In this paper, simultaneous inversions for hypocentres and three-dimensional (3-D) crustral P-wave velocitystructure of Ningxia and its neighborhood are performed, by using the data of direct P wave, reflected Pm andr...In this paper, simultaneous inversions for hypocentres and three-dimensional (3-D) crustral P-wave velocitystructure of Ningxia and its neighborhood are performed, by using the data of direct P wave, reflected Pm andrefracted Pn phases from the Moho discontinuity. The number of arrival-time applied to the inversion is 11 816total, which are recorded by the Seismic Station Network of Ningxia from 1 107 local natural earthquakes happened since 1970. The LSQR algorithm with damping that has been developed in recent years to solve the largescale sparse matrix is adopted. At different steps of iterative computing process, weighting is made on the actionsof each earthquake at first and on each ray further, to aim at the inhomogeneous features of spatial distribution ofearthquake and ray. Numerical analogue and computational results of actual multi-group data and different iterative control processes, show that under a certain residual standard, there is obvious trade-off on the assignment oftravel-time residuals between medium parameters and earthquakes parameters (especially the origin time anddepth of earthquake), so the obtained solution is related to the selected initial values of medium parameters tosome extent, but there are the basically same variation features on different results in the almost same area. That isthe solution of surface layer has a close relation to the strata and landform. In Yinchuan basin there is obvious lowvelocity feature. and it coincides with the results of a man-made earthquake section crossing the region, tomographic patterns show that there are many low velocity regions in middle-lower crust, and it seems to have someconnections between the positions of historical strong earthquakes and the low velocity region or the anomalousvariations of velocity gradient.展开更多
In this paper, an improvement is made on the method of the pattern recognition ICHAM. It is proposed to use the iterative centre as the Hamming kernel. And new weight coefficient calculating the Euclidean distance is ...In this paper, an improvement is made on the method of the pattern recognition ICHAM. It is proposed to use the iterative centre as the Hamming kernel. And new weight coefficient calculating the Euclidean distance is given. Through varying the control parameter, the minimum ratio of the erroneous recognition is sought. Through classsificatory recognition on two calculative examples and strong earthquakes in the north section of the North-South Seismic Belt, the results indicate that the classificatory effect of the method improved in this paper is better than the ICHAM method. It is more suitable to do the classificatory recognition for general distributive samples.展开更多
On the basis of previous studies, this paper in studying the coda Q-valuc of near shocks, has proposed using the sampling depth to describe the effect of lapse time on the Q-value, and has investigated the dependence...On the basis of previous studies, this paper in studying the coda Q-valuc of near shocks, has proposed using the sampling depth to describe the effect of lapse time on the Q-value, and has investigated the dependence of coda wave of earthquakes on frequency and sampling depth. Analysis of digital seismograms recorded by the Yinchuan Telemetric Seismic Network, Ningxia, shows that not only the coda wave Q-value of shocks is strongly dependent on frequency but also its dependence on Samling depth cannot be neglected. In the commonly used formula that describes the dependence cbaracteristics of coda Q-value of endquakes, Q = Qof', the parameter Qo rises obviously whilc n drops when the sampling depth increases, and their changes can be fitted by linear relations. This paper has explained such a characteristic. Whether this characteristic exists universally needs to be verified by more study results because the genetic mechanism of coda wave of earthquakes is more complex.展开更多
文摘In this paper, simultaneous inversions for hypocentres and three-dimensional (3-D) crustral P-wave velocitystructure of Ningxia and its neighborhood are performed, by using the data of direct P wave, reflected Pm andrefracted Pn phases from the Moho discontinuity. The number of arrival-time applied to the inversion is 11 816total, which are recorded by the Seismic Station Network of Ningxia from 1 107 local natural earthquakes happened since 1970. The LSQR algorithm with damping that has been developed in recent years to solve the largescale sparse matrix is adopted. At different steps of iterative computing process, weighting is made on the actionsof each earthquake at first and on each ray further, to aim at the inhomogeneous features of spatial distribution ofearthquake and ray. Numerical analogue and computational results of actual multi-group data and different iterative control processes, show that under a certain residual standard, there is obvious trade-off on the assignment oftravel-time residuals between medium parameters and earthquakes parameters (especially the origin time anddepth of earthquake), so the obtained solution is related to the selected initial values of medium parameters tosome extent, but there are the basically same variation features on different results in the almost same area. That isthe solution of surface layer has a close relation to the strata and landform. In Yinchuan basin there is obvious lowvelocity feature. and it coincides with the results of a man-made earthquake section crossing the region, tomographic patterns show that there are many low velocity regions in middle-lower crust, and it seems to have someconnections between the positions of historical strong earthquakes and the low velocity region or the anomalousvariations of velocity gradient.
文摘In this paper, an improvement is made on the method of the pattern recognition ICHAM. It is proposed to use the iterative centre as the Hamming kernel. And new weight coefficient calculating the Euclidean distance is given. Through varying the control parameter, the minimum ratio of the erroneous recognition is sought. Through classsificatory recognition on two calculative examples and strong earthquakes in the north section of the North-South Seismic Belt, the results indicate that the classificatory effect of the method improved in this paper is better than the ICHAM method. It is more suitable to do the classificatory recognition for general distributive samples.
文摘On the basis of previous studies, this paper in studying the coda Q-valuc of near shocks, has proposed using the sampling depth to describe the effect of lapse time on the Q-value, and has investigated the dependence of coda wave of earthquakes on frequency and sampling depth. Analysis of digital seismograms recorded by the Yinchuan Telemetric Seismic Network, Ningxia, shows that not only the coda wave Q-value of shocks is strongly dependent on frequency but also its dependence on Samling depth cannot be neglected. In the commonly used formula that describes the dependence cbaracteristics of coda Q-value of endquakes, Q = Qof', the parameter Qo rises obviously whilc n drops when the sampling depth increases, and their changes can be fitted by linear relations. This paper has explained such a characteristic. Whether this characteristic exists universally needs to be verified by more study results because the genetic mechanism of coda wave of earthquakes is more complex.
