Alteration and mass transfer inferred from the Hirabayashi GSJ drill penetrating the Nojima Fault, Japan

Abstract Mineralogical and geochemical studies on the fault rocks from the Nojima–Hirabayashi borehole, south-west Japan, are performed to clarify the alteration and mass transfer in the Nojima Fault Zone at shallow depths. A complete sequence from the hornblende–biotite granodiorite protolith to the fault core can be observed without serious disorganization by surface weathering. The parts deeper than 426.2 m are in the fault zone where rocks have suffered fault-related deformation and alteration. Characteristic alteration minerals in the fault zone are smectite, zeolites (laumontite, stilbite), and carbonate minerals (calcite and siderite). It is inferred that laumontite veins formed at temperatures higher than approximately 100°C during the fault activity. A reverse component in the movement of the Nojima Fault influences the distribution of zeolites. Zeolite is the main sealing mineral in relatively deep parts, whereas carbonate is the main sealing mineral at shallower depths. Several shear zones are recognized in the fault zone. Intense alteration is localized in the gouge zones. Rock chemistry changes in a different manner between different shear zones in the fault zone. The main shear zone (MSZ), which corresponds to the core of the Nojima Fault, shows increased concentration of most elements except Si, Al, Na, and K. However, a lower shear zone (LSZ-2), which is characterized by intense alteration rather than cataclastic deformation, shows a decreased concentration of most elements including Ti and Zr. A simple volume change analysis based on Ti and Zr immobility, commonly used to examine the changes in fault rock chemistry, cannot account fully for the different behaviors of Ti and Zr among the two gouge zones.     

The upper Miocene diatomaceous sediments of the northernmost Mediterranean region: A lamina-scale investigation of an overlooked palaeoceanographic archive

During the late Miocene the Mediterranean experienced a dramatic intensification of opaline accumulation, recorded by the deposition of diatomaceous sediments. The fine lamination of these deposits potentially records annual to sub-annual palaeoceanographic processes that occurred during a critical phase of the geodynamic evolution of the Mediterranean basin, which eventually led to the Messinian salinity crisis. The diatomaceous facies has been interpreted by previous researchers as the product of intensified upwelling currents and of bottom anoxia formation in the Mediterranean basin. However, until now, no efforts have been made to unravel the sedimentological and micropalaeontological content of these deposits at the lamina-scale. This paper presents the first case study of a systematic scanning electron microscope-based morphological investigation of the diatomaceous sediments deposited during the late Miocene at the northernmost offshoot of the Mediterranean basin (Piedmont Basin, north-west Italy). Using a non-invasive analytical approach, six faciological components (laminae, laminated packets, non-laminated intervals, burrows, opal-rich aggregates and mixed pelletal structures) and their relationships are described and interpreted herein. Following the lamina-scale study of these sediments, an annual sedimentary cycle could be identified and an accumulation rate (ca 50 cm kyr⁻¹) inferred that is atypical for a setting actively influenced by upwelling. The role played by the entanglement of diatom valves in creating a physical barrier to the bioturbation is here emphasized as the main process responsible for the preservation of the laminated fabric of diatomaceous sediments, challenging the supposed role of deep anoxia. These results suggest that the late Miocene diatomaceous deposition in the Piedmont Basin cannot be univocally considered as a by-product of upwelling intensification and seafloor oxygen depletion.     

Determination of the freshwater origin of Coastal Oyashio Water using humic-like fluorescence in dissolved organic matter

Coastal Oyashio Water (COW), defined as a water mass with a temperature lower than 2 °C and a salinity lower than 33.0, is distributed in the North Pacific Ocean off southeastern Hokkaido, Japan, from winter to spring. COW is rich in macronutrients and dissolved iron and is thus considered to affect the spring phytoplankton blooms in the Oyashio region. Although river water and sea-ice melt water have been considered freshwater end-members of COW, the contributions of these freshwater sources to COW have not been well described. In this study, the humic-like components in dissolved organic matter were first applied as a parameter to evaluate the freshwater end-members of COW in March 2015. Linear regressions with negative slopes were determined between the humic-like components and the salinity of COW. The intercepts of the regressions against the humic-like components were within the ranges of those observed for the local rivers of Hokkaido but were very different from those of sea ice. These findings suggest that river water contributed to the COW observed here as a freshwater end-member, although the contribution of sea-ice melt water to COW could not be evaluated. This novel approach also highlighted two different less-saline water masses in COW. The first was characterized by a lower temperature and relatively high levels of humic-like components, while the second was higher in temperature and had higher levels of humic-like components. It is suggested that these different characteristics are due to the contributions of water from different rivers and/or different effects of sea-ice melt water.     

Long-term slow slip events are not necessarily caused by high pore fluid pressure at the plate interface: an implication from two-dimensional model calculations

A recent tomographic study proposed that high-pore pressure in the deeper portion of the locked zone of a subduction thrust resulting from metamorphic dehydration reactions may cause long-term slow slip events. The study used the concept of 'critical fault stiffness', which derives from laboratory-derived rate- and state-dependent friction laws. To test the proposition, we execute 2-D model calculations using laboratory-derived rate- and state-dependent friction laws. Our numerical result is against the proposition, but it can also be explained by the concept of the critical fault stiffness. We agree that metamorphic dehydration reactions definitely produce a bulk property of high fluid saturation, but we caution that they do not necessarily lead to high-pore pressure in the fault zone.     

