Abstract We use crosscorrelations of seismic noise data from 151stations in southern California to extract the group velocities of surface waves between the station pairs for the purpose determining the surface-wave velocity structure.We developed and automated procedure estimating the green’s functions and subsequent tomographic inversion from the 11,235 station pairs based on the charactestics of thenoise field we eliminate specific events by by a procedurethat does not introduce any spurious spectral disturtion on the band of interest,0.05-0.2 Hz.Further we only used the emerging arrival structure above a t hreshold signal-to-noise ratio.The result is that mostly station pairs with their axes oriented to ward the sea are used, consistent with the noise having a microseism origin. Finally,it is the time derivative of the correlation function that is actually related to the Green’sfunction.The emergence of the time-domain Green’s function is proportional to the square root of the recording time and inversely proportional to the square root of the distance between stations. The tomographic inversion yields a surface-wave velocity map that compares favorably with more conventional and elaborate experimental procedures.