关键词: 海原断裂带, 流动地震台阵, 背景噪声成像, Rayleigh波相速度, 地壳, 方位各向异性

Abstract: Haiyuan fault zone is a large NWW-trending boundary fault zone located on the northeastern margin of the Qinghai-Tibet Plateau. In order to study the crustal velocity structure and deformation characteristics of this region, the Cross-Haiyuan Fault Zone temporary Seismic Array set up by the Institute of Earthquake Forecasting, China Earthquake Administration (SACHY-Array) and vertical continuous waveform data of a total of 61 stations (including 40 temporary stations and 21 permanent stations) of permanent seismic stations in the study area were used. Based on the background noise cross-correlation method, the surface wave phase velocity dispersion curve were extracted, and the Rayleigh wave phase velocity and azimuth anisotropy images with a period range of 5~30 s and a resolution of 1°×1° were obtained by inversion. The results show that, within a short period of 5~10 s, the eastern Hexi Corridor transition zone, the northwestern Ordos Block, and the southern Yinchuan graben all present low-velocity anomalies, while the eastern Qilian orogenic fold belt presents relatively high-velocity; the southwest side of the Haiyuan fault zone presents fast waves the polarization directions are NWW and NW. The polarization direction of fast waves in the western margin of Ordos Block and its adjacent areas is mainly near NS, and the anisotropy direction is basically consistent with the regional fault strike. In the period of 15~30 s, the low-velocity anomalies in the east of the Hexi Corridor transition zone and the southern part of the Yinchuan Graben gradually weakened, and the range continued to decrease. Around the 15 s period, the low-velocity bodies in the east of the Hexi Corridor transition zone were staggered under the Yantongshan fault zone. There are high-speed anomalies in the center of the Longzhong Basin and the southwestern margin of Ordos; the direction of azimuthal anisotropy is basically consistent with the short period, but the anisotropy intensity is weak. The authors believe the Haiyuan fault zone is a transition zone between high and low velocities. The Hexi Corridor transition zone on the north side of the fault zone exhibits low velocity anomalies, while the Qilian fold orogenic belt on the south side exhibits high velocity anomalies, indicating that the Haiyuan fault zone and its adjacent areas have complex crustal structures and may have local crustal deformation and destruction; the azimuthal anisotropy of the crust is an important constraint index of crustal deformation, indicating that the anisotropy of the Haiyuan fault zone and its adjacent areas may be mainly caused by the shear deformation of the crust in the northeastern margin of the Qinghai-Tibet Plateau, the north-east pushing of the Qinghai-Tibet Plateau is the main source of dynamic in this area.

Key words: Haiyuan fault, Temporary seismic array, Ambient noise tomography, Rayleigh wave phase velocity, Crust, Azimuthal anisotropy