The calibration of the velocity model in microseismic jobs is critical to achieve statistically reliable microseismic locations. Indeed, the lack of knowledge of the wave propagation medium is the main source of location inaccuracy. This paper presents a non-linear calibration method of velocity models for passive, microseismic surveys. This method analyzes multiple time and polarization arrivals and uses a non-linear inversion, simulated annealing algorithm, which prevents the velocity solution from converging to a local minimum, to minimize the residuals and the location error measurements. This method calibrates complex velocity models which can be described, by velocities (P&S), velocity gradients, dip of layers or 3d surface layers. We present an example that demonstrates a significant decrease in location errors of microseisms as compared to typical methods.


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