THREE-DIMENSIONAL SEISMIC PHYSICAL SCALE-MODELING WITH APPLICATIONS TO THE DETECTION OF UNDERGROUND CAVITIES (ULTRASONIC)

This thesis introduces a method of conducting in the laboratory realistic three-dimensional (3-D) seismic physical scale-model studies for land-type seismic exploration and reconnaisance. The scale-modeling procedure is based on the premise of being able to satisfy the scale-factor constraints in terms of length, frequency, material density, P-velocity and S-velocity, simultaneously.;The modeling procedure thus developed was tested by designing and constructing a three-dimensional scale-model of a geological medium, comprising four layers, an unconformity, and four underground karstic cavities and man-made tunnels.;In order to conduct the scale-model seismic experiments using the common-source-point (CSP) or almost-zero-offset (AZO) data gathering geometries, a pair of piezoelectric transducers was used; one to act as a source and the other as a receiver of ultrasonic waves. Apart from digital filtering for high frequency noise suppression, both CSP and AZO time sections were processed by using complex trace analysis to enhance the seismogram features for ease of interpretation.;The reflected seismic signals emanating from the scale-modeled underground cavities and tunnels lying at various depths were successfully detected, and interpreted with varying degrees of success.;A variety of filler materials were used for loading a matrix material, epoxy, after which the density, P-velocity and S-velocity characteristics of the resulting binary mixes were determined experimentally. The results showed a continuously variable range of 0.97 - 3.13 gm/cc for density, 2.16 - 3.40 km/sec for P-velocity, and 0.97 - 1.58 km/sec for S-velocity. The model construction materials were selected from these binary filler/matrix composites and other single component materials so as to simultaneously minimize the density, P- and S-velocity scale-factor errors in each of the materials constituting the scale-model.;It is concluded that 3-D seismic physical scale-modeling is indeed a feasible and efficient forward modeling technique that makes available "lab-real" data for developing more realistic numerical and analytical forward modeling and inversion schemes, and for acquiring more physical insight into the complex nature of seismic wave propagation in earth-like materials.