Effects of free-surface topography on moving-seismic-source modeling

Abstract

A curved-grid velocity-stress formulation for viscoelastic wave modeling is used with an arbitrary number of relaxation mechanisms to model a desired [Formula: see text]-behavior. These equations are discretized by high-order staggered finite differences (FDs) in the interior of the medium, and we gradually reduce the FD order to two at the stress-free surface, where we implement our boundary conditions for an arbitrary topographic surface. A moving source is simulated along the surface of a relatively general and locally steep surface topography and, for comparison, along a plane surface. The topography consists of a significant hill surrounded by a valley. Similar two-layered geologic models are used with both topographic surfaces, with the upper layer being a lossy sedimentary layer having a relatively strong contrast with the lower, higher-velocity half-space. Local topographic highs create varying amplitude amplifications at different times during motion of the source. A pronounced wavefield accumulation is evident at the topographic highs in all components. This is very different from the even pattern produced by the same source along the same path for the plane topographic surface, even in the presence of the strong material discontinuity between the two geologic layers. The effect is, however, similar to real records for nonmoving sources of long duration; over time, the direction of incidence becomes less significant, and amplitude amplification occurs in all directions for waves trapped in a topographic high. These spatial focusing effects should be taken into account in inversion for vehicle tracking to avoid target mislocation and/or misidentification.

Modeling seismic wave propagation within complex structures

“…Currently the finite difference method (FDM) is widely used because of its computational effi ciency in seismic modeling, (Carcione et al, 2002;Wang and Liu, 2007). However, the defects of FDM reveal themselves in the situations listed above, such as strong numerical dispersion and the diffi culty of dealing with irregular boundaries (Alford et al, 1974;Lines et al 1999;Hestholm et al, 2006;Thore 2006;and Xu et al 2007). Many improvements have been made in FDM to solve these problems (Tessmer, 2000;Oliveira, 2003;Ma et al 2004;Zhang and Chen 2006;and Moubarak et al 2007).…”

A fast topographic characterization of seismic station locations in Iran through integrated use of digital elevation models and GIS

“…Karimzadeh et al (2014) used a couple of influential local parameters including ASTER topography map for simulation of ground shaking map in Tabriz, Iran. Hestholm et al (2006) used an elevation model for simulation of a moving source along the locally steep surface topography. De Reu et al (2013) did a topographic classification for a geoarchaeological project in NW Belgium using a DEMbased analysis on high-density light detection and ranging (LiDAR) data between 2001 and 2004.…”

Ray tracing of turning wave in elliptically anisotropic media with an irregular surface

“…How to accurately describe the geological model with undulating interfaces is very important for solving the seismic wave propagation. The methods always used include the approximation method with ladderlike grids , the model expansion method with regular grids (Hole 1992;Ma and Zhang 2014), the nonuniform grid spacing method (Sun et al 2012a, b), the hybrid grid spacing method (Sun et al 2009(Sun et al , 2012aBai et al 2010Bai et al , 2013Li et al 2013), the curved grid spacing method (Thompson et al 1985;Ruud 1994, 1998;Dong 2005;Wang and Liu 2006;Hestholm et al 2006;Lan et al 2012;Zhang 2011, 2013a, b;Ma and Zhang 2014) and the triangulated meshing method (Fomel 1997;Sethian 1999;Xu et al 2006Xu et al , 2010Kao et al 2008;Yu et al 2010;Bai et al 2012). The triangular grids are simple and flexible in modeling and can describe any undulating terrain with high degree of approximation.…”