Slow waves in blocky rock mass

Parts of the Earth’s crust have a blocky structure at different scales. It is reported in the literature that the waves propagating in blocky media can exhibit unusually low wave velocities (pendulum-type waves). Blocky structures are often characterised by: (1) very soft interfaces between the blocks as compared to the blocks themselves; (2) the ability of blocks for mutual rotations. The latter leads, in the presence of compression, to the effect of negative stiffness. This paper shows that both features can produce considerable reduction in wave velocities and, in the case of block rotation to considerable dispersion. Understanding these phenomena can provide additional means for exploring the Earth’s crust structure.