Attenuation of seismic coda waves in Joao Câmara (Rio Grande do Norte)

Seismic coda Q attenuation (Q c) in the frequency range from 6 to 20 Hz of two distinct S coda windows (early and later portions) are compared to analyse the effects of both coda windows on crustal seismic attenuation estimates around Samambaia fault (Joao Câmara — Northeastern Brazil). Q c values associated with the later portion are systematically higher than those related to the early portion. These values follow a frequency (ƒ) function given by Q c(ƒ) = Q 0ƒη, where Q 0 = 117 ± 39 and η = 1.00 ± 0.06. In general, Q 0 estimate is less sensitive to site effects and stabler than that obtained from the early portion of S coda waves, while its corresponding frequency dependence is similar to that obtained from the early portion of S coda waves. It suggests that η parameter does not depend on coda window’s location along the seismic signal. A comparative analysis of both Q 0 and η values with those found recently shows that there is no difference in using early or later portion of S coda waves in the stations located on Pre-Cambrian basement in the Joao Câmara area. This comparison also shows that the major variations in Q 0 values were observed at seismic stations installed on sedimentary terrain. Differences in the seismic attenuation, in both sides of the Samambaia fault, were also observed in this study, and it is in agreement with the hypothesis that Samambaia fault is a kind of boundary between two seismic attenuation zones.