The data of short-period (1~18 s) surface waves recorded by 23 stations belonging to the digital seismic network of Yunnan Province of China are used in this paper. From these data, the dispersion curves of phase velo...The data of short-period (1~18 s) surface waves recorded by 23 stations belonging to the digital seismic network of Yunnan Province of China are used in this paper. From these data, the dispersion curves of phase velocities of the fundamental mode Rayleigh wave along 209 paths are determined by using the two-station narrowband filtering cross-correlation method. Adopting tomography method, the distribution maps of phase velocities at various peri-ods in Yunnan region are inverted. The maps of phase velocities on profiles along 24N, 25N, 26N, 27N and 100.5E and the distribution maps of phase velocities at 3 periods in the study region are given. The results show that the phase velocity distribution in Yunnan region has strong variations in horizontal direction, and the phase velocity distribution in short-period range is closely related to the thickness of sedimentary layers in the shallow crust. The phase velocity in southern part of the Sichuan-Yunnan rhombic block encircled by the Honghe fault and Xiaojiang fault is obviously lower than that in surrounding areas. The epicentral locations of strong earthquakes in Yunnan region are mainly distributed in transitional zones between low and high phase velocities.展开更多
The study of seismic attenuation property is a major subject in seismology. Seismic waves recorded by seismic stations (seismographs) contain source effect, seismic wave propagation effect, site response of seismic ...The study of seismic attenuation property is a major subject in seismology. Seismic waves recorded by seismic stations (seismographs) contain source effect, seismic wave propagation effect, site response of seismic stations and instrumental response. The path effect of seismic wave propagation, site response of seismic stations and instrumental response must be taken out in the study of source property with seismic data. The path effect of seismic wave propagation (seismic attenuation) involves an important influential factor, the anelastic attenuation of medium, which is measured with quality factor Q, apart from geometric attenuation with the distance. As a basic physical parameter of the Earth medium, Q value is essential for quantitative study of earthquakes and source property (e.g. determination of source parameters), which is widely used in earthquake source physics and engineering seismology.展开更多
The Wenchuan earthquake coseismic deformation field is inferred from the coseismic dislocation data based on a 3-D geometric model of the active faults in Sichuan-Yunnan region. Then the potential dislocation displace...The Wenchuan earthquake coseismic deformation field is inferred from the coseismic dislocation data based on a 3-D geometric model of the active faults in Sichuan-Yunnan region. Then the potential dislocation displacement is inverted from the deformation field in the 3-D geometric model. While the faults' slip velocities are inverted from GPS and leveling data, which can be used as the long-term slip vector. After the potential dislocation displacements are projected to long-term slip direction, we have got the influence of Wenchuan earthquake on active faults in Sichuan-Yunnan region. The results show that the northwestern segment of Longmenshan fault, the southern segments of Xianshuihe fault, Anninghe fault, Zemuhe fault, northern and southern segments of Daliangshan fault, Mabian fault got earthquake risks advanced of 305, 19, 12, 9.1 and 18, 51 years respectively in the eastern part of Sichuan and Yunnan. The Lijiang-Xiaojinhe fault, Nujiang fault, Longling-Lancang fault, Nantinghe fault and Zhongdian fault also got earthquake risks advanced in the western part of Sichuan-Yunnan region. Whereas the northwestern segment of Xianshuihe fault and Xiaojiang fault got earthquake risks reduced after the Wenchuan earthquake.展开更多
The Bouguer gravity anomaly data of Sichuan-Yunnan region and its vicinity were analyzed with wavelet trans- formation method. In the process, complete orthogonal wavelet function system with good symmetry and higher ...The Bouguer gravity anomaly data of Sichuan-Yunnan region and its vicinity were analyzed with wavelet trans- formation method. In the process, complete orthogonal wavelet function system with good symmetry and higher vanishing moment was selected to decompose the gravity anomaly into two parts. With the power spectral analysis on the decomposed anomalies, we interpreted that the two parts of anomalies represent the density variation in upper and middle crust, and in deep crust and uppermost mantle, respectively. The two parts of anomalies indicate the difference between shallow and deep tectonics. The results of shallow-layer apparent density mapping reveal that: a) the crustal density in Sichuan basin is higher than that in Songpan-Garze orogenic zone; b) the density of Kangdian rhombic block is heterogeneous; c) the boundary faults of Kangdian block are of different density fea- tures, suggesting different tectonic signification. The results of deep-layer apparent density mapping show a similar, but not the same, density distribution pattern as the shallow results, and indicate that the tectonics of shallow and deep crust are different, they may be in a status of incomplete coupling. Our results also show that the earthquakes in this area are controlled not only by the fracture zones but also by the deep density distribution.展开更多
