Influence of shear angle on hangingwall deformation during tectonic inversion

Tectonic inversion is a common phenomenon in island arc settings, especially in back‐arc basins. The reactivation of normal faults as thrusts, triggered by tectonic inversion, produces typical inversion fault‐related folds and thrusts in the hangingwall. These hangingwall inversion geometries are affected by two factors: the geometry of the underlying master fault and the angle of inclined simple shear relative to the regional dip of strata, in the case that the deformation is approximated by simple shear. This study employed numerical simulations to analyse the influence of the antithetic shear angle on the geometry of the hangingwall and displacement along the master fault. The simulation results reveal that a steeply inclined shear vector during extension produces a narrow, steep‐sided half‐graben, whereas a gently inclined shear produces a wide, open basin. After tectonic inversion, a tight anticline is formed under steeply inclined shear, whereas an open anticline is formed under gently inclined shear. Antithetic shear results in reduced total displacement along the master fault, and the greater the angle between the shear direction and the regional dip, the greater the displacement along the master fault. Because the deformation geometry of syn‐extension layers is affected by extension followed by contraction, a change in the shear angle during tectonic inversion produces a wide variety of deformation geometries. Comparison of the simulation results with the results of analogue modelling suggests that the shear angle decreases by 5° during the transition from extension to tectonic inversion and that such a change may be commonly observed in natural geological structures. These results highlight the benefits of numerical simulations, which can be used to readily examine a variety of constraining parameters and thereby lead to a better understanding of the mechanism of hangingwall deformation, avoiding erroneous estimates of the amount of fault displacement.     

Dissecting large earthquakes in Japan: Role of arc magma and fluids

We synthesized information from recent high-resolution tomographic studies of large crustal earthquakes which occurred in the Japanese Islands during 1995–2008. Prominent anomalies of low-velocity and high Poisson's ratio are revealed in the crust and uppermost mantle beneath the mainshock hypocenters, which may reflect arc magma and fluids that are produced by a combination of subducting slab dehydration and corner flow in the mantle wedge. Distribution of 164 crustal earthquakes ( M 5.7–8.0) that occurred in Japan during 1885–2008 also shows a correlation with the distribution of low-velocity zones in the crust and uppermost mantle. A qualitative model is proposed to explain the geophysical observations recorded so far in Japan. We consider that the nucleation of a large earthquake is not entirely a mechanical process, but is closely related to the subduction dynamics and physical and chemical properties of materials in the crust and upper mantle; in particular, the arc magma and fluids.     

Carboniferous foraminifers from the lower part of Paleo-Tethyan seamount-type carbonates in the Changning-Menglian Belt, western Yunnan, Southwest China

The Changning-Menglian Belt in West Yunnan, Southwest China is well-known as a closed remnant of the Paleo-Tethys Ocean in East Asia (Wu et al., 1995; Liu et al., 1996). It is delineated to the east with the Lincang Massif by the Changning-Shuangjiang Fault and to the west with the Baoshan Block by the Kejie-Nandinghe Fault, and is generally subdivided into three zones: east, central, and west zones. In the central zone, various kinds of oceanic rocks such as harzburgite, cumulate websterite, gabbro, both mid-oceanic ridge basalt and oceanic island basalt, Devonian-Triassic radiolarian chert, and Carbonifer-ous-Permian massive and huge carbonates with basaltic effusives as their pedestal are exposed (Liu et al., 1991, 1996; Wu et al., 1995; Ueno et al., 2003). These Central zone rocks are now interpreted to have been emplaced as nappes structurally overlying the East and West zones, which are considered as consisting mainly of passive margin sediments of the Baoshan Block (Wu, 1991; Ueno et al., 2003).     

Mixed Land Use and Obesity: An Empirical Comparison of Alternative Land Use Measures and Geographic Scales

Obesity is a growing epidemic in the United States. Walkable neighborhoods, characterized as having the three Ds of walkability (population Density, land use Diversity, and pedestrian-friendly Design), have been identified as a potentially promising factor to prevent obesity for residents. Past studies examining the relationship between obesity and walkability vary in geographic scales of neighborhood definitions and methods of measuring the three Ds. To better understand potential influences of these sometimes arbitrary choices, we test how four types of alternative measures of land use diversity measured at three geographic scales relate to body mass index for 4,960 Salt Lake County adults. Generalized estimation equation models demonstrate that optimal diversity measures differed by gender and geographic scale and that integrating walkability measures at different scales improved the overall performance of models.     