Integration of Satellite Telemetry Data and Land Cover Imagery: A Study of Migratory Cranes in Northeast Asia

The present study describes a procedure for quantitatively analyzing satellite telemetry data to identify interspecific land use differences among four threatened crane species. The inherent inaccuracy of satellite telemetry data points, the temporal autocorrelation of those points, and the resolution of two land‐cover imagery products from the IGBP‐DISCover Global Land‐Cover Characterization Project (derived from AVHRR data) were assessed and integrated in a GIS. Satellite telemetry is a system where animals are tracked using battery‐operated transmitters and locations are calculated using triangulation from satellites. Using the variable spatial inaccuracy of the telemetry locations, each point was buffered using a radius based on the accuracy of the point, and then intersected with the land cover imagery. The research concluded that the methodology is valuable for studies of birds at a regional scale, with interspecific differences clearly evident, but that diurnal and nocturnal differences were not discernable due to the coarse resolution of both satellite telemetry and land‐cover data.     

TRENDS IN THE VARIABILITY OF SURFACE AIR TEMPERATURE,CANADIAN ARCTIC

A measure of temperature variability was calculated using annual temperature records obtained from 40 stations in the Canadian Arctic, records beginning between 1929 and 1958, and concluding for this study in 1983. Long-term trends in the frequency of extreme temperature conditions were obtained for eight regions in the Arctic. The results indicate that temperatures in the Canadian Arctic, as a whole, have not become more variable. In the last 15 to 20 years of the period considered in this study, the occurrence of extreme temperature conditions has increased only in three of the eight regions.     

Interannual variability of the surface heat budget over the northern North Atlantic and North Pacific Oceans

Summary The January anomaly time series for each term of the surface heat budget (solar and longwave radiation, sensible and latent heat fluxes) are calculated for Ocean Weather Stations (OWSs) in the North Pacific and North Atlantic Oceans. The data set used is the Comprehensive Ocean-Atmosphere Data Set (COADS). The dominant term is the latent heat flux. The results for OWS P in the northern North Pacific show that the interannual variability of the heat budget parameters is correlated with the synoptic variability of the Aleutian low. There is also an interdecadal signal present in the heat budget anomaly time series, with the sign of the anomaly persisting for about 8–10 years. In contrast, for OWS J in the northern North Atlantic, no correlation is found between the variability of the heat budget parameters and the corresponding synoptic variability of the Icelandic low. The station J air-sea heat fluxes also show a higher frequency variability, compared to those of station P. The results suggest the variability of the January air-sea heat exchange processes are fundamentally different over the two ocean basins.With 3 Figures     

The Hayabusa Spacecraft Asteroid Multi-band Imaging Camera (AMICA)

The Hayabusa Spacecraft Asteroid Multi-band Imaging Camera (AMICA) has acquired more than 1400 multispectral and high-resolution images of its target asteroid, 25143 Itokawa, since late August 2005. In this paper, we summarize the design and performance of AMICA. In addition, we describe the calibration methods, assumptions, and models, based on measurements. Major calibration steps include corrections for linearity and modeling and subtraction of bias, dark current, read-out smear, and pixel-to-pixel responsivity variations. AMICA v-band data were calibrated to radiance using in-flight stellar observations. The other band data were calibrated to reflectance by comparing them to ground-based observations to avoid the uncertainty of the solar irradiation in those bands. We found that the AMICA signal was linear with respect to the input signal to an accuracy of ?1% when the signal level was <3800 DN. We verified that the absolute radiance calibration of the AMICA v-band (0.55 μm) was accurate to 4% or less, the accuracy of the disk-integrated spectra with respect to the AMICA v-band was about 1%, and the pixel-to-pixel responsivity (flat-field) variation was 3% or less. The uncertainty in background zero level was 5 DN. From wide-band observations of star clusters, we found that the AMICA optics have an effective focal length of 120.80 ± 0.03 mm, yielding a field-of-view (FOV) of 5.83° × 5.69°. The resulting geometric distortion model was accurate to within a third of a pixel. We demonstrated an image-restoration technique using the point-spread functions of stars, and confirmed that the technique functions well in all loss-less images. An artifact not corrected by this calibration is scattered light associated with bright disks in the FOV.     

Complex Earthquake Cycle Simulations Using a Two-Degree-of-Freedom Spring-Block Model with a Rate- and State-Friction Law

Numerical simulations of complex earthquake cycles are conducted using a two-degree-of-freedom spring-block model with a rate- and state-friction law, which has been supported by laboratory experiments. The model consisted of two blocks coupled to each other and connected by elastic springs to a constant-velocity, moving driver. By widely and systematically varying the model parameters, various slip patterns were obtained, including the periodic recurrence of seismic and aseismic slip events, and several types of chaotic behaviour. The transition in the slip pattern from periodic to chaotic is examined using bifurcation diagrams. The model system exhibits typical period-doubling sequences for some parameter ranges, and attains chaotic motion. Simple relationships are found in iteration maps of the recurrence intervals of simulated earthquakes, suggesting that the simulated slip behaviour is deterministic chaos. Time evolutions of the cumulative slip distance in chaotic slip patterns are well approximated by a time-predictable model. In some cases, both seismic and aseismic slip events occur at a block, and aseismic slip events complicate the earthquake recurrence patterns.