Velocity Structure Near the Northern Manila Trench: An OBS Refraction Study

Based on Huygens' principle,the authors present an accurate andcomputationally efficient method to compute the shortest raypath andtraveltime in a two- and three-dimensional(2-D and 3-D)space of a discrete block model.The efficiency of the method is achieved through approximation,while the accuracy of the calculated traveltime solely dependson machine precession.The accuracy of the raypath is realized by the smallincrement in the orientation of the ray incidence.Whether the computational efficiency and accuracy can be justified depends on the model's complexity and requirements in its own application.In addition,the feasibilityof implementing the algorithm on the Cray T3D Massively Parallel Processors (MPP)is proposed. The velocity distribution in a 2-D space is discretized into homogeneouspolygonal cells.The search for the shortest traveltime and path betweentwo given points can be reduced to a discrete graph searching.In the general 3D case,the velocity model is characterized by discrete convex blocksbounded by polyhedral surfaces.Although the 3-D algorithm is a straight-forward extension of the 2-D case,the computing operations in 3-D aremuch more CPU intensive.The method is demonstrated with examples showing raypaths andwavefronts in 2D and 3D block models.On the basis of these examples,theproposed algorithm is capable of solving the optimal raypaths from different source points in parallel on the MPP system.

並列關鍵字

Ocean-Bottom Seismograph ； Velocity Structure ； Manila Trench

國際替代計量

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