Simultaneous inversion with multiple traveltimes within 2-D complex layered media

The newly developed multiple (reflected, transmitted and converted) arrival tracking algorithm and the conjugated gradient method are used to solve the constrained, damped least squares problem. We discuss and analyze the simultaneous inversion algorithm with different travel time datasets. In the inversion process we introduce different weighting factors according to the different picking errors of different arrivals, and normalize different parameters in Jacobian matrix elements to balance the influence on travel time due to the different contributions of velocity variation and depth of reflector. In order to overcome the velocity overestimation (or underestimation) in some regions where the ray density is very high (or low), the concept of equal weighted ray density is introduced into inversion process. The numerical results (including the noise-sensitivity tests both in travel times and velocity model perturbation) show that it is a practical and efficient way to improve the spatial resolution and reduce the artifact in reconstructing velocity distribution and reflective interface.