We analyzed digital seismogram data of 5668 earthquakes that occurred in Yunnan region between July of 1999 and December of 2003. Among the 22 seismic stations, six ones, namely Baoshan, Yongsheng, Lijiang, Heqing, Yi...We analyzed digital seismogram data of 5668 earthquakes that occurred in Yunnan region between July of 1999 and December of 2003. Among the 22 seismic stations, six ones, namely Baoshan, Yongsheng, Lijiang, Heqing, Yimen, and Luquan, were selected and their attenuations of P and S waves were measured by using the extended coda-normalization method. The six stations were classified into three regions according to their location, that is, Baoshan area, Yongsheng-Lijiang-Heqing (YLH) area and Luquan-Yimen (LY) area. The values of QS-1 and QP-1 are expressed as QS-1=0.00867 f-0.86, QP-1=0.01155 f-0.93, QS-1=0.01824 f-0.92, QP-1=0.02288 f-0.92, and QS-1=0.01647 f-0.91, QP-1=0.02826 f-0.97 in Baoshan, YLH, LY areas respectively. The attenuation of YLH, LY are closer to each other, however, Baoshan area is apparently lower. Comparing attenuation in the three areas with other areas of the world using the same method, it is suggested that the attenuations of P and S waves in YLH and LY areas are close to Kanto of Japan, but much higher than southeast of South Korea. The QS-1 and QP-1 in Baoshan area are slightly higher than southeastern South Korea. Furthermore, the results indicate that our QS-1 in Yunnan area is close to others by analyzing the coda attenuation.展开更多
On the basis of distribution of active fault and regional rheological structure, a three-dimensional finite element model of Sichuan-Yunnan region, China, is constructed to simulate contemporary crustal motion and str...On the basis of distribution of active fault and regional rheological structure, a three-dimensional finite element model of Sichuan-Yunnan region, China, is constructed to simulate contemporary crustal motion and stress distribution and discuss the dynamic mechanism of crustal motion and deformation in the Sichuan-Yunnan region. Linear Maxwell visco-elastic model is applied, which includes the active fault zones, the elastic upper crust and viscous lower crust and upper mantle. Four different models with different boundary conditions and deep structure are calculated. Some conclusions are drawn through comparison. Firstly, the crustal rotation about the eastern syntaxis of the Himalaya in the Sicuan-Yunnan region may be controlled by the special dynamic boundary condition. The drag force of the lower-crust on the upper crust is not negligible. At the same time, the main active fault zones play an important role in the contemporary crustal motion and deformation in Sichuan-Yunnan region.展开更多
Based on the spatial orientation and slip direction of the fault plane solutions, we present the expression of corresponding mechanical axis tensor in geographic coordinate system, and then put forward a method for ca...Based on the spatial orientation and slip direction of the fault plane solutions, we present the expression of corresponding mechanical axis tensor in geographic coordinate system, and then put forward a method for calculating average mechanical axis tensor and its eigenvalues, which involves solving the corresponding eigenequation. The method for deducing mean stress field from T, B, and P axes parameters of a number of focal mechanism solutions has been verified by inverting data of mean stress fields in Fuyun region and in Tangshan region with fitting method of slip direction, and both results are consistent. To study regional average stress field, we need to choose a population of focal mechanism solutions of earthquakes in the massifs where there are significant tectonic structures. According to the focal mechanism solutions of 256 moderate-strong earthquakes occurred in 13 seismic zones of Sichuan-Yunnan region, the quantitative analysis results of stress tensor in each seismic zone have been given. The algorithm of such method is simple and convenient, which makes the method for analyzing tectonic stress field with large amount of focal mechanism solution data become quantified.展开更多
Based on the lateral segmentation and vertical stratification characteristics of the crustal medium in Sichuan-Yunnan region,and the asymmetry of the static dislocations on the coseismic fault plane of the Wenchuan M_...Based on the lateral segmentation and vertical stratification characteristics of the crustal medium in Sichuan-Yunnan region,and the asymmetry of the static dislocations on the coseismic fault plane of the Wenchuan M_S8.0 earthquake,we built a three-dimensional viscoelastic finite element model of the crust in the Sichuan-Yunnan region.The postseismic impact of the Wenchuan M_S8.0 earthquake on the Sichuan-Yunnan region was studied.The results show that:①The far-field horizontal deformation caused by the viscoelastic relaxation of the medium in the 10 years after the earthquake is about 0-20 mm within the Sichuan-Yunnan diamond-shaped block,which has a greater influence on north side and smaller on south side.②In the 10 years after the earthquake,the far-field vertical deformation caused by the viscoelastic relaxation effect of the medium is small,and it shows an increase of about 0-4 mm in most areas of the Sichuan-Yunnan diamond-shaped block.③The Xianshuihe fault and the eastern segment of the East Kunlun fault,which are close to the seismogenic fault,show a high gradient on deformation fields after the earthquake.④In order to compare with the strong earthquake activity in the SichuanYunnan region after the Wenchuan earthquake,the horizontal stress state and the Coulomb failure stress change of the active block boundary are also calculated.From the spatial distribution of the coseismic and postseismic displacement field,the fault activity characteristics reflected by the stress state and the stress loading of the fault layer reflected by the Coulomb failure stress change,there is a certain correlation with the spatial distribution of strong earthquake activity in this region.展开更多
