On 21 May 2021(UTC),an MW 7.4 earthquake jolted the east Bayan Har block in the Tibetan Plateau.The earthquake received widespread attention as it is the largest event in the Tibetan Plateau and its surroundings since...On 21 May 2021(UTC),an MW 7.4 earthquake jolted the east Bayan Har block in the Tibetan Plateau.The earthquake received widespread attention as it is the largest event in the Tibetan Plateau and its surroundings since the 2008 Wenchuan earthquake,and especially in proximity to the seismic gaps on the east Kunlun fault.Here we use satellite interferometric synthetic aperture radar data and subpixel offset observations along the range directions to characterize the coseismic deformation of the earthquake.Range offset displacements depict clear surface ruptures with a total length of~170 km involving two possible activated fault segments in the earthquake.Coseismic modeling results indicate that the earthquake was dominated by left-lateral strike-slip motions of up to 7 m within the top 12 km of the crust.The well-resolved slip variations are characterized by five major slip patches along strike and 64%of shallow slip deficit,suggesting a young seismogenic structure.Spatial-temporal changes of the postseismic deformation are mapped from early 6-day and 24-day InSAR observations,and are well explained by time-dependent afterslip models.Analysis of Global Navigation Satellite System(GNSS)velocity profiles and strain rates suggests that the eastward extrusion of plateau is diffusely distributed across the east Bayan Har block,but exhibits significant lateral heterogeneities,as evidenced by magnetotelluric observations.The block-wide distributed deformation of the east Bayan Har block along with the significant co-and post-seismic stress loadings from the Madoi earthquake imply high seismic risks along regional faults,especially the Tuosuo Lake and Maqên-Maqu segments of the Kunlun fault that are known as seismic gaps.展开更多
The Wenchuan earthquake induced large amounts of debris flows and catastrophic incidents triggered by subsequent rainstorms occurred frequently in the past 6 rainy seasons, and thus resulted in serious casualties, hug...The Wenchuan earthquake induced large amounts of debris flows and catastrophic incidents triggered by subsequent rainstorms occurred frequently in the past 6 rainy seasons, and thus resulted in serious casualties, huge economic loss and long-term impact. In this paper, post-seismic debris flows distributed in 10 Wenchuan earthquake extremely stricken counties were verified and debris flow database consisting of 609 debris flows was established based on detailed investigation organized by Land and Resources Department of Sichuan Province. Combined with database and related studies, the impact of Wenchuan earthquake on debris flows was analyzed. And then variation of formation conditions including rainfall threshold and landform condition was analyzed by contrasting pre-seismic and post-seismic debris flows. Followed are some typical viewpoints on initiation mechanism of post-seismic debris flows. In the end of this paper, characteristics of postseismic debris flows triggered by subsequent rainstorms were comprehensively summarized, such as regional group occurrence, high frequency, high viscosity, chain effect, huge dynamics, large scale and long duration. We hope this paper will be helpful in understanding the formation mechanism, disaster characteristics and prevention countermeasures of post-seismic debris flows in Wenchuan earthquake extremely stricken areas.展开更多
Co- and post-seismic vertical displacements of the Wenchuan earthquake derived from two measurements in 2008 and 2010 along two partly-damaged leveling lines near the epicenter show the following features： Co-seismic...Co- and post-seismic vertical displacements of the Wenchuan earthquake derived from two measurements in 2008 and 2010 along two partly-damaged leveling lines near the epicenter show the following features： Co-seismic displacement at Beichuan-Yingxiu fault was as large as 4. 711 m near Beichuan, where the maximum observed fault offset was 5.1 m. In contrast, the observed co-seismic offset of the Qingchuan fault in Pingwu County was only 0. 064 m. During 2008 - 2010, the post-seismic displacement rate was 5 - 27 mm/a near Beichuan-Yingxiu fault in Beichuan area, 20.6 mrn/a at Jiangyou-Guangyuan fault near Dakang, and only 0.2 - 1.3 mm/a at Qingehuan fault near Gucheng.展开更多
