A Linear Inversion Approach to Measuring the Composition and Directionality of the Seismic Noise Field

We develop a linear inversion technique for measuring the modal composition and directionality of ambient seismic noise. The technique draws from similar techniques used in astrophysics and gravitational-wave physics, and relies on measuring cross-correlations between different seismometer channels in a seismometer array. We characterize the sensitivity and the angular resolution of this technique using a series of simulations and real-world tests. We then apply the technique to data acquired by the three-dimensional seismometer array at the Homestake mine in Lead, SD, to estimate the composition and directionality of the seismic noise at microseism frequencies. We show that, at times of low-microseism amplitudes, noise is dominated by body waves (P and S), while at high-microseism times, the noise is dominated by surface Rayleigh waves.

Mineralogy of Phoscorites of the Arbarastakh Complex (Republic of Sakha, Yakutia, Russia)

The Arbarastakh ultramafic carbonatite complex is located in the southwestern part of the Siberian Craton and contains ore-bearing carbonatites and phoscorites with Zr-Nb-REE mineralization. Based on the modal composition, textural features, and chemical compositions of minerals, the phoscorites from Arbarastakh can be subdivided into two groups: FOS 1 and FOS 2. FOS 1 contains the primary minerals olivine, magnetite with isomorphic Ti impurities, phlogopite replaced by tetraferriphlogopite along the rims, and apatite poorly enriched in REE. Baddeleyite predominates among the accessory minerals in FOS 1. Zirconolite enriched with REE and Nb and pyrochlore are found in smaller quantities. FOS 2 has a similar mineral composition but contains much less olivine, magnetite is enriched in Mg, and the phlogopite is enriched in Ba and Al. Of the accessory minerals, pyrochlore predominates and is enriched in Ta, Th, and U; baddeleyite is subordinate and enriched in Nb. Chemical and textural differences suggest that the phoscorites were formed by the sequential introduction of different portions of the melt. The melt that formed the FOS 1 was enriched in Zr and REE relative to the FOS 2 melt; the melt that formed the FOS 2 was enriched in Al, Ba, Nb, Ta, Th, U, and, to a lesser extent, Sr.

Deformation Microstructures of Phyllite in Gunsan, Korea, and Implications for Seismic Anisotropy in Continental Crust

Muscovite is a major constituent mineral in the continental crust that exhibits very strong seismic anisotropy. Muscovite alignment in rocks can significantly affect the magnitude and symmetry of seismic anisotropy. In this study, deformation microstructures of muscovite-quartz phyllites from the Geumseongri Formation in Gunsan, Korea, were studied to investigate the relationship between muscovite and chlorite fabrics in strongly deformed rocks and the seismic anisotropy observed in the continental crust. The [001] axes of muscovite and chlorite were strongly aligned subnormal to the foliation, while the [100] and [010] axes were aligned subparallel to the foliation. The distribution of quartz c-axes indicates activation of the basal<a>, rhomb<a> and prism<a> slip systems. For albite, most samples showed (001) or (010) poles aligned subnormal to the foliation. The calculated seismic anisotropies based on the lattice preferred orientation and modal compositions were in the range of 9.0–21.7% for the P-wave anisotropy and 9.6–24.2% for the maximum S-wave anisotropy. Our results indicate that the modal composition and alignment of muscovite and chlorite significantly affect the magnitude and symmetry of seismic anisotropy. It was found that the coexistence of muscovite and chlorite contributes to seismic anisotropy constructively when their [001] axes are aligned in the same direction.

Gabbronorite from Jijal Complex, Kamila Amphibolite Belt and Chilas Complex, Northern Pakistan: Implications for Arc Genesis

