A linear traveltime perturbation interpolation me-thod for seismic ray tracing
Li Tongyu1,3, Zhang Jianzhong1,2,3
1. Key Laboratory of Submarine Geosciences and Prospecting Techniques, Ministry of Education, Qingdao, Shandong 266100, China; 2. Laboratory of Marine Mineral Resources Evaluation and Detection Techniques, National Laboratory for Marine Science and Technology, Qingdao, Shandong 266061, China; 3. College of Marine Geosciences, Ocean University of China, Qingdao, Shandong 266100, China
Abstract：The linear traveltime interpolation (LTI) method assumes that traveltime is linear along a cell boundary,and the traveltime at any point on a cell boundary can be computed by interpolating the known traveltimes at adjacent grid nodes.In reality,however,the traveltime is not linear along a cell boundary,and the linear assumption may result in big calculation errors especially in large grid cells.To solve this problem,we calculate the traveltime with a linear traveltime perturbation interpolation (LTPI) method.In this method,the traveltime at a grid node is decomposed into two parts:a traveltime perturbation and a reference traveltime propagating in an equivalent homogeneous medium.The traveltime perturbation is much less than the reference traveltime.We assume that the traveltime perturbation is linear along the cell boundary,while the reference traveltime is nonlinear.We discretize the complex media with undulant topography and interfaces into a series of irregular cells.We also derive the LTPI formula for 2D irregular cells.Based on the LTPI,we propose a ray tracing method.Numerical experiments indicate that the LTPI is more accurate and stable than the LTI in computing wavefront traveltimes and ray paths.The LTPI performs better than the LTI in complex media.Under a certain accuracy requirement,the LTPI is more efficient than the LTI.
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