenic structure for the earthquake and possible seismogenic fault are discussed in this paper. It is suggested that the Zhangbei-Shangyi earthquake is a result of the latest movement along the northwestern termination of the Zhangjiakou-Penglai fault zone and we should pay serious attention to the future trend of seismic activity along this fault zone.  相似文献   

11.
2008年5月12日汶川8.0级地震是有史以来对乐山市波及范围最广、人员伤亡最多、经济损失最大、社会影响最强烈的地震。本文回顾了近几年乐山市在地震应急准备方面所做的工作和汶川特大地震波及乐山后的应急工作,认为坚持不懈地抓好地震应急准备是做好大地震之后应急工作的重要前提,及时有效地开展应急工作是防震减灾部门的重要职责,震后恢复重建中防震减灾部门可以发挥重要作用。  相似文献   

12.
In 1997 - 2003, 27 earthquakes with M≥ 5.0 occurred in the Jiashi-Bachu area of Xinjiang. It was a rare strong earthquake swarm activity. The earthquake swarm has three time segments of activity with different magnitudes in the years 1997, 1998 and 2003. In different time segments, the seismic activity showed strengthenin-qguiet changes in various degrees before earthquakes with M ≥ 5.0. In order to delimitate effectively the precursory meaning of the clustering （strengthening） quiet change in sequence and to seek the time criterion for impending prediction, the nonlinear characteristics of seismic activity have been used to analyze the time structure characteristics of the earthquake swarm sequence, and further to forecast the development tendency of earthquake sequences in the future. Using the sequence catalogue recorded by the Kashi Station, and taking the earthquakes with Ms≥ 5.0 in the sequence as the starting point and the next earthquake with Ms = 5.0 as the end, statistical analysis has been performed on the time structure relations of the earthquake sequence in different stages. The main results are as follows： （1） Before the major earthquakes with M ≥ 5.0 in the swarm sequence, the time variation coefficient （δ-value） has abnormal demonstrations to different degrees. （2） Within 10 days after δ= 1, occurrence of earthquakes with M ≥ 5.0 in the swarm is very possible. （3） The time variation coefficient has three types of change. （4） The change process before earthquakes with M5.0 is similar to that before earthquakes with M6.0, with little difference in the threshold value. In the earthquake swarm sequence, it is difficult to delimitate accurately the attribute of the current sequences （foreshock or aftershock sequence） and to judge the magnitude of the follow-up earthquake by δ-value. We can only make the judgment that earthquakes with M5.0 are likely to occur in the sequence. （5） The critical clustering characteristics of the sequence are hierarchical. Onl  相似文献   

13.
A statistical analysis on earthquake activity in the Kashi-Wuqia intersection area triggered by earth tide is done by Schuster＇s test and the Permutation test on daily and monthly scales. The north-south, east-west component of the tidal force and tidal body stress are chosen as the tidal curve in the daily scale. The results show that most of the earthquakes occurred near the maximum 0° of the three kinds of tidal curves, the predominant tidal phases of the earthquake are - 5. 86°, 6. 60° and - 15. 52°, and the frequency of the earthquakes increases with the increase of the tide; with three kinds of tidal curves （the north-south, east-west component of the tidal force and tidal body stress ）, the Ps of Schuster＇s test for all the earthquakes is 10. 52 %, 2. 40 % and 2. 06 %, and the pp of the Permutation test is 10. 90%, 2. 40% and 2. 06%, and the results ofps andpp based on the east-west component of the tidal force and tidal body stress are below the threshold of 0. 05 that tidal triggering of earthquakes. In the monthly scale, both the Ps and pp are very low （ close to 0 ）, far below the threshold of 0. 05 of tidal triggering of earthquakes, and the predominant tidal phase for earthquake triggering is - 18. 95°, close to the maximum 0° （ new moon and full moon） of the earth tide in monthly scale. Regarding the statistical test result of tidal triggering of earthquakes, a preliminary explanation is given as to why the trigger effect in the east-west direction is greater than that in north-south direction.  相似文献   

