Analytical and experimental studies of borehole seismic methods

Thesis/Dissertation · Thu Jan 01 04:00:00 EST 1987

OSTI ID:5711437

Mok, Y J

The crosshole and downhole seismic methods are widely used in engineering as a reliable means of in situ determination of the variation of elastic moduli with depth. The crosshole method is more expensive to conduct in the field than the downhole method, but it is also easier to analyze the seismic results. However, if a soft layer is sandwiched between hard layers, it is often difficult to identify the first arrival of the direct shear wave in crosshole records. To investigate this problem, theoretical seismograms were developed based upon ray theory. Interference from reflected and refracted (head) waves on the direct shear wave was studied. By comparing theoretical seismograms and real records, it was found that converted reflected waves are more critical than head waves in interfering with the first arrival of the direct shear wave. The lack of a sophisticated and mathematically rigorous analysis method of downhole data results in a less detailed shear wave velocity profile than determined by the crosshole method. This lack of detail prevents one from exploiting some of the advantages of the downhole method such as low cost, ease of operation, and use of a simple seismic source. A new method of analyzing downhole data is developed. The method is based on inverse theory and permits determination of detailed shear wave velocity profiles. The inversion method is shown to be clearly superior to conventional analysis methods.

• Research Organization: Texas Univ., Austin (USA)
• OSTI ID: 5711437
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580201* -- Geophysics-- Seismology & Tectonics-- (1980-1989)
BOREHOLE LINKING
BOREHOLES
CAVITIES
GEOPHYSICAL SURVEYS
REFLECTION
REFRACTION
SEISMIC S WAVES
SEISMIC SURVEYS
SEISMIC WAVES
SURVEYS
VELOCITY