Galerkin boundary integral equation method for spontaneous rupture propagation problems: SH-case

We develop a Galerkin finite element boundary integral equation method (GaBIEM) for spontaneous rupture propagation problems for a planar fault embedded in a homogeneous full 2-D space. A 2-D antiplane rupture propagation problem, with a slip-weakening friction law, is simulated by the GaBIEM. This method allows one to eliminate the strong singularities from the integral representation of the traction, and to separate explicitly the expression for the traction into an instantaneous component; static and time-dependent components with weakly (logarithmic) singular kernels; and a dynamic component and a quasi-static component, with continuous, bounded, kernels. Simulated results throw light into the performance of the GaBIEM and highlight differences with respect to that of the traditional, collocation, boundary integral equation method (BIEM). Both methods converge with a power law with respect to grid size, with different exponents. There is no restriction on the CFL stability number for the GaBIEM since an implicit, unconditionally stable method is used for the time integration. The error of the approximation increases with the time step, as expected, and it can remain below that of the BIEM.     

Near-field beam pattern measurement of qualification model of ALMA band 8 (385–500 GHz) cartridge receiver

We have developed a near-field vector beam measurement system covering the range of frequencies from 385 to 500 GHz. The measurement set-up is capable of measurements with dynamic range exceeding 50 dB and amplitude and phase stability respectively of 0.1 dB/h and 1 degree/5 min at room temperature. Beam patterns of the ALMA band 8 corrugated horns and receiver optics block were measured at room temperature and lately compared with physical optics calculations obtained in the far-field. Both co-polar and cross-polar beam patterns of a qualification model of the ALMA band 8 cartridge cooled in a cartridge-test-cryostat have also been measured in the near-field as a detector of a submillimeter vector network analyzer. The measurements presented in this work refer to the lowest, middle and upper frequencies of band 8. The comparisons between software model and experimental measurements at these frequencies show good agreement down to ?30 dB for the main polarization component. The cross-polarization level of the beam propagating through the receiver optics block was also characterized. We found that a cross-polarization level better than ?28 dB can be achieved at all measured frequencies. The measured beam pattern of this receiver corresponds to efficiency of greater than 92% at the sub reflector (diameter of 750 mm) of the ALMA 12 m optics.     

Young,olivine xenocryst-bearing alkali-basalt from the oceanward slope of the Japan Trench

Young (6 Ma) alkali-basalts were collected from the toe of the oceanward slope of the northern Japan Trench. Two types of olivine are present in these lavas, xenocrysts with reaction rims and magmatic. The forsterite (Fo) (no. 91–92) values and NiO contents (0.3–0.5 wt%) of the xenocrysts are similar in composition to those of the depleted mantle peridotite. The groundmass olivines have relatively lower Fo values (no. 81–88) and NiO contents (0.1–0.5 wt%). Reaction rims and the vicinity of the silicate inclusion in xenocrysts show the intermediate compositions between the xenocryst and magmatic olivines. Chromian spinel inclusions in the xenocrysts also show the depleted composition in the range of abyssal peridotite. CO₂ fluid inclusions in the xenocryst records pressures before entrainment into the host magma up to 0.4 GPa, which corresponds to a depth of up to 14 km of lithospheric mantle. These data indicate that the xenocrysts originate from MORB-depleted mantle.     

Identification of 1771 Meiwa Tsunami deposits using a combination of radiocarbon dating and oxygen isotope microprofiling of emerged massive Porites boulders

The Meiwa Tsunami, one of the largest tsunamis recorded in historical documents in Japan struck Ishigaki Island and neighboring islands of the Ryukyu Arc in April 1771 AD, killing more than 12 000 people. An enormous number of massive Porites coral boulders are scattered on the shore and in the reef moat of eastern Ishigaki Island. Although these boulders likely were cast ashore by the Meiwa Tsunami, a detailed examination has not yet been conducted. When the marine reservoir effect is taken into account, one of mode values of calibrated radiocarbon dates possibly corresponds to the time of the 1771 event. However, the range of calibrated radiocarbon ages indicates that the transport of the boulders cannot be ascribed solely to the tsunami. Oxygen isotope microprofiling, which indicates sea-surface temperature variation, was therefore conducted to further investigate the mechanism of transport. The results suggest that the skeletal growth of most coral colonies was interrupted in summer or autumn; hence, tropical storms and typhoons are also very likely to be agents of transport. Thus, by combining radiocarbon dating with oxygen isotope microprofiling to investigate Porites coral boulders, it is possible to separate paleotsunami boulders from those transported by storm events as far as tsunamis occurred during the non-storm season.     

Ice core record of Be over the past millennium from Dome Fuji, Antarctica: A new proxy record of past solar activity and a powerful tool for stratigraphic dating

The cosmogenic nuclide ¹⁰Be was analyzed by using accelerator mass spectrometry on an ice core drilled at the Dome Fuji station, inland Antarctica, for 700–1900 yr CE. The measured concentration of ¹⁰Be in the Dome Fuji ice core and the derived ¹⁰Be flux show similar fluctuations, with both increasing at known solar-activity minima over the last millennium in agreement with earlier observations of ¹⁰Be and ¹⁴C. Based on the similar nature of the ¹⁰Be flux to the reconstructed ¹⁴C production rate patterns, a ¹⁰Be–¹⁴C correlation age model for the Dome Fuji ice core was successfully constructed. This age model agrees well with the initial version of the tephrochronology of the core. The ¹⁰Be-flux record contains information on variability in the amount of cosmic radiation incident on the atmosphere, which is mainly attributable to high-frequency change in solar activity and low-frequency background intensity adjustment of the geomagnetic field. High-resolution ¹⁰Be analyses of the Dome Fuji ice cores promise to provide potentially important information on the history of cosmic radiation intensity over the past several hundred thousand years.     

