Multiscale acoustics in dense granular media; geophysical implications

We overview sound interactions with dense granular packings, dry, wet or saturated by liquid, in which acoustic waves are served not only as a probe to monitor the fragile and heterogeneous contact networks, but also as a pump to fluidize the medium and trigger the shear instability. First, we describe the linear sound propagation in jammed granular solid: coherent waves and multiple scattering [1], as well as acoustic probing of elastic heterogeneities [2], and plastic rearrangements [3]. Then, we investigate the nonlinear acoustic waves dominated by the hysteresis due to micro-slips at contacts [4] and the huge softening of shear wave velocity in transient elastography [5]. Finally, we discuss the triggering of granular avalanches by high-amplitude ultrasound [6], through the acoustic lubrication of contacts (micro-plasticity) without visible grains motions. This work helps to understand landslides triggered by seismicity. [1] X. Jia, Phys. Rev. Lett. 93, 154303 (2004). [2] S. Wildenberg et al., Europhys. Lett. 115, 34005 (2016). [3] Y. Khidas and X. Jia, Phys. Rev. Express 85, 051304 (2012). [4] X. Jia, T. Brunet, and J. Laurent, Phys. Rev. Express 84, 020301(R) (2011). [5] J. Brum et al., Phys. Rev. Eexpress 99, 042902 (2019). [6] J. Léopoldès, X. Jia, A. Tourin, and A. Mangeney, Phys. Rev. Express 102, 042901 (2020).