Temporal stress variations along a seismogenic megasplay fault in the subduction zone: An example from the Nobeoka Thrust,southwestern Japan

The Nobeoka Thrust, an ancient megasplay fault in the Shimanto Belt, southwestern Japan, contains fault rocks from the seismogenic zone, providing an accessible analog of active megasplay faults in deep subduction settings. In this study, the paleostress along the Nobeoka Thrust was analyzed using multiple inversion techniques, including k‐means clustering of fault datasets acquired from drillcores that intersected the thrust. The six resultant stress orientation clusters can be divided into two general groups: stress solutions with north–south‐trending σ₁ axes, and those with east–west‐trending σ₁ axes. These groups are characterized by the temporal changes for the orientations of the σ₁ and σ₃ principal stress axes that involve alternation between horizontal and vertical. The findings are probably due to a change in stress state before and after earthquakes that occurred on the fault; similar changes have been observed in active tectonic settings, such as the 2011 Tohoku‐Oki earthquake (Japan).     

Consistent DOF reduction of tall steel frames

This paper presents an energy‐consistent approach for reducing the number of degrees‐of‐freedom (DOFs) in tall steel frames. In the present approach, the moment resistance of beams and columns in each story is represented by the moment resistance of a rotational spring and a beam‐column element, respectively. The shear resistance provided by braces in each story is represented by the shear resistance of a shear spring. Furthermore, the resistance to the overturning moment provided by axial resistance of columns in each story is represented by the moment resistance of a rotational spring. These representations are carried out by achieving the equivalence between the strain energy stored and dissipated in the elements in the full (unreduced) DOF models and the strain energy stored and dissipated in the corresponding elements in the reduced DOF models. The accuracy of the present approach is demonstrated through numerical examples, which compare the results of nonlinear time history analyses obtained using the full and reduced DOF models. In the numerical examples, the response is estimated for 20‐story and 40‐story steel frames with and without buckling‐restraint braces subjected to a suite of near‐fault and far‐fault ground motions. The present approach is useful in estimating the response of tall steel frames having non‐regular member arrangements to a suite of intense ground motions including near‐fault ones, where it is crucial to capture the influence of higher mode effects on collapse mechanisms. Copyright © 2017 John Wiley & Sons, Ltd.     

Diurnal Cycle of Sound Scatterers and Measurements of Turbidity Using ADCP in Beppu Bay

From September 20 to 22 in 1994, the vertical profiles of echo intensity and three-component velocities were measured with a bottom-mounted 300 kHz broadband acoustic Doppler current profiler (ADCP) in Beppu Bay in the Seto Inland Sea of Japan. A very strong thermocline was observed from 50 to 60 m. A pronounced diurnal cycle of backscatter strength (BS) was found above the thermocline. However, it was not found under the thermocline where there was a lack of dissolved oxygen. We suggest that the diurnal cycle of BS is caused by the vertical migration of zooplankton. The downward and upward migration occurred in early morning and late afternoon, respectively. The migration speeds estimated from BS isopleth displacements were about 1 cm s^–1. Further, the contribution of turbidity (Tur) to BS was examined by separating out the effect of migrating zooplankton. There was a significant correlation between BS and turbidity under the thermocline. The maximum contributions of the Tur, migrating zooplankton and non-migrating plankton on BS were estimated at 3, 12, 25 dB, respectively. These data suggest that when using an ADCP to estimate Tur, it is very important to consider carefully the backscatter signal from zooplankton.     

The Origin Of The 1998 June BoöTid Meteor Shower

We compare various objects as the possible parent comet of the1998 June Boötid, by using the Tisserand invariant and the D-discriminant. Furthermore,in order to investigate the behaviour of the meteoric stream orbit, wesimulate the orbital evolution of test particles that are released from7P/Pons–Winnecke. We show firstly that the parent comet of the 1998 June Boötids, is 7P/Pons–Winnecke, and secondly that the meteoroids which constitute 1998 June Boötids were released in 1819 and 1869 from the parent comet. In themid-1900s the meteoroids started to transfer to Earth-colliding orbitsby Jovian perturbations.     