The M_(w)7.3 Sarpol Zahab earthquake that occurred in the Zagros Fold-Thrust Belt(ZFTB) of Iran on November 12,2017 is the largest earthquake instrumentally recorded in the region.This earthquake provides an opportuni...The M_(w)7.3 Sarpol Zahab earthquake that occurred in the Zagros Fold-Thrust Belt(ZFTB) of Iran on November 12,2017 is the largest earthquake instrumentally recorded in the region.This earthquake provides an opportunity to investigate the slip behaviour and frictional properties of the fault,which is significant for assessing future seismic potential.In this study,we use Sentinel-1 images to map the coand post-seismic deformation to invert for the fault slip.The result indicates that most of the coseismic slip is buried in the depth range of 11-17 km,and the maximum slip is about 3.8 m at a depth of 15 km.The coseismic slip induces an increase of Coulomb stress in the unruptured area of the seismogenic fault plane,driving the afterslip.Based on the stress-driven afterslip,we obtain a frictional parameter of(ab)=(0.001-0.002) for the updip afterslip zone and(a-b)=0.0002 for the downdip afterslip zone in the framework of rate-and-state friction.The constitutive parameter(a-b) of the fault is very small,suggesting that the fault segments are close to velocity-neutral and may experience coseismic rupture.展开更多
Many studies revealed that the Earth medium＇s lateral heterogeneity can cause considerable effects on the co- and post-seismic deformation field. In this study, the threedimensional finite element numerical method ar...Many studies revealed that the Earth medium＇s lateral heterogeneity can cause considerable effects on the co- and post-seismic deformation field. In this study, the threedimensional finite element numerical method are adopted to quantify the effects of lateral heterogeneity caused by material parameters and fault dip angle on the co- and postseismic deformation in the near- and far-field. Our results show that： 1） the medium＇s lateral heterogeneity does affect the co-seismic deformation, with the effects increasing with the medium＇s lateral heterogeneity caused by material parameters; 2） the Lame parameters play a more dominant role than density in the effects caused by lateral heterogeneity; 3） when a fault＇s dip angle is smaller than 90, the effects of the medium＇s lateral heterogeneity on the hanging wall are greater than on the footwall; 4） the impact of lateral heterogeneity caused by the viscosity coefficient on the post-seismic deformation can affect a large area, including the near- and far-field.展开更多
We have examined the aftershock sequence and the post-seismic deformation process of the Parkfield earthquake （2004, M = 6, California, USA） source area using GPS data. This event was chosen because of the possibili...We have examined the aftershock sequence and the post-seismic deformation process of the Parkfield earthquake （2004, M = 6, California, USA） source area using GPS data. This event was chosen because of the possibility of joint analysis of data from the rather dense local GPS network （from SOPAC Internet archive） and of the availability of the rather detailed aftershock sequence data （http：]/www.ncedc.org[ ncedc[catalog-search.html）. The relaxation process of post-seismic deformation prolongs about the same 400 days as the seismic aftershock process does. Thus, the aftershock process and the relaxation process in deformation could be the different sides of the same process. It should be noted that the ratio of the released seismic energy and of the GPS obtained deformation is quite different for the main shock and for the aftershock stage. The ratio of the released seismic energy to the deformation value decreases essentially for the post-shock process. The similar change in the seismic energy[deformation value ratio is valid in a few other strong earthquakes. Thus, this decrease seems typical of aftershock sequences testifying for decrease of ratio of elastic to inelastic deformation in the process of post-shock relaxation when the source area appears to be mostly fractured after the main shock occurs, but the healing process had no yet sufficient time to develop.展开更多