14.
A trend increase in apparent resistivity has been observed in the N30°E monitoring direction at Garze Seismic Station since July 2011. This increase trend in geo-electric resistivity has been observed in the N60°W direction since 2012. During the period of the increase, the national highway No.317 was expanded in the monitoring area, so the potential electrodes in the N30°E direction had to be moved 10m towards the current electrodes. We interpreted the electric sounding data of Garz6 Seismic Station with a horizontally layered model. Analysis based on this model showed that the shift of potential electrodes can cause a 4 l-l.m rise to the measurements in the N30°E direction. Therefore, apparent resistivity of the two directions increased in the same time in 2012 after offsetting the effects from electrodes shift. Sensitivity coefficients of the two observation directions were also obtained using the model. Sensitivity coefficients of both directions were negative for the shallow layers, which can well explain the unexpected annual variations of Garze Seismic Station. In order to quantitatively analyze the effects from the expansion of the national highway on the observation, we constructed a finite element model based on the electrical structure. Analysis results also suggested that the expansion of the national highway could only cause a 0. 15 Ω·m decrease in the N60°W monitoring direction and 0. 1 Ω· m increase in the N30°E direction. Additionally, the valley values of annual variation of 2013 were distinctively higher than that of other years since 2008, meaning that there was an abnormal rise in apparent resistivity in the two observation directions at Garz~ Seismic Station before the Lushan earthquake. However, the rise was contrary to the decline variation before the Wenchuan earthquake. Therefore, it is still unsure whether or not the rise variation is related to the Lushan earthquake.  相似文献   

15.
5·12汶川特大地震造成人民生命财产重大损失。四川省防震减灾科普示范学校由于平时注重在学生中进行防震减灾知识教育和避震应急演练,在此次地震中均能做到临危不乱,快速撤到安全地带,将灾害损失降到了最低。鲜活的事例说明,有无防震减灾知识和自救互救技能,地震后的效果大不一样。  相似文献   

16.
The paper begins with a brief review of the research history of earthquake size measurement. On this basis, the author pointed out the following points： ① In recent decades, ML, mb （mH ）, Ms magnitude scales are widely used as measures of earthquake size. However, these magnitude scales have a deficiency of ＂overgeneralization＂ and ＂magnitude saturation＂. Moreover, since they do not fully take into account the regional difference of seismic attenuation, especially the difference of site effects on the amplification of ground motion, these magnitude scales are but inaccurate measures of earthquake size. ② Seismic moment M0 not only has clear physical meaning, but also overcomes the deficiencies existing in ML, mb （mB ） and Ms magnitude scales, so it is the most suitable physical quantity for measuring earthquake size scientifically. In order to continue to use the term ＂magnitude＂, Kanamori defined the moment magnitude scale Act. Although its prerequisite assumptions remain to be studied, it is still a reasonable scale used as a measure of the relative size of an earthquake. ③ For measuring the earthquake size more scientifically, we must make full use of a large amount of waveform data from modern regional digital seismograph networks, strengthen the research on seismic wave attenuation characteristics, site effect, calculation of source parameters and the related scaling relations. In improving the measurement methods for ML, mb （mB ） and Ms magnitude, we should focus on the improvement of Mw scale and carry forward the work as gradually taking Mw magnitude scale as the uniform physical quantity to measure the relative size of earthquakes, so as to lay a more solid foundation for research in earthquake science and earthquake prediction.  相似文献   

17.
The change of the confined aquifer level reflects the pore pressure change, and the pore pressure change of the aquifer is closely related to the aquifer pressure. This paper uses the tidal response of the well water level data in the North China region to calculate the tidal factor of each well and extract the effective water trend information. Then, the volumetric strain of an existing confined aquifer well in the North China region is inverted, and the contour maps are plotted on a half-year scale from 2009 to 2012. Results show that it can reflect the state of stress and strain in deep crust to a certain extent in the North China region.  相似文献   

