NS41B-1924
Improving Horizontal Resolution of High-frequency Surface-wave Methods Using Travel-time Tomography

Thursday, 17 December 2015
Poster Hall (Moscone South)
Xiaofei Yin1, Jianghai Xia1, Shida Sun2 and Chao Shen1, (1)China University of Geosciences, Wuhan, Hubei, China, (2)China University of Geosciences Wuhan, Wuhan, China
Abstract:
In surface-wave methods, horizontal resolution can be defined as the ability to distinguish anomalous objects that are laterally displaced from each other. And the horizontal length of a recognizable geological anomalous body is measured by the lateral variation of S-wave velocity. Multichannel analysis of surface waves (MASW) method is an efficient tool to determine near-surface shear-wave velocities. The acquisition of the MASW method involves the same source-receiver configuration moved successively by a fixed distance interval (a few to several stations) along a linear survey line, which is called a roll-along acquisition geometry. A pseudo-2D S-wave velocity section is constructed by aligning 1D models, and each inverted 1D S-wave velocity model reflects the vertical S-wave velocity variation at the midpoint of each geophone spread. Although the MASW method can improve the horizontal resolution of S-wave velocity sections to some degree, the amount of fieldwork is increased by the roll-along acquisition geometry. We propose surface-wave tomography method to investigate horizontal resolution of surface-wave exploration. Phase-velocity dispersion curves are calculated by a pair of traces within a multichannel record through cross-correlation combined with a phase-shift scanning method. Then with the utilization of travel-time tomography, we can obtain high resolution pure-path dispersion curves with diverse sizes of grids at different frequencies. Finally, the pseudo-2D S-wave velocity structure is reconstructed by inverting the pure-path dispersion curves. Travel-time tomography of surface waves can extract accurate dispersion curves from a record with a short receiver spacing, and it can effectively enhance the ability of random noise immunity. Synthetic tests and a real-world example have indicated that travel-time tomography has a great potential for improving the horizontal resolution of surface waves.

Keywords: Travel-time tomography of surface waves, Horizontal resolution, Dispersion curves, Pseudo-2D S-wave velocity section.