Characterization of Nonlinearities in the Propagation of High Frequency Seismic Waves
Abstract
An austo-electromagnetic land mine detection technique is being investigated. A two-dimensional finite-difference model for elastic waves has also been developed, but it is a purely linear model. Strong nonlinearities are typical of the soils in which mines are buried. The purpose of this thesis is to characterize these nonlinearities for the propagation of high frequency seismic waves (30 - 2000 Hz) in moist, compacted sand so that the parameters used in acousto-electromagnetic land mine detection may be improved and the nonlinearities may be incorporated in the computer model. The frequency response of the soil model was recorded as a function of drive amplitude and propagation distance. The amplitude response of the soil model was recorded as a function of frequency and propagation distance. The fundamental and first five harmonics were saved for each. Three elastic wave transducers (shakers) were characterized so that source nonlinearities could be compared to propagation path nonlinearities. Characterization of the shakers included foot motion under unloaded and sand-loaded conditions. The source and propagation path produced nonlinearities as shown by harmonic generation in accelerometers mounted to the shaker foot and radar measurements of the soil surface displacement. Frequencies in the 100 - 600 Hz band propagated best while frequencies above 600 Hz attenuated rapidly. Once the shaker foot to sand coupling was changed results did not repeat with the same precision as when it was left alone.
Document Details
- Document Type
- Technical Report
- Publication Date
- Apr 01, 2000
- Accession Number
- ADA376823
Entities
People
- Blace C. Albert
Organizations
- Georgia Tech