Premium
A hybrid fast algorithm for first arrivals tomography
Author(s) -
Mendes Manuela
Publication year - 2009
Publication title -
geophysical prospecting
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.735
H-Index - 79
eISSN - 1365-2478
pISSN - 0016-8025
DOI - 10.1111/j.1365-2478.2008.00755.x
Subject(s) - eikonal equation , algorithm , monte carlo method , linearization , tomography , synthetic data , seismic tomography , computer science , grid , mathematical optimization , geology , mathematics , physics , geodesy , mathematical analysis , optics , statistics , nonlinear system , quantum mechanics
A hybrid algorithm, combining Monte‐Carlo optimization with simultaneous iterative reconstructive technique (SIRT) tomography, is used to invert first arrival traveltimes from seismic data for building a velocity model. Stochastic algorithms may localize a point around the global minimum of the misfit function but are not suitable for identifying the precise solution. On the other hand, a tomographic model reconstruction, based on a local linearization, will only be successful if an initial model already close to the best solution is available. To overcome these problems, in the method proposed here, a first model obtained using a classical Monte Carlo‐based optimization is used as a good initial guess for starting the local search with the SIRT tomographic reconstruction. In the forward problem, the first‐break times are calculated by solving the eikonal equation through a velocity model with a fast finite‐difference method instead of the traditional slow ray‐tracing technique. In addition, for the SIRT tomography the seismic energy from sources to receivers is propagated by applying a fast Fresnel volume approach which when combined with turning rays can handle models with both positive and negative velocity gradients. The performance of this two‐step optimization scheme has been tested on synthetic and field data for building a geologically plausible velocity model.This is an efficient and fast search mechanism, which permits insertion of geophysical, geological and geodynamic a priori constraints into the grid model and ray path is completed avoided. Extension of the technique to 3D data and also to the solution of ‘static correction’ problems is easily feasible.