Ambient Noise Tomography Of Jinan

Jinan is an important city in eastern China.This region is rich in groundwater.There are four famous springs in the urban area and there is plenty of underground water in the northern part,which makes the migration of the groundwater in this area a very important issue.To study the shallow shear wave velocity structure and the groundwater migration in Jinan,we utilized the continuous waveform data(nearly a month)of 175 short period seismometers deployed by Chinese Academy of Geological Sciences to calculate the cross-correlation function,got stable surface wave signal and picked 7749 group dispersion curves and 6117 phase dispersion curves with a period range 0.2-2S.Through inversion,we got the fine three-dimensional shear wave velocity and azimuthal anisotropy structure(0?2km).We also performed ambient noise waveform inversion using data from a profile and got small-scale structure beneath it.When the result is combined with local geological and hydrological data,we can get following conclusions:(1)There are widespread high velocity anomalies in the region between Qianfoshan Fault and Wenhuaqiao Fault,and in the east of Wenhuaqiao Fault,which may be related to the intrusive gabbro(known as Jinan Intrusive Rock).(2)Jinan Intrusive Rock is not an unbroken rock.It may be broken with the movement of crust.The two parts are called western and eastern Jinan Intrusive Rock.(3)There is obvious low velocity layer under the intrusive rock.This could be the channel of groundwater migration.The precipitation in the southern mountain region seeps down the ground,then it's blocked by the Jinan Intrusive Rock and can only go down to deeper part,where the ground water is heated by the geothermal gradient.At last,the heated water arrives at the north part and forms the geothermal water here.(4)The depth of the low velocity layer beneath the Jinan Intrusive Rock varied laterally,which may indicate that the depth of the groundwater migration is different beneath the western and eastern Jinan Intrusive Rock.(5)There is strong azimuthal anisotropy in southern Jinan,with near west-east fast wave direction.This may be related to the tilt limestone layering structure.