Analysis Of Seismic Anisotropy Of The Typical Slate From The Gaoligong Mountains, Yunnan Province,China

As a special kind of low-grade metamorphic, Slate has a wide distribution in our country, which is limited between the layered shale and schist, therefore the fine distinction of such transitional rocks by the anslysis of its seismic properties is very improtant.Through the research of the relevant date and papers, we can found that most of the research on slate tend to focus on such as its mechanical properties and anisotropy, water features, structural components and so on in the past few decades. And the study of its seismic wave speed characteristic was left in the basket, in order to better recognize and identify this typical kind of rock, conduct research on its features of seismic wave speed is very necessary, and it will help for the study of the upper crust anisotropy.Measurements of P-and S-wave velocities (Vp and Vs) and their directional dependence (shear wave splitting and velocity anisotropy) of the Slate samples,which collected from Bingzhongluo, Yunnan,were performed during both pressurization and depressurization in laboratory at hydrostatic confining pressures ranging from0to600MPa using the pulse transmission technique. The measurement of high pressure was done in the Dalhousie High Pressure Laboratory, Halifax, nova scotia Canada.While the hydrostatic confining pressures ranging from10to200MPa Experimental equipment has been used is autolab2000c petrophysical test system which manufactured by NER company in the United States, the system can complete the measurement of permeability, electrical conductivity, the three dimensional physical parameters of seismic wave velocity and so on as requested of cylinder samples.Wave velocities in different directions were obtained (X is parallel to the stretching lineation, Y parallel to the folition but perpendicular to the lineation, and Z normal to the folition),and the Vp of the slate in X,Y,Z are6.58km/s、6.46km/s、5.91km/s,while the mean Vp is6.30km/s, and the mean Vs is3.62km/s, as well as Vp/Vs=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 were caused by the closure of microcracks in samples with increasing hydrostatic pressure, and then increase slowly and linearly in velocity at high pressures as the mineral (biotite and actinolite) orientation become the main induced factor. And the anisotropy of the Vp and Vs reached13%and16%.Whereas the upper crust is accessible to geological sampling and mapping, the deeper portions of the crust and upper mantle are relatively inaccessible. Much of our knowledge on the composition, structure and evolution of the deep crust and upper mantle has been derived from various seismic refraction and reflection measurements. Interpretation of these seismic data in terms of lithology, mineralogical and chemical compositions is largely constrained by comparing in situ observed seismic velocities with those of relevant rocks or mineral assemblages thought to exist in the ranges of temperature and pressure of interest. This study is of more than academic interest. The obtained date and understanding of seismic properties of the slate in this paper will help the development of geodynamics, earthquake monitoring, and resource exploration and other work, as well as provides the basis of the determine of the preferred orientation of microfractures, the analysis of the upper crust and the fine distinction of lithology in the upper crust.