Well-logs show that heterogeneities occur at many different spatial scales. In this paper, we want to characterize how waves are affected by these heterogeneities, and we study how reflection and transmission coefficients depend on temporal frequency and spatial scale. We use wavelet transformations to filter certain spatial scales from the velocity logs. The scale-filtered logs serve as input ...

We address the problem of estimating seismic velocities inside the Earth which is necessary for obtaining seismic images in regular Cartesian coordinates. The main goals are to develop algorithms to convert time-migration velocities to true seismic velocities, and to convert time-migrated images to depth images in regular Cartesian coordinates. Our main results are three-fold. First, we establi...

Deciphering the origin of seismic velocity heterogeneities in the mantle is crucial to understanding internal structures and processes at work in the Earth. The spin crossover in iron in ferropericlase (Fp), the second most abundant phase in the lower mantle, introduces unfamiliar effects on seismic velocities. First-principles calculations indicate that anticorrelation between shear velocity (...

Wave-equation, finite-frequency imaging and inversion still face many challenges in addressing the inversion of highly complex velocity models as well as in dealing with nonlinear imaging e.g., migration of multiples, amplitude-preserving migration . Extended images EIs are particularly important for designing image-domain objective functions aimed at addressing standing issues in seismic imagi...

Nonlinear reverse-time migration is a modified reverse-time migration that accounts for the nonlinear relation between seismic data and model in order to image multiply scattered waves including multiples. The illumination of multiply scattered waves yields a representation of the Earth’s subsurface that is more sensitive to model parameters, which allows for advanced seismic interpretation. Th...

Velocity dispersion and attenuation in rocks are coupled properties that depend on the pore fluids and fluid flow. Attenuation shows a peak at high partial gas saturation. The amplitude of this peak increases with frequency. With full saturation, velocities rise but dispersion remains approximately constant. A substantial frequency shift occurs with decreasing permeability or fluid mobility. Th...

Seismic imaging produces images of contrasts in physical parameters in the subsurface, e.g., velocity or impedance. To build such images, a background model describing the wave kinematics in the earth is necessary. In practice, the structural image and background velocity model are unknown and have to be estimated from the acquired data. Migration velocity analysis deals with estimation of the ...

In this paper, we summarize some recent results of measurements of temporal changes of active volcanoes using seismic noise cross-correlations. We first present a novel approach to estimate volcano interior temporal seismic velocity changes. The proposed method allows to measure very small velocity changes (≈ 0.1%) with a time resolution as small as one day. The application of that method to Pi...

Aligned vertical fractures introduce velocity anisotropy which is directly related to parameters, such as fracture density, fracture shape and fracture contents. Effective medium models allow us to study qPand qS-wave velocity anisotropy in rocks with aligned vertical fractures, intersecting fracture sets and aligned fractures with smallscale porosity. Spatially varying fracture density distrib...

We calculate the vertical mass discharge rate from Mount St. Helens for the first few minutes of the May 18, 1980 cataclysmic eruption using a new method based on seismic constraints. The observed seismic waves indicate that the seismic source is a series of single forces. We model these forces as thrusts due to a combination of the momentum flux of the erupted products and the pressure of the ...