RFLP analysis of a mitochondrial gene,cytochrome oxidase I (COI) of three species of the genusCalyptogena around Japan

Phylogenetic relationship among three species of deep-sea vesicomyid bivalvesCalyptogena, i.e.,C. soyoae, C. solidissima, C. fausta and an undescribed species of the Iheya Ridge, Okinawa Trough was analyzed on the basis of the RFLP analysis of the fragment (about 1 kbp) of cytochrome oxidase I. Both the two populations ofC. soyoae (off Hatsushima and Okinoyama Bank, Sagami Bay) consisted of two haplotypes, which could be discriminated by only one restriction site (1.7% sequence divergence).Calyptogena of the Iheya Ridge could not be distinguished from one of the two haplotypes ofC. soyoae. Nucleotide substitution rates between species were calculated and dendrograms were constructed.     

Global mapping of the degree of space weathering on asteroid 25143 Itokawa by Hayabusa/AMICA observations

Abstract— We obtained color images of near‐Earth asteroid 25143 Itokawa by the Hayabusa multiband imaging camera to characterize the regional color properties. Images were obtained for the whole disk from the gate position (GP) and home position (HP) at a spatial resolution of 0.8–3.7 m/pixel. Whole‐disk spectra are adjusted to the telescopic data obtained by the University of Hawai'i's 88‐inch telescope using the Eight Color Asteroid Survey (ECAS) system. The disk‐resolved measurements show large variations in the three visible channels. We present a map of an index related to the degree of space weathering, which has been newly developed based on laboratory measurements. We find large variations in the degree of space weathering on Itokawa. Fresh materials are observed in regions of steep slopes and craters, whereas mature materials are ubiquitously distributed. This result suggests that pristine ordinary chondrite‐like materials have been exposed through weathered layers by excavation. By also examining close‐up images obtained during touchdown rehearsal, we find that most rocks in Itokawa's rough terrains are weathered. Instead of a regolith blanket, the surface of this small asteroid is covered with weathered rocks and gravels.     

Physics-Based 3-D Simulation for Earthquake Generation Cycles at Plate Interfaces in Subduction Zones

The generation of interplate earthquakes can be regarded as a process of tectonic stress accumulation and release, driven by relative plate motion. We completed a physics-based simulation system for earthquake generation cycles at plate interfaces in the Japan region, where the Pacific plate is descending beneath the North American and Philippine Sea plates, and the Philippine Sea plate is descending beneath the North American and Eurasian plates. The system is composed of a quasi-static tectonic loading model and a dynamic rupture propagation model, developed on a realistic 3-D plate interface model. The driving force of the system is relative plate motion. In the quasi-static tectonic loading model, mechanical interaction at plate interfaces is rationally represented by the increase of tangential displacement discontinuity (fault slip) across them on the basis of dislocation theory for an elastic surface layer overlying Maxwell-type viscoelastic half-space. In the dynamic rupture propagation model, stress changes due to fault slip motion on non-planar plate interfaces are evaluated with the boundary integral equation method. The progress of seismic (dynamic) or aseismic (quasi-static) fault slip on plate interfaces is governed by a slip- and time-dependent fault constitutive law. As an example, we numerically simulated earthquake generation cycles at the source region of the 1968 Tokachi-oki earthquake on the North American-Pacific plate interface. From the numerical simulation, we can see that postseismic stress relaxation in the asthenosphere accelerates stress accumulation in the source region. When the stress state of the source region is close to a critical level, dynamic rupture is rapidly accelerated and develops over the whole source region. When the stress state is much lower than the critical level, the rupture is not accelerated. This means that the stress state realized by interseismic tectonic loading essentially controls the subsequent dynamic rupture process.     

A preparation zone for volcanic explosions beneath Naka-dake crater,Aso volcano,as inferred from magnetotelluric surveys

