Frequency-dependent near-surface Q factor measurements via a cross-hole survey

摘要

We have measured near-surface absorption in a site of Daqing Oilfield, China, by using a cross-hole survey. The near-surface was divided into two layers according to the water table depth, the weathering and sub-weathering layers. The seismic attenuation for each layer was analysed in detail to estimate the quality factor Q and investigate its dependency on frequency. The absorption model was estimated using tomographic absorption inversion without source effect. The inverse Q factor for the weathering layer is much smaller than that for the sub-weathering layer, indicating that absorption decreases when the near-surface is saturated with water. The Q(-1) factors for the two layers vary with frequency in a similar way, increasing with frequency at the low frequency end, reaching its maximum value at a characteristic frequency and then decreasing with increasing frequency. The results closely match theoretical predictions and laboratory measurements and therefore can be treated as reliable evidence of frequency-dependent Q factor. (C) 2015 Elsevier By. All rights reserved.