The post-seismic horizontal and vertical deformations following the 2008 Ms8.0 Wenchuan earth- quake are inferred from GPS and precise leveling data. The post-seismic relaxation process is measured using GPS data from...The post-seismic horizontal and vertical deformations following the 2008 Ms8.0 Wenchuan earth- quake are inferred from GPS and precise leveling data. The post-seismic relaxation process is measured using GPS data from campaign stations located around the Longmenshan fault, and the derived decay time constant is 12 days. The evolution of the post-seismic vertical deformation is obtained from precise leveling data measured near the surface rupture. The results demonstrate that the hanging wall is uplifting and the foot wall is subsi- ding. The amplitude of the post-seismic deformation is lower than that of the co-seismic deformation. The re- gion with the largest post-seismic displacement is located on the leveling route between Maoxian and Beichuan on the hanging wall.展开更多
On a long time(>1 a)scale,the viscoelastic properties of mantle media significantly affect post-seismic deformation.The stress field disturbance in viscoelastic medium caused by fault slip gradually relax,and the r...On a long time(>1 a)scale,the viscoelastic properties of mantle media significantly affect post-seismic deformation.The stress field disturbance in viscoelastic medium caused by fault slip gradually relax,and the relaxation process and its temporal-spatial characteristics are determined by the viscoelastic model.In this paper,we assume that the mantle media are types of common linear rheological models,i.e.,the Burgers body,the standard linear solid,and the Maxell body,and we calculate the dislocation Love number and Green function for a spherically symmetric,non-rotating,viscoelastic,and isotropic(SNRVEI)Earth model.The characteristics of the post-seismic relaxation deformations corresponding to the different models are compared.Our results show that for a short time period,the Burgers body and standard linear solid are similar;while for the long time period,the Burgers body and Maxwell body are similar.This suggests that the observations of post-seismic deformation on the surface have a great potential for the inversion of underground viscoelastic structures.However,the potential of using surface displacement to distinguish different rheological models is limited when the observation period is not long enough.展开更多
The viscosity of lower crust of Qinghai-Tibet Plateau on earth should be determined. It has become a predominant problem in quantitative research on geodynamics. Its order of magnitude will have a great influence on t...The viscosity of lower crust of Qinghai-Tibet Plateau on earth should be determined. It has become a predominant problem in quantitative research on geodynamics. Its order of magnitude will have a great influence on the results of quantitative modeling. To obtain the viscosity of lower crust of Qinghai-Tibet Plateau, this parameter was calculated by three methods. The first is based on the estimation on the temperature state of Qinghai-Tibet Plateau in the deep part, and the viscosity of lower crust of northern Plateau was recomputed with strain rate derived from rheology law and GPS observation. Effective viscosity of middle crust in Kunlun region is between 1020 and 1022 Pa·s, and that of lower crust is be- tween 1019 and 1021 Pa·s; the second is based on three kinds of rheological models used to fit the post-seismic deformation recorded by cross-over fault GPS sites set after Ms8.1 Kunlun earthquake in 2001. The viscosity of lower crust obtained by this method is of 1017 Pa·s order of magnitude. However, higher viscosity is required to fit the data of south fault better, and the lower one is required to fit the data of north fault better. The viscosity of lower crust, which was obtained by fitting the cross-over fault post-seismic deformation after Ms7.6 Luhuo earthquake in 1973, is of 1019 Pa·s order of magnitude. Non-linear relationship between effective viscosity and strain rate is ignored in the former research of effective viscosity. This research shows the difference of effective viscosity obtained from laboratory experiment, and shorter and longer time post-seismic deformation after large earthquakes can be explained in phase.展开更多
具有屈服后硬化刚度减震结构的输入能计算中,等效速度谱一般通过改变结构阻尼比获得,这与实际不符,而不同的反应谱对输入能的计算精度影响较大。本文旨在构建综合考虑结构参数、场地类别和地震类型的等效速度谱,为相关减震结构能量设计...具有屈服后硬化刚度减震结构的输入能计算中,等效速度谱一般通过改变结构阻尼比获得,这与实际不符,而不同的反应谱对输入能的计算精度影响较大。本文旨在构建综合考虑结构参数、场地类别和地震类型的等效速度谱,为相关减震结构能量设计提供参考。基于此,首先,建立了考虑屈服后硬化刚度影响的能量平衡方程及其运动方程,并构建了具有屈服后硬化刚度单自由度(single degree of freedom,SDOF)体系等效速度谱计算程序;其次,选取了不同场地类别和地震类型的120条地震记录,利用上述程序分析了屈服后硬化刚度、阻尼比、延性系数、场地类别和地震类型等五种因素对等效速度的影响规律;最后,利用数据拟合工具提出了综合考虑多因素影响的等效速度谱计算公式并与程序计算结果对比。研究表明:等效速度随硬化刚度系数的增大呈减小趋势,但对等效速度谱的下降段影响较小,同时,等效速度随延性系数和阻尼比增大也有减小趋势,但阻尼比影响更为显著。展开更多
基金supported by the Natural Science Foundation of Jiangsu Province(Grant No.SBK2020043202)by Key Laboratory of Geospace Environment and Geodesy,Ministry of Education,Wuhan University(No.19-01-08).
