Frequency dependence of the quality factor in the upper crust: a deep seismic sounding approach

Abstract

Ray amplitudes are computed in a one-dimensional velocity structure where the quality factor Q varies continuously with depth. An iterative process is then proposed to derive the quality factor distribution in the upper crust from deep sounding data. Results for compressional waves in the French Massif Central and for a signal frequency close to 20 Hz show that Q increases in a rather linear way from about 40 in surface up to 600 at 7 km depth. Q seems to be higher in the Central Alps: 180 in surface, 1600 at 5 km depth (at 20 Hz). Using proper signal processing, the frequency dependence of Q is finally investigated in the frequency range 10-25 Hz. The results indicate a dependence of the form Q = QofQ, where a! = 0.25 k 0.1.

Deep Earth Structure: Q of the Earth from Crust to Core

“…Regional and near-distance studies of P-and S-wave attenuation (or their respective quality factors Q P and Q S ) often cancel the source by utilizing several stations at varying distances (e.g., Carpenter and Sanford, 1985;Nuttli, 1978Nuttli, , 1980Thouvenot, 1983).…”

Velocity and Attenuation Characterization of the LIGO Site near Livingston, Louisiana

“…The presented method is also based on the assumption that the Q value is independent of frequency, at least within the ranges of 10-50 Hz for body waves and 0.4-10 Hz for the surface waves. The results reported in Thouvenot (1983) indicate that Q values can depend quite strongly on frequency, but one has to be careful interpreting the results because Q values were estimated by observing a decrease in seismic amplitude as a function of distance under the assumption that reflection or refraction from discontinuities do not occur. Because these effects are frequency dependent in layered geologies, as mentioned previously in this paper, the frequency dependence of Q may be overestimated.…”

Simultaneous Inversion of Source Spectra, Attenuation Parameters, and Site Responses: Application to the Data of the French Accelerometric Network

“…Records corresponding to distances between 15 and 200 km are kept. Figure 2 presents the location of the two regions with earthquake epicenters, stations, Modiano and Hatzfeld (1982) 180-350 15-50 Sg Pyrenees Nicolas et al (1982) 100 to 1000 depending on f 0.8 0.5-16 Pn, SnPg, Sg France Thouvenot (1983) 180 to 1600 depending on depth 0.25 20 for Q 0 10 to 20 for α Pn Alps Gagnepain-Beyneix (1987) 30-142 0.7-1.1 2-40 Coda Pyrenees Eva et al (1991) 100 to 1000 depending on f 2-16 Coda Alps Campillo et al (1985) 290 0.5 0. Figure 3, we plot the recording distances for each station for the two areas.…”

“…Modiano and Hatzfeld (1982) used the high frequency part of Fourier spectra, assuming a source decay as f 2 , to estimate a constant quality factor. Thouvenot (1983) used ray integrals and a depth-dependent quality factor to compute anelastic attenuation for compressional waves. Other authors used the decay of Lg waves at large distance in order to estimate a frequency-dependent quality factor (Nicolas et al, 1982;Campillo et al, 1985;Campillo and Plantet, 1991), or the decay of coda waves (Herráiz and Mezcua, 1984;Gagnepain-Beyneix, 1987;Eva et al, 1991), where the single scattering model is used.…”