Seismic Surface Waves in a Laterally Inhomogeneous Earth

ISBN-13: 9789401068857 / Angielski / Miękka / 2011 / 304 str.

V. I. Keilis-Borok; Anatoli L. Levshin; T. Yanovskaya

Opis

Surface waves form the longest and strongest portion of a seismic record excited by explosions and shallow earthquakes. Traversing areas with diverse geologic structures, they 'absorb' information on the properties of these areas which is best retlected in dispersion, the dependence of velocity on frequency. The other prop erties of these waves - polarization, frequency content, attenuation, azimuthal variation of the amplitude and phase - arc also controlled by the medium between the source and the recording station; some of these are affected by the properties of the source itself and by the conditions around it. In recent years surface wave seismology has become an indispensable part of seismological practice. The maximum amplitude in the surface wave train of virtually every earthquake or major explosion is being measured and used by all national and international seismological surveys in the determination of the most important energy parameter of a seismic source, namely, the magnitude M, . The relationship between M, and the body wave magnitude fI1t, is routinely employed in identification of underground nuclear explosions. Surface waves of hundreds of earthquakes recorded every year are being analysed to estimate the seismic moment tensor of earthquake sources, to determine the periods of free oscillations of the Earth, to construct regional dispersion curves from which in turn the crustal and upper mantle structure in various areas is derived, and to evaluate the dissipative parameters of the mantle material.

Spis treści

1. Theory.- 1. Surface waves in vertically inhomogeneous media.- 1.1. Equations of motion for an elastic medium.- 1.2. Sources of seismic disturbance.- 1.3. Surface waves due to a point source in a vertically varying half-space.- 1.4. Physical interpretation; some simple examples.- 1.5. Sphericity corrections; variational formulas.- 1.6. Effects of anelasticity.- 1.7. Synthetic seismograms.- 2. Surface waves in media with weak lateral inhomogeneity.- 2.1. Formulation of problems of surface wave propagation in a half-space with weak lateral inhomogeneity.- 2.2. Propagation of harmonic surface waves.- 2.3. Propagation of transient surface waves.- 2.4. Calculation of geometrical spreading for space-time rays.- 2.5. Reflection and refraction of space-time rays at a discontinuity.- 2.6. Space-time rays and geometrical spreading in the spherical case.- 2.7. On the configuration of space-time rays.- 3. Surface waves in media involving vertical contacts.- 3.1. Statement of the problem.- 3.2. A review of available theoretical results.- 3.3. Approximate calculation of surface wave reflection and transmission coefficients at a contact.- 3.4. A numerical method for determining the displacement field.- 3.5. Oblique contact and other possible refinements.- 4. Computation techniques for surface waves.- 4.1. On the matrix method for one-dimensional boundary value problems.- 4.2. A numerical method for solving one-dimensional boundary value problems.- 4.3. Dynamic ray tracing.- 4.4. Calculation of reflection and transmission coefficients.- 2. Interpretation of Surface Wave Observations.- 5. Recording, identification, and measurement of surface wave parameters.- 5.1. Recording techniques and equipment in surface wave observations.- 5.2. Basics of surface wave processing.- 5.3. Frequency-time analysis.- 5.4. Linear polarization analysis.- 5.5. Spatial analysis of surface waves.- 6. Methods for quantitative interpretation of observations.- 6.1. A review of recent approaches to the inversion of surface wave data.- 6.2. Least squares and singular value decomposition.- 6.3. Quadratic programming methods.- 6.4. Modelling experimental data in a block structure.- 6.5. Backus—Gilbert method.- 6.6. Surface wave tomography based on a combined use of phase and group velocities for different periods.- 6.7. The influence of lateral inhomogeneity on the measurement of surface wave attenuation.- 6.8. Anisotropy or inhomogeneity?.- 6.9. Estimation of earthquake source parameters.- 7. Some results from studies of regional lithospheric structure by surface waves.- 7.1. The method of path elimination in a study of the Eurasian crust.- 7.2. Results obtained by the Backus—Gilbert method.- 7.3. Anomalous Rayleigh surface waves in northeast Eurasia.- References.