Sensitivity of SS precursors to topography on the upper‐mantle 660‐km discontinuity

Abstract

Abstract. The sensitivity of SS precursors to the presence of topography on the 660-kin discontinuity is addressed using an axisymmetric finite difference approximation to the $H wave propagation in the Earth mantle. Numerical experiments are lead to quantify the bias in both wavelength and amplitude committed in estimating depth information on the upper-mantle discontinuities from ray inversion of .SdS arrival times. It is further shown that long period $660S arrival-times do not provide information on the deepening of the '660' in presence of a velocity increase expected as the thermal signature of a subducting slab.

The Spectral-Element Method, Beowulf Computing, and Global Seismology

“…Unfortunately, most of the current techniques come with severe restrictions, and they are frequently limited to two-dimensional (2D) axi-symmetric models to reduce the computational burden. Because of its simplicity and ease of implementation, the finite-difference technique has been introduced to simulate global seismic wave propagation (13,14 ). In this differential or "strong" formulation of the wave equation, displacement derivatives are approximated using differences between adjacent grid points, which makes the implementation of accurate boundary conditions difficult.…”

Seismic wave propagation in fully anisotropic axisymmetric media

“…The axisymmetric approach has three major advantages over full 3-D methods: (1) it enables the storage of the wavefields that provide the basis for computing Fréchet sensitivity kernels (Dahlen et al 2000), which is not feasible with full 3-D methods due to disk space requirements; (2) it allows the inclusion 2.5-D lateral heterogeneities that are effectively modelled as ringlike structures around the symmetry axis giving rise to various applications in a high-frequency approximation that are not tractable with 1-D methods and (3) it is computationally several orders of magnitude less expensive than full 3-D methods and hence allows the simulation of higher frequencies. Axisymmetric approaches have been presented earlier using finite difference (Alterman & Karal 1968;Igel & Weber 1995, 1996Chaljub & Tarantola 1997;Thomas et al 2000;Takenaka et al 2003;Toyokuni et al 2005) or pseudospectral methods (Furumura et al 1998), but most of these studies assume azimuthally symmetric sources (monopoles) and hence cannot model arbitrary earthquake sources, but rather resemble explosive sources or a certain geometry for strike slip events (Jahnke et al 2008). More recently, Toyokuni & Takenaka (2006 generalized their method to include moment tensor sources, attenuation and the Earth centre.…”

Optimized viscoelastic wave propagation for weakly dissipative media

“…Other axisymmetric approaches to global and local wave propagation have been presented (Alterman & Karal 1968;Igel & Weber 1995, 1996Chaljub & Tarantola 1997;Furumura et al 1998;Thomas et al 2000;Takenaka et al 2003;Toyokuni et al 2005;Jahnke et al 2008), but only recently Toyokuni & Takenaka (2006, 2012 generalized their method to include moment tensor sources, attenuation and the Earth's centre. These methods are all based on isotropic media and especially the finite-difference methods among them have to deal with large dispersion errors for interface-sensitive waves such as surface waves and diffracted waves (Igel & Weber 1995;.…”