Analysis of seismic anisotropy of slate and its application of slate

As a special type of low-grade metamorphic rocks, slate has a wide distribution in China, which is limited between the layered shale and schist. The therefore the fine distinction of such transitional rocks by the anslysis of its seismic properties is thus very important and it will help for the study of the upper crust anisotropy. Measurements of P- and S-wave velocities (V-P and V-S) and their directional dependence (shear wave splitting and velocity anisotropy) of the slate samples from Bingzhongluo, Yunnan, were performed during both pressurization and depressurization in laboratory at hydrostatic confining pressures up 10 to 600 MPa using the pulse transmission technique. Wave velocities in different directions were obtained (X is parallel to the stretching lineation, Y parallel to the foliation but perpendicular to the lineation, and Z normal to the foliation),and the V-p of the slate in X,Y and Z are 6.58, 6.46 and 5.91 km/s, respectively; with an arerage V-P value of 6.30 km/s. The mean Vs is 3.62 km/s, yielding V-P/V-S = 1.74. The pressure dependence of P- and S-wave velocities, seismic anisotropy and shear wave splitting in the slate rocks were observed and analyzed in this paper, and their relationships have been described. For the samples, both the pressurization and depressurization (anisotropy-confinig) curves display a rapid, nonliner increase in velocity with pressure at low pressure which was caused by the closure of microcracks in samples with increasing hydrostatic pressure, and then increase slowly and linearly in velocity at high pressures which the lattice preferred orientation of the constituent minerals such as mica and actinolite became the main factor. The anisotropy of the V-P and V-S reached 13% and 16%, respectively. The seismic properties of the slate documented in this paper will help the development of geodynamics, earthquake monitoring, and resource exploration, and also provide an experimental basis for the fine distinction of lithology in the upper crust.