文摘On 21 May 2021(UTC),an MW 7.4 earthquake jolted the east Bayan Har block in the Tibetan Plateau.The earthquake received widespread attention as it is the largest event in the Tibetan Plateau and its surroundings since the 2008 Wenchuan earthquake,and especially in proximity to the seismic gaps on the east Kunlun fault.Here we use satellite interferometric synthetic aperture radar data and subpixel offset observations along the range directions to characterize the coseismic deformation of the earthquake.Range offset displacements depict clear surface ruptures with a total length of~170 km involving two possible activated fault segments in the earthquake.Coseismic modeling results indicate that the earthquake was dominated by left-lateral strike-slip motions of up to 7 m within the top 12 km of the crust.The well-resolved slip variations are characterized by five major slip patches along strike and 64%of shallow slip deficit,suggesting a young seismogenic structure.Spatial-temporal changes of the postseismic deformation are mapped from early 6-day and 24-day InSAR observations,and are well explained by time-dependent afterslip models.Analysis of Global Navigation Satellite System(GNSS)velocity profiles and strain rates suggests that the eastward extrusion of plateau is diffusely distributed across the east Bayan Har block,but exhibits significant lateral heterogeneities,as evidenced by magnetotelluric observations.The block-wide distributed deformation of the east Bayan Har block along with the significant co-and post-seismic stress loadings from the Madoi earthquake imply high seismic risks along regional faults,especially the Tuosuo Lake and Maqên-Maqu segments of the Kunlun fault that are known as seismic gaps.
基金supported by the National Science Foundation of China(Grant No.41102226)the Project of China Special Project of Basic Work of Science and Technology(Grant No.2011FY110100-1)
文摘The Wenchuan earthquake induced large amounts of debris flows and catastrophic incidents triggered by subsequent rainstorms occurred frequently in the past 6 rainy seasons, and thus resulted in serious casualties, huge economic loss and long-term impact. In this paper, post-seismic debris flows distributed in 10 Wenchuan earthquake extremely stricken counties were verified and debris flow database consisting of 609 debris flows was established based on detailed investigation organized by Land and Resources Department of Sichuan Province. Combined with database and related studies, the impact of Wenchuan earthquake on debris flows was analyzed. And then variation of formation conditions including rainfall threshold and landform condition was analyzed by contrasting pre-seismic and post-seismic debris flows. Followed are some typical viewpoints on initiation mechanism of post-seismic debris flows. In the end of this paper, characteristics of postseismic debris flows triggered by subsequent rainstorms were comprehensively summarized, such as regional group occurrence, high frequency, high viscosity, chain effect, huge dynamics, large scale and long duration. We hope this paper will be helpful in understanding the formation mechanism, disaster characteristics and prevention countermeasures of post-seismic debris flows in Wenchuan earthquake extremely stricken areas.
基金supported by the Special Earthquake Research ProjectGrant from China Earthquake Administration( 200908029)
文摘Co- and post-seismic vertical displacements of the Wenchuan earthquake derived from two measurements in 2008 and 2010 along two partly-damaged leveling lines near the epicenter show the following features： Co-seismic displacement at Beichuan-Yingxiu fault was as large as 4. 711 m near Beichuan, where the maximum observed fault offset was 5.1 m. In contrast, the observed co-seismic offset of the Qingchuan fault in Pingwu County was only 0. 064 m. During 2008 - 2010, the post-seismic displacement rate was 5 - 27 mm/a near Beichuan-Yingxiu fault in Beichuan area, 20.6 mrn/a at Jiangyou-Guangyuan fault near Dakang, and only 0.2 - 1.3 mm/a at Qingehuan fault near Gucheng.
