Evaluation of the seismic quality factor of the Carillon Dam (Quebec)

The seismic attenuation in concrete has seldom been studied, although it is an important parameter for survey design. In this paper, the seismic Q fac tor is estimated from data measured at the Carillon dam. Three methods were used for this study: amplitude decay yielding a value of 5.1 +/- 1.6, spec tral ratio giving a value of 8.3 +/- 3.5, and a value of 7.5 +/- 14.9 was o btained from the rise-time technique. These values are weak compared with w hat is generally observed in rocks, and slightly lower than values obtained on laboratory concrete samples. However, the average P wave velocity measu red on the investigated area is 4081 +/- 95 m.s(-1), an indication of the g ood quality of the material. Consequently, this strong attenuation could be attributed on one hand to energy loss, and on the other hand to scattering caused by the intrinsic cement-aggregate composition of concrete. It is al so possible that an inadequate sensor coupling had the effect of reducing t he observed Q value.