| Thu February 26th 2009 11:00 ZH286 | Seminar | Friction induced amplification of guided elastic waves Bruno Andreotti |
Details:Different open geological problems such as dynamic earthquake triggering in fault gouges or booming avalanches involve the interaction between seismic waves and shearing motion. Here we show experimentally that guided waves are amplified when they propagate along shear bands. We investigate the spontaneous emission of elastic waves during the discharge of granular matter through a vertical tube and directly evidence their exponential amplification in the direction opposite to the flow. Performing the linear stability analysis, we relate the observed instability to the friction of grains on the boundary, which pumps energy from the mean flow to coherent elastic waves. We predict that the most amplified wavelength is proportional to the ratio of the tube radius to the friction coefficient, in good agreement with experimental measurements. | ||
