HR: 0800h
AN: S51E-1065    [Abstracts]
TI: Displacement Field Reciprocity, Nonlinearity, and Time Reversal: An Experimental Exploration
AU: * Ulrich, T
EM: tju@lanl.gov
AF: Los Alamos National Laboratory, Geophysics Group EES-11 MS D443, Los Alamos, NM 87545 United States
AU: Guyer, R A
EM: guyer@physics.umass.edu
AF: University of Massachussetts, Physics Dept., Amherst, MA 01002 United States
AB: The use of the time reversal mirror (TRM) has recently been applied in three dimensional elastic solids, including earth materials. The applications of the TRM in solids is being developed for nondestructive testing as well as gaining information about earthquake sources. A fundamental requirement for using the TRM is the concept of reciprocity, which has been brought into question due mainly to P → S mode conversion and nonlinearity. This paper reports on experimental tests of reciprocity in a set of reverberant cavities, including Berea sandstone. A quantitative measure of reciprocity is introduced and used to test the reciprocity of direct signals, A→ B and B→ A, and the reciprocity of focused time reversed signals, A→ BT^-1B→ A and B→ AT^-1A→ B. The influence of sample preparation, source characteristics and deliberately introduced scatters is examined for direct signals. Focused time reversed signals obey reciprocity in a linear cavity. Departure from reciprocity of focused time reversed signals in a nonlinear cavity (sandstone block) is associated with the production of higher harmonics due to the nonlinearity of the sandstone.
DE: 5102 Acoustic properties
DE: 5144 Wave attenuation
DE: 7203 Body waves
DE: 7299 General or miscellaneous
DE: 9810 New fields (not classifiable under other headings)
SC: Seismology [S]
MN: Fall Meeting 2005