Shear wave anisotropy beneath the volcanic front in South Kyushu area, Japan: Development of C-type olivine CPO under H2O-rich conditions

Shear wave splitting from local intermediate-depth earthquakes is investigated to detect the anisotropic structure in the mantle wedge beneath the South Kyushu area, Japan. We observed shear wave splitting with NEE-SWW to NWW-SEE polarization directions and delay times of 0.04-0.63 s. Trench-normal shear wave polarization anisotropy with a delay time greater than 0.3 s probably overlaps in the high VP/VS region at a depth of 100-150 km beneath the volcanic front. Model calculations for the cause of the anisotropy suggest that the development of "C-type" olivine crystallographic preferred orientation (CPO) with a trench-parallel b axis concentration and a trench-normal a axis concentration best reproduces observations compared to A-, B-, or E-type olivine CPOs and antigorite CPO. We conclude that a thick anisotropic layer, approximately 50 km, is formed by concentration of interstitial fluid in peridotite. We briefly discuss the mechanism carrying water to the deep mantle wedge. A possible explanation is that interstitial fluids in the mantle wedge are effectively released because of a decrease in dihedral angles of olivine-fluid interfaces at 150 km depth. Our results imply a close relation between the high density of explosive volcanoes in the South Kyushu area and the underlying water-rich mantle. © 2013. American Geophysical Union. All Rights Reserved

Quantitative analysis of major elements in igneous rocks with X-ray fluorescence spectrometer “ZSX primus II” using a 1:10 dilution glass bead

Detailed procedures of sample processing including preparation of a 1: 10 dilution glass bead and evaluations of calibration lines of the X-ray fluorescence spectrometer for major element compositions of igneous rock samples are presented. We used 11 igneous rock standard samples of the Geological Survey of Japan and the synthetic material for the calibration. A powdered rock sample ignited at 900 ° C for four hours and lithium tetraborate as an alkali flux ignited at 700 ° C for four hours are weighed 0.4000 ± 0.0001 g and 4.0000 ± 0.0001 g, respectively. The mixture of rock powder sample and lithium tetraborate is put into a platinum crucible and fused to a glass bead. The calibration lines for basalts and andesites named "Major12" analyze 10 major elements such as Si, Ti, Al, Fe, Mn, Mg, Ca, Na, K and P in 10 minutes. The result of repeated analyses of six standard materials shows that the relative standard deviations are less than 3% and relative errors are less than 1.2%. Therefore, the calibration lines "Major12" are sufficient to be applied to routine measurement of igneous rocks. For analysis of ultramafic rocks, another set of calibration lines "majorOl\u27\u27 was made based on standard samples including synthesized materials of SiO, and MgO reagents, and the calibration lines cover wider Si, Mg, Ni and Cr ranges than "Major12". The calibration lines "majorOl\u27\u27 successfully reproduced concentrations of nine major element compositions (Si, Ti, Al, Fe, Mn, Mg, Ca, Ni, Cr) of the standard samples of ultramafic rocks

Two types of antigorite serpentinite controlling heterogeneous slow-slip behaviours of slab-mantle interface

It is known that plate boundaries in subduction zones show heterogeneous slip nature with strongly coupled seismogenic zones and various types of episodic tremor and slip (ETS) zones. In order to examine the petrological controls on the large-scale structure, we compared recent geophysical observations in the Shikoku area, southwest Japan with petrological models of the hanging wall mantle wedge. As a result, we found a close relationship between mineral assemblages in the mantle wedge and the characteristics of slow slip behaviour recorded in the Shikoku area: Short-term ETSs take place in the antigorite + olivine stability field and silent long-term slow slip events (SSEs) take place in the antigorite+brucite stability field. Based on observations of natural antigorite serpentinites, we propose a model that the dominant serpentinization reaction in the mantle wedge changes with increasing depth resulting in variable extents of pore fluid pressures along slip planes. The serpentinization reaction in the antigorite+brucite stability field (olivine + H2O → antigorite + brucite) proceeds at the expense of water. This is consistent with moderately elevated pore pressures inferred for long-term SSEs. The existence of weak brucite enhances the development of shear zones oblique to the main foliation. The resultant anastomosing network provides fluid pathways that may help reduce pore pressures on slip planes. In contrast, progress of the serpentinization reaction in the antigorite + olivine stability field (olivine + H2O + SiO2 → antigorite) results in a large amount of residual water that contributes to further increase pore fluid pressures on slip planes of short-term SSEs. Our results imply that understanding of serpentinization reactions and their contributions to fluid networks in mantle wedge is important in constructing quantitative 3-D models for strain evolutions along plate boundaries. © 2014 Elsevier B.V

