Seismic hazard analysis is gaining increased attention in the present era because of the catastrophic effects of earthquakes.Scientists always have as a goal to develop new techniques that will help forecast earthquak...Seismic hazard analysis is gaining increased attention in the present era because of the catastrophic effects of earthquakes.Scientists always have as a goal to develop new techniques that will help forecast earthquakes before their reoccurrence. In this research,we have performed a shear failure experiment on rock samples with prefabricated cracks to simulate the process of plate movement that forms strike-slip faults. We studied the evolution law of the deformation field to simulate the shear failure experiment, and these results gave us a comprehensive understanding of the elaborate strain distribution law and its formation process with which to identify actual fault zones. We performed uniaxial compression tests on marble slabs with prefabricated double shear cracks to study the distribution and evolution of the deformation field during shear failure. Analysis of the strain field at different loading stages showed that with an increase in the load, the shear strain field initially changed to a disordered-style distribution. Further, the strain field was partially concentrated and finally completely concentrated near the crack and then distributed in the shape of a strip along the crack. We also computed coefficients of variation(CVs) for the physical quantities u, v, and exy, which varied with the load. The CV curves were found to correspond to the different loading stages. We found that at the uniform deformation stage, the CV value was small and changed slowly,whereas at the later nonuniform deformation stage, the CV value increased sharply and changed abruptly. Therefore, the precursor to a rock sample breakdown can be predicted by observing the variation characteristics of CV statistics. The correlation we found between our experimental and theoretical results revealed that our crack evolution and sample deformation results showed good coupling with seismic distribution characteristics near the San Andreas Fault.展开更多
The stress field, controlling the developmental process of a shallow focus inland earthquake, is regarded as the superposition of the fundamental and the variational stress field, but the latter often plays an...The stress field, controlling the developmental process of a shallow focus inland earthquake, is regarded as the superposition of the fundamental and the variational stress field, but the latter often plays an important role. In this paper we focus on two kinds of problems generating the variational stress field, which is related to geotherm. One is the local high temperature region problem, which includes the situations of the heat carrying fluid intruding into the vertical or horizontal cracks and the case of existence of the static state local high temperature region. The other is the problem that the thermal energy is released as the fault emerges displacement discontinuities,during the steady state extension. The two problems can be idealized into the three dimension thermoelastic quasi static problems and their solutions can be given, respectively. Thereby,we may obtain the approximate expressions of some additional seismic precursor fields generated on the plane near the ground surface,for examples, the temperature, the body strain and the underground water, the vertical deformation and the ground tilt vector fields etc. We discuss their space time distribution feature on the plane and get some qualitative results by contrasting them with each other. lt may provide some clues for further studying the comprehensive applications of the preseismic observations.展开更多
The conductivity anisotropy behaviour is described for certain environment in the Earths crust and the MT inversion method for a layered symmetrically anisotropic model is presented. The inversion interpretations of t...The conductivity anisotropy behaviour is described for certain environment in the Earths crust and the MT inversion method for a layered symmetrically anisotropic model is presented. The inversion interpretations of the anisotropic model from the observational data are helpful to identify the earthquake precusors as indicated by the deep conductivity anisotropic variations, and also provide some useful information to investigate the stress states and deformation bands in the deep crust of the Earth.展开更多
In this paper, the fault deformation abnormality, dynamic evolution features of gravity and vertical deformation field in the seismogenic process of the Yongdeng, Gansu Province earthquake on July 22, 1995 are studied...In this paper, the fault deformation abnormality, dynamic evolution features of gravity and vertical deformation field in the seismogenic process of the Yongdeng, Gansu Province earthquake on July 22, 1995 are studied primarily. There appeared α β γ tri stage anomaly at three sites near the epicenter, and there appeared anomalies of step and sudden jump at more than 10 sites in outer region since 1993. The high value area before shock, coseismic effect and process of recovery aftershock were monitored by portable gravity data. Data reflects the changing process of fault movement from the quasi linear to the nonlinear in the near source region during seismogenic development of the Yongdeng earthquake and evolution of gravity field from heterogeneity of seismogenic term to quasi homogeneity of postseismic term. There exists close relationship between strong earthquake and dynamic evolution of regional stress strain field. Considering all above, the experience and lessons in this medium short term prediction test are summarized.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
Two rock samples with different structures and materials were deformed under a biaxial loading system, and multi-point strain measurements were performed for each sample. The distribution of strain anomalies during th...Two rock samples with different structures and materials were deformed under a biaxial loading system, and multi-point strain measurements were performed for each sample. The distribution of strain anomalies during the deformation and the instability process were analyzed by using Cv value put forward by WANG Xiao-qing and CHEN Xue-zhong, et al, a parameter to describe the heterogeneous distribution of earthquake precursors, so as to examine the method of Cv value and to explore its physical meaning experimentally. The result shows that the change of Cv value is correlated to the change of deformation characteristics and is an effective parameter to describe the heterogeneity of precursor distribution. Cv value increases firstly and then decreases before the instability, and the instability occurs when Cv value decreases to the level before increasing. This indicates that Cv value may be a useful parameter for earthquake prediction.展开更多
The ultra-low frequency (ULF) magnetic field data at a station very close to the 2008 Sichuan earthquake (EQ) (on 12 May, 2008;M = 8.0) are extensively studied on the basis of combined statistical and natural time ana...The ultra-low frequency (ULF) magnetic field data at a station very close to the 2008 Sichuan earthquake (EQ) (on 12 May, 2008;M = 8.0) are extensively studied on the basis of combined statistical and natural time analyses. Two effects in ULF are treated: one is the well-known ULF radiation from the lithosphere, and the other is the non-conventional depression of ULF horizontal magnetic field. The simple statistical analysis has yielded: 1) no clear evidence of the presence of precursory ULF radiation, and 2) a significant effect of depression of ULF horizontal field a few days before the EQ (as a signature of ionospheric perturbations). The recently introduced natural time analysis has also been performed in order to study the critical features of the lithosphere and essentially new information has been brought about. The parameter “polarization”, as the ratio of vertical to horizontal components, showed critical features in the time period of 17 - 27 April, about one month to two weeks before the EQ as a signature of lithospheric radiation. Then, the natural time analysis has reconfirmed the presence of ionospheric perturbations a few days before the EQ, together with an additional time window found on 19 - 23 April, about one month before the EQ, exhibiting critical features in the ULF depression.展开更多
On the basis of the three-dimensional elastic inclusion model, the analytic expression of viscoelastic strain field is derived, i.e., the analytic expression of viscoelastic strain at an arbitrary point (x, y, z) in x...On the basis of the three-dimensional elastic inclusion model, the analytic expression of viscoelastic strain field is derived, i.e., the analytic expression of viscoelastic strain at an arbitrary point (x, y, z) in x-axis, y-axis and z-axis produced by three-dimension inclusion in the semi-infinite rheologic medium defined by the standard linear rheologic model, namely the normal strains exx(r, t), eyy(r, t) and ezz(r, t), the shear strains exy(r, t) and eyx(r, t), eyz(r, t) and ezy(r, t), exz(r, t) and ezx(r, t), and the bulk-strain q (r, t). By computing the spatial-temporal variation of bulk strain on the ground produced by a spherical rheologic inclusion in a semi-infinite rheologic medium, we obtained some significant results that the bulk-strain variation with time produced by a hard inclusion has three stages (a, b, g) with different characteristics, which are similar to those of most geodetic deformation curves, but not the case for those by a soft inclusion. It is meaningful that these theoretical results have been applied to explain preliminarily the characteristics of stage variation of spatial-temporal evolution, the pattern and quadrant distribution of earthquake precursors, the changeability, spontaneity and complexity of short-term and imminent-term precursors. It offers a theoretical base to found the physical model of earthquake precursors and a reference to predict physically the earthquakes.展开更多
The article is devoted to the problem of forecasting strong earthquakes by the geomagnetic method. The geomagnetic method is widely used on this problem in seismically active regions of the world as one of the promisi...The article is devoted to the problem of forecasting strong earthquakes by the geomagnetic method. The geomagnetic method is widely used on this problem in seismically active regions of the world as one of the promising, informative and operational geophysical methods. The results of long-term geomagnetic studies on the problem of forecasting strong earthquakes in Uzbekistan are presented. Geomagnetic studies were carried out on the territories of the Tashkent, Ferghana, and Kyzylkum geodynamic polygons in the epicentral zones of strong earthquakes that occurred. Long-term, medium- and short-term precursors of earthquakes have been identified. Anomalous changes in the geomagnetic field associated with the decline in aftershock activity were also revealed. The dependence between the duration of the manifestation of long-term magnetic precursors and the magnitude of earthquakes is determined. Absolute proton magnetometers MMP-1, MV-01 (Russia), and G-856 (USA) were used to measure the geomagnetic field.展开更多
