Higher-order elastic properties of single crystalline corundum

Corundum is frequently used for high-pressure and high-temperature applications. Its second-order pressure derivatives are, however, not measurable. A static rigid-ion lattice model for corundum, utilizing exponential-type repulsive force, is developed. The lattice parameters are determined from measured data of the bulk modulus and C33. Using these lattice parameters first-order pressure derivatives of bulk modulus and C33 are computed and compared to measured values, respectively. The deviations do not exceed 33%. The second-order pressure derivatives of bulk modulus and C33 are predicted and the results come out positive. These are usually negative for oxide mineral of cubic structure

Crustal structure in Southern Korea from joint analysis of teleseismic receiver functions and surface wave dispersion

Abstract We estimated crustal structures under 18 broadband stations in southern Korea by combining receiver functions and surface-wave dispersion with the genetic algorithm (GA). Estimated crustal structures were analyzed together with previously determined structures under four stations (GKP, INCN, SNU, and TJN) i

VALIDITY OF RAY THEORY APPROXIMATIONS FOR THE COMPUTATION OF TELESEISMIC SV WAVES.

Teleseismic SV waves have been generally ignored in wave propagation and source studies because of known complications in wave propagation for structure near the source and near the receiver. The validity of common optic ray and WKBJ seismogram methods for computing SV synthetic seismograms is examined by computing synthetic seismograms using these techniques and comparing them to SV synthetics produced from a wavenumber integration technique. Both ray methods give a poor approximation to the wave propagation for distances less than 60 degree . Diffracted Sp and the SPL wave interfere with near-source phases, such as S, pS, and sS for a shallow seismic source, producing anomalously high amplitudes and complex waveforms in agreement with observational experience

A WKBJ spectral method for computation of SV synthetic seismograms in a cylindrically symmetric medium

Summary. A method of synthetic seismogram computation for teleseismic SV‐waves is developed in order to treat quantitatively SV‐waves in problems of body wave source inversion and source—receiver structure studies. The method employs WKBJ theory for a generalized ray in a vertically inhomogeneous half‐space and the propagator matrix technique for waves in near‐surface homogeneous layers. Wavenumber integration is done along the real axis of the wavenumber plane and anelasticity is included by using complex velocity in all regions of the earth model. The near‐surface source structure is taken into account in the computation for the case of the shallow source by allowing a point source to be located in the homogeneous layers. Source and receiver area structures are also allowed to differ. A general moment tensor point source is considered. Copyright © 1985, Wiley Blackwell. All rights reserve

Joint analysis of teleseismic receiver functions and surface wave dispersion using the genetic algorithm

Teleseismic P-wave receiver function data and Rayleigh-wave phase velocity measurements are combined using the genetic algorithm, a global optimization technique, to model crustal structure in southern Korea. The two datasets complement each other because receiver functions are sensitive to shear-wave velocity contrasts in layered structures, while surface wave dispersion is sensitive to averages of shear-wave velocities. The genetic algorithm is more useful than linearized inversion in regions where there is little a priori information about local velocity structure because it is not sensitive to the initial model. The stability and variability of resulting crustal model parameters are quantified by using a Monte Carlo technique in specifying a suite of initial models. Depths to the Moho discontinuity in southern Korea were estimated to be 29-30 km for stations near the western coast and 33-36 km for inland stations. A well-resolved crustal low-velocity zone was inferred for some stations

Shear‐coupled PL

Summary. Observed teleseismic shear‐coupled PL‐waves (SPL) display a variety of waveforms depending on factors such as source depth, source type and velocity structure. Using a WKBJ spectral method for SV‐wave propagation, synthetic seismograms of SPL are produced to examine the factors important in SV and SPL excitation. Results show that SPL is preferentially excited by shallow sources compared to deep sources. This is due to large source area reverberations which consequently leak as SV‐waves into the mantle. Interaction at the receiver area then sets up the classic prograde elliptical motion by which SPL can be identified. This is in accordance with the teleseismic observations and indicates that most previous models for the propagation of SPL were not appropriate for shallow source since emphasis was placed on wave interactions occurring only near the receiver. Copyright © 1985, Wiley Blackwell. All rights reserve

Efficient finite difference calculation of partial derivative seismic wavefield using reciprocity and convolution

Seismic waveform inversion is commonly studied by the least-squares method which transforms the inverse problem to an iterative minization problem of residuals between the synthetic model response and observed data. One can solve this problem using the gradient method, the Gauss-Newton method or the full Newton method. The performance of the inverse method depends on the algorithm for calculating the partial derivative seismic wavefield due to perturbations in the subsurface. In this work, 2-D elastic staggered-grid finite difference method is used to explicitly calculate the partial derivative wavefields by utilizing the source-receiver reciprocity and the convolution

Time domain Gauss-Newton seismic waveform inversion in elastic media

We present a seismic waveform inversion methodology based on the Gauss-Newton method from pre-stack seismic data. The inversion employs a staggered-grid finite difference solution of the 2-D elastic wave equation in the time domain, allowing accurate simulation of all possible waves in elastic media. The partial derivatives for the Gauss-Newton method are obtained from the differential equation of the wave equation in terms of model parameters. The resulting wave equation and virtual sources from the reciprocity principle allow us to apply the Gauss-Newton method to seismic waveform inversion. The partial derivative wavefields are explicitly computed by convolution of forward wavefields propagated from each source with reciprocal wavefields from each receiver. The Gauss-Newton method for seismic waveform inversion was proposed in the 1980s but has rarely been studied. Extensive computational and memory requirements have been principal difficulties which are addressed in this work. We used different sizes of grids for the inversion, temporal windowing, approximation of virtual sources, and parallelizing computations. With numerical experiments, we show that the Gauss-Newton method has significantly higher resolving power and convergence rate over the gradient method, and demonstrate potential applications to real seismic data

Elastic waveform inversion using Gauss‐Newton method

Seismic waveform inversion has been solved usually by a gradient type approach for acoustic media. In this paper, we present an elastic waveform inversion method based on the Gauss‐Newton method. Elastic wave propagation simulation and inversion are both implemented in the time domain. The partial derivative wavefields are computed explicitly using convolutions of forward and reciprocal wavefields. Numerical experiments show that the Gauss‐Newton elastic waveform inversion significantly improves of resolving power and convergence rate over the gradient type inversion