18.
This paper calculates the static Coulomb stress changes generated by four earthquakes in the Yutian area during 2008 ~ 2014 separately, then discusses the triggering influence, their accumulated Coulomb stress changes and their influence on nearby faults. The results indicate that the Ms5. 5 earthquake in 2011 and the Ms7. 3 earthquake in 2014 are both in the regions where the Coulomb stress change is positive, the stress changes are 0. 004MPa and 0. 021MPa, respectively, meaning they are triggered by prior earthquakes. The Ms6. 2 earthquake in 2012 occurred in the place where Coulomb stress change was negative, so it is postponed by the prior earthquakes. The image of Coulomb stress changes of the Ms 7. 3 earthquake in 2014 is in accord with aftershocks （ML ≥ 3. 0 ） distribution, but some regions on the fault where the Coulomb stress change is positive have few aftershocks, and strong aftershocks may occur at these districts in future. In addition, this paper calculates the Coulomb stress change on nearby faults, and finds that the Coulomb stress changes of different elements in the GGC fault are very different, and must receive strong triggered-influence, though the result may be influenced by the input finite fault model, so there is still a large earthquake-risk. The GGN, PLC, PLW and LBW faults were also triggered by the four earthquakes occurring between 2008 ~ 2014. Their maximum Coulomb stress changes all exceed 0. 002MPa, so they also have a strong earthquake hazard.  相似文献   

19.
It is well known that quantitative estimation of slip distributions on fault plane is one of the most important issues for earthquake source inversion related to the fault rupture process. The characteristics of slip distribution on the main fault play a fundamental role to control strong ground motion pattern. A large amount of works have also suggested that variable slip models inverted from longer period ground motion recordings are relevant for the prediction of higher frequency ground motions. Zhang et al. （Chin J Geophys 56：1412-1417, 2013） and Wang et al. （Chin J Geophys 56：1408-1411,2013） published their source inversions for the fault rupturing process soon after the April 20, 2013 Lushan earthquake in Sichuan, China. In this study, first, we synthesize two forward source slip models： the value of maximum slip, fault dimension, size, and dimension of major asperities, and comer wave number obtained from Wang＇s model is adopted to constrain the gen- eration of k-2 model and crack model. Next, both inverted and synthetic slip models are employed to simulate the ground motions for the Lushan earthquake based on the stochastic finite-fault method. In addition, for a comparison purpose, a stochastic slip model and another k-2 model （k 2 model II） with 2 times value of comer wave number of the original k-2 model （k 2 model I） are also employed for simulation for Lushan event. The simulated results characterized by Modified Mer- calli Intensity （MMI） show that the source slip models based on the inverted and synthetic slip distributions could capture many basic features associated with the ground motion patterns. Moreover, the simulated MMI distributions reflect the rupture directivity effect and the influence of the shallow velocity structure well. On the other hand, the simulated MMI bystochastic slip model and k 2 model II is apparently higher than observed intensity. By contrast, our simulation results show that the higher frequency ground motion is sensitive to the degree of sli  相似文献   

20.
Xizhang trench is located 10 km northwest of Taiyuan city, Shanxi Province, in front of a NNW-trending scarp of 4.6m height on the northern segment of the Jiaocheng fault zone. The dimensions of the trench are 108m in length, 8m in width, and 10m in depth. There are 18 horizons revealed in the trench. The upper strata are sandy loam; the upper strata of the downthrown block of the fault are gravels, the lower ones are an interbed of brown loam and sandy loam. The strata on the upthrown block of the fault are sandy loam containing gravel. The trench shows 3 fault planes, and the upper offset point on the fault plane is 1.5m below the ground surface, the newest dislocated stratum is （3.74±0.06） ka BP. The trench reveals a lot of deformation traces, such as fault planes, dislocated strata, colluvial wedges and formation tilting. The relationship between strata and faults in the trench shows that 3 paleoearthquake events have occurred at the Jiaocheng fault zone since the Early Holocene, they are about （3.74±0.06）- （3.06±0.26）ka BP, （8.35±0.09）ka- （3.74±0.06）ka BP, and（ 10.66±0.85） - （8.35±0.09）ka BP. The average interval among the events is 2.6 - 3.6ka. The minimum coseismic vertical displacements of the 3 events are 3.0m, 2.5m and 3.2m, respectively. The significance of Xizhang trench is that the Jiaocheng fault used to be active thousands of years ago, though there is no M ≥ 7.0 earthquake recorded in historical documents. Evidence of new Jiaocheng fault zone activity during the Holocene is important for the earthquake safety assessment of Taiynan city in the future.  相似文献   

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