HR: 1340h
AN: S23B-0313    [Abstracts]
TI: Weak Localization of Seismic Waves
AU: * LAROSE, \ F
EM: eric.larose@ujf-grenoble.fr
AF: Laboratoire de G\'eophysique Interne et Tectonophysique, Universit\'e Joseph FOURIER and CNRS, BP 53, GRENOBLE, 38041 France
AU: MARGERIN, L
EM: ludovic.margerin@ujf-grenoble.fr
AF: Laboratoire de G\'eophysique Interne et Tectonophysique, Universit\'e Joseph FOURIER and CNRS, BP 53, GRENOBLE, 38041 France
AU: CAMPILLO, M
EM: michel.campillo@ujf-grenoble.fr
AF: Laboratoire de G\'eophysique Interne et Tectonophysique, Universit\'e Joseph FOURIER and CNRS, BP 53, GRENOBLE, 38041 France
AU: CAMPILLO, M
EM: michel.campillo@ujf-grenoble.fr
AF: Laboratoire de Physique et Mod\'elisation des Milieux Condens\'es, Universit\'e Joseph FOURIER and CNRS, Maison des Magist\`eres, BP 166, GRENOBLE, 38042 France
AU: Van TIGGELEN, B A
EM: Bart.Van-Tiggelen@grenoble.cnrs.fr
AF: Laboratoire de Physique et Mod\'elisation des Milieux Condens\'es, Universit\'e Joseph FOURIER and CNRS, Maison des Magist\`eres, BP 166, GRENOBLE, 38042 France
AB: In the heterogeneous Earth the wave propagation is complex and wave scattering results in a "seismic coda", which forms the tail of the seismograms. We propose to study the energy distribution of coda waves in space and time. A field experiment was conducted on a volcano in the French Auvergne using 24 aligned geophones. A moment after the energy release at the source (a sledgehammer strike in our case), seismic energy is expected to be uniformly distributed along the sensor network, as predicted by radiative transfer and diffusion theory that are common tools to interpret the coda decay. These theories are consistent with our experimental results except that in the late coda, we observe a persistent energy enhancement around the source within a spot of width a wavelength. This intensity peak is interpreted as follows: when waves have encountered at least two scatterers and are detected exactly at the source, reciprocal paths (between source and receiver) have random but equal phases, which results in constructive interference. Away from the source, the phase difference between reciprocal waves is random, interferences are averaged out, and standard diffusion theory applies. This effect is known as Weak Localisation, also referred to as coherent backscattering in acoustics and optics. Our observations are in good agreement with the near-field theory for weak localization, and also with previous numerical studies. Our work shows the relevance of mesoscopic physics to seismology and its necessity to interpret the seismic coda. We propose a technique for estimating the scattering mean free time, which quantifies the internal heterogeneity without the bias of absorption. This parameter also quantifies the transition from the simple scattering regime where standard imaging techniques are valid to the multiple scattering regime.
UR: http://scitation.aip.org/prl/covers/93_4.jsp
DE: 7260 Theory and modeling
DE: 7280 Volcano seismology (8419)
DE: 5139 Transport properties
DE: 5144 Wave attenuation
DE: 0935 Seismic methods (3025)
SC: Seismology [S]
MN: 2004 AGU Fall Meeting