Seismic Tomography Algorithm (Hole’s Code) Omar Ochoa

Outline Background Data Flow Diagram Research questions Status Conclusion

Background 3-Dimensional seismic travel time tomography for determining three-dimensional velocity structure from first arrival travel time –A back-projection method It is a non-linear tomographic procedure that minimizes computational time –provides a relatively high-resolution model –can handle structures with large velocity contrasts. Described in: Hole, 1992, Journal of Geophysical Research, v97,

Background Implemented in Fortran and C Wrapped with scripts Executes in a Unix environment Two versions of Hole’s code –Original scripts created by Hole to execute his programs –New scripts developed by Piotr Sroda to increase usability

Data Flow Diagram Each subroutine is a process Input and output data is piped between each process Data Flow Diagram models scripts

DFD There are 6 programs inside Hole’s Code vel1d punc cover tomosm duadd addc

DFD-1 Converts a set of data points to an equally sampled 3d velocity model

DFD-2 Calculates the first arrival travel times for each shot point using the initial velocity model

DFD-3 Calculates the ray from the shot point to the receiver and then determines how the travel time residuals affect each cell using the shot point locations within a 3D time field

DFD-4 Calculates model perturbations at each cell corner, adds the ray perturbations for all adjacent cells and averages it out to smooth it

DFD-5 Coarser smoothing of model perturbation and adds the perturbation to the 3d velocity model

DFD-6 Merge previous 3d velocity model with new velocity model

Research Questions How can we capture Hole’s algorithm as a a workflow? Can we expose Hole’s code as a service for other scientists? Are there any reusable components in this workflow? What properties are of interest to a scientist in this algorithm? How can we provide assurance about the execution of this software service to scientists?

Status Working on executing examples to understand how the algorithm works Visualizing the output Validating the output by meeting with Dr. Miller

Conclusion There is this great piece of software that geologists want to use Requires a lot of computer knowledge to execute –Not geology related