Intra-oceanic island arc origin for Iratsu eclogites of the Sanbagawa belt,central Shikoku,southwest Japan

New geochemical and Sr–Nd isotopic data for the Iratsu eclogite and surrounding metamorphic rocks of the Sanbagawa belt, Japan, show that, while the protoliths of the metamorphic rocks formed in a variety of tectonic settings, the Iratsu body represents a deeply subducted and accreted island arc. The igneous protoliths of eclogites and garnet amphibolites were probably generated from a mantle source that had components of both a depleted mantle modified by slab-released fluid (as seen in a negative Nb anomaly) and an enriched mantle, similar to that of ocean island basalts (OIB). Fractional crystallization modeling indicates that the protoliths of some garnet clinopyroxenites from the Iratsu body are cumulates from a basaltic magma that crystallized under high O₂ and H₂O fugacities in the middle to lower crust. The source characteristics and crystallization conditions suggest that the protoliths of the Iratsu rocks formed in an oceanic island arc. Quartz eclogites from the marginal zone of the Iratsu body have geochemical signatures similar to turbidites from the Izu–Bonin island arc (as seen in a negative Nb anomaly and a concave REE pattern). The protoliths might be volcaniclastic turbidites that formed in a setting proximal to the oceanic island arc. Geochemical and isotopic signatures of the surrounding mafic schists are similar to normal (N-) and enriched (E-) mid-ocean-ridge basalt (MORB), and distinct from the rocks from the Iratsu body. The protoliths of the mafic schists likely formed in a plume-influenced mid-ocean ridge or back-arc basin. Pelitic schists from the surrounding rocks and pelitic gneisses from the marginal zone of the Iratsu body have evolved, continental geochemical signatures (as seen in a negative ε_Nd(t) value (~?5)), consistent with their origin as continent-derived trench-fill turbidites.     

Mixing of magmatic CO2 into volcano groundwater flow at Aso volcano assessed combining carbon and water stable isotopes

To understand deep groundwater flow systems and their interaction with CO₂ emanated from magma at depth in a volcanic edifice, deep groundwater samples were collected from hot spring wells in the Aso volcanic area for hydrogen, oxygen and carbon isotope analyses and measurements of the stable carbon isotope ratios and concentrations of dissolved inorganic carbon (DIC). Relations between the stable carbon isotope ratio (δ¹³C_DIC) and DIC concentrations of the sampled waters show that magma-derived CO₂ mixed into the deep groundwater. Furthermore, groundwaters of deeper areas, except samples from fumarolic areas, show higher δ¹³C_DIC values. The waters' stable hydrogen and oxygen isotope ratios (δD and δ¹⁸O) reflect the meteoric-water origin of that region's deep groundwater. A negative correlation was found between the altitude of the well bottom and the altitude of groundwater recharge as calculated using the equation of the recharge-water line and δD value. This applies especially in the Aso-dani area, where deeper groundwater correlates with higher recharge. Groundwater recharged at high altitude has higher δ¹³C_DIC of than groundwater recharged at low altitude, strongly suggesting that magmatic CO₂ is present to a much greater degree in deeper groundwater. These results indicate that magmatic CO₂ mixes into deeper groundwater flowing nearer the magma conduit or chamber.     

Ground subsidence in Semarang-Indonesia investigated by ALOS–PALSAR satellite SAR interferometry

The focus of this study is investigation of land subsidence in Semarang city Indonesia with the use of Interferometry Synthetic Aperture Radar (InSAR) of ALOS–PALSAR satellite. We processed 22 ascending SAR images during January 2007 to January 2009 plus two descending SAR images acquired on 6 June 2006 and 17 June 2007. The time series analysis of interferometry was performed by using 12 pairs of interferogram relative to 21 January 2007 and 8 pairs of interferogram relative 24 January 2008. The topographic phase contribution was removed using the 3-arcsec (90 m) Shuttle Radar Topography Mission (SRTM), Digital Elevation Model (DEM). We performed precision baseline estimation to vanish the fringes from baseline effect between master and slave data. In order to investigate the contribution of horizontal movement in our analysis, we constructed two interferograms of ascending orbit and descending orbit. The time series results exhibited that the area is subsiding continuously without a significant seasonal effect during January 2007 to January 2009. The land subsidence observed from InSAR data is approximately up to 8 cm/year. Three cross sections on image displacement show the extreme land subsidence occurred especially along the coastal area and lowland area where this area is considered as industrial with high-density settlements, consuming a lot of groundwater, and land is changed from agriculture and cultivation purposes to industrial estates and house. Our result also shows a consistency with historical pattern of subsidence measured by leveling data. The results highlight the potential use of InSAR measurements to provide better constraints for land subsidence in Semarang city Indonesia.     