Sichuan-Yunnan region in China, a tectonic transition belt where earthquakes occurred frequently and intensely, has a distinct variation characteristic of gradient zone of Bouguer gravity anomaly (BGA). Many deep fa...Sichuan-Yunnan region in China, a tectonic transition belt where earthquakes occurred frequently and intensely, has a distinct variation characteristic of gradient zone of Bouguer gravity anomaly (BGA). Many deep faults and epicenters of severe earthquake scatter along the BGA gradient zones. Here we apply two forward models (Airy model and Vening Meinesz model) of isostatic gravity mechanisms (local versus regional) in this region to calculated the isostatic gravity anomaly (IGA). Afterwards, the relationship between IGA and distribution of faults as well as seismicity is also illustrated. The IGA results show that the two models are similar and most parts of the study area are in an isostatic state. Most featured faults are distributed along the steep anomaly gradient zones; earthquakes tend to occur in the non-isostatic area and steep gradient belt of IGA. The distribution of root thickness based on regional mechanism can be associated with the main trend of BGA variation. The regional mechanism is more plausible and closer to the reality because of its relatively further consideration of the horizontal forces derived from adjacent particles in the crust. Then we analyze the effect of isostasy on the tectonic movements and find that the isostatic adjustment is not the main cause of the continuous uplift process of Longmenshan Mountain fault zone. which is due to the Indian-Eurasian continental collision.展开更多
The deep structure background of earth medium for strong earthquakes ccurrence in Yunnan area is discussed inthis paper, by using the results on the study of the velocity structure, elect fieal conductivity stricture,...The deep structure background of earth medium for strong earthquakes ccurrence in Yunnan area is discussed inthis paper, by using the results on the study of the velocity structure, elect fieal conductivity stricture, geothermalstructure in the crust and upper mantle in Yunnan area. The results show that the occurrence of strong earthquakes in Yunnan region is obviously related to the deep medium and tectonic environment such as the existenceof the high velocity zone in the upper crust, the low velocity zone or high electrical conductivity layer in themiddle crust, local uplift in the upper mantle, high geothermal activity and deep and large fault, etc. The large earthquakes could not take place at anywhere, they often occur at some regions which have a certainbackground in the deep medium structure. The activity of the earthquakes with magnitude of 5 or less is quite random,the occurrence of them have not the obvious background of the deep medium strUcture.展开更多
The ground motion attenuation models for PGA,PGV and response spectrum at rock sites and soils sites are derived separately from the digital strong motion records of moderate earthquakes in the Sichuan-Yunnan region a...The ground motion attenuation models for PGA,PGV and response spectrum at rock sites and soils sites are derived separately from the digital strong motion records of moderate earthquakes in the Sichuan-Yunnan region after 2007. By comparison with Yu Yanxiangs attenuation model for rock sites in western China,reliability of the model is verified for moderate earthquake. According to the distribution of strong motion data against magnitude and epicentral distance,the applicability and reliability of the results in this paper are discussed.展开更多
Based on analyzing space inhomogeneous image of strong earthquake activity, the image of source rupture and the mechanical property of the source fault in Sichuan-Yunnan region, the relations among the strong earthqua...Based on analyzing space inhomogeneous image of strong earthquake activity, the image of source rupture and the mechanical property of the source fault in Sichuan-Yunnan region, the relations among the strong earthquake activity, active fault, modern movement status of active blocks and structural background of the deep media have been discussed, and the characteristics of strong earthquake activity and possible mechanism have been also discussed.展开更多
In this paper, using focal mechanism solutions of moderate-strong earthquakes in Yunnan and its adjacent areas, and based on the statistical analysis of the parameters of focal mechanism solutions, we discussed in det...In this paper, using focal mechanism solutions of moderate-strong earthquakes in Yunnan and its adjacent areas, and based on the statistical analysis of the parameters of focal mechanism solutions, we discussed in detail the earthquake fault types and the characteristics of the modern tectonic stress field in the Yunnan region. The results show that most moderate-strong earthquakes occurring in the Yunnan region are of the strike-slip type, amounting to 80% of the total. Normal faulting and normal with strike-slip and reverse and reverse with strike-slip earthquakes is almost equivalent in proportion, about 8% each. The tectonic stress field of the Yunnan region is near-horizontal, and the dips of earthquake fault planes are large. There are three main dynamic sources acting on the Yunnan region: one is the NE, NNE and NNW-directed acting force from Myanmar, Laos and Vietnam; the second is the SE-SSE directed force from the Sichuan and Sichuan-Yunnan rhombus block and the third is the NW-NNW directed force from the South China block. These three acting forces have controlled the faulting behavior of the main faults and the characteristics of strong earthquake activity of Yunnan and its adjacent regions.展开更多