Slow slip rate and excitation efficiency of deep low-frequency tremors beneath southwest Japan

金沢大学理工研究域地球社会基盤学系Background and purpose: Hemodynamic impairments are considered risk factors of cerebral hyperperfusion after carotid artery stenting (CAS); measurement by Single-photon emission computed tomography (SPECT) using a subjective region of interest (ROI) method lacks consistency and reproducibility. Materials and methods: The present study compared objective perfusion analysis (stereotactic extraction estimation [SEE] method) with the ROI method for preoperative SPECT to predict the hyperperfusion phenomenon (HPP) after CAS. Preoperative resting asymmetry index (cerebral blood flow [CBF] ratio from the affected to unaffected hemisphere) and cerebrovascular reactivity (CVR) to acetazolamide were measured by N-isopropyl-p-[123I]-iodoamphetamine SPECT using the SEE and ROI method in 84 patients. CBF was also measured the day after CAS. Perfusion data with the highest area under the curve (AUC) by receiver-operating characteristic (ROC) analysis was considered a perfusion risk factor of HPP. Multivariate analyses for clinical characteristics and perfusion risk factors were performed to determine predictors of HPP. Results: The HPP was observed in 10 patients (11.9%). Female sex, contralateral stenosis, and degree of stenosis were significantly associated with HPP development on univariate analysis, and symptomatic stenosis was not found to be a significant factor. On SPECT analysis, CVR in the MCA area by SEE method had the highest AUC (0.981). Multivariate analysis showed that CVR in the MCA area was a significant predictor of HPP (P = 0.041). To predict hyperperfusion, the ROC curve of the CVR showed a cutoff value of –0.60%, sensitivity of 94.6%, and specificity of 100% (P < 0.001). Conclusions: Objective SEE method had better a predictive capability than ROI method to identify risk of hyperperfusion after CAS. © 2018 Elsevier Masson SASEmbargo Period 12 monthe

Variations in the Characteristic Amplitude of Tectonic Tremor Induced by Long-Term Slow Slip Events

金沢大学理工研究域地球社会基盤学系Long-term slow slip events (L-SSEs) often excite short-term slow slips events (S-SSEs) and tectonic tremor in the zone of episodic tremor and slip (ETS). However, the factors controlling the occurrence of primary versus excited tremor events remain unclear. To elucidate these factors, we analyzed tectonic tremor events in and around the Bungo Channel (Nankai subduction zone), where L-SSEs are known to excite tremor and S-SSEs in the ETS zone. We focused on the spatial distribution of the characteristic amplitude (CA) of tremor, determined from the duration-amplitude distributions of tremor events, as an indicator of the properties of the tremor source. CAs are large in L-SSE slip areas and small in adjacent areas. The difference between CA values during tremor-excitation periods (L-SSEs) and the intervening periods (ΔCA) is positive in the slip area, negative in adjacent areas, and tends toward zero in the far field. We suggest that the heterogeneous distributions of CA and ΔCA reflect the heterogeneous effective strengths of tremor patches, which might be related to petrological properties, and stress and pore-fluid pressure variations induced by L-SSEs, respectively. The upward migration of fluid from the ETS zone along the plate interface might modulate the effective stress and strength states of tremor patches during L-SSEs

Structural analysis of crystalline R(+)-α-lipoic acid-α-cyclodextrin complex based on microscopic and spectroscopic studies

R(+)-α-lipoic acid (RALA) is a naturally-occurring substance, and its protein-bound form plays significant role in the energy metabolism in the mitochondria. RALA is vulnerable to a variety of physical stimuli, including heat and UV light, which prompted us to study the stability of its complexes with cyclodextrins (CDs). In this study, we have prepared and purified a crystalline RALA-αCD complex and evaluated its properties in the solid state. The results of 1H NMR and PXRD analyses indicated that the crystalline RALA-αCD complex is a channel type complex with a molar ratio of 2:3 (RALA:α-CD). Attenuated total reflection/Fourier transform infrared analysis of the complex showed the shift of the C=O stretching vibration of RALA due to the formation of the RALA-αCD complex. Raman spectroscopic analysis revealed the significant weakness of the S–S and C–S stretching vibrations of RALA in the RALA-αCD complex implying that the dithiolane ring of RALA is almost enclosed in glucose ring of α-CD. Extent of this effect was dependent on the direction of the excitation laser to the hexagonal morphology of the crystal. Solid-state NMR analysis allowed for the chemical shift of the C=O peak to be precisely determined. These results suggested that RALA was positioned in the α-CD cavity with its 1,2-dithiolane ring orientated perpendicular to the plane of the α-CD ring. © 2015 by the authors; licensee MDPI, Basel, Switzerland

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements