The 2008 Nura Mw6.7 earthquake occurred in front of the Trans-Alai Range, central Asia. We present Interferometric Synthetic Aperture Radar （InSAR） measurements of its coseismic ground deformation that are available...The 2008 Nura Mw6.7 earthquake occurred in front of the Trans-Alai Range, central Asia. We present Interferometric Synthetic Aperture Radar （InSAR） measurements of its coseismic ground deformation that are available for a major earthquake in the region. Analysis of the InSAR data shows that the earthquake ruptured a secondary fault of the Main Pamir Thrust for about 20 kin. The fault plane striking N46~E and dipping 48~SE is dominated by thrust slip up to 3 m, most of which is confined to the uppermost 2-5 km of the crust, similar to the nearby 1974 MwT.0 Markansu earthquake. The elastic model of interseismic deformation constrained by GPS measurements suggests that the two earthquakes may have resulted from the failures of two high-angle reverse faults that are about 10 km apart and rooted in a locked dScollement at depths of 5-6 kin. The elastic strain is built up by a freely creeping decollement at about 16 mm/a.展开更多
Knowledge of the spatial distribution of interseismic deformations is essential to better understand earthquake cycles.The existing methods for improving the reliability of the obtained deformations often rely on visu...Knowledge of the spatial distribution of interseismic deformations is essential to better understand earthquake cycles.The existing methods for improving the reliability of the obtained deformations often rely on visual inspection and prior model corrections that are time-consuming,labor-intensive,and do not consider the spatial distribution of interseismic deformations.Interferometric Synthetic Aperture Radar(InSAR)data provides wide-scale coverage for interseismic deformation monitoring over a wide area.However,the interseismic signal featured as millimeter-scale and long-wave deformations is often contaminated with noise.In the present study,a new workfow to correct the interferometric phase and quantitatively select interferograms is proposed to improve the accuracy of interseismic deformation measurements.Initially,the Generic Atmospheric Correction Online Service(GACOS),Intermittent Code for Atmospheric Noise Depression through Iterative Stacking(I-CANDIS),and plate model are combined to correct the atmospheric screen and long-wave ramp phase.Subsequently,the Pearson’s Correlation Coefcient(PCC)between the interferometric phase and the Global Navigation Satellite System(GNSS)constrained interseismic model as well as the STandard Deviation(STD)of the interferometric phase are introduced as criteria to optimize the selection of interferograms.Finally,the intermittent stacking method is used to generate an average velocity map.A comprehensive test using Sentinel-1 images covering the Haiyuan Fault Zone validate the efectiveness of our workfow in measuring interseismic deformations.This demonstrates that the proposed joint InSAR-GNSS workfow can be extended to study the subtle interseismic deformations of major fault systems in Tibet and worldwide.展开更多
Geodetic observations have shown that there exist large differences in the viscosity of the deep lithosphere across many large strike-slip faults.Heterogeneity in lithospheric viscosity structure can influence the eff...Geodetic observations have shown that there exist large differences in the viscosity of the deep lithosphere across many large strike-slip faults.Heterogeneity in lithospheric viscosity structure can influence the efficiency of stress transfer and thus may have a significant effect on the earthquake cycle.Until now,how the lateral viscosity variation across strike-slip faults affects the earthquake cycles is still not well understood.Here,we investigate the effects of across-strike viscosity variation on long-term earthquake behaviors with a three-dimensional strike-slip fault model.Our model is a quasi-static model which is controlled by the slip-weakening friction law and powerlaw rheology.By comparing with the reference case,we find that low viscosity on one side of the fault results in a smaller rupture area but with a higher Coulomb stress drop on the ruptured fault region.In addition,low viscosity also leads to a small Coulomb stress accumulation rate.These combined effects increase the earthquake recurrence interval by approximately 10%and the earthquake moments by about 30%when the low viscosity is related to a geothermal gradient of 30 K/km.In addition,across-strike viscosity variation causes asymmetric interseismic ground surface deformation rate.As the viscosity contrast increases,the difference in the interseismic ground surface deformation rate between the two sides of the fault gradually increases,although the asymmetric feature is not pronounced.This asymmetry of interseismic ground deformation rate across a strike-slip fault is supposed to result in asymmetric coseismic deformation if the long-term plate motion velocity is invariant.As a result,this kind of asymmetry of interseismic deformation may influence the evaluation of potential earthquake hazards along large strike-slip faults with lateral viscosity contrast.展开更多
