민동주 교수

Abstract We develop a new finite-difference scheme that reduces the number of grid points per wavelength required in frequency-domain elastic modeling. Our approach computes weighted averages of the spatial second-order derivative and the mass acceleration terms using a 25-point computational stencil. By determining the weighting coefficients to minimize numerical dispersion and numerical anisotropy, we reduce the number of grid points to 3.3 per shear wavelength, with a resulting error in veloc

Abstract One of the applications of refraction-traveltime tomography is to provide an initial model for waveform inversion and Kirchhoff prestack migration. For such applications, we need a refraction-traveltime tomography method that is robust for complicated and high-velocity-contrast models. Of the many refraction-traveltime tomography methods available, we believe wave-based algorithms to be best suited for dealing with complicated models. We developed a new wave-based, refraction-tomography

We present a weighted-averaging frequency-domain finite-element method for an accurate and efficient 2D elastic wave modeling technique. Our method introduces three kinds of supplementary element sets in addition to a basic element set that is used in the standard finite-element method. By constructing global stiffness and mass matrices for four kinds of element sets and then averaging them with weighting coefficients, we obtain a new global stiffness and mass matrix. With optimal weighting coef

We design a new frequency-domain, finite-difference approach, based on a displacement formulation, which correctly describes the stress-free conditions at a free surface. In the conventional, displacement-based finite-difference method, we assign both displacements and material properties such as density and Lame constants to nodal points (a node-based grid set), whereas in our new finite-difference method, displacements are still defined at nodal points but material properties within cells (a c

Because of the limitations of conventional metal-oxide-based electrodes, studies on organic redox-active materials as alternative electrodes for secondary batteries are emerging. However, reported organic electrode materials are still limited to a few kinds of organic redox groups. Therefore, the development of new redox-active groups for high-performance electrode materials is indispensable. Here, we evaluate s-tetrazine derivatives as a new electrode material in Li-ion batteries and study thei

ABSTRACT Waveform inversion can lead to faint images for later times due to geometrical spreading. The proper scaling of the steepest‐descent direction can enhance faint images in waveform inversion results. We compare the effects of different scaling techniques in waveform inversion algorithms using the steepest‐descent method. For the scaling method we use the diagonal of the pseudo‐Hessian matrix, which can be applied in two different ways. One is to scale the steepest‐descent direction at ea

We propose a strategy to overcome the high sensitivity to early-time noise of the Laplace-domain waveform inversion. In deep-sea seismic data, this problem is particularly crucial to obtaining accurate velocity structures. To this end, rather than simply filtering or muting early-time data, we propose replacing the original, noise-contaminated direct waves with analytically computed noise-free waves. To reconstruct the noise-free direct waves, we compute Green′s functions for half-space media, e

SUMMARY Seismic anisotropy is an important physical phenomenon that significantly affects wave propagation in complex sedimentary basins. When geological structures exhibit steep dips or severe folding, the symmetry axis of the transversely isotropic (TI) representation of the region can be rotated, leading to tilted transversely isotropic (TTI) media. We seek to find the optimal full-waveform inversion (FWI) strategy to estimate both the seismic velocities and the anisotropic parameters, includ

To enhance the feasibility of seismic full waveform inversion (FWI) for various types of geological structures, the model parameters should be updated along directions such that both long- and short-wavelength structures can be properly resolved. These long- and short-wavelength structures are primarily influenced by the low- and high-frequency components of the gradients, respectively. In some cases, however, the gradients are not flexible to reconstruct both the long- and the short-wavelength

ABSTRACT Reflection traveltime tomography has been used to describe subsurface velocity structures which, in practice, can be used as a background or initial model for pre‐stack depth migration or full waveform inversion. Conventional reflection traveltime tomography is performed by solving an optimization problem based on a ray‐tracing method. As a result, reflection traveltime tomography requires heavy computational efforts to carry out ray tracing and solve a large matrix equation. In additio

금속광산탐사에서 많이 이용되는 물리탐사 방법 중의 하나인 쌍극자-쌍극자 배열 전기비저항탐사의 실제 광산탐사에 대한 적용성을 평가하기 위하여 단순화된 광상구조에 대하여 현장자료 시뮬레이션 및 역산해석을 수행하였다. 실제 광상모형으로는 국내 여러 금속광상 중에서 가장 분포 빈도가 높은 맥상광상을 대상으로 하였다. 국내 맥상광상의 맥폭이 대부분 수십 cm에서 2 m 이내라는 점에 기초하여 맥폭을 변화시키고, 광맥의 물성을 변화시켰으며, 쌍극자-쌍극자 배열 전기비저항탐사의 전극간격은 40 m로 가정하였다. 맥폭이 1 m 이하일 경우 주변암과 광맥의 전기적 물성차가 300배이상 되는 경우에도 저비저항대가 나타나지 않았다. 맥폭이 커질수록 그리고 비저항의 차가 클수록 저비저항대가 뚜렷하게 나타났으나, 넓은 전극간격과 역산에 이용된 셀 크기가 심부로 갈수록 커져서 대체로 저 비저항대의 폭이 과장되게 나타났고, 깊이 또한 실제 깊이보다 깊게 나타났다. 실제 천열수광상 모형을 가정하고 현재 가행 중

P264 FREE SURFACE BOUNDARY CONDITION IN FINITE-DIFFERENCE ELASTIC WAVE MODELING Summary 1 Free-surface boundary condition is one of the most important factors governing the accuracy of elastic wave modeling technique that can efficiently be used in seismic inversion and migration. We devised a method that exactly describes free surface boundary in finitedifference elastic wave modeling. Our method is to assign material properties such as density and Lamé constants to the areas rather than the no