Zhaolun Liu, a PhD Student from the Earth Science and Engineering Program, supervised by Professor Gerard Schuster, was awarded “best student presentation” at the 2017 SEG Full-Waveform inversion and Beyond Workshop (held 20-22 November 2017 in Beijing, China) for his presentation on “3D Wave-Equation Dispersion Inversion of Surface Waves.”

The paper on which the presentation was based was co-authored by Zhaolun Liu, Jing Li (a postdoc in the group) and Professor Schuster. Their paper describes a new and robust method called wave equation dispersion inversion (WD) that they use for inverting surface waves for the complex S-wave velocity distribution in the Earth or in engineering structures.

The propagation velocity of surface waves at different frequencies is determined by the lateral and depth variations of the subsurface geology. Professor Schuster’s research group made the unexpected discovery that surface waves can be used to establish the location of shallow Potash deposits while assessing the feasibility of using seismic imaging to locate Potash deposits for the Ma’aden Mining Company during field experiments in Saudi Arabia, What they did not have, however, was an inversion methodology to accurately identify the location of the deposits.  Their subsequent research with postdoctoral scientist Jing Li and research Professor Sherif Hanafy, partly funded by a CRG Grant, led to the development of their WD methodology.

The key innovation of WD is that it overcomes the previous restrictions of a layered medium assumption to model smooth velocity variations and cycle-skipping in FWI. This methodology has recently been extended by Jing Li to inversion of P-waves in wave guides. The Group’s WD methodology will be relevant to earthquake seismology, non-destructive engineering, mining geophysics, and exploration seismology.