A Field Study of Seismic Attenuation In Layered Sedimentary Rocks-Ii. Crosshole Data

Abstract

S U M M A R YA series of crosshole seismic experiments have been performed at the Imperial College borehole test site in Northumberland, England using a detonator source and hydrophone receivers. The holes have been drilled through a horizontally layered sequence of Carboniferous limestones, shales and sandstones. Estimates of intrinsic Q were obtained for frequencies between approximately 500 Hz and 1.5 kHz. A comparison with the results of Part I suggests evidence of frequency-dependent intrinsic Q with attenuation at 1 kHz being significantly greater than at 100 Hz. No change of intrinsic attenuation with ray direction from horizontal ( O O ) to 60" was observed. However, since no high-frequency crosshole data for ray angles between 60" and vertical is available, we cannot entirely discount the possibility that the difference in intrinsic Q estimates from the vertical VSP data (Part I) and the crosshole data is due, at least in part, to anisotropic intrinsic attenuation.

Quality-factor and reflection-coefficient estimation using surface-wave ghost reflections from subvertical structures

“…A traditional method for estimating Q is the spectral-ratio method (e.g. Jannsen et al, 1985;Portsmouth et al, 1993;Tonn, 1991). It can be applied to transmission measurements using recordings at multiple seismic receivers from the same seismic source (common-shot gather) or from multiple sources at the same receiver (common-receiver gather).…”