Seismic tomography software tools at Barcelona Center for Subsurface Imaging

Seismic methods are one of the most powerful existing geophysical tools to extract information on the structure of the Earth’s subsurface. These techniques continue to be widely used to obtain images of the sediments and crust and to map the variations in physical properties. Particularly the P-wave velocity (Vp) distribution is the most commonly modelled property. 

The most widely applied seismic method to retrieve velocity models is seismic tomography, using either travel-time information as in travel-time tomography (TTT) or a more complete set of waveform attributes in full-waveform inversion (FWI). Whereas TTT is a robust, moderately non-linear technique providing coarse models, FWI is strongly non-linear and computationally demanding, but with the potential to provide higher resolution models. TTT and FWI are considered to be complementary, so that they are often combined and applied together. TTT is applied first to get a moderate-resolution model, which is then used as an initial model for FWI. In fact, the key to successfully apply FWI to seismic data, is the usage of a kinematically correct initial model, in which simulated and recorded waveforms are not cycle-skipped at the lowest frequency available. On this basis, it is crucial to extract the travel-time information of the refracted waves as accurate as possible. Particularly for marine multichannel reflection seismic (MCS) acquisition systems, where most refractions are masked by reflections and noise, data processing techniques like Downward Continuation (DC) allows to better retrieve refractions, and this is achieved by virtually redatuming streamer field data to the seafloor. 

 

We aim at showing the different user-friendly open source HPC software designed and built in the Barcelona Center for Subsurface Image (BCSI) to process seismic data from marine experiments, recorded by ocean bottom seismometers (OBS) and/or multichannel seismic (MCS) data recorded by towed streamers. The three tools, DC, TTT, and FWI, which can be used independently and/or combined together for a better performance, have the potential to produce high resolution models of the physical properties of the subsurface. While DC software is designed for 2D seismic data, the TTT tool also read 3D data, and allows the joint inversion of Vp, Vs and anisotropic properties for active and passive data, including earthquake relocation. At present, DC and TTT software tools are freely available and the last version updated at GitHub repositories and the FWI tool for 2D data is under development.