3 research outputs found
Elastic Time Reversal Mirror Experiment in a Mesoscopic Natural Medium at the Low Noise Underground Laboratory of Rustrel, France
A seismic time reversal experiment based on Time Reversal Mirror (TRM)
technique was conducted in the mesoscopically scaled medium at the LSBB
Laboratory, France. Two sets of 50 Hz geophones were distributed at one meter
intervals in two horizontal and parallel galleries 100 m apart, buried 250 m
below the surface. The shot source used was a 4 kg sledgehammer. Analysis shows
that elastic seismic energy is refocused in space and time to the shot
locations with good accuracy. The refocusing ability of seismic energy to the
shot locations is roughly achieved for the direct field, and with excellent
quality, for the early and later coda. Hyper-focussing is achieved at the shot
points as a consequence of the fine scale randomly heterogeneous medium between
the galleries. TRM experiment is sensitive to the roughness of the mirror used.
Roughness induces a slight experimental discrepancy between recording and
re-emitting directions degrading the quality of the reversal process.Comment: 7 pages, 7 figures - This paper aimed at describing time reversal
mirror method applied at mesoscopic scale to a natural medium in the frame of
an active seismic experiment. The results confirm the hyper-focusing process
in an anelastic medium and the efficiency of scattered waves within the coda
to refocus at the source using the time reversal mirro
Simulation des mouvements du sol a distances regionales et telesismiques en milieu heterogene - Methode et applications
SIGLEINIST T 73310 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc
A boundary integral equationâdiscrete wavenumber representation method to study wave propagation in multilayered media having irregular interfaces
International audienceWe present a method which combines boundaryâintegral equation techniques with the discrete wavenumber Greenâs function representation to study wave propagation in multilayered media having irregular interfaces. The approach is based on the representation of the interfaces by distributions of body forces, the radiation from which is equivalent to the scattered wave field produced by the diffracting boundaries. The Greenâs functions are evaluated by the discrete wavenumber method. Propagator matrices are introduced to relate force distributions on neighboring interfaces. The solution then requires the inversion of a matrix at each interface. The dimensions of the linear system are independent of the number of layers considered, and the computation time varies linearly with the number of interfaces. We apply the method to calculate surface and vertical seismic profiles in the presence of synclinal or anticlinal structures