Strong, sharp, negative seismic discontinuities, velocity decreases with depth, are observed beneath the Pacific seafloor at ∼60 km depth. It has been suggested that these are caused by an increase in radial anisotropy with depth, which occurs in global surface wave models. Here we test this hypothesis in two ways. We evaluate whether an increase in surface wave radial anisotropy with depth is ...

An improved method for determining plane-layered earth models that accurately represent the important features controlling the amplitude and wave form of surface waves is presented. The method includes a formal inversion of phase and group velocity data determined from observed seismograms and is applied to the Rayleigh waves from Nevada Test Site (NTS) explosions recorded at Albuquerque, New M...

This article outlines a new approach to rapidly estimate the damage to tall buildings immediately following a large earthquake. The preevent groundwork involves the creation of a database of structural responses to a suite of idealized ground-motion waveforms. The postevent action involves (1) rapid generation of an earthquake source model, (2) near real-time simulation of the earthquake using ...

Observations of shear-wave splitting in the Northeastern US Appalachians and in the foredeep of the Urals vary signiicantly with the back azimuth and incidence angle of the incoming phase. These variations suggest two or more layers within the upper mantle with diierent anisotropic properties. Synthetic seismograms for simple multilayered anisotropic structures show that shear-wave splitting pa...

We present a scheme for generating synthetic point-source seismograms for shear dislocation sources using line source (two-dimensional) theory. It is based on expanding the complete three-dimensional solution of the wave equation expressed in cylindrical coordinates in an asymptotic form which provides for the separation of the motions into SH and P-SV systems. We evaluate the equations of moti...

Although synthetic borehole seismograms routinely can be computed for a wide range of borehole conditions, the physical nature of shear and compressional head waves in fluid-filled boreholes is poorly understood. This paper presents a series of numerical experiments designed to provide insight into the physical mechanisms controlling head wave propagation in boreholes. These calculations demons...

S U M M A R Y We propose a new approach to full seismic waveform inversion on continental and global scales. This is based on the time–frequency transform of both data and synthetic seismograms with the use of timeand frequency-dependent phase and envelope misfits. These misfits allow us to provide a complete quantification of the differences between data and synthetics while separating phase a...