Multiple arrival tracking within irregular triangular or tetrahedral cell model

Abstract

The focus of this research is to introduce a triangular shortest-path method incorporating a multistage scheme for tracking multiple arrivals composed of any kind of combinations of transmissions, conversions and reflections in complex 2D or 3D layered media, in which a triangular (2D) or a tetrahedral (3D) cell is used to parameterize the velocity model. The basic principle is to divide a layered model into several different computational domains using irregular triangular (or tetrahedral) cells in model parameterization, and then to apply the multistage technique to trace the multiple arrivals. Meanwhile, a second level of forward star technique (where a forward star represents a geometric arrangement of network connections, or possible ray branching points into adjacent nodes), previously defined in gridded model, is first introduced into the triangular (or tetrahedral) cell model. The results show that using irregular triangular (or tetrahedral) cells can effectively approximate the undulated subsurface and velocity discontinuity, easily define the velocity distribution across the irregular subsurface interface, and hence greatly improve the computational accuracy. Several examples (including the Marmousi model) are used to demonstrate the viability and versatility of the multistage triangular shortest-path method in heterogeneous media, even in the presence of high-velocity contrasts involving interfaces of relatively high curvature. With the introduction of the second level of the forward star scheme, the total number of nodes is reduced sufficiently (normally by half), and therefore the computer memory required is less. Most important is that the computing accuracy with the second level forward star scheme can be greatly improved (say, 2-3 times in general) over those with the first level of forward star scheme applied. © 2012 Nanjing Geophysical Research Institute.