Study On Velocity Structure Of Ningdu Basin Based On Ambient Noise Tomography

Jiangxi province located on two major geological units: the Yangtze quasi-platform and the south China fold system.This area has many times of magma activities over the historical period.There are a wide realm and bright prospects for the exploration of underground resources in Jiangxi province.The Ningdu Basin is located in the southeast of Jiangxi Province.This detective area has complex structure.The faulted basin was well developed.It is good for storage geothermal resources.We can get the important information to exploring the distribution of geothermal resources by studying the velocity structure of the basin.At present,previous research has low resolution ratio at velocity structure studies in this region.So it is impossible to obtain the velocity structure information,basement burial depth and major fault distribution in Ningdu basin.Therefore,this paper research for the structure and construction of Ningdu basin based on the seismic ambient noise tomography.About 35 portable seismographs were deployed in Ningdu basin for a month.The waveform data were preprocessed by those way: removing the instrument response,de-trend,de-average and de-inclination,etc.We get the cross-correlation function between stations by the cross-correlation method,and then overlay those functions.The dispersion curves of short-period Rayleigh surface waves of 0.6?6 s were extracted by using the multiple filtering.The group velocity imaging results of 0.6?5.8 s were obtained based on the Fast Marching Method(FMM).The three-dimensional S-wave velocity structure within the depth range of5.8 km was obtained by the Neighborhood algorithm.S-wave velocity can be better constrained in the shallow section by the dense array ambient noise tomography technique.The results of multiple sections show that there are obvious characteristics of low velocity in the center of the basin and the basement interface of the basin is clearly reflected.We identified a fault initially in this area by synthesizing the results of velocity imaging and geological data.This fault controls the tectonic pattern and stratigraphic distribution of the basin.Due to the subsidence structure by fault displacement and the influence of sedimentation,we can conclude that the closer to the center of the basin,the smaller the velocity and the larger the range of anomalies.Combined with the regional geology,geophysical exploration and drilling data,the burial depth of granite is about 2 km in the central area of the basin,and the burial depth is about 700 m in the edge of the basin.The granite's burial depth is low.This place had a good sedimentary cap.All of them provide a good geological conditions for geothermal exploration.It provides a basis for exploration of geothermal resources,occurrence and enrichment rules,and preservation conditions in the area.