Abstract
Earlier attenuation studies for the South American continent indicate that for Sn and Lg waves there is low attenuation in the shield region east of the Andes, whereas in the west of South America, with some exceptions, there is high attenuation. Those studies, however, were nonquantitative. In this study theQ 0 (1-Hz values) for Lg waves for South America are presented, based on a scattering model ofAki (1969) as extended byHerrmann (1980) for the coda waves of shallow local and near-regional earthquakes. The results of the codaQ method are compared with those obtained byNuttli's method (1973). TheseQ 0 values are in good agreement with the apparentQ 0 of Lg waves obtained by the latter method. The data were obtained from over 100 local and regional earthquakes recorded by 12 WWSSN stations throughout continental South America. They provided a range of frequencies from 0.4 to 1.4 Hz, for which the frequency dependence ofQ was investigated by assumingQ=Q 0(f/f 0)ζ. The observed data indicate that the tectonic region of western South America is characterized by lowQ 0 and a large frequency-dependent factor ζ, the values ranging from 150 to 350 and 0.4 to 0.7, respectively. TheQ 0 values increase in the shield region east of the Andes, but frequency dependence decreases. The average crustalQ 0 for north and central Argentina ranges from 420 to 580, and ζ ranges from 0.2 to 0.3. TheQ 0 is larger in the Brazil region, ranging from 580 to 980, and ζ varies from 0.0 to 0.2. In the lower-attenuation region of eastern South America higher values of attenuation correlate with greater thickness of the sedimentary layers.
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Raoof, M.M., Nuttli, O.W. Attenuation of high-frequency earthquake waves in South America. PAGEOPH 122, 619–644 (1984). https://doi.org/10.1007/BF01101871
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DOI: https://doi.org/10.1007/BF01101871