Study of Anisotropy Characteristics of Bogor Volcanic Soil

Anisotropy in soil results from the deposition process which describes the characteristics of the soil grains or is caused by stress or from the consequences of stresses caused during deposition and subsequent erosion. All soils behave in general anisotropy and some exhibit undrained shear strength. This study conducted 2 tests, namely the first field testing with original soil samples in the form of CPTu and dilatometer. The CPTu test's objective is to determine the vertical soil parameters, while the dilatometer is to determine the horizontal soil parameters. This study indicates that the indication of anisotropy in all shear strength tests is evident in the results of the CPTu test and the Dilatometer test. TX - UU and consolidation show that the horizontal shear strength (Suh) is greater than the vertical slope shear strength (Suv). In this case, the ratio obtained for shear strength is Suh = 1.3 Suv. And from the results of the consolidation test in the laboratory, it was found that the horizontal compression index parameter (Cc horizontal) was greater than the vertical (Cc vertical) and the horizontal coefficient of consolidation (Ch) is greater than the vertical coefficient of consolidation (Cv).

Seismic wave modeling in vertically varying viscoelastic media with general anisotropy

Seismic anisotropy, wave attenuation and dispersion are critical phenomena of wave propagation in real media. Full wavefield modeling of wave behavior in such media plays an important role in investigating dynamic features of the earth’s interior and in full-waveform inversion (FWI) of anisotropic parameters and velocity dispersion. We present a numerical scheme to model full-waveform response from a point source in a vertically varying viscoelastic medium of arbitrary anisotropy. The method is implemented in the frequency domain, so the complexity of anelasticity and anisotropy can be simply described by a complex elastic stiffness matrix, and frequency-dependent moduli can also be readily incorporated. In the proposed scheme, we solve the elastodynamic equations for general anisotropy through finite element method in the frequency-wavenumber domain and use the stiffness reduction method (SRM) to suppress reflections from artificial boundaries along the depth direction. A non-uniform 2-D Fourier transform strategy is developed to reconstruct the spatial-domain counterparts from the wavenumber-domain solutions. The time-domain responses are then obtained by taking inverse fast Fourier transform with respect to frequency. We validate the method by comparing numerical results with exact solutions for a homogeneous transversely isotropic model and a two-layered model. In the application example, we further proved the feasibility and generality of the scheme using an attenuative, dispersive model with both velocity and attenuation anisotropy. The proposed scheme enjoys significant advantages in incorporating various viscoelastic/dispersive behaviors and general anisotropy, and thus provides a useful tool for numerical simulation of dynamic response in practical application.

REGULARITIES OF FORMATION OF SYNTHETIC OPTICAL ANISOTROPY OF POLYMETHYL METHACRYLATE FOR POLARIMETRIC APPLICATION

General principles of wav plate manufacturing are considered. The possibility of the formation of synthetic optical anisotropy of polymethyl methacrylate (PMMA) by the method of its uniaxial stretching is investigated. The most promising is a method for manufacturing waveplates, which includes the stage of controlled stretching of the polymer material to the required phase shift value, which would generally exclude the stage of machining the plates. The general orderliness of the molecules in the polymer resulting from stretching (orientation) leads to the oriented state of the polymer, and, consequently, to the general anisotropy of the physical and optical properties. In this state, a clearly pronounced uniaxial orientation of polymer chains is observed. As a result, chain macromolecules, randomly (statistically) oriented in the initial PMMA, acquire orientation under the influence of an external directed tensile force. The anisotropy of the optical properties of uniaxially stretched PMMA is manifested in the fact that it has different refractive indices for light polarized parallel to the direction of stretching (orientation) and in the perpendicular direction (birefringence). The regularities of the formation of the synthetic optical anisotropy of PMMA have been studied. The dependences of the birefringence values of uniaxially stretched PMMA on the initial sheet thickness, stretching temperature, and degree of stretching have been measured. It has been shown that the value of birefringence is directly proportional to the thickness of the initial sheet and the degree of stretching and inversely proportional to the stretching temperature. The spectral dependence of the birefringence value is measured. Achromatic and superachromatic waveplates were made from uniaxially stretched PMMA. The spectral characteristics of the phase shift of the manufactured waveplates are given. The availability of the starting material, the technological simplicity of the formation of the initial components for waveplates, as well as the possibility of manufacturing waveplates of large dimensions and high quality, make polymethyl methacrylate with artificially induced anisotropy a promising material for the manufacture of achromatic and superachromatic waveplates.

A database for the seismic properties of slow spreading mid-ocean ridges gabbros

<p>Gabbros are the main component of the oceanic crust and represent ~2/3 of the total magmatic crustal thickness. At the interface between magmatic, tectonic and hydrothermal processes, gabbros from slow spreading ridges may have a complex mineralogy and microstructural evolution. This includes structures that vary from purely magmatic fabrics, with layering and magmatic alignment of minerals, to rocks deformed from subsolidus temperatures to the lower-T brittle-ductile conditions. Such a variation is normally accompanied with changes in mineralogy, microstructures and crystallographic preferred orientations (CPO) of the main phases of these rocks, which in turn affect their seismic properties. Here we present a database of the CPO-derived seismic properties of 70 samples collected during the IODP Expedition 360 (site U1473). Initial results show that the dominant phases are plagioclase and clinopyroxene[MOU1] , and different samples may have different contents of olivine, enstatite, magnetite, ilmenite, chlorite and amphibole. Maximum velocities can be either parallel to the strongest concentration of (010) poles of plagioclase or olivine/clinopyroxene [001], depending on the proportions between these phases. Anisotropy of P waves vary from ~5% in the more isotropic gabbros with weak magmatic fabric to a maximum of ~10% in more mylonitic terms. A similar effect is observed for the S-waves. Destructive interference between plagioclase CPO vs. clinopyroxene/olivine reducing anisotropy is possibly observed. This is because the maximum Vp in a foliated gabbro is parallel to the maximum concentration of poles to (010), and perpendicular to olivine and clinopyroxene. As the lineation in our gabbros is generally marked by olivine and clinopyroxene [001] (instead of the fast direction [100]), this possibly cause anisotropy reduction. When present in the more mylonitized gabbros, amphibole has strong CPOs and help to increase the general anisotropy of P and S waves. The elastic constants calculated from these aggregates will be used as input for more physically robust calculations using differential effective medium approaches to better understand the effect of melt inclusions in these rocks by the time of their deformation in the lower crust.</p><p> </p>