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In order to improve the efficiency of 3D near-surface velocity model building,we develop a layer-stripping method using seismic first-arrival times.The velocity model within a Common Mid-Point(CMP) gather is assumed to be stratified into thin layers,and the velocity of each layer varies linearly with depth.The thickness and velocity of the top layer are estimated using minimum-offset first-arrival data in a CMP gather.Then the top layer is stripped and the second layer becomes a new top layer.After removing the effect of the top layer from the former first-arrival data,the new first-arrival data are obtained and then used to estimate the parameters of the second layer.In this manner,the velocity model,being regarded as that at a CMP location,is built layer-by-layer from the top to the bottom.A 3D near-surface velocity model is then formed using the velocity models at all CMP locations.The tests on synthetic and observed seismic data show that the layer-stripping method can be used to build good near-surface velocity models for static correction,and its computation speed is approximately hundred times faster than that of grid tomography.
In order to improve the efficiency of 3D near-surface velocity model building, we develop a layer-stripping method using seismic first-arrival times. Velocity model within a Common Mid-Point (CMP) gather is assumed to be stratified into thin layers , and the velocity of each layer varies linearly with depth. The thickness and velocity of the top layer are estimated using minimum-offset first-arrival data in a CMP gather. The top layer is stripped and the second layer becomes a new top layer . After removing the effect of the top layer from the first first-arrival data, the new first-arrival data are obtained and then used to estimate the parameters of the second layer. In this manner, the velocity model, being considered as that at a CMP location, is built-layer-by-layer from the top to the bottom. A 3D near-surface velocity model is then formed using the velocity models at all CMP locations. The tests on synthetic and observed seismic data show that the layer- stripping method can be used to b uild good near-surface velocity models for static correction, and its computation speed is about hundred times faster than that of grid tomography.