Seismic Attenuation Computed from GLIMPCE Reflection Data and Comparison with Refraction Results

Instantaneous frequency matching has been used to compute differential t* values for seismic reflection data from the Great Lakes International Multidisciplinary Program on Crustal Evolution (GLIMPCE) experiment. The differential attenuation values were converted to apparent Q 1 models by a fitting procedure that simultaneously solves for the interval Q 1 values using non-negative least squares. The bootstrap method was then used to estimate the variance in the interval Q 1 models. The shallow Q 1 structure obtained from the seismic reflection data corresponds closely with an attenuation model derived using instantaneous frequency matching on seismic refraction data along the same transect. This suggests that the effects of wave propagation and scattering on the apparent attenuation are similar for the two data sets. The Q 1 model from the reflection data was then compared with the structural interpretation of the reflectivity data. The highest interval Q 1 values (\0.01) were found near the surface, corresponding to the sedimentary rock sequence of the upper Keweenawan. Low Q 1 values (B0.0006) are found beneath the Midcontinent rift’s central basin. In addition to structural interpretation, seismic attenuation models derived in this way can be used to correct reflection data for dispersion, frequency and amplitude effects, and allow for improved imaging of the subsurface.