基金This work was supported by the Second Tibetan Plateau Scientific Expedition and Research Program(STEP)(2019QZKK0901)National Natural Science Foundation of China(41874020)+1 种基金Guang-dong Province Introduced Innovative R&D Team of Geological Processes and Natural Disasters around the South China Sea(2016ZT06N331)Deep Earth Exploration and Resource Environment(2017ZT07Z066)。
文摘The M_(w)7.3 Sarpol Zahab earthquake that occurred in the Zagros Fold-Thrust Belt(ZFTB) of Iran on November 12,2017 is the largest earthquake instrumentally recorded in the region.This earthquake provides an opportunity to investigate the slip behaviour and frictional properties of the fault,which is significant for assessing future seismic potential.In this study,we use Sentinel-1 images to map the coand post-seismic deformation to invert for the fault slip.The result indicates that most of the coseismic slip is buried in the depth range of 11-17 km,and the maximum slip is about 3.8 m at a depth of 15 km.The coseismic slip induces an increase of Coulomb stress in the unruptured area of the seismogenic fault plane,driving the afterslip.Based on the stress-driven afterslip,we obtain a frictional parameter of(ab)=(0.001-0.002) for the updip afterslip zone and(a-b)=0.0002 for the downdip afterslip zone in the framework of rate-and-state friction.The constitutive parameter(a-b) of the fault is very small,suggesting that the fault segments are close to velocity-neutral and may experience coseismic rupture.
基金co-supported by the National Natural Science Foundation of China (41431069)the State Key Development Program for Basic Research of China (2013CB733304, 2013CB733303)+1 种基金the Doctoral Fund of Ministry of Education of China (20110141130010)China Postdoctoral Science Foundation funded project (2013M542062)
文摘Many studies revealed that the Earth medium＇s lateral heterogeneity can cause considerable effects on the co- and post-seismic deformation field. In this study, the threedimensional finite element numerical method are adopted to quantify the effects of lateral heterogeneity caused by material parameters and fault dip angle on the co- and postseismic deformation in the near- and far-field. Our results show that： 1） the medium＇s lateral heterogeneity does affect the co-seismic deformation, with the effects increasing with the medium＇s lateral heterogeneity caused by material parameters; 2） the Lame parameters play a more dominant role than density in the effects caused by lateral heterogeneity; 3） when a fault＇s dip angle is smaller than 90, the effects of the medium＇s lateral heterogeneity on the hanging wall are greater than on the footwall; 4） the impact of lateral heterogeneity caused by the viscosity coefficient on the post-seismic deformation can affect a large area, including the near- and far-field.
文摘We have examined the aftershock sequence and the post-seismic deformation process of the Parkfield earthquake （2004, M = 6, California, USA） source area using GPS data. This event was chosen because of the possibility of joint analysis of data from the rather dense local GPS network （from SOPAC Internet archive） and of the availability of the rather detailed aftershock sequence data （http：]/www.ncedc.org[ ncedc[catalog-search.html）. The relaxation process of post-seismic deformation prolongs about the same 400 days as the seismic aftershock process does. Thus, the aftershock process and the relaxation process in deformation could be the different sides of the same process. It should be noted that the ratio of the released seismic energy and of the GPS obtained deformation is quite different for the main shock and for the aftershock stage. The ratio of the released seismic energy to the deformation value decreases essentially for the post-shock process. The similar change in the seismic energy[deformation value ratio is valid in a few other strong earthquakes. Thus, this decrease seems typical of aftershock sequences testifying for decrease of ratio of elastic to inelastic deformation in the process of post-shock relaxation when the source area appears to be mostly fractured after the main shock occurs, but the healing process had no yet sufficient time to develop.
基金supported by the Special Earthquake Research Project Granted by the China Earthquake Administration(201208006)the National Natural Science Foundation of China(41174083,40974062)
文摘The post-seismic horizontal and vertical deformations following the 2008 Ms8.0 Wenchuan earth- quake are inferred from GPS and precise leveling data. The post-seismic relaxation process is measured using GPS data from campaign stations located around the Longmenshan fault, and the derived decay time constant is 12 days. The evolution of the post-seismic vertical deformation is obtained from precise leveling data measured near the surface rupture. The results demonstrate that the hanging wall is uplifting and the foot wall is subsi- ding. The amplitude of the post-seismic deformation is lower than that of the co-seismic deformation. The re- gion with the largest post-seismic displacement is located on the leveling route between Maoxian and Beichuan on the hanging wall.
