T* - AN UNSUITABLE PARAMETER TO CHARACTERIZE ANELASTIC ATTENUATION IN THE EASTERN CARPATHIANS

Abstract

Investigation of teleseismic P-wave recordings at a temporary network in the Eastern Carpathians, equipped with predominantly short-period sensors, is compared with synthetic modelling of anelastic attenuation of teleseismic waves in the upper mantle. Using the t* approach, we examine variations of amplitude decrease over frequency for teleseismic recordings in the frequency band 0.5-1.5 Hz. The results reveal a consistent pattern of increased t* values in the centre of the network, in the Vrancea region at the bend of the Carpathian Arc, although the magnitude of the observed variation in t* is much higher than expected. Synthetic t* parameter computations for the same event-receiver configurations reproduce the observed pattern in terms of relative variations. However, the amplitude of the synthetic t* values explains only 10-20 per cent of the observed variation in t*. t* is not a direct measure for anelastic attenuation but rather for a combination of anelastic and other attenuating effects such as scattering and amplitude fluctuation related to velocity inhomogeneities. If regional amplitude variations are solely attributed to anelastic attenuation, all other effects are mapped into Q. We discuss the role of anelastic attenuation and other effects in the case of the Eastern Carpathians and conclude that t* is an unsuitable parameter to characterize anelastic attenuation in the Eastern Carpathians.