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pure and applied geophysics

, Volume 132, Issue 1–2, pp 289–310 | Cite as

Effect of anelastic and scattering structures of the lithosphere on the shape of local earthquake coda

  • Bernard Chouet
Article

Abstract

A simple model of single acoustic scattering is used to study the dependence of the shape of local earthquake coda on the anelastic and scattering structures of the lithosphere. The model is applied to the coda of earthquakes located near Stone Canyon, central California, and provides an explanation for the features observed in the data, which include an interesting temporal variation in the coda shape. A surficial layer with aQ of 50 and thickness of 10 or 25 km underlain by a zone with aQ of 1000 extending to the bottom of the lithosphere, together with a scattering scale length,a, that varies with depthz according to the relationa=0.3 exp[-(z/45)2] are found to constitute the simplest structure of the medium compatible with the coda data and with body and surface wave attenuation data. The profile of heterogeneity sizes implies that the scattering strength increases strongly with depth, a constraint required by the necessity to boost the energy of the later coda without forcing the intrinsicQ to be excessively high in the uppermost mantle. This constraint is viewed as an artifact of the single scattering model which overstimates the scattering coefficient due to the neglect of multiple scattering. The observed temporal variation of the signal is difficult to explain by a simple change of the intrinsicQ at some depth. Rather, it is suggested that the scattering properties at depth changed with time through a variation of the fractional rms velocity fluctuation on the order of one percent.

Key words

High frequency seismic waves coda waves attenuation scattering heterogeneity quality factor of coda 

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Copyright information

© Birkhäuser Verlag 1990

Authors and Affiliations

  • Bernard Chouet
    • 1
  1. 1.U.S. Geological SurveyMenlo ParkUSA

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