Seismic attribute inversion for velocity and attenuation structure using data from the GLIMPCE Lake Superior experiment

Abstract

A simultaneous inversion for velocity and attenuation structure using multiple seismic attributes has been applied to refraction data from the 1986 GLIMPCE Lake Superior experiment. The seismic attributes considered include envelope amplitude, instantaneous frequency, and travel time of first arrival data. Instantaneous frequency is converted to t * using a matching procedure which approximately removes the effects of the source spectra. The derived seismic attributes are then used in an iterative inversion procedure referred to as AFT inversion for amplitude, (instantaneous) frequency, and time. Uncertainties and resolution of the velocity and attenuation models are estimated using covariance calculations and checkerboard resolution maps. A simultaneous inversion of seismic attributes from the GLIMPCE data results in a velocity model similar to that of previous studies across Lake Superior. A central rift basin and a northern basin are the most prominent features with an increase in velocity near the Isle Royale fault. Although there is an indication of the central and northern basins in the attenuation model for depths greater than 4 km, the separation is not evident for shallower depths. This may result from microfractures masking compositional variations in the attenuation model for shallower depths. Attenuation Q values range from approximately 60 near the surface to near 500 at 10 km depth. A relationship between inverse Q and velocity of Q −1 =0.0210–0.0028* v was found with a correlation coefficient of −0.96. This suggests a nearly linear, inverse relationship between Q −1 and velocity beneath Lake Superior which supports previous laboratory results. The inverted velocity and attenuation models provide important constraints on the lithology and physical properties of the Midcontinent rift beneath Lake Superior.