Seismic Absorption and Modulus Measurements in Porous Rocks Under Fluid and Gas Flow-Physical and Chemical Effects: a Laboratory Study

This paper describes the culmination of a research project in which we investigated the complex modulus change in partially fluid saturated porous rocks. The investigation started with simple flow experiments over ''clean'' and ''contaminated'' surfaces, progressed to moduli measurements on partially filled single cracks, to measurements in ''clean'' and ''contaminated'' porous rocks and finally to a feasibility study in the field. For the experiments with the simple geometries we were able to measure fundamental physical properties such as contact angles of the meniscus and time dependent forces required to get the meniscus moving and to keep it moving at various velocities. From the data thus gathered we were able to interpret the complex elastic moduli data we measured in the partially saturated single cracks. While the geometry in real rocks is too complex to make precise calculations we determined that we had indeed identified the mechanisms responsible for the changes in the moduli we had measured. Thus encouraged by the laboratory studies we embarked on a field experiment in the desert of Arizona. The field site allowed for controlled irrigation. Instrumentation for fluid sampling and water penetration were already in place. The porous loosely consolidated rocks at the site were not ideal for finding the effects of the attenuation mechanism we had identified in the lab, but for logistic and cost constraint reasons we chose to field test the idea at that site. Tiltmeters and seismometers were installed and operated nearly continuously for almost 3 years. The field was irrigated with water in the fall of 2003 and with water containing a biosurfactant in the fall of 2004. We have indications that the biosurfactant irrigation has had a notable effect on the tilt data

Characterization of Cracks in Thick Plates by Lamb Wave Diffraction Studies

The object of the work is a combined theroretical and experimental study of diffraction of Lamb waves by two- and three-dimensional cracks in a plate. An important motivation for this project is the desire to develop a technique capable of detecting and characterizing cracks in weldments in plates. We want to analyze the dependence of the scattered signals on the dimension, angle of inclination and depth of burial of the crack. The basic measurement techniques requires the accurate determination of minute normal surface displacements at ultrasonic frequencies. Such measurements have recently been made possible by the development in our laboratory of a new surface displacement capacitive tranducer [1]. The measured displacements will be compared with the theoretical predictions.</p

The interface between orthodontics and aesthetic dentistry.

The object of the work is a combined theroretical and experimental study of diffraction of Lamb waves by two- and three-dimensional cracks in a plate. An important motivation for this project is the desire to develop a technique capable of detecting and characterizing cracks in weldments in plates. We want to analyze the dependence of the scattered signals on the dimension, angle of inclination and depth of burial of the crack. The basic measurement techniques requires the accurate determination of minute normal surface displacements at ultrasonic frequencies. Such measurements have recently been made possible by the development in our laboratory of a new surface displacement capacitive tranducer [1]. The measured displacements will be compared with the theoretical predictions