Open AccessRayleigh‐wave amplitudes from earthquakes in the range 0–150°
Author(s) -
Thomas J. H.,
Marshall P.D.,
Douglas A.
Publication year - 1978
Publication title -
geophysical journal of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0016-8009
DOI - 10.1111/j.1365-246x.1978.tb03737.x
Subject(s) - amplitude , rayleigh wave , attenuation , magnitude (astronomy) , seismology , range (aeronautics) , geodesy , dispersion (optics) , rayleigh scattering , geology , physics , surface wave , optics , astrophysics , materials science , composite material
Summary . Vertical component Rayleigh‐wave amplitudes from 1461 shallow earthquakes recorded in the distance range 0–150° are analysed to separate the effects of earthquake size, epicentral distance (Δ) and recording station. The estimated decay of amplitude with distance has the form of a theoretical curve for the decay of Rayleigh waves with distance if the assumption is made that the decay due to dispersion for the data analysed is that of an Airy phase. Writing the decay due to anelastic attenuation as exp (‐ k Δ), k is estimated to be 0.676/rad over the whole range of distance. If the distance effects are represented by a straight line of the form h log Δ+ constant, h is estimated to be 1.15. The calibration function for computing M s derived from the estimated distance effects is very similar to that of Marshall & Basham. Station effects on Rayleigh‐wave amplitudes though statistically significant are small, and can probably be ignored in the computation of M s . Comparing the estimated surface‐wave magnitudes (earthquake size) obtained in this study with the long and short period body‐wave magnitudes ( m LP b and m SP b respectively) obtained by Booth, Marshall & Young for the same earthquake shows that m LP b is about equal to M s over the magnitude range of interest (˜4.0–7.0). The m LP b and M s relationship shows that the greater the long‐period energy radiated by an earthquake the smaller proportionately is the short‐period energy.