Estimation of attenuation characteristics of Aswan reservoir region, Egypt

Abstract

The attenuation characteristics of Aswan reservoir region in Egypt was estimated using microearthquakes records. Frequency-dependent attenuation characteristic of S wave was estimated using coda normalization method. The evaluated quality factor (Q s ) shows strong frequency dependence with its value increasing with increasing frequency. For Aswan region, the average frequency-dependent relation is given by Q s = (34.2 ± 2.9)f(1.023 ± 0.107). The low values of Q s lie within those observed for seismically active regions of the world, although the study area is seismically moderately active and known to be a region where reservoir-induced seismicity occurs. The low value of Q s would mean that the medium is highly heterogeneous. Separation of intrinsic and scattering Q was carried out using estimated Q s values and values of coda Q (Q c ) estimated earlier by other workers from the same data set. It is observed from this that S and coda wave attenuation is primarily controlled by intrinsic attenuation at 1-Hz frequency. At higher frequencies, intrinsic and scattering attenuations contribute almost equally as seismic albedo at 1-Hz frequency is 0.04, and at higher frequencies, it varies between 0.34 and 0.55. Extinction length varies between 16.4 and 23.6 km. The frequency-dependent relationship for scattering Q (Q sc ) and intrinsic Q (Q i ) are Q sc = (699.3 ± 334.5)f (0.13 ± 0.06) and Q i = (52.9 ± 5.6)f (1.09 ± 0.03).