A Combination of Seismic First Arrival Travel Time Inversion with and without Ray Tracing

In order to efficiently and effectively invert seismic first arrival travel times into near surface velocities, we propose a combined approach to solve the problem of first arrival travel time inversion. Firstly, based on the near surface model with one inclined refractor and rugged topography, we perform a linear inversion of the refraction wave travel times without ray tracing. Secondly, after calculating the first arrival travel times on a floating horizontal datum through the inverted low velocity layer velocity, we directly invert the diving wave travel times into the near surface velocities of a hypothesized linear v(z) medium without ray tracing. And finally, after building an initial near-surface velocity model by merging the two inversion results of refraction waves and diving waves, we carry out the conventional first arrival travel time tomography with ray tracing based on a grid near-surface model. The real data example shows that the combined inversion scheme can significantly improve the computational efficiency and turn out more accurate inversion results.