A3Mark: Seismic attribute benchmarking

Seismic attribute computation is one of the most active research and engineering topics in the computational geophysics world. Although numerous algorithms for seismic attribute computation have been developed, relatively little work has been done on scientifically characterizing their quality and accuracy. Seismic attribute characterization effort is largely qualitative and subjective. We have developed a robust and reliable scientific process for functionally comparing similar attributes. Structural seismic attributes are addressed, including discontinuity, dip angle, dip azimuth, and curvature. To establish a common software platform, and collection of data sets for efficient fully automatic evaluation, a stand-alone flexible online web service is designed. It is based on a C#-MATLAB implementation, and it is called A3Mark. The publicly available web service enables the automatic evaluation of individual categories of seismic attributes using customized quality metrics. It can be easily extended to include new algorithms. Several new synthetic data sets covering various structural measurements are also created, including noise, with ground truth, and they are made publicly available through the web service. Finally, a comparative evaluation of some current seismic attribute algorithms is given with quantitative and qualitative results.

Full-waveform inversion, Part 1: Forward modeling

Since its reintroduction by Pratt (1999) , full-waveform inversion (FWI) has gained a lot of attention in geophysical exploration because of its ability to build high-resolution velocity models more or less automatically in areas of complex geology. While there is an extensive and growing literature on the topic, publications focus mostly on technical aspects, making this topic inaccessible for a broader audience due to the lack of simple introductory resources for newcomers to computational geophysics. We will accomplish this by providing a hands-on walkthrough of FWI using Devito ( Lange et al., 2016 ), a system based on domain-specific languages that automatically generates code for time-domain finite differences.

Immersive boundary conditions: Theory, implementation, and examples

Many applications in computational geophysics involve the modeling of seismic wave propagation on a set of closely related subsurface models. In such scenarios, it is of interest to recompute the seismic wavefields locally (only in the regions of change), instead of in the full subsurface model. We have developed a method for local acoustic wavefield recomputation that makes it possible to fully immerse a local modeling domain within a larger domain of arbitrary extent and complexity, such that the wave propagation in the full domain is completely accounted for. The method enables wavefield modeling on much smaller local domains, while relying on the up-front generation of a large number of Green’s functions and a wavefield extrapolation step at each time step of the simulation. A Kirchhoff-Helmholtz extrapolation integral is used to predict the interaction of the wavefield leaving the local domain with the exterior domain. The outward propagating wavefield and the wavefield reentering the local domain are applied as a boundary condition along the edges. Thanks to these dynamically calculated boundary conditions, all higher order long-range interactions between the two domains are fully accounted for. We have implemented the method in a conventional finite-difference time-domain scheme and determined that the locally calculated wavefields are equal to wavefields generated on the full domain to within numerical precision. The efficiency of the local modeling algorithm will greatly depend on the nature and size of the problem.