Based on historical earthquake data, we use statistical methods to study integrated recurrence behaviors of strong earthquakes along 7 selected active fault zones in the Sichuan-Yunnan region. The results show that re...Based on historical earthquake data, we use statistical methods to study integrated recurrence behaviors of strong earthquakes along 7 selected active fault zones in the Sichuan-Yunnan region. The results show that recurrences of strong earthquakes in the 7 fault zones display near-random, random and clustering behaviors. The recurrence processes are never quasi-periodic, and are neither strength-time nor time-strength dependent. The more independent segments for strong earthquake rupturing a fault zone has, the more complicated the corresponding recurrence process is. And relatively active periods and quiescent periods for earthquake activity occur alternatively. Within the active periods, the distribution of recurrence time intervals between earthquakes has relatively large discretion, and can be modelled well by a Weibull distribution. The time distribution of the quiescent periods has relatively small discretion, and can be approximately described by some distributions as the normal. Both the durations of the active periods and the numbers of strong earthquakes within the active periods vary obviously cycle by cycle, leading to the relatively active periods having never repeated quasi-periodically. Therefore, the probabilistic assessment for middle- and long-term seismic hazard for entireties of active fault zones based on data of historical strong earthquakes on the fault zones still faces difficulty.展开更多
We analyzed 223 earthquakes with M ≥5. 0 that occurred in the Yunnan region during1965- 2014,among which 74( about 33. 2%) had foreshocks. There are great differences in foreshock populations in different tectonic bl...We analyzed 223 earthquakes with M ≥5. 0 that occurred in the Yunnan region during1965- 2014,among which 74( about 33. 2%) had foreshocks. There are great differences in foreshock populations in different tectonic blocks: the most abundant foreshocks occurred in the Lancang-Gengma and Tengchong-Baoshan blocks,which have the most abundant foreshocks in the Yunnan region. The predominant magnitude difference,time interval and spatial distance are 0. 5- 2. 9,within 10 days and within 20 km,respectively.These characteristics can be used to forecast the mainshock after the identification of a foreshock.展开更多
In this paper,the long time series data of the well water-level data of 12 wells in the Sichuan and Yunnan area is analyzed by the Baytap-G tidal analysis software,and well water level tidal response characteristic pa...In this paper,the long time series data of the well water-level data of 12 wells in the Sichuan and Yunnan area is analyzed by the Baytap-G tidal analysis software,and well water level tidal response characteristic parameters( amplitude ratio and phase change)are extracted. We analyzed the features of the shape and stage change,and characteristic parameters of the tidal response of well water level before and after the earthquakes,which can provide a new method and approach to analyzing the response relationships between well water level and earth tide and barometric pressure. The results show that Luguhu Well and 9 other wells are affected by earth tides,and their well water level amplitude ratios and phases are relatively stable; the Nanxi Well and Dayao Well water level changes are affected by the barometric pressure combined with tide force,and their well water level amplitude ratios and phases are more discrete. The water level amplitude ratios and phases of Jiangyou Well,Luguhu Well and Dongchuan Well are significant to large earthquakes,and the relationship between seismic energy density and water level amplitude ratios and phases of M_2 wave of the three wells are presented.展开更多
Since the 20 thcentury,the time intervals of M ≥6.7 strong earthquakes in the SichuanYunnan region show obvious regularity.Using the years of the strong events,a twodimensional time coordinate system is generated,bas...Since the 20 thcentury,the time intervals of M ≥6.7 strong earthquakes in the SichuanYunnan region show obvious regularity.Using the years of the strong events,a twodimensional time coordinate system is generated,based on which,the time prediction model is constructed for strong earthquakes in the Sichuan-Yunnan region.Prediction analysis shows that there is risk of generating four earthquakes with M ≥ 6.7 in the Sichuan-Yunnan region in the future 16 years,and there are strong signals for M ≥6.7earthquakes for periods 2012-2021 and 2025-2029.The strong earthquakes may occur around 2014-2015,2019 and 2027.展开更多
Analysis of deformation data measured across the faults, regional vertical deformation data and GPS measurements in the Sichuan-Yunnan region made since the 1980s permitted us to conclude that the crustal deformation ...Analysis of deformation data measured across the faults, regional vertical deformation data and GPS measurements in the Sichuan-Yunnan region made since the 1980s permitted us to conclude that the crustal deformation in the region during this period of time was relatively weak and caused the occurrence of earthquakes (M S≥6.0), which were not distributed along the major boundary active faults in the region after the 1981 Dawu M S 6.9 earthquake and that the seismic activity is characterized by quasi-clockwise migration. Thus, it follows that earthquake prediction research should be focused on the central part of the Sichuan-Yunnan region in the coming years. Finally, a concept of temporal division of the region into active blocks is suggested and the preliminary result of the division is given in the paper.展开更多
基金Joint Seismological Science Foundation of China (101086) and the key project Digital Crustal and Mantle Structure of Chinese Mainland from China Earthquake Administration.
