Abstract:There exist some disadvantages in the traditional tomographic determination of seismic velocity model. For example, repeated migration process is required during the iteration to update velocity model that results in expensive computation. Besides, it is difficult to calculate the reflected ray angles when tracing ray through complicated geological medium. To tackle these problems, this paper proposes a velocity inversion method based on the theory of common focus point (CFP) technology. Firstly, the method obtains the time-reversed focusing operator using the time difference picked from the differential time shift (DTS) panel. Then, the positions of focusing points are corrected by using the focusing operator and time residual. Finally the velocity at each grid point are updated through the coefficients obtained in the algebraic reconstruction technique. The final model is obtained by alternatively updating the focusing positions and velocity at each grid point. Compared with the conventional velocity inversion method, the CFP method uses one-way travel time to solve the inversion without considering the reflection of complex structure and does not need to repeat the migration process in each iteration. This method avoids the inversion of a large matrix and only considers the groups of geometric points on the reflection interface, which thus saves computational time. The experimental results show that even if the initial velocity model is poor, fast convergence can be achieved, with satisfactory results obtained.
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