By using precise leveling data observed between 1985 and 2010 across the south section of the Longmenshan fault zone,and eliminating the coseismic displacements caused by the Wenchuan Ms 8.0 earthquake,the interseismi...By using precise leveling data observed between 1985 and 2010 across the south section of the Longmenshan fault zone,and eliminating the coseismic displacements caused by the Wenchuan Ms 8.0 earthquake,the interseismic vertical deformation field was obtained.The result shows that the Lushan region,located between the Shuangshi–Dachuan fault(front range of the Longmenshan fault) and the Xinkaidian fault(south section of the Dayi fault),is situated in the intersection zone of positive and negative vertical deformation gradient zones,indicating that this zone was locked within 25 years before the Lushan earthquake.Based on leveling data across the rupture zone surveyed between 2010 and 2013,and by eliminating the vertical deformation within 3 years before the earthquake,the coseismic vertical displacement was derived.The coseismic vertical displacement for the benchmark DD35,which is closest to the epicenter,is up to198.4 mm(with respect to MY165A).The coseismic displacement field revealed that the northwest region(hanging wall) moved upwards in comparison with the southeastern region(foot wall),suggesting that the seismogenic fault mainly underwent thrust faulting.By comparing the coseismic and interseismic vertical deformation fields,it was found that the mechanisms of this earthquake are consistent with the elastic rebound theory; the elastic strain energy(displacement deficit) accumulated before the Lushan earthquake was released during this quake.展开更多
Radar interferograms are usually influenced by factors such as atmospheric artifacts,orbital errors,and terrain errors.It is difficult to reduce the influence by using the conventional small baseline subset(SBAS)metho...Radar interferograms are usually influenced by factors such as atmospheric artifacts,orbital errors,and terrain errors.It is difficult to reduce the influence by using the conventional small baseline subset(SBAS)method when determining the deformation rate.This study uses the adjustment model with systematic parameters to improve the conventional SBAS method and employs it to determine the interseismic deformation rate of the Haiyuan fault system,providing a data reference for exploring the locking depth,strain accumulation state,and potential seismic risk assessment of different segments of the Haiyuan fault system.The results are as follows:(1)the simulation experiment verifies the feasibility and robustness of the modified SBAS method.This method can effectively reduce the influence of residual signals such as atmospheric artifacts,orbital errors and terrain errors in the interferograms.The deformation rate map can be significantly improved;(2)the deformation rate field in the radar’s Line of Sight(LOS)direction shows that there are obvious differences between the north and south sides of Haiyuan fault system,which is consistent with the characteristics of the left-lateral strike-slip movement of the Haiyuan fault system.The deformation rate field and profiles reflect the complex trends among different segments of Haiyuan fault system in detail.(3)the deformation rate of the Jingtai pull-apart basin is higher than that of the surrounding areas,possibly indicating strong regional activity,which provides a reference for studying the seismic risk of the Jingtai pull-apart basin;and(4)the interseismic deformation rate and profiles across the fault show that the middle section of the Lao Hu Shan(LHS)segment and the western and middle sections of the Haiyuan segment are locked.展开更多
基于贝叶斯理论的线性与非线性模型反演方法(Fukuda-Johnson,F-J)已广泛应用于地球物理模型的线性-非线性参数反演。但F-J方法的反演结果可能受马尔可夫链蒙特卡洛采样(Markov chain Monte Carlo,MCMC)经验参数选择的影响,而反复调试合...基于贝叶斯理论的线性与非线性模型反演方法(Fukuda-Johnson,F-J)已广泛应用于地球物理模型的线性-非线性参数反演。但F-J方法的反演结果可能受马尔可夫链蒙特卡洛采样(Markov chain Monte Carlo,MCMC)经验参数选择的影响,而反复调试合适的经验参数需耗费大量计算时间。对线性与非线性模型进行线性化后,也可以利用迭代最小二乘方法反演,但该方法难以选择合适的初始值。为提高参数反演计算效率和避免参数初值选择影响,提出了一种以F-J方法模型解为初始值的迭代最小二乘方法。该方法只需计算一次F-J方法模型解和有限次最小二乘迭代,既提高了F-J方法的反演效率,又能获得迭代最小二乘全局最优解。针对模拟数据实验和实际数据算例,分别采用F-J方法、随机生成初始值的迭代最小二乘方法和以F-J方法结果为初值的迭代最小二乘方法进行参数反演。结果表明,直接使用F-J方法时,MCMC采样参数会影响反演结果;直接进行迭代最小二乘反演时,初始值选取不当会导致迭代无法收敛到正确的结果;以F-J方法的结果作为迭代最小二乘方法的初始值进行反演,可以充分发挥F-J方法的全局最优性和迭代最小二乘方法计算量小、稳定性好的优势。展开更多
基金The study is funded by the National Natural Science Foundation of China(41274027,41274037,41374030 and 41474097)
文摘The 2008 Nura Mw6.7 earthquake occurred in front of the Trans-Alai Range, central Asia. We present Interferometric Synthetic Aperture Radar （InSAR） measurements of its coseismic ground deformation that are available for a major earthquake in the region. Analysis of the InSAR data shows that the earthquake ruptured a secondary fault of the Main Pamir Thrust for about 20 kin. The fault plane striking N46~E and dipping 48~SE is dominated by thrust slip up to 3 m, most of which is confined to the uppermost 2-5 km of the crust, similar to the nearby 1974 MwT.0 Markansu earthquake. The elastic model of interseismic deformation constrained by GPS measurements suggests that the two earthquakes may have resulted from the failures of two high-angle reverse faults that are about 10 km apart and rooted in a locked dScollement at depths of 5-6 kin. The elastic strain is built up by a freely creeping decollement at about 16 mm/a.
