关键词: 背景噪声, 面波层析成像, 地壳上地幔, 宁夏及邻区

Abstract: In this study,data from 90seismic stations in Ningxia and its adjacent regions were used to obtain high resolution Rayleigh wave tomography.By selecting the vertical components of continuous waveform data of these stations recorded from January 2012 to December 2013,the waveform cross-correlation and stack operations were carried on each pair of these stations,and obtained the empirical Green's functions of these pairs.Then,by using software CPS(computer programs in seismology),we got 4 005group velocity frequency dispersion curves of Rayleigh surface waves.Using empirical Green's functions to which SNR are greater than 10,we screened out 3 182dispersion curves of the station couples.With inversion,we eventually got the image of Rayleigh wave group velocity distribution of the study area,whose period is between 6~50sand resolution is 0.5degree. Different velocity distribution images with different periods indicate that the group velocitydistribution of the Rayleigh wave in this study area has a good correlation with the geological structure.Yinchuan basin in 6~26speriod shows obviously a low velocity anomaly,which is not uniform and shows a tendency of gradually weakening;Guanzhong Basin in 6~22sshows a strip of low velocity anomaly and demonstrates a transverse inhomogeneity,whose velocity in the southeast is slightly faster than that in the northwest;in 30~50speriod it shows that in Yinchuan graben basin and its southern area exist a large area of low velocity anomaly area,which moves from northeast to southwest.It shows that between the main active tectonic zones,like mountains and basins,there exist obvious geomorphologic boundaries.For example,the deep fault near Liupan mountain is the dividing line between two large tectonic units of east and west of China.The inversion results have good correlation with the geological structure and the stratigraphic landform.The results are consistent with the results of artificial seismic section tomography across the basin.It provides an important basis for the dynamics of active tectonic zones and the mechanism ofearthquake occurrence in this area.

Key words: Surface wave tomography, Crust and upper mantle, Background noise, Ningxia and its adjacent areas