High‐pressure polymorphs of magnesian orthopyroxene from a shock vein in the Yamato‐000047 lherzolitic shergottite

Abstract– We found a simple thin shock vein, less than or equal to about 60 μm in width and 1.8 mm in length, in the poikilitic area in the Yamato (Y‐) 000047 lherzolitic shergottite. The shock vein occurs only in magnesian Ca‐poor clinopyroxene, which may have transformed from orthopyroxene during the pressure increase at the shock event. The shock vein consists of (Mg_0.8,Fe_0.2)SiO₃ pyroxene polymorphs, such as columnar akimotoite, two kinds of pyroxene glasses, dendritic akimotoite, and framboidal pyroxene glass, in the order from the periphery to the center. The compositions and textures suggest that columnar akimotoite in the periphery of the shock vein crystallized from solid‐state phase transition of clinopyoroxene during the cooling of the vein, and the remains in the shock vein solidified from shock‐produced melt. The glass includes two kinds of massive glass in the vein and framboidal glass in the vein center. The framboidal glass is the most magnesian and may have been vitrified from perovskite crystallized from high‐pressure melt produced at high temperature ≥3000 °C and high‐pressure 23–40 GPa. Dendritic akimotoites in the vein center metastably crystallized from residual shock melt. The formation sequences of the constituent phases in the shock vein happen in the following order: columnar akimotoites, rim glass, center glass, framboidal glass, and dendritic akimotoites. The increase of the Raman intensity of 660–670 cm^?1 in the order of rim glass, center glass, and framboidal glass suggests that the formation of the pyroxene chain proceeds faster in the vein center than in the vein rim due to its slower cooling. The finding of the shock vein consisting merely of high‐pressure polymorphs of pyroxene, akimotoite, and framboidal glass (vitrified perovskite) is the first reported among all Martian meteorites.     

Noble gas record and cosmic‐ray exposure history of the new CO3 chondrite Moss––Comparison with Lancé and other CO chondrite falls

Abstract– The Moss meteorite is the first CO chondrite fall after a time period of 70 yr and the least terrestrially contaminated member of its group. Its cosmic‐ray exposure (CRE) age (T₃ ～ 13.5 Ma; T₂₁ ～ 14.6 Ma) is distinct among CO chondrites and, within witnessed falls is the shortest after Lancé, which we have reanalyzed. Gas retention ages are approximately 3.95 × 10⁹ yr (U/Th‐He) and approximately 4.43 × 10⁹ yr (K/Ar), respectively. Trapped Ar, Kr, and Xe are present in Moss in abundances typical for CO chondrites, with “planetary” elemental and isotopic compositions. Presence of HL‐xenon from presolar diamonds is observed in the stepwise release analysis of Lancé. It may also be present in Moss, but it is difficult to ascertain in single‐step bulk analyses. It follows from our new data combined with a survey of the literature that the abundance of trapped gases in CO chondrites is not a good indicator of their petrological subtype.     

Feeding Strategy of Japanese Sand Lance Larvae in Relation to Ciliated Protozoa in the Vicinity of a Thermohaline Front

Larval feeding and survival strategies are described on a Japanese sand lance, Ammodytes personatus Girard, collected in the vicinity of a thermohaline front in the Ise Bay, in comparison with those of other predominant larvae, Hexagrammos spp. and Sebastiscus marmoratus (Cuvier). First-feeding A. personatus larvae (3.1–3.9 mm NL) fed primarily on tintinnid ciliates, subsequently switching to copepod nauplii (4.0–7.9 mm NL larvae) and post-naupliar copepods (8.0–11.3 mm NL larvae). First-feeding Hexagrammos spp. larvae (6.5–6.9 mm NL) fed primarily on post-naupliar copepods, and first-feeding S. marmoratus larvae (<4.0 mm NL), mostly on copepod nauplii. The different food preferences of these species at first-feeding were related to their different mouth widths (0.15–0.19, 0.52–0.56 and 0.32–0.40 mm, respectively) and/or body size (3.1–3.9, 6.5–6.9 and 3.2–3.9 mm NL, respectively). Ciliate-feeding by first-feeding A. personatus larvae was strongly related to the convergence of the larvae and their prey near the thermohaline front, densities of both being greater on the inshore side of the frontal zone. In conclusion, the aggregation of ciliates near the thermohaline front may have improved feeding conditions and survival of first-feeding A. personatus larvae.     

A real-time observation network of ocean-bottom-seismometers deployed at the Sagami trough subduction zone,central Japan

We installed a real-time operating regional observation network of Ocean-Bottom-Seismometers, connected to an electro-optical fiber communication cable, at the Sagami trough subduction zone, just south of the Tokyo metropolitan area, central Japan. The network, called ETMC, has six seismic observation sites at approximately 20 km spacing. In addition, there are three tsunami observation sites along the ETMC network to monitor the propagation process of tsunamis around the Sagami trough region.The on-line data from the ETMC has been improving the detection capability of smaller-magnitude earthquakes even at areas close to the margin of the trough. The ETMC data analyzing system, which has a function of real-time digital filtering for each seismic channel, can read the arrival times of P- and S-waves precisely, constraining well the automatic on-line hypocenter locations. The network has been providing useful information regarding the bending and downgoing process of the Philippine sea plate at the Sagami trough subduction zone.The pressure sensors of the installed network have a detection capability of tsunami wave trains with an amplitude of less than 1 cm. For example, the sensors recorded the full time history of tsunami wave trains, with mm order resolution, originating from a tsunami earthquake with 5.7 M_W and the tsunami magnitude of 7.5 occurred near Tori Shima (Tori Is.) of the Izu-Bonin Is. arc on September 4, 1996. The maximum amplitude of the tsunami signals on the trough-floor was approximately 1 cm (P-P), in contrast with approximately 20 cm (0-P) at a coastal site on Izu-Oshima, near the trough. Also, the pressure sensors observed tsunamis due to a large tsunami earthquake (7.1 M_W) at the northern New Guinea, on July 17, 1998.     