Biaxial effects in modelling earthquake response of R/C structures

Recent studies reveal that R/C structural members subjected to biaxial flexure due to two-dimensional earthquake excitation can deform much more than would be predicted by conventional one-dimensional response analysis. The biaxial flexure may therefore have a significant effect on the dynamic collapse process of structures subjected to intense ground motions. The present paper is intended to develop a new formulation of the two-dimensional restoring force model of R/C columns acted upon by biaxial bending moments, and to discuss the dynamic response properties of R/C structures. The model considered is a two-dimensional extension of various non-linear models for one-dimensional response analysis, including the degrading trilinear stiffness model which is one of the simpler idealizations of the restoring force characteristics of flexural-failure-type R/C structures. The modelling validity is then examined by comparison with experimental data on the biaxial bending behaviour of R/C columns. Calculations are made to study the role of different system properties on the influence of inelastic biaxial bending on the dynamic structural response. It is shown that the inelastic biaxial effect is generally significant and, in some cases, critical in the case of R/C structures with stiffness-degrading properties, while the effect is not so important for the non-degrading inelastic cases.     

Determination of Ti, K, Sm and Gd Values in Geological Survey of Japan Reference Materials by Prompt Gamma Neutron Activation Analysis

Prompt gamma neutron activation analysis was applied to the determination of the titanium, potassium, samarium and gadolinium contents of nine Geological Survey of Japan (GSJ) reference materials (JB-1, 1a, 2, 3; JA-1, 2, 3; JR-1, 2). Firstly, the values in JB-1 were determined by the standard addition method: pressed powder disks of JB-1 were used for neutron irradiation and gamma-ray measurements, after known quantities of standard reagents had been added. Secondly, the contents of eight other reference materials were determined by comparison methods using JB-1 as the comparative standard. The precision of analyses were obtained by replicate determinations on these samples. The relative standard deviation was generally less than 5%. For most samples, analysed values agreed well (< 5%) with the recommended values.     

Experimental analysis of recruitment patterns of coral reef fishes in seagrass beds: Effects of substrate type, shape, and rigidity

Habitat choice of reef fish larvae at settlement is one of the mechanisms proposed to explain spatial patterns in the distribution of fishes and the corresponding spatial structure of communities. Field experiments using Pomacentridae were conducted at Iriomote Island, southern Japan, in order to determine if rare recruitment of coral reef fishes in seagrass beds is due to larval settlement preference. When three types of natural patch treatments (branching coral patch, seagrass patch, and control without patches) were established in cleared seagrass squares in the center of a seagrass bed, four pomacentrid species, Amblyglyphidodon curacao, Dischistodus prosopotaenia, Cheiloprion labiatus, and Dascyllus aruanus, recruited exclusively onto the coral patches, indicating that larvae distributed in the seagrass bed may have preferred a coral rather than seagrass substrate as a settlement habitat. The effects of differences in physical shape (grid structure for branching coral vs. vertical structure for seagrass leaves) and rigidity (rigid substrate for coral vs. flexible substrate for seagrass) between coral and seagrass substrates on such recruitment patterns were investigated using artificial coral and seagrass units. When artificial habitat units with predator exclusion cages were established in the cleared seagrass squares as above, high densities of A. curacao and D. prosopotaenia recruits were observed on the rigid rather than flexible habitat units (both unit types having similar shape), whereas differences in recruit numbers of the two species were unclear in differently shaped units. These results demonstrated that even though pomacentrid larvae are distributed in the seagrass bed, they do not settle on the seagrass substrate owing to their habitat choice being partially based on a preference for substrate rigidity. Moreover, non-recruitment of C. labiatus and D. aruanus on artificial habitat units suggested that the presence of living coral substrates rather than physical shape/rigidity of substrates are an important cue for habitat choice of these fishes.     

Overview of NOPACCS (Northwest Pacific Carbon Cycle Study)

The Northwest Pacific Carbon Cycle Study (NOPACCS) was a program aimed at investigating the carbon cycle of the North Pacific Ocean, which can be thought of as a large reservoir of carbon dioxide. NOPACCS was also aimed at estimating the North Pacific's capacity as a carbon sink. Project design, scientific results, and data availability, and subsequent projects resulting from this project are also described in this review. Studies of the upper ocean processes focused on the latitudinal differences in the fugacity of carbon dioxide; and on the detail of plankton community structures. Intermediate water was studied in relation to the formation of North Pacific Intermediate Water and the amount of accumulated anthropogenic carbon. The sedimentation process, past carbon cycle and coral reefs were also studied during the project. A preliminary, overall view of the carbon cycle of the North Pacific was drawn from the results of the project and compared to global values.