Focal region field of a two dimensional Gregorian system coated with chiral medium is analyzed at high frequency. Maslov's method is used because the Geometrical Optics approximation fails at focal points. Maslov...Focal region field of a two dimensional Gregorian system coated with chiral medium is analyzed at high frequency. Maslov's method is used because the Geometrical Optics approximation fails at focal points. Maslov’s method combines the simplicity of ray theory and the generality of Fourier transform. Fields patterns are calculated numerically and the results are plotted. The effects of thickness of chiral layer, chirality parameter of the chiral medium and permittivity of the medium are analyzed. The problem of simple dielectric layer is discussed as a special case of this problem.展开更多
We determined focal mechanism solutions of 627 earthquakes of magnitude M ≥ 3.0 in Yunnan from January 2008 to May 2018 by using broadband waveforms recorded by 287 permanent and temporary regional stations. The resu...We determined focal mechanism solutions of 627 earthquakes of magnitude M ≥ 3.0 in Yunnan from January 2008 to May 2018 by using broadband waveforms recorded by 287 permanent and temporary regional stations. The results clearly revealed predominantly strike-slip faulting characteristics for earthquakes in Yunnan, with focal depths concentrated in the top 10 km of the crust. The earthquake mechanisms obtained were combined with the global centroid moment tensor solutions of 80 additional earthquakes from 1976 to 2016 to invert for the regional variations of stress field orientation by using a damped regional-scale stress inversion scheme.Results of the stress field inversion confirmed that the Yunnan region is under a strike–slip stress regime, with both maximum and minimum stress axes being nearly horizontal. The maximum compressional axes are primarily oriented in a northwest-southeast direction, and they experience a clockwise rotation from north to south, whereas the maximum extensional axes are oriented largely northeast-southwest. The maximum compressional axes are in line with the global positioning system–inferred horizontal velocity field and the southeastward escape of the Sichuan–Yunnan Rhombic Block, whereas the maximum extensional axes are consistent with anisotropy derived from SKS splitting. Against the strike–slip background, normal faulting stress regimes can be seen in the Tengchong volcanic area as well as in other areas with complex crisscrossing fault zones.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
An earthquake with magnitude 6.6 occurred on November 16,1983 in the Kaoiki,Hawii.The hierarchical clustering analyses were made by stages for the focal mechanism solutions of 74 earthquakes with M≥3.0 in this area f...An earthquake with magnitude 6.6 occurred on November 16,1983 in the Kaoiki,Hawii.The hierarchical clustering analyses were made by stages for the focal mechanism solutions of 74 earthquakes with M≥3.0 in this area from 1977 to 1985,it was found that each type of focal mechanism is roughly with invariable percentage,and that the strike-slip events including the mainshock,which did not appear in other stages,occurred in the stage around M=6.6 mainshock.The dominant types in the other stages were depressed in the period around the mainshock. This is a believable precursor phenomena.orientation of the principal axes of stress field was inversed by fitting slip vector based on the focal mechanisms in the different periods.The results show that the stress field around the main shock with M=6.6 was more stable,its maximum and minimum principal axes is nearly horizontal in EW and NS direction respectively,the middle one is nearly vertical.The middle principal axis of stress field in the other periods appeared to be horizontal and the corresponding seismic rupture horizontally slip with a small dip.The significant difference between the stress field of source region in the period around the strong shock and that in the other periods shows that the seismogeny and occurrence of the strong shock were controlled by the variation of stress field.The characteristic environment factors of Kaoiki region and its effects were discussed.展开更多
文摘Focal region field of a two dimensional Gregorian system coated with chiral medium is analyzed at high frequency. Maslov's method is used because the Geometrical Optics approximation fails at focal points. Maslov’s method combines the simplicity of ray theory and the generality of Fourier transform. Fields patterns are calculated numerically and the results are plotted. The effects of thickness of chiral layer, chirality parameter of the chiral medium and permittivity of the medium are analyzed. The problem of simple dielectric layer is discussed as a special case of this problem.
基金supported by the Basic Research Fund of the Institute of Earthquake Forecasting,China Earthquake Administration(2015IES010302)the State Key Laboratory of Geodesy and Earth’s Dynamics,Institute of Geodesy and Geophysics,Chinese Academy of Sciences(SKLGED2018-4-3-E)
文摘We determined focal mechanism solutions of 627 earthquakes of magnitude M ≥ 3.0 in Yunnan from January 2008 to May 2018 by using broadband waveforms recorded by 287 permanent and temporary regional stations. The results clearly revealed predominantly strike-slip faulting characteristics for earthquakes in Yunnan, with focal depths concentrated in the top 10 km of the crust. The earthquake mechanisms obtained were combined with the global centroid moment tensor solutions of 80 additional earthquakes from 1976 to 2016 to invert for the regional variations of stress field orientation by using a damped regional-scale stress inversion scheme.Results of the stress field inversion confirmed that the Yunnan region is under a strike–slip stress regime, with both maximum and minimum stress axes being nearly horizontal. The maximum compressional axes are primarily oriented in a northwest-southeast direction, and they experience a clockwise rotation from north to south, whereas the maximum extensional axes are oriented largely northeast-southwest. The maximum compressional axes are in line with the global positioning system–inferred horizontal velocity field and the southeastward escape of the Sichuan–Yunnan Rhombic Block, whereas the maximum extensional axes are consistent with anisotropy derived from SKS splitting. Against the strike–slip background, normal faulting stress regimes can be seen in the Tengchong volcanic area as well as in other areas with complex crisscrossing fault zones.
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.
文摘An earthquake with magnitude 6.6 occurred on November 16,1983 in the Kaoiki,Hawii.The hierarchical clustering analyses were made by stages for the focal mechanism solutions of 74 earthquakes with M≥3.0 in this area from 1977 to 1985,it was found that each type of focal mechanism is roughly with invariable percentage,and that the strike-slip events including the mainshock,which did not appear in other stages,occurred in the stage around M=6.6 mainshock.The dominant types in the other stages were depressed in the period around the mainshock. This is a believable precursor phenomena.orientation of the principal axes of stress field was inversed by fitting slip vector based on the focal mechanisms in the different periods.The results show that the stress field around the main shock with M=6.6 was more stable,its maximum and minimum principal axes is nearly horizontal in EW and NS direction respectively,the middle one is nearly vertical.The middle principal axis of stress field in the other periods appeared to be horizontal and the corresponding seismic rupture horizontally slip with a small dip.The significant difference between the stress field of source region in the period around the strong shock and that in the other periods shows that the seismogeny and occurrence of the strong shock were controlled by the variation of stress field.The characteristic environment factors of Kaoiki region and its effects were discussed.