基金the National Natural Science Foundation of China(42174023)Frontier cross research project of Central South University(Grant number:2023QYJC006).
文摘Knowledge of the spatial distribution of interseismic deformations is essential to better understand earthquake cycles.The existing methods for improving the reliability of the obtained deformations often rely on visual inspection and prior model corrections that are time-consuming,labor-intensive,and do not consider the spatial distribution of interseismic deformations.Interferometric Synthetic Aperture Radar(InSAR)data provides wide-scale coverage for interseismic deformation monitoring over a wide area.However,the interseismic signal featured as millimeter-scale and long-wave deformations is often contaminated with noise.In the present study,a new workfow to correct the interferometric phase and quantitatively select interferograms is proposed to improve the accuracy of interseismic deformation measurements.Initially,the Generic Atmospheric Correction Online Service(GACOS),Intermittent Code for Atmospheric Noise Depression through Iterative Stacking(I-CANDIS),and plate model are combined to correct the atmospheric screen and long-wave ramp phase.Subsequently,the Pearson’s Correlation Coefcient(PCC)between the interferometric phase and the Global Navigation Satellite System(GNSS)constrained interseismic model as well as the STandard Deviation(STD)of the interferometric phase are introduced as criteria to optimize the selection of interferograms.Finally,the intermittent stacking method is used to generate an average velocity map.A comprehensive test using Sentinel-1 images covering the Haiyuan Fault Zone validate the efectiveness of our workfow in measuring interseismic deformations.This demonstrates that the proposed joint InSAR-GNSS workfow can be extended to study the subtle interseismic deformations of major fault systems in Tibet and worldwide.
基金supported by the National Natural Science Foundation of China (4207410592155204)the Joint Open Fund of Mengcheng National Geophysical Observatory (No. MENGO-202004)
文摘Geodetic observations have shown that there exist large differences in the viscosity of the deep lithosphere across many large strike-slip faults.Heterogeneity in lithospheric viscosity structure can influence the efficiency of stress transfer and thus may have a significant effect on the earthquake cycle.Until now,how the lateral viscosity variation across strike-slip faults affects the earthquake cycles is still not well understood.Here,we investigate the effects of across-strike viscosity variation on long-term earthquake behaviors with a three-dimensional strike-slip fault model.Our model is a quasi-static model which is controlled by the slip-weakening friction law and powerlaw rheology.By comparing with the reference case,we find that low viscosity on one side of the fault results in a smaller rupture area but with a higher Coulomb stress drop on the ruptured fault region.In addition,low viscosity also leads to a small Coulomb stress accumulation rate.These combined effects increase the earthquake recurrence interval by approximately 10%and the earthquake moments by about 30%when the low viscosity is related to a geothermal gradient of 30 K/km.In addition,across-strike viscosity variation causes asymmetric interseismic ground surface deformation rate.As the viscosity contrast increases,the difference in the interseismic ground surface deformation rate between the two sides of the fault gradually increases,although the asymmetric feature is not pronounced.This asymmetry of interseismic ground deformation rate across a strike-slip fault is supposed to result in asymmetric coseismic deformation if the long-term plate motion velocity is invariant.As a result,this kind of asymmetry of interseismic deformation may influence the evaluation of potential earthquake hazards along large strike-slip faults with lateral viscosity contrast.