基金Support for this research was provided by the National Key R&D Program of China(grant numbers 2018YFC1504203 and SQ2017YFSF040025)
文摘Seismic hazard analysis is gaining increased attention in the present era because of the catastrophic effects of earthquakes.Scientists always have as a goal to develop new techniques that will help forecast earthquakes before their reoccurrence. In this research,we have performed a shear failure experiment on rock samples with prefabricated cracks to simulate the process of plate movement that forms strike-slip faults. We studied the evolution law of the deformation field to simulate the shear failure experiment, and these results gave us a comprehensive understanding of the elaborate strain distribution law and its formation process with which to identify actual fault zones. We performed uniaxial compression tests on marble slabs with prefabricated double shear cracks to study the distribution and evolution of the deformation field during shear failure. Analysis of the strain field at different loading stages showed that with an increase in the load, the shear strain field initially changed to a disordered-style distribution. Further, the strain field was partially concentrated and finally completely concentrated near the crack and then distributed in the shape of a strip along the crack. We also computed coefficients of variation(CVs) for the physical quantities u, v, and exy, which varied with the load. The CV curves were found to correspond to the different loading stages. We found that at the uniform deformation stage, the CV value was small and changed slowly,whereas at the later nonuniform deformation stage, the CV value increased sharply and changed abruptly. Therefore, the precursor to a rock sample breakdown can be predicted by observing the variation characteristics of CV statistics. The correlation we found between our experimental and theoretical results revealed that our crack evolution and sample deformation results showed good coupling with seismic distribution characteristics near the San Andreas Fault.
文摘The stress field, controlling the developmental process of a shallow focus inland earthquake, is regarded as the superposition of the fundamental and the variational stress field, but the latter often plays an important role. In this paper we focus on two kinds of problems generating the variational stress field, which is related to geotherm. One is the local high temperature region problem, which includes the situations of the heat carrying fluid intruding into the vertical or horizontal cracks and the case of existence of the static state local high temperature region. The other is the problem that the thermal energy is released as the fault emerges displacement discontinuities,during the steady state extension. The two problems can be idealized into the three dimension thermoelastic quasi static problems and their solutions can be given, respectively. Thereby,we may obtain the approximate expressions of some additional seismic precursor fields generated on the plane near the ground surface,for examples, the temperature, the body strain and the underground water, the vertical deformation and the ground tilt vector fields etc. We discuss their space time distribution feature on the plane and get some qualitative results by contrasting them with each other. lt may provide some clues for further studying the comprehensive applications of the preseismic observations.
文摘The conductivity anisotropy behaviour is described for certain environment in the Earths crust and the MT inversion method for a layered symmetrically anisotropic model is presented. The inversion interpretations of the anisotropic model from the observational data are helpful to identify the earthquake precusors as indicated by the deep conductivity anisotropic variations, and also provide some useful information to investigate the stress states and deformation bands in the deep crust of the Earth.
文摘In this paper, the fault deformation abnormality, dynamic evolution features of gravity and vertical deformation field in the seismogenic process of the Yongdeng, Gansu Province earthquake on July 22, 1995 are studied primarily. There appeared α β γ tri stage anomaly at three sites near the epicenter, and there appeared anomalies of step and sudden jump at more than 10 sites in outer region since 1993. The high value area before shock, coseismic effect and process of recovery aftershock were monitored by portable gravity data. Data reflects the changing process of fault movement from the quasi linear to the nonlinear in the near source region during seismogenic development of the Yongdeng earthquake and evolution of gravity field from heterogeneity of seismogenic term to quasi homogeneity of postseismic term. There exists close relationship between strong earthquake and dynamic evolution of regional stress strain field. Considering all above, the experience and lessons in this medium short term prediction test are summarized.
