Kirchhoff synthetics for seismic reflections and diving waves in two dimensions and application to the D" layer

The Kirchhoff-Helmholtz (KH) integration has been used to model the reflected and the diving waves from an interface with a positive velocity gradient. The modelling is carried out for a spherical boundary and for a sinusoidal topography with a long-scale wavelength.
An artefact, which is a major problem in modelling the seismic response using the KH integration, has been reduced by introducing a Hilbert transform sign manipulation. Cleaner synthetic seismograms with correct amplitudes have been produced by this method. A discretization in larger surface elements has been made possible by introducing a smoothing factor that suppresses the noise that normally follows the constructed signal if a large element size is taken.     

What can be learned from rotational motions excited by earthquakes?

One answer to the question posed in the title is that we will have more accurate data for arrival times of SH waves, because the rotational component around the vertical axis is sensitive to SH waves although not to P-SV waves. Importantly, there is another answer related to seismic sources, which will be discussed in this paper.
Generally, not only dislocations commonly used in earthquake models but also other kind of defects could contribute to producing seismic waves. In particular, rotational strains at earthquake sources directly generate rotational components in seismic waves. Employing the geometrical theory of defects, we obtain a general expression for the rotational motion of seismic waves as a function of the parameters of source defects.
Using this expression, together with one for translational motion, we can estimate the rotational strain tensor and the spatial variation of slip velocity in the source area of earthquakes. These quantities will be large at the edges of a fault plane due to spatially rapid changes of slip on the fault and/or a formation of tensile fractures.     

Measuring surface-wave overtone phase velocities using a mode-branch stripping technique

We present a method for the retrieval of the phase velocities of surface-wave overtones. The 'single-station' method is successful for several Love and Rayleigh overtone branches (up to at least four) in mode-specific period ranges between 40 and 200 s. It uses mode-branch cross-correlation functions and relies on adjusting the phase and amplitude of the mode branches one at a time. A standard statistical optimization technique is used. We discuss in detail the a priori information that is added to stabilize the retrieval procedure. In addition, we present a technique to estimate the reliability of individual phase and amplitude measurements. The retrieval method and the technique to estimate reliabilities can be used together in a highly automated way, making the methods especially suited for studying the large volume of digital data now available.
We include several applications to synthetic and recorded waveforms. We will discuss in detail an experiment with 90 waveforms that have travelled along very similar paths from Vanuatu to California. For this path, we will present average overtone phase velocities and an average 1-D velocity structure.     

Synthetic SH seismograms in a laterally varying medium by the discrete wavenumber method

Summary. We present a new method to calculate the SH wavefield produced by a seismic source in a half-space with an irregular buried interface. The diffracting interface is represented by a distribution of body forces. The Green's functions needed to solve the boundary conditions are evaluated using the discrete wavenumber method. Our approach relies on the introduction of a periodicity in the source-medium configuration and on the discretization of the interface at regular spacing. The technique developed is applicable to boundaries of arbitrary shapes and is valid at all frequencies. Some examples of calculation in simple configurations are presented showing the capabilities of the method.