A visage of early Paleozoic Japan: Geotectonic and paleobiogeographical significance of Greater South China

The current state of knowledge on the early Paleozoic evolution of Japan is reviewed. Although early Paleozoic Japan marked the foundation of long‐lasting subduction‐related orogenic growth throughout the Phanerozoic, details of this have not been fully revealed. Nevertheless, U‐Pb dating of zircons both in Paleozoic granitoids and sandstones is revealing several new aspects of early Paleozoic Japan. The timing of the major tectonic change, from a passive continental margin setting (Stage I) to an active one (Stage II), was constrained to the Cambrian by identifying the oldest arc granitoid, high‐P/T blueschist, and terrigenous clastics of arc‐related basins. Ages of recycled zircons in granitoids and sandstones provided critical information on the homeland of Japan, i.e. the continental margin along which proto‐Japan began to grow. The early Paleozoic continental margin that hosted the development of an arc‐trench system in proto‐Japan had cratonic basement composed mostly of Proterozoic crust with a minor Archean component. The predominant occurrence of Neoproterozoic zircons in Paleozoic rocks, as xenocrysts in arc granitoids and also as detrital grains in terrigenous clastics, indicates that the relevant continental block was a part of South China, probably forming a northeastern segment of Greater South China (GSC) together with the Khanka/Jiamsi/Bureya mega‐block in Far East Asia. GSC was probably twice as large as the present conterminous South China on mainland Asia. Paleozoic Japan formed a segment of a mature arc‐trench system along the Pacific side of GSC, where the N–S‐trending Pacific‐rim orogenic belt (Nipponides) developed with an almost perpendicular relationship with the E–W‐trending Central Asian orogenic belt. The faunal characteristics of the Permian marine fauna in Japan, both with the Tethyan and Boreal elements, can be better explained than before in good accordance with the relative position of GSC with respect to the North China block during the late Paleozoic.     

Measuring geographic segregation: a graph-based approach

Residential segregation is a multidimensional phenomenon that encompasses several conceptually distinct aspects of geographical separation between populations. While various indices have been developed as a response to different definitions of segregation, the reliance on such single-figure indices could oversimplify the complex, multidimensional phenomena. In this regard, this paper suggests an alternative graph-based approach that provides more detailed information than simple indices: The concentration profile graphically conveys information about how evenly a population group is distributed over the study region, and the spatial proximity profile depicts the degree of clustering across different threshold levels. These graphs can also be summarized into single numbers for comparative purposes, but the interpretation can be more accurate by inspecting the additional information. To demonstrate the use of these methods, the residential patterns of three major ethnic groups in Auckland, namely Māori, Pacific peoples, and Asians, are examined using the 2006 census data.     

On the coefficient of shear diffusion

The approximate relation of the coefficient of shear diffusion against time is shown by means of a two-level model.     

Event pattern analysis: Spatial clustering of sequential events and temporal change of events over time

This article develops a method for analyzing spatial and temporal event patterns. Events in this article refer to zero-dimensional objects in the spatiotemporal dimension, which represent the occurrence of crimes, traffic accidents, earthquakes, and so forth. The spatial clustering of sequential events and the increase and decrease in events over time are discussed. These patterns are often observed and analyzed in various academic fields, such as criminology, epidemiology, and geography. However, analytical methods for these patterns have not yet been fully developed. To fill the research gap, this article proposes a new method for analyzing these event patterns. Two statistical measures are utilized, one represents the degree of the spatial clustering of sequential events, and the other evaluates the increase and decrease of events over time. The method is applied to the analysis of the spatial and temporal patterns of the openings of new shops and restaurants in Shibuya-ku, Tokyo. The results gave us interesting empirical findings and indicated the soundness of the method.     

饱和珊瑚砂液化特性动三轴试验研究

为调查饱和珊瑚砂液化相关特性与发展规律,针对饱和Chibishi珊瑚砂,开展一系列不排水循环三轴试验,研究相对密度D_r和循环应力比CSR对饱和Chibishi珊瑚砂的超孔隙水压力Δu、轴向应变ε_a及动强度特性的影响,并分析不同地区珊瑚砂抗液化强度的差异性。结果表明,饱和Chibishi珊瑚砂的Δu发展模式根据不同的CSR水平可以分为前期均匀增长型、前期突增型和后期突增型;此外,采用一种新的孔压模型对前期均匀增长型、前期突增型的孔压比r_u进行表征,Chibishi珊瑚砂在相同的D_r条件下,双幅应变ε_DA达到5%的循环次数N随着CSR水平的增加而逐渐减小;各珊瑚砂在同一里氏震级对应的等效循环振动次数下,抗液化强度CRR的增长模式存在显著差异。研究结果可丰富对珊瑚砂液化特征的认知,同时对近岸和沿海工程的抗震设计提供参考依据。     

GIS中地图注记尺寸和文字信息的损失

地图注记是地理信息系统中不可缺少的组成内容。它将与空间目标有关的各种属性联系起来,如目标的名称、面积、周长等。ＧＩＳ中都有将注记配置的功能。地图注记的可读性取决于多种因素。字符尺寸是其中最重要的影响因素之一,通常大字符往往比小字符易读。但当地图注记以...