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.
基金Chinese Joint Earthquake Sciences Foundation (9507435).
文摘Two rock samples with different structures and materials were deformed under a biaxial loading system, and multi-point strain measurements were performed for each sample. The distribution of strain anomalies during the deformation and the instability process were analyzed by using Cv value put forward by WANG Xiao-qing and CHEN Xue-zhong, et al, a parameter to describe the heterogeneous distribution of earthquake precursors, so as to examine the method of Cv value and to explore its physical meaning experimentally. The result shows that the change of Cv value is correlated to the change of deformation characteristics and is an effective parameter to describe the heterogeneity of precursor distribution. Cv value increases firstly and then decreases before the instability, and the instability occurs when Cv value decreases to the level before increasing. This indicates that Cv value may be a useful parameter for earthquake prediction.
文摘The ultra-low frequency (ULF) magnetic field data at a station very close to the 2008 Sichuan earthquake (EQ) (on 12 May, 2008;M = 8.0) are extensively studied on the basis of combined statistical and natural time analyses. Two effects in ULF are treated: one is the well-known ULF radiation from the lithosphere, and the other is the non-conventional depression of ULF horizontal magnetic field. The simple statistical analysis has yielded: 1) no clear evidence of the presence of precursory ULF radiation, and 2) a significant effect of depression of ULF horizontal field a few days before the EQ (as a signature of ionospheric perturbations). The recently introduced natural time analysis has also been performed in order to study the critical features of the lithosphere and essentially new information has been brought about. The parameter “polarization”, as the ratio of vertical to horizontal components, showed critical features in the time period of 17 - 27 April, about one month to two weeks before the EQ as a signature of lithospheric radiation. Then, the natural time analysis has reconfirmed the presence of ionospheric perturbations a few days before the EQ, together with an additional time window found on 19 - 23 April, about one month before the EQ, exhibiting critical features in the ULF depression.
基金Chinese Joint Seismological Science Foundation (101105).
文摘On the basis of the three-dimensional elastic inclusion model, the analytic expression of viscoelastic strain field is derived, i.e., the analytic expression of viscoelastic strain at an arbitrary point (x, y, z) in x-axis, y-axis and z-axis produced by three-dimension inclusion in the semi-infinite rheologic medium defined by the standard linear rheologic model, namely the normal strains exx(r, t), eyy(r, t) and ezz(r, t), the shear strains exy(r, t) and eyx(r, t), eyz(r, t) and ezy(r, t), exz(r, t) and ezx(r, t), and the bulk-strain q (r, t). By computing the spatial-temporal variation of bulk strain on the ground produced by a spherical rheologic inclusion in a semi-infinite rheologic medium, we obtained some significant results that the bulk-strain variation with time produced by a hard inclusion has three stages (a, b, g) with different characteristics, which are similar to those of most geodetic deformation curves, but not the case for those by a soft inclusion. It is meaningful that these theoretical results have been applied to explain preliminarily the characteristics of stage variation of spatial-temporal evolution, the pattern and quadrant distribution of earthquake precursors, the changeability, spontaneity and complexity of short-term and imminent-term precursors. It offers a theoretical base to found the physical model of earthquake precursors and a reference to predict physically the earthquakes.
文摘The article is devoted to the problem of forecasting strong earthquakes by the geomagnetic method. The geomagnetic method is widely used on this problem in seismically active regions of the world as one of the promising, informative and operational geophysical methods. The results of long-term geomagnetic studies on the problem of forecasting strong earthquakes in Uzbekistan are presented. Geomagnetic studies were carried out on the territories of the Tashkent, Ferghana, and Kyzylkum geodynamic polygons in the epicentral zones of strong earthquakes that occurred. Long-term, medium- and short-term precursors of earthquakes have been identified. Anomalous changes in the geomagnetic field associated with the decline in aftershock activity were also revealed. The dependence between the duration of the manifestation of long-term magnetic precursors and the magnitude of earthquakes is determined. Absolute proton magnetometers MMP-1, MV-01 (Russia), and G-856 (USA) were used to measure the geomagnetic field.
