Abstract:In this paper,we conduct background noise seismic tomography of the Tarim Basin and adjacent regions.The Tarim Basin of northwestern China,which is the focus of the study,includes the northern edge of the Tibetan Plateau,major mountain belts （the West Kunlun Mountains,Altyn Tagh,and Tianshan）,and other important oil-and gas-bearing basins （the Junggar and Qaidam basins）.Due to its complex topography and geological structure,the Tarim Basin and adjacent regions have become a prime place to understand the processes of continental collision,the mechanisms of mountain building and the interaction of tectonic blocks.The data used for the study include 9 months （January to September 2009） of horizontal component continuous data recorded at 74 seismic stations of the newly updated China Provincial Digital Seismic Networks and the regional Kyrgyzstan and Kazakhstan networks.Empirical Love wave Green＇ s functions were obtained from interstation cross-correlations.Phase velocity dispersion curves for Love waves for periods between 8 and 30 S were measured for each interstation path by applying the multiple-filter analysis method with phase-matched processing.The high-resolution phase velocity maps show clear lateral variations that correlate well with major geological structures and tectonic units in the study area.Because of the thick sedimentary layers in the basins,we can clearly see that the phase velocity for Love waves with periods between 8 and 30 s is relatively low,while the phase velocity for mountain areas is high.This significant difference in the phase velocity may be related to the sharp changes in the surface topography and terrain elevation from the basin at low altitude to the high mountain areas.It is also possible that the phase velocity is quite different because of the different seismic wave transmission mediums in the study area.The basin is filled with sedimentary rock,and the Tibetan Plateau and the mountain areas are mostly metamorphic rock.The seismic wave velocity of sediments is far lower than that of the metamorphic rock.In addition,our results reveal obvious lateral phase velocity changes in the crust beneath the Tarim Basin.In the upper crust,the eastern basin has a lower velocity than the western basin; however,the northern basin has a lower velocity than the southern basin.The Manjaer depression in the northeast has a very thick sedimentary layer （nearly 20 km）,however,the Bachu uplift has a relative thin sedimentary cover,therefore the Manjaer depression in the eastern Tarim Basin has a very low velocity and the Bachu uplift in the Tarim Basin has a high velocity.These areas have been shown to be places with hydrocarbon enrichment.This is mainly affected by the terrain differences,the sedimentary differences,the thickness of sediments and the sedimentary cover,and it is possible that some velocity variations are connected with the central suture of Presinian bedrock blocks in the northern Tarim Basin.In the Tarim Basin and adjacent regions,exploring the relationship between the different phase velocities for different times and geological formations is helpful for our understanding of the deep structural characteristics and dynamics in the Tarim Basin and its adjacent areas.
