The D′′ region in the lowermost mantle beneath the Caribbean and Central America is investigated using shear waves from South American earthquakes recorded by seismic stations in North America. We present a large-scale, composite study of volumetric shear velocity heterogeneity, anisotropy, and the possible presence of a D′′ discontinuity in the region. Our data set includes: 328 S(Sdiff )-SKS ...

Earthquakes can be triggered by local changes in the stress field (static triggering) due to nearby earthquakes or by stresses caused by the passage of surface (Rayleigh and Love) waves from a remote, large earthquake (dynamic triggering). However, the mechanism, frequency, controlling factors and the global extent of dynamic triggering are yet to be fully understood. Because Rayleigh waves inv...

Basis pursuit inversion of seismic reflection data for reflection coefficients is introduced as an alternative method of incorporating a priori information in a seismic inversion process. The inversion is accomplished by building a dictionary of functions, representing seismic reflection responses, and constituting the seismic trace as a superposition of these responses. Basis pursuit decomposi...

Lamont-Doherty Earth Observatory (LDEO) at Columbia University is evaluating a method of locating seismic sources (earthquakes, explosions) based on the use of waveform cross-correlation (WCC) measurements instead of using the conventional measurements of seismic wave arrival time (phase picks). WCC measurements have been demonstrated to be 10 to 100 times more accurate, where they can be used....

S U M M A R Y Azimuthal seismic anisotropy, the dependence of seismicwave speeds on propagation azimuth, is largely due to fabrics within the Earth’s crust and mantle, produced by deformation. It thus provides constraints on the distribution and evolution of deformation within the upper mantle. Here, we present a new global, azimuthally anisotropic model of the crust, upper mantle and transitio...

For purposes of monitoring compliance with the Comprehensive Nuclear Test-Ban Treaty, it is desirable to be able to locate seismic events routinely to within an uncertainty not greater than 1000 square km. From more than five years of experience with publication of the Reviewed Event Bulletin (REB) by the Prototype International Data Centre (PIDC), resulting in estimated locations for more than...

The accuracy of the finite-difference method for generating synthetic seismograms of SH wave propagation in cylindrically symmetric media is discussed. The finite-difference method has the advantage that arbitrary density and velocity fields in the medium may be specified. A point source is generated by a simple transformation of a line source. The accuracy of the finite-difference seismograms ...

The accuracy of the fi!lite-difference method for generating synthetic seismograms of SH wave propagation in cylindrically symmetric media is discussed. The finite-difference method has the advantage that arbitrary density and velocity fields in the medium may be specified. A point source is generated by a simple transformation of a line source. The accuracy of the finite-difference seismograms...

Knowledge of particle motion polarization aids in identifying phases on threecomponent seismograms. The scheme of Montalbetti and Kanasewich (1970) is extended to analytic three-component seismograms, where the imaginary part of the signal is the Hilbert transform of the real part. This scheme has only one free parameter, the length of the time window over which the polarization parameters are ...

In this paper, we address the relocation, magnitudes, and the style of faulting of the Lompoc earthquake from a sparse assortment of teleseismic and regional seismograms. The highest quality teleseismic waveform data come from a station at De Bilt (Netherlands) that remains in operation. Thus, recordings of numerous modern events in central coastal California (i.e., the 1969 Santa Lucia Banks, ...