基金Basic research program from Institute of Earthquake Science China Earthquake Administration (690206)Social Welfare Research Program from Ministry of Science and Technology of China (2005DIB3J119)
基金Joint Seismological Science Foundation of China (101086) and the key project "Digital Crustal and Mantle Structure of Chinese Mainland" from China Earthquake Administration.
文摘The data of short-period (1~18 s) surface waves recorded by 23 stations belonging to the digital seismic network of Yunnan Province of China are used in this paper. From these data, the dispersion curves of phase velocities of the fundamental mode Rayleigh wave along 209 paths are determined by using the two-station narrowband filtering cross-correlation method. Adopting tomography method, the distribution maps of phase velocities at various peri-ods in Yunnan region are inverted. The maps of phase velocities on profiles along 24N, 25N, 26N, 27N and 100.5E and the distribution maps of phase velocities at 3 periods in the study region are given. The results show that the phase velocity distribution in Yunnan region has strong variations in horizontal direction, and the phase velocity distribution in short-period range is closely related to the thickness of sedimentary layers in the shallow crust. The phase velocity in southern part of the Sichuan-Yunnan rhombic block encircled by the Honghe fault and Xiaojiang fault is obviously lower than that in surrounding areas. The epicentral locations of strong earthquakes in Yunnan region are mainly distributed in transitional zones between low and high phase velocities.
基金Early-stage study project of the national key foundation research (2002CCD01700) and the key project of Yunnan Province during the 10th Five-year plan.
文摘The study of seismic attenuation property is a major subject in seismology. Seismic waves recorded by seismic stations (seismographs) contain source effect, seismic wave propagation effect, site response of seismic stations and instrumental response. The path effect of seismic wave propagation, site response of seismic stations and instrumental response must be taken out in the study of source property with seismic data. The path effect of seismic wave propagation (seismic attenuation) involves an important influential factor, the anelastic attenuation of medium, which is measured with quality factor Q, apart from geometric attenuation with the distance. As a basic physical parameter of the Earth medium, Q value is essential for quantitative study of earthquakes and source property (e.g. determination of source parameters), which is widely used in earthquake source physics and engineering seismology.
基金supported by the Key Project of Chinese Programs for Fundamental Research and Development (2004CB418406)
文摘The Wenchuan earthquake coseismic deformation field is inferred from the coseismic dislocation data based on a 3-D geometric model of the active faults in Sichuan-Yunnan region. Then the potential dislocation displacement is inverted from the deformation field in the 3-D geometric model. While the faults' slip velocities are inverted from GPS and leveling data, which can be used as the long-term slip vector. After the potential dislocation displacements are projected to long-term slip direction, we have got the influence of Wenchuan earthquake on active faults in Sichuan-Yunnan region. The results show that the northwestern segment of Longmenshan fault, the southern segments of Xianshuihe fault, Anninghe fault, Zemuhe fault, northern and southern segments of Daliangshan fault, Mabian fault got earthquake risks advanced of 305, 19, 12, 9.1 and 18, 51 years respectively in the eastern part of Sichuan and Yunnan. The Lijiang-Xiaojinhe fault, Nujiang fault, Longling-Lancang fault, Nantinghe fault and Zhongdian fault also got earthquake risks advanced in the western part of Sichuan-Yunnan region. Whereas the northwestern segment of Xianshuihe fault and Xiaojiang fault got earthquake risks reduced after the Wenchuan earthquake.
基金National Natural Science Foundation of China (403334041)
文摘The Bouguer gravity anomaly data of Sichuan-Yunnan region and its vicinity were analyzed with wavelet trans- formation method. In the process, complete orthogonal wavelet function system with good symmetry and higher vanishing moment was selected to decompose the gravity anomaly into two parts. With the power spectral analysis on the decomposed anomalies, we interpreted that the two parts of anomalies represent the density variation in upper and middle crust, and in deep crust and uppermost mantle, respectively. The two parts of anomalies indicate the difference between shallow and deep tectonics. The results of shallow-layer apparent density mapping reveal that: a) the crustal density in Sichuan basin is higher than that in Songpan-Garze orogenic zone; b) the density of Kangdian rhombic block is heterogeneous; c) the boundary faults of Kangdian block are of different density fea- tures, suggesting different tectonic signification. The results of deep-layer apparent density mapping show a similar, but not the same, density distribution pattern as the shallow results, and indicate that the tectonics of shallow and deep crust are different, they may be in a status of incomplete coupling. Our results also show that the earthquakes in this area are controlled not only by the fracture zones but also by the deep density distribution.
