Interpretation of Lg

Abstract

Lg waves are shown to be identified with higher mode Love wave propagation. The complete demonstration shows that the observations of Lg can be explained only by taking into account the anelasticity of the crust-mantle system, the selective frequency response of the seismograph, and above all, the complicated features of the propagation of Love waves for a number of higher modes, including the relative spectral excitations of these modes. It is not necessary to introduce crustal low-velocity channels to explain the character of the Lg seismogram.

Frequency-Dependent Lg Attenuation in the Indian Platform

“…The effect of the source radiation pattern is minimized because the Lg phase is constructed as a superposition of many higher-mode surface waves (Knopoff et al, 1973;Panza and Calcagnille, 1975) sampling a major portion of the focal sphere. Lg is modeled accordingly as constructively interfering highermode surface waves (Knopoff et al, 1973;Nuttli, 1973;Panza and Calcagnille, 1975) and it is therefore assumed that the frequency-domain geometrical spreading scales with the square root of distance . ( R) Ί Taking log 10 of equation (1) vQ This is the equation of a straight line, whose intercept is given by the source term and slope by the Q term.…”

“…For continental earthquakes at regional distances the Lg phase is often a largeamplitude arrival typically constituting the main portion of the wave-train energy. High-frequency, higher-mode Rayleigh waves combine to produce the vertical component Lg phase (Knopoff et al, 1973). Lg can also be considered to arise from the interference of multiple reflected S waves propagating in the crustal wave guide (Bouchon, 1982;Kennett, 1985).…”

Collaborative Research: High-Resolution Seismic Velocity and Attenuation Models of Western China

“…Fundamental mode Rayleigh and Love waves are most sensitive to earth structure at depths corresponding to ~1/3 and ~1/4 of their dominant wavelengths, respectively (Knopoff et al, 1973). Surface waves are dispersive, i.e.…”

Analysis of source spectra, attenuation, and site effects from central and eastern United States earthquakes

“…Press and Ewing (1952), the regional phase, Lg, can be considered either as a surface-wave phase consisting of higher modes of Rayleigh and Love waves (e.g. Ewing, 1957, 1958;Knopoff et al, 1973), or as the superposition of post-critically reflected S waves trapped in the continental crust (e.g. Bouchon, 1982;Olsen et al, 1983;Campillo, 1990).…”