Importance of intracellular Fe pools on growth of marine diatoms by using unialgal cultures and on the Oyashio region phytoplankton community during spring

We report on the ability for luxury Fe uptake and the potential for growth utilizing intracellular Fe pools for 4 coastal centric diatom isolates and in situ phytoplankton assemblages, mainly composed of diatoms. Iron uptake of the diatom isolates and natural phytoplankton assemblages in the Oyashio region during spring blooms were prevented by adding hydroxamate siderophore desferrioxamine B (DFB). After the addition of DFB, intracellular Fe in the diatom isolates supported 2.4–4.2 cell divisions with 1.2–2.6 Chl a doublings. The intracellular Fe was primarily used for cell generation rather than Chl a production, leading to a reduction in the Chl a cell quota in the Fe-starved cells with time. The metabolic properties of the Fe-starved cells with their cell morphologies were different among species or genera. An on-deck incubation experiment also exhibited 1.9 cell divisions and 0.81 Chl a doublings of phytoplankton after the addition of DFB, also indicating the preference of cell generation over Chl a production. A decrease in the level of cellular Chl a, a main light-harvesting pigment in Fe-starved diatoms, may become a superior survival strategy to protect the cells from high irradiance that can cause photo-oxidative damages through photosynthesis. Such relatively low-Fe with high-light conditions could often occur in surface waters of the Oyashio region from spring to summer.     

Empirical ocean-color algorithms to retrieve chlorophyll-a, total suspended matter, and colored dissolved organic matter absorption coefficient in the Yellow and East China Seas

A bio-optical dataset collected during the 1998?C2007 period in the Yellow and East China Seas (YECS) was used to provide alternative empirical ocean-color algorithms in the retrieval of chlorophyll-a (Chl-a), total suspended matter (TSM), and colored dissolved organic matter (CDOM) absorption coefficients at 440 nm (ag₄₄₀). Assuming that remote-sensing reflectance (Rrs) could be retrieved accurately, empirical algorithms for T_Chl (regionally tuned Tassan??s Chl-a algorithm) in case-1 waters (T_Chl2i in case-2 waters), T_TSM (regionally tuned Tassan??s TSM algorithm), and T_ag440 or C_ag440 (regionally tuned Tassan??s or Carder??s ag₄₄₀ algorithm) were able to retrieve Chl-a, TSM, and ag₄₄₀ with uncertainties as high as 35, 46, and 35%, respectively. Applying the standard SeaWiFS Rrs, T_Chl was not viable in the eastern part of the YECS, which was associated with an inaccurate SeaWiFS Rrs retrieval because of improper atmospheric correction. T_Chl behaved better than other algorithms in the turbid case-2 waters, although overestimation was still observed. To retrieve more reliable Chl-a estimates with standard SeaWiFS Rrs in turbid water (a proxy for case-2 waters), we modified T_Chl for data with SeaWiFS normalized water-leaving radiance at 555 nm (nLw₅₅₅) > 2 mW cm^?2 ??m^?1 sr^?1 (T_Chl2s). Finally, with standard SeaWiFS Rrs, we recommend switching algorithms from T_Chl2s (for case-2 waters) to MOC_Chl (SeaWiFS-modified NASA OC4v4 standard algorithm for case-1 waters) for retrieving Chl-a, which resulted in uncertainties as high as 49%. To retrieve TSM and ag₄₄₀ using SeaWiFS Rrs, we recommend empirical algorithms for T_TSM (pre-SeaWiFS-modified form) and MT_ag440 or MC_ag440 (SeaWiFS Rrs-modified forms of T_ag440 or C_ag440). These could retrieve with uncertainties as high as 82 and 52%, respectively.     

Is there any seasonal variation in marine nematodes within the sediments of the intertidal zone?

The sediment parameters and nematode assemblages in the intertidal zone of the Hichirippu shallow lagoon, Hokkaido, Japan, were investigated. The objectives of this study were to observe the seasonal variation in the nematodes in the sediment, and to investigate the relationships between the nematodes and environmental factors. Samples were collected bi-monthly from five stations on the tidal flat from April 2003 to February 2004. It was found that the sediment parameters (Chl a concentration, AVS, TOC and TN contents) varied throughout the 10-month study. Fifty-four species of nematodes were found in the study area. The density and biomass of the nematodes varied in accordance with the sediment temperature during the sampling period. In this study, there was a seasonal variation in the nematode assemblage found in the intertidal zone of this shallow lagoon. The important factors affecting this variation were sediment temperature, and food competition among the nematodes themselves. The seasonal variation of the nematode also showed a relationship with the Chl a concentration in the sediment during the sampling period.