基金supported by National Special Fund for Earthquake Scientific Research in Public Interest(201408014,201208009)the National Natural Science Foundation of China(41174083)
文摘By using precise leveling data observed between 1985 and 2010 across the south section of the Longmenshan fault zone,and eliminating the coseismic displacements caused by the Wenchuan Ms 8.0 earthquake,the interseismic vertical deformation field was obtained.The result shows that the Lushan region,located between the Shuangshi–Dachuan fault(front range of the Longmenshan fault) and the Xinkaidian fault(south section of the Dayi fault),is situated in the intersection zone of positive and negative vertical deformation gradient zones,indicating that this zone was locked within 25 years before the Lushan earthquake.Based on leveling data across the rupture zone surveyed between 2010 and 2013,and by eliminating the vertical deformation within 3 years before the earthquake,the coseismic vertical displacement was derived.The coseismic vertical displacement for the benchmark DD35,which is closest to the epicenter,is up to198.4 mm(with respect to MY165A).The coseismic displacement field revealed that the northwest region(hanging wall) moved upwards in comparison with the southeastern region(foot wall),suggesting that the seismogenic fault mainly underwent thrust faulting.By comparing the coseismic and interseismic vertical deformation fields,it was found that the mechanisms of this earthquake are consistent with the elastic rebound theory; the elastic strain energy(displacement deficit) accumulated before the Lushan earthquake was released during this quake.
基金supported by the National Natural Science Foundation of China(41874011,41861134009)the National Key Research and Development Program of China(2018YFC1503603)
文摘Radar interferograms are usually influenced by factors such as atmospheric artifacts,orbital errors,and terrain errors.It is difficult to reduce the influence by using the conventional small baseline subset(SBAS)method when determining the deformation rate.This study uses the adjustment model with systematic parameters to improve the conventional SBAS method and employs it to determine the interseismic deformation rate of the Haiyuan fault system,providing a data reference for exploring the locking depth,strain accumulation state,and potential seismic risk assessment of different segments of the Haiyuan fault system.The results are as follows:(1)the simulation experiment verifies the feasibility and robustness of the modified SBAS method.This method can effectively reduce the influence of residual signals such as atmospheric artifacts,orbital errors and terrain errors in the interferograms.The deformation rate map can be significantly improved;(2)the deformation rate field in the radar’s Line of Sight(LOS)direction shows that there are obvious differences between the north and south sides of Haiyuan fault system,which is consistent with the characteristics of the left-lateral strike-slip movement of the Haiyuan fault system.The deformation rate field and profiles reflect the complex trends among different segments of Haiyuan fault system in detail.(3)the deformation rate of the Jingtai pull-apart basin is higher than that of the surrounding areas,possibly indicating strong regional activity,which provides a reference for studying the seismic risk of the Jingtai pull-apart basin;and(4)the interseismic deformation rate and profiles across the fault show that the middle section of the Lao Hu Shan(LHS)segment and the western and middle sections of the Haiyuan segment are locked.
文摘基于贝叶斯理论的线性与非线性模型反演方法(Fukuda-Johnson,F-J)已广泛应用于地球物理模型的线性-非线性参数反演。但F-J方法的反演结果可能受马尔可夫链蒙特卡洛采样(Markov chain Monte Carlo,MCMC)经验参数选择的影响,而反复调试合适的经验参数需耗费大量计算时间。对线性与非线性模型进行线性化后,也可以利用迭代最小二乘方法反演,但该方法难以选择合适的初始值。为提高参数反演计算效率和避免参数初值选择影响,提出了一种以F-J方法模型解为初始值的迭代最小二乘方法。该方法只需计算一次F-J方法模型解和有限次最小二乘迭代,既提高了F-J方法的反演效率,又能获得迭代最小二乘全局最优解。针对模拟数据实验和实际数据算例,分别采用F-J方法、随机生成初始值的迭代最小二乘方法和以F-J方法结果为初值的迭代最小二乘方法进行参数反演。结果表明,直接使用F-J方法时,MCMC采样参数会影响反演结果;直接进行迭代最小二乘反演时,初始值选取不当会导致迭代无法收敛到正确的结果;以F-J方法的结果作为迭代最小二乘方法的初始值进行反演,可以充分发挥F-J方法的全局最优性和迭代最小二乘方法计算量小、稳定性好的优势。