The 1st crater of Naka-dake, Aso volcano, is one of the most active craters in Japan, and known to have a characteristic cycle of activity that consists of the formation of a crater lake, drying-up of the lake water, and finally a Strombolian-type eruption. Recent observations indicate an increase in eruptive activity including a decrease in the level of the lake water, mud eruptions, and red hot glows on the crater wall. Temporal variations in the geomagnetic field observed around the craters of Naka-dake also indicate that thermal demagnetization of the subsurface rocks has been occurring in shallow subsurface areas around the 1st crater. Volcanic explosions act to release the energy transferred from magma or volcanic fluids. Measurement of the subsurface electrical resistivity is a promising method in investigating the shallow structure of the volcanic edifices, where energy from various sources accumulates, and in investigating the behaviors of magma and volcanic fluids. We carried out audio-frequency magnetotelluric surveys around the craters of Naka-dake in 2004 and 2005 to determine the detailed electrical structure down to a depth of around 1 km. The main objective of this study is to identify the specific subsurface structure that acts to store energy as a preparation zone for volcanic eruption. Two-dimensional inversions were applied to four profiles across the craters, revealing a strongly conductive zone at several hundred meters depth beneath the 1st crater and surrounding area. In contrast, we found no such remarkable conductor at shallow depths beneath the 4th crater, which has been inactive for 70 years, finding instead a relatively resistive body. The distribution of the rotational invariant of the magnetotelluric impedance tensor is consistent with the inversion results. This unusual shallow structure probably reflects the existence of a supply path of high-temperature volcanic gases to the crater bottom. We propose that the upper part of the conductor identified beneath the 1st crater is mainly composed of hydrothermally altered zone that acts both as a cap to upwelling fluids supplied from deep-level magma and as a floor to infiltrating fluid from the crater lake. The relatively resistive body found beneath the 4th crater represents consolidated magma. These results suggest that the shallow conductor beneath the active crater is closely related to a component of the mechanism that controls volcanic activity within Naka-dake.     

Simultaneous Analysis of Natural Free Estrogens and Their Conjugates in Wastewater by GC‐MS

A solid‐phase extraction (SPE)‐gas chromatography (GC)‐mass spectrometry (MS) analytical method was developed for the simultaneous analysis of natural free estrogens and their conjugates in wastewater samples. Natural free estrogens and their conjugates in wastewater were successfully separated by the oasis hydrophilic‐lipophilic balance solid phase extraction (Oasis HLB SPE) method, and the conjugates were initially enzyme hydrolyzed by β‐glucuronidase or arylsulfatase from Helix pomatia prior to derivatization. N‐methyl‐N‐(tert‐butyldimethylsilyl)trifluoroacetamide (MTBSTFA) plus 1% tert‐butyldimetheylchlorosilane (TBDMCS) was chosen as the derivatization reagent, and the most appropriate conditions of derivatization were determined to be at 95°C for 90 min. The recovery ratios of nine target chemicals were determined by spiking them in 1 L of ultra‐purified water or the influent of a wastewater treatment plant (WWTP). The recovery ratios of six out of nine for the analytes ranged from 73.3–114.9% with relative standard deviations (RSD) from 1.6–19.9%. The established method was successfully applied to environmental wastewater samples which were collected from one municipal wastewater treatment plant (WWTP) in Osaka, Japan, for the determination of natural free estrogens and their conjugates. In the influent sample, E1, E2, E1‐3S, E3‐3S, and E1‐3G were detected at concentrations of 16.6, 9.6, 8.2, 21.9, and 3.2 ng L^–1, respectively. However, only E1 was detected at a high concentration of 44 ng L^–1 in the effluent sample, suggesting that it is the dominant natural free estrogen in the effluent.     

A unique, (almost) unaltered spinel-rich fine-grained inclusion in Kainsaz

Abstract We report a unique, spinel-rich, extremely porous fine-grained inclusion in the Kainsaz (CO3) meteorite. This inclusion is the least altered fine-grained inclusion yet discovered, having escaped almost entirely the secondary alterations experienced by Allende fine-grained inclusions. The inclusion is comprised of loosely packed 5–30 μm spinel grains mantled by thin layers of melilite, anorthite, and diopsidic pyroxene. The inclusion, which has over 30 vol% void space, is one of the most spinel-rich, most porous fine-grained inclusions seen to date. The mineralogy of the inclusion matches that which has been predicted for a precursor of the altered mineral assemblages of Allende fine-grained inclusions, though a lack of interstitial material in the Kainsaz inclusion reduces the likelihood of a direct genetic relationship between the two (Allende fine-grained inclusions contain abundant interstitial material). Its mineralogical composition confirms that the precursors of other, more altered, fine-grained inclusions were assemblages of refractory minerals exclusively.