基金The specialized fund for pre-study of national key basic study (2002CCD01700)national key project of science and technology from China Ministry of Science and Technology during the 10th Five-year Plan (2004BA601B01-04-03)
文摘We analyzed digital seismogram data of 5668 earthquakes that occurred in Yunnan region between July of 1999 and December of 2003. Among the 22 seismic stations, six ones, namely Baoshan, Yongsheng, Lijiang, Heqing, Yimen, and Luquan, were selected and their attenuations of P and S waves were measured by using the extended coda-normalization method. The six stations were classified into three regions according to their location, that is, Baoshan area, Yongsheng-Lijiang-Heqing (YLH) area and Luquan-Yimen (LY) area. The values of QS-1 and QP-1 are expressed as QS-1=0.00867 f-0.86, QP-1=0.01155 f-0.93, QS-1=0.01824 f-0.92, QP-1=0.02288 f-0.92, and QS-1=0.01647 f-0.91, QP-1=0.02826 f-0.97 in Baoshan, YLH, LY areas respectively. The attenuation of YLH, LY are closer to each other, however, Baoshan area is apparently lower. Comparing attenuation in the three areas with other areas of the world using the same method, it is suggested that the attenuations of P and S waves in YLH and LY areas are close to Kanto of Japan, but much higher than southeast of South Korea. The QS-1 and QP-1 in Baoshan area are slightly higher than southeastern South Korea. Furthermore, the results indicate that our QS-1 in Yunnan area is close to others by analyzing the coda attenuation.
基金Ministry of Science and Technology (2004CB418406, 2005DKA64000)the Basic Science Research Plan of the Institute of Earthquake Science, China Earthquake Administration (02076902-03).
文摘On the basis of distribution of active fault and regional rheological structure, a three-dimensional finite element model of Sichuan-Yunnan region, China, is constructed to simulate contemporary crustal motion and stress distribution and discuss the dynamic mechanism of crustal motion and deformation in the Sichuan-Yunnan region. Linear Maxwell visco-elastic model is applied, which includes the active fault zones, the elastic upper crust and viscous lower crust and upper mantle. Four different models with different boundary conditions and deep structure are calculated. Some conclusions are drawn through comparison. Firstly, the crustal rotation about the eastern syntaxis of the Himalaya in the Sicuan-Yunnan region may be controlled by the special dynamic boundary condition. The drag force of the lower-crust on the upper crust is not negligible. At the same time, the main active fault zones play an important role in the contemporary crustal motion and deformation in Sichuan-Yunnan region.
基金State Key Basic Research Development Program (2004CB418404) and the Joint Seismological Science Foundation of China (105004).
文摘Based on the spatial orientation and slip direction of the fault plane solutions, we present the expression of corresponding mechanical axis tensor in geographic coordinate system, and then put forward a method for calculating average mechanical axis tensor and its eigenvalues, which involves solving the corresponding eigenequation. The method for deducing mean stress field from T, B, and P axes parameters of a number of focal mechanism solutions has been verified by inverting data of mean stress fields in Fuyun region and in Tangshan region with fitting method of slip direction, and both results are consistent. To study regional average stress field, we need to choose a population of focal mechanism solutions of earthquakes in the massifs where there are significant tectonic structures. According to the focal mechanism solutions of 256 moderate-strong earthquakes occurred in 13 seismic zones of Sichuan-Yunnan region, the quantitative analysis results of stress tensor in each seismic zone have been given. The algorithm of such method is simple and convenient, which makes the method for analyzing tectonic stress field with large amount of focal mechanism solution data become quantified.
基金the Seismological Science and Technology Spark Program of the China Earthquake Administration,“A Study of the Impacts and Observations of the Wenchuan Earthquake on the Post-earthquake in the Sichuan-Yunnan Region”(XH16058Y)the Youth Earthquake Tracking Project of the China Earthquake Administration Monitoring and Forecasting Division(2017010219)
文摘Based on the lateral segmentation and vertical stratification characteristics of the crustal medium in Sichuan-Yunnan region,and the asymmetry of the static dislocations on the coseismic fault plane of the Wenchuan M_S8.0 earthquake,we built a three-dimensional viscoelastic finite element model of the crust in the Sichuan-Yunnan region.The postseismic impact of the Wenchuan M_S8.0 earthquake on the Sichuan-Yunnan region was studied.The results show that:①The far-field horizontal deformation caused by the viscoelastic relaxation of the medium in the 10 years after the earthquake is about 0-20 mm within the Sichuan-Yunnan diamond-shaped block,which has a greater influence on north side and smaller on south side.②In the 10 years after the earthquake,the far-field vertical deformation caused by the viscoelastic relaxation effect of the medium is small,and it shows an increase of about 0-4 mm in most areas of the Sichuan-Yunnan diamond-shaped block.③The Xianshuihe fault and the eastern segment of the East Kunlun fault,which are close to the seismogenic fault,show a high gradient on deformation fields after the earthquake.④In order to compare with the strong earthquake activity in the SichuanYunnan region after the Wenchuan earthquake,the horizontal stress state and the Coulomb failure stress change of the active block boundary are also calculated.From the spatial distribution of the coseismic and postseismic displacement field,the fault activity characteristics reflected by the stress state and the stress loading of the fault layer reflected by the Coulomb failure stress change,there is a certain correlation with the spatial distribution of strong earthquake activity in this region.
基金supported by the China Earthquake Administration,Institute of Seismology Foundation(IS201416141)Spark Plan(XH17022)
文摘Sichuan-Yunnan region in China, a tectonic transition belt where earthquakes occurred frequently and intensely, has a distinct variation characteristic of gradient zone of Bouguer gravity anomaly (BGA). Many deep faults and epicenters of severe earthquake scatter along the BGA gradient zones. Here we apply two forward models (Airy model and Vening Meinesz model) of isostatic gravity mechanisms (local versus regional) in this region to calculated the isostatic gravity anomaly (IGA). Afterwards, the relationship between IGA and distribution of faults as well as seismicity is also illustrated. The IGA results show that the two models are similar and most parts of the study area are in an isostatic state. Most featured faults are distributed along the steep anomaly gradient zones; earthquakes tend to occur in the non-isostatic area and steep gradient belt of IGA. The distribution of root thickness based on regional mechanism can be associated with the main trend of BGA variation. The regional mechanism is more plausible and closer to the reality because of its relatively further consideration of the horizontal forces derived from adjacent particles in the crust. Then we analyze the effect of isostasy on the tectonic movements and find that the isostatic adjustment is not the main cause of the continuous uplift process of Longmenshan Mountain fault zone. which is due to the Indian-Eurasian continental collision.
文摘The deep structure background of earth medium for strong earthquakes ccurrence in Yunnan area is discussed inthis paper, by using the results on the study of the velocity structure, elect fieal conductivity stricture, geothermalstructure in the crust and upper mantle in Yunnan area. The results show that the occurrence of strong earthquakes in Yunnan region is obviously related to the deep medium and tectonic environment such as the existenceof the high velocity zone in the upper crust, the low velocity zone or high electrical conductivity layer in themiddle crust, local uplift in the upper mantle, high geothermal activity and deep and large fault, etc. The large earthquakes could not take place at anywhere, they often occur at some regions which have a certainbackground in the deep medium structure. The activity of the earthquakes with magnitude of 5 or less is quite random,the occurrence of them have not the obvious background of the deep medium strUcture.
基金sponsored jointly by the special fund for basic research and operating expenses of Institute of Crustal Dynamics,CEA(ZDJ2013-04)"National Nature Science Foundation of China(51278469)
文摘The ground motion attenuation models for PGA,PGV and response spectrum at rock sites and soils sites are derived separately from the digital strong motion records of moderate earthquakes in the Sichuan-Yunnan region after 2007. By comparison with Yu Yanxiangs attenuation model for rock sites in western China,reliability of the model is verified for moderate earthquake. According to the distribution of strong motion data against magnitude and epicentral distance,the applicability and reliability of the results in this paper are discussed.
基金"Strong Earthquake Mechanism and Forecast in China’s Continent(95-13-05-05)and the Natural Science Funds of Yunnan Province(97D015G),China.
文摘Based on analyzing space inhomogeneous image of strong earthquake activity, the image of source rupture and the mechanical property of the source fault in Sichuan-Yunnan region, the relations among the strong earthquake activity, active fault, modern movement status of active blocks and structural background of the deep media have been discussed, and the characteristics of strong earthquake activity and possible mechanism have been also discussed.
基金sponsored by the important projects of Yunnan Province,entitled"The regularity of strong earthquake activities and the plate margindynamic mechanism on the eastern margin of the Qinghai-Tibet plateau"(2010CC006)"Study on relationship between evolutionary dynamics of geophysical and geochemistry field and strong seismic activity in Yunnan"(JCYB200806015)
文摘In this paper, using focal mechanism solutions of moderate-strong earthquakes in Yunnan and its adjacent areas, and based on the statistical analysis of the parameters of focal mechanism solutions, we discussed in detail the earthquake fault types and the characteristics of the modern tectonic stress field in the Yunnan region. The results show that most moderate-strong earthquakes occurring in the Yunnan region are of the strike-slip type, amounting to 80% of the total. Normal faulting and normal with strike-slip and reverse and reverse with strike-slip earthquakes is almost equivalent in proportion, about 8% each. The tectonic stress field of the Yunnan region is near-horizontal, and the dips of earthquake fault planes are large. There are three main dynamic sources acting on the Yunnan region: one is the NE, NNE and NNW-directed acting force from Myanmar, Laos and Vietnam; the second is the SE-SSE directed force from the Sichuan and Sichuan-Yunnan rhombus block and the third is the NW-NNW directed force from the South China block. These three acting forces have controlled the faulting behavior of the main faults and the characteristics of strong earthquake activity of Yunnan and its adjacent regions.
