Branched flows in anisotropic random media
Even very small fluctuations in the ocean depth can randomly focus tsunami waves leading to an order of magnitude variation in their energy flux density in random directions, with severe implications for the predictability of tsunamis. This is an example of a branched flow: When waves propagate through weakly scattering but correlated, disordered environments they are randomly focused into pronounced branch-like structures. This phenomenon has been studied in a range of systems including the sound propagation in the ocean, electron transport in two-dimensional electron gases, microwave transmission through random arrangements of scatterers and the dynamics of wind-driven ocean waves. In contrast to these systems, which are well characterized as isotropic random media, the structures in the ocean floor topography that scatter tsunami waves show a pronounced anisotropy. This motivated us to study the influence of anisotropy on the natural focusing events in branched flows, which occur in a wide range of physical systems. We found a strong and non-intuitive dependence on the propagation angle in the fluctuations and even the mean intensity of the flow .