Rocks of gabbronoritic composition occur in three principal tectono-stratigraphic units forming the lower andmiddle parts of the Kohistan Island arc (KIA). These include the Jijal complex (JC), the Kamila Amphibolite belt (KAB)and the Chilas complex (CHC). The Jijal complex constitutes the lowermost part and hence is regarded as the root zoneof KIA. Its north-eastern part adjacent to KAB contains gabbronorite as a minor component in the form of small irregularpatches and layers within garnet granulite. The JC gabbronorite is sub-equigranular, medium to coarse grained, largelymassive and consists of variable amounts of plagioclase (53-71 %), orthopyroxene (14-27 %) and clinopyroxene (11-19%) as essential constituents and accessory to minor amounts of amphibole (1-9 %), opaque ore (1-6 %) and orthoclase(1-4 %). The occurrence and distribution of biotite, epidote, chlorite, clay, sericite, muscovite, quartz and actinolite inthe studied samples suggest their formation through alteration and/ or reaction between pre-existing minerals. In manycases, these minerals are disposed such that a variety of simple and complex corona structures are produced. The principalpetrographic features (modal composition, optical properties of the major mineral phases, exsolution in pyroxenes,products of alteration and reactions and the resulting corona textures) of the JC gabbronorite are broadly similar togabbronorites from both the KAB and CHC. Although the observed similarities could reflect identical physico-chemicalconditions during subsolidus or metamorphic re-equilibration, the possibility of a genetic relationship amonggabbronorites from all the three tectono-magmatic units of the KIA (i.e. the JC, KAB and CHC) cannot be ruled out.

Sedimentology and maturity of Ajali formation, Benin flank Anambra basin, Nigeria

The Ajali Sandstone, western flank, Anambra Basin, was studied for textural characteristics and maturity of the sediments. Grain size analysis (51 samples), thin section and heavy mineral analysis (15 samples each) and XRF fusion for metallic oxides (15 samples) were analyzed. The textural parameters show that the Ajali Sandstone are medium sand, poorly to moderately sorted, coarse to strongly coarse skewed with mesokurtic to leptokurtic grains. The thin section analysis reveals grains that are sub-angular to sub-rounded (this typifies grains that have travelled fairly long distance to the deposition site), of moderate to well sorted grains, with both monocrystalline and polycrystalline quarts-grains type, with a modal composition of Q F and L . A mineralogical maturity 90.4, 2.3 2.9 index (MMI) of 17.04, SiO /Al O ratio of 180.24, and a ZTR index of 67.96% were obtained. The values for the 2 2 3 MMI and SiO /Al O indicates mineralogical matured sediments, the ZTR index shows a chemically immature 2 2 3 to sub-mature sandstone, and the modal composition values are consistent with a texturally and compositionally matured sands. The mineralogical maturity is indicative of high degree of chemical weathering of source area. Furthermore, the high quartz and silica content make the sandstone prospective for glass and glassware production. Key words: Anambra Basin, Maturity, Mineralogical maturity index, Textural characteristics, Glass

Hydrochloric Acidic Processing of Titanite Ore to Produce a Synthetic Analogue of Korobitsynite

The modal composition of (apatite)-nepheline-titanite ore and its geological setting within apatite deposits of the Khibiny Massif allow selective mining of titanite ore and its hydrochloric acidic processing. The reaction of titanite with concentrated hydrochloric acid produces hydrated titanosilicate precipitate (TSP) which, in turn, can be a precursor in titanosilicate synthesis. It is particularly noteworthy that a synthetic analogue of korobitsynite, Na5(Ti3Nb)[Si4O12]2O2(OH)2·7H2O, was synthesized by means of TSP alteration by alkaline hydrothermal solution at 200 °C within three days. The titanosilicate obtained this way has comparatively weak cation-exchange properties regarding Cs+ and Sr2+ cations and considerable photocatalytic activity occurring under visible light, which allows the use of a synthetic korobitsynite analogue (SKR) for production of self-cleaning, sterilizing, and anti-fouling building materials.

Vibration energy and repeated-root modes of disc rotor for high-frequency brake squeal

In this paper, the generation mechanism of high-frequency brake squeal is revealed from the perspective of vibration energy. Based on a closed-loop coupling model, vibration energy transfer paths at the friction coupling interface between brake pads and disc are derived. Vibration energy equilibrium analysis is used to verify the reliability and accuracy of the derivation and the presented result demonstrates that vibration energy transferred from disc rotor to pads is the dominant transfer path. It is also demonstrated that the disc rotor is the key substructure affecting high-frequency brake squeal. As the disc rotor is axisymmetric, its repeated-root modes may lead to unreasonable calculated results by using the substructure modal composition method for analyzing the brake squeal. In this study, these repeated-root modes are processed by using a modified substructure modal composition method to obtain one unique integrated substructure modal composition coefficient of each disc repeated-root modes. Finally, the presented method is applied to analyze the brake squeal in the 13 kHz frequency band. The results easily identify the key vibration modes of the disc affecting high-frequency brake squeal, verifying the reliability of the presented method.