SEISMIC ATTENUATION IN A PARTIALLY SATURATED, ARTIFICIAL CRACK DUE TORESTRICTED CONTACT LINE MOTION

Attenuation and stiffness measurements have been made on partially sat urated, artificial cracks over the frequency range 2 mHz to 10 Hz. The wedge-shaped cracks are open systems composed of glass slides separat ed by wires. A non-zero, frequency independent attenuation has been me asured at low frequencies for these cracks. Additionally, the low freq uency stiffness of a partially saturated crack is larger than that of a dry crack. For this geometry and frequency range, no dissipative flu id flow is expected. Local fluid flow models predict zero attenuation and no stiffening for these open systems. We have developed a model ba sed on the restricted motion of the fluid meniscus to explain the meas ured low frequency results. In this model, physicochemical interaction s between the fluid and solid are responsible for restricting motion o f the three phase boundary between liquid, solid and gas (the contact line). We compare model predictions with data measured in artificial c racks partially saturated with deionized water. Contact line mobility is varied by exposing the crack surfaces to increasing concentrations of sodiumdodecylsulfate (SDS) in deionized water. Increases in low fre quency attenuation (below .1 Hz) and crack stiffness correlate with in creasing surface exposure to SDS. These measured trends can be qualita tively modeled by reducing meniscus mobility as the surface contaminat ion increases.