基金the National Natural Science Foundation of China(Nos.41774088,41974093,41331066,and 41474059)the Key Research Program of Frontier Sciences,Chinese Academy of Sciences(No.QYZDY-SSW-SYS003)+1 种基金the China Postdoctoral Science Foundation(2020M680649)the Special Research Assistant Program of the Chinese Academy of Sciences.
文摘On a long time(>1 a)scale,the viscoelastic properties of mantle media significantly affect post-seismic deformation.The stress field disturbance in viscoelastic medium caused by fault slip gradually relax,and the relaxation process and its temporal-spatial characteristics are determined by the viscoelastic model.In this paper,we assume that the mantle media are types of common linear rheological models,i.e.,the Burgers body,the standard linear solid,and the Maxell body,and we calculate the dislocation Love number and Green function for a spherically symmetric,non-rotating,viscoelastic,and isotropic(SNRVEI)Earth model.The characteristics of the post-seismic relaxation deformations corresponding to the different models are compared.Our results show that for a short time period,the Burgers body and standard linear solid are similar;while for the long time period,the Burgers body and Maxwell body are similar.This suggests that the observations of post-seismic deformation on the surface have a great potential for the inversion of underground viscoelastic structures.However,the potential of using surface displacement to distinguish different rheological models is limited when the observation period is not long enough.
基金Supported by National Basic Research Program of China (Grant No. 2004CB418405)National Natural Science Foundation of China (Grant No. 40774048)+1 种基金Important Direction Item of Knowledge Innovation Project of Chinese Academy of Sciences (Grant No. KZCX2-YW-123)Basic Scientific Research Project of Earthquake (Grant No. 02076902-05)
文摘The viscosity of lower crust of Qinghai-Tibet Plateau on earth should be determined. It has become a predominant problem in quantitative research on geodynamics. Its order of magnitude will have a great influence on the results of quantitative modeling. To obtain the viscosity of lower crust of Qinghai-Tibet Plateau, this parameter was calculated by three methods. The first is based on the estimation on the temperature state of Qinghai-Tibet Plateau in the deep part, and the viscosity of lower crust of northern Plateau was recomputed with strain rate derived from rheology law and GPS observation. Effective viscosity of middle crust in Kunlun region is between 1020 and 1022 Pa·s, and that of lower crust is be- tween 1019 and 1021 Pa·s; the second is based on three kinds of rheological models used to fit the post-seismic deformation recorded by cross-over fault GPS sites set after Ms8.1 Kunlun earthquake in 2001. The viscosity of lower crust obtained by this method is of 1017 Pa·s order of magnitude. However, higher viscosity is required to fit the data of south fault better, and the lower one is required to fit the data of north fault better. The viscosity of lower crust, which was obtained by fitting the cross-over fault post-seismic deformation after Ms7.6 Luhuo earthquake in 1973, is of 1019 Pa·s order of magnitude. Non-linear relationship between effective viscosity and strain rate is ignored in the former research of effective viscosity. This research shows the difference of effective viscosity obtained from laboratory experiment, and shorter and longer time post-seismic deformation after large earthquakes can be explained in phase.
文摘具有屈服后硬化刚度减震结构的输入能计算中,等效速度谱一般通过改变结构阻尼比获得,这与实际不符,而不同的反应谱对输入能的计算精度影响较大。本文旨在构建综合考虑结构参数、场地类别和地震类型的等效速度谱,为相关减震结构能量设计提供参考。基于此,首先,建立了考虑屈服后硬化刚度影响的能量平衡方程及其运动方程,并构建了具有屈服后硬化刚度单自由度(single degree of freedom,SDOF)体系等效速度谱计算程序;其次,选取了不同场地类别和地震类型的120条地震记录,利用上述程序分析了屈服后硬化刚度、阻尼比、延性系数、场地类别和地震类型等五种因素对等效速度的影响规律;最后,利用数据拟合工具提出了综合考虑多因素影响的等效速度谱计算公式并与程序计算结果对比。研究表明:等效速度随硬化刚度系数的增大呈减小趋势,但对等效速度谱的下降段影响较小,同时,等效速度随延性系数和阻尼比增大也有减小趋势,但阻尼比影响更为显著。
