• Guillemot, Antoine
• Larose, Éric
• Théry, Romain
• Abraham, Odile

Abstract

Seismic and ultrasonic waves are sometimes used to track fluid injections, propagation, infiltrations in complex material, including geological and civil engineered ones. In most cases, one use the acoustic velocity changes as a proxy for water content evolution. Here wepropose to test an alternative seismic or acoustic observable : the waveform decorrelation.We use a sample of compacted millimetric sand as a model medium of highly porous multiplescattering materials. We fill iteratively the sample with water, and track changes in ultrasonicwaveforms acquired for each water level. We take advantage of the high sensitivity of diffusecoda waves (late arrivals) to track small water elevation in the material. We demonstratethat in the mesoscopic regime where the wavelength, the grain size and the porosity are in thesame order of magnitude, Coda Wave Decorrelation (waveform change) is more sensitive tofluid injection than Coda Wave Interferometry (apparent velocity change). This observationis crucial to interpret fluid infiltration in concrete with ultrasonic record changes, as well asfluid injection in volcanoes or snow melt infiltration in rocky glaciers. In these applications,Coda Wave Decorrelation might be an extremely interesting tool for damage assessment andalert systems.

Topics

• porous
• impedance spectroscopy
• grain
• grain size
• melt
• ultrasonic
• porosity
• interferometry