Slate, as one of the low-degree metamorphic rocks, is widely distributed in China. Research on the seismic velocity of slate can help distinguish this kind of transitional rocks as well as understand anisotropy of the upper crust. This paper presents laboratory research on the seismic velocity of slate samples collected from the Bingzhongluo district of Yunnan Province, and part of the experiment was conducted at the Dalhousie High Pressure Laboratory, Canada. The laboratory testing yielded the seismic velocities in different structural directions as a function of pressures. The seismic velocities in the three directions ( X , Y and Z ) are 6.58, 6.46 and 5.91 km/s at the confining pressure of 600 MPa, respectively, with an average velocity of 6.30 km/s. S wave has an average velocity of 3.62 mm/s and a V p / V s ratio of 1.74. The preliminary analysis shows the changing law of seismic velocities and shear wave splitting of slate, revealing that the seismic anisotropy of slate decreases significantly with pressurization at low confining pressures (<150 MPa). This is primarily attributed to the orientation alignment of microcracks within slate. With progressive increase of confining pressure (>150 MPa), all the microcracks are largely closed. Thus, the orientation alignment of flaky minerals such as biotite and actinolite is a leading factor for seismic anisotropy. With the pressure up to 600 MPa, the anisotropy of V p and V s stabilizes at 13% and 16%. Therefore, laboratory data and seismic property of the slate documented in this paper will provide basis for determination of preferential orientations of microcracks in the upper crust, anisotropy analysis in the shallow crust, and geophysical model constraints.

A method of determining elastoplastic parameters in laboratory is given in the paper. For marble samples from Fangshan area in Beijing, systematic measurement has been done by tri-axial test, and the whole stress-strain curves can be simplified as a four-linear model corresponding to initial and peak and residual yield surface. Using the isotropic Mohr-Coulomb model, elastoplastic parameters was calculated, such as cohesion strength and friction angle vary with the internal plastic variable. The stress-strain curves of whole process of marble samples can be simplified described by a four-linear model, for there is strong plastic hardening before the peak strength and softening after the peak strength. Using these parameters a slop stability was analyzed by finite element model (FEM) strength reduction method. The results indicated that the degree of plastic deformation will be underestimated if the hardening properties of marble rock not be considered, and the slope safety factor calculated would be greatly increased about 23.6% at the same time. These are useful for engineering design.

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.

According to the GPS data, the fault-slip model for MW9.0 earthquake in March 2011 was inversed by using the finite element method. On the basis of the inversion, co-seismic displacement and stress fields were calculated, and the distribution of displacement and stress was given. The results show that fault-slip was up to 25 m. Northeast Japan was moved eastward by 1~6 meters, and the maximum displacement in the epicentral area was up to 24.25 m. After the earthquake, the surface was uplifted by about 5.6 meters near the epicenter. There was a depression area of 0.8 meters in the east coast of Northeast Japan. The calculated co-seismic surface displacement is consistent with GPS measurements. Stress was changed by the earthquake, resulting in the decrease of the post-earthquake stress. Stress change was about 9.9 MPa near the epicenter, 32 MPa in the depths, and less than 4.4 MPa in Northeast Japan. Earthquake-induced stress changes were mainly horizontal stress, whereas vertical stress changes were very small.

Conventional Mohr-Coulomb strength criterion only describing the relationship between normal stress and shear stress on the failure surface at the peak strength is used as a criterion to determine whether the rock has failed. This study expands the concept of the Mohr-Coulomb strength criterion by suggesting that the Mohr-Coulomb yield criterion can express the stress relationship of strain and stress of failure surface under various stress states after plastic deformation occurs. Based on the experimental study, an experiment approach which employs triaxial compression testing data to determine plastic parameters c and phi which vary with the internal variable kappa was established, and parameter expression used to assess the accuracy of isotropic modeling and some testing results were given. The Mohr-Coulomb yield criterion of isotropic hardening or softening, in which stress-strain curves of whole process is simplified into a four-line model using initial, peak and remnant parameters of rock, is more applicable than the trilinear model by Toshikazu. The result in this study provides theoretical and experimental basis for engineering and geological numerical simulation, thus being of instructive importance.