Another Approach to Model Attenuation

Attenuation in the upper crust is a complex problem and a full understanding of where intrinsic attenuation remains problematic. This is particularly true in earth materials saturated with highly viscous liquids such as magma or bitumens. In fluid saturated materials, attenuation mechanisms have focused primarily on global and local type of fluid displacements. That is, the mechanisms have assumed that attenuation was produced only by fluid motions relative to the solids. Less emphasis has been placed on the potential mechanism for absorption within the fluids themselves. Here, we examine the mechanism of attenuation within the fluids themselves via rheological relaxation theory approach. In particular, the role of viscosity is generally examined with results on the frequency dependence on wave speed dispersion and attenuation. The evolution of elastic waveforms through such absorbing materials are also studied to evaluate the potential effects on seismic wave propagation. This work may also have implications towards the use of ultrasonic laboratory measurements in the interpretation of seismic frequency measurements.