文摘Based on historical earthquake data, we use statistical methods to study integrated recurrence behaviors of strong earthquakes along 7 selected active fault zones in the Sichuan-Yunnan region. The results show that recurrences of strong earthquakes in the 7 fault zones display near-random, random and clustering behaviors. The recurrence processes are never quasi-periodic, and are neither strength-time nor time-strength dependent. The more independent segments for strong earthquake rupturing a fault zone has, the more complicated the corresponding recurrence process is. And relatively active periods and quiescent periods for earthquake activity occur alternatively. Within the active periods, the distribution of recurrence time intervals between earthquakes has relatively large discretion, and can be modelled well by a Weibull distribution. The time distribution of the quiescent periods has relatively small discretion, and can be approximately described by some distributions as the normal. Both the durations of the active periods and the numbers of strong earthquakes within the active periods vary obviously cycle by cycle, leading to the relatively active periods having never repeated quasi-periodically. Therefore, the probabilistic assessment for middle- and long-term seismic hazard for entireties of active fault zones based on data of historical strong earthquakes on the fault zones still faces difficulty.
基金funded by the Database Establishment of Foreshocks before the M_W≥6.0 Earthquakes Worldwidethe Science and Technology Project of the Earthquake Administration of Yunnan Province
文摘We analyzed 223 earthquakes with M ≥5. 0 that occurred in the Yunnan region during1965- 2014,among which 74( about 33. 2%) had foreshocks. There are great differences in foreshock populations in different tectonic blocks: the most abundant foreshocks occurred in the Lancang-Gengma and Tengchong-Baoshan blocks,which have the most abundant foreshocks in the Yunnan region. The predominant magnitude difference,time interval and spatial distance are 0. 5- 2. 9,within 10 days and within 20 km,respectively.These characteristics can be used to forecast the mainshock after the identification of a foreshock.
基金sponsored by the Spark Program of Earthquake Technology of CEA in 2017(XH17026)Combination Project with Monitoring,Prediction and Scientific Research of Earthquake Technology,CEA(162205)
文摘In this paper,the long time series data of the well water-level data of 12 wells in the Sichuan and Yunnan area is analyzed by the Baytap-G tidal analysis software,and well water level tidal response characteristic parameters( amplitude ratio and phase change)are extracted. We analyzed the features of the shape and stage change,and characteristic parameters of the tidal response of well water level before and after the earthquakes,which can provide a new method and approach to analyzing the response relationships between well water level and earth tide and barometric pressure. The results show that Luguhu Well and 9 other wells are affected by earth tides,and their well water level amplitude ratios and phases are relatively stable; the Nanxi Well and Dayao Well water level changes are affected by the barometric pressure combined with tide force,and their well water level amplitude ratios and phases are more discrete. The water level amplitude ratios and phases of Jiangyou Well,Luguhu Well and Dongchuan Well are significant to large earthquakes,and the relationship between seismic energy density and water level amplitude ratios and phases of M_2 wave of the three wells are presented.
文摘Since the 20 thcentury,the time intervals of M ≥6.7 strong earthquakes in the SichuanYunnan region show obvious regularity.Using the years of the strong events,a twodimensional time coordinate system is generated,based on which,the time prediction model is constructed for strong earthquakes in the Sichuan-Yunnan region.Prediction analysis shows that there is risk of generating four earthquakes with M ≥ 6.7 in the Sichuan-Yunnan region in the future 16 years,and there are strong signals for M ≥6.7earthquakes for periods 2012-2021 and 2025-2029.The strong earthquakes may occur around 2014-2015,2019 and 2027.
文摘Analysis of deformation data measured across the faults, regional vertical deformation data and GPS measurements in the Sichuan-Yunnan region made since the 1980s permitted us to conclude that the crustal deformation in the region during this period of time was relatively weak and caused the occurrence of earthquakes (M S≥6.0), which were not distributed along the major boundary active faults in the region after the 1981 Dawu M S 6.9 earthquake and that the seismic activity is characterized by quasi-clockwise migration. Thus, it follows that earthquake prediction research should be focused on the central part of the Sichuan-Yunnan region in the coming years. Finally, a concept of temporal division of the region into active blocks is suggested and the preliminary result of the division is given in the paper.