Azimuthal dependence on amplifications for long-period ground motions propagating in the Kanto Basin,Japan

Journal of Seismology - In the Kanto Basin, Japan, it has been reported that the dominant periods of long-period ground motions vary depending on the areas where earthquakes occurred. This suggests...     

Effects of salinity on the growth,Na partitioning,and Na dynamics of a salt-tolerant tree,Populus alba L.

To obtain the basic information required before using Populus alba L. to phytoremediate degraded saline environments, we investigated the effects of saline irrigation on the growth, survival, Na partitioning, and Na dynamics of 1-year-old rooted cuttings. The plants were grown in a greenhouse in lysimeters containing sandy soil and were watered with field water (control) or solutions containing either 2000 or 5000 mg L^?1 of a mixture of NaCl and CaCl₂ (low- and high-salt treatments, respectively). All plants in the control and the low-salt treatment survived after 1 year of treatment, but the high-salt treatment significantly decreased growth and caused 20% mortality. Strong Na partitioning was observed in the roots in all three treatments, suggesting that this is an important salt tolerance mechanism in P. alba. Total Na uptake was similar in the low-salt and high-salt treatments, and was about 3 times the value in the control. However, the compartmentalization of Na in fallen leaves, dead leaves and dead branches in the high-salt treatment was about twice the level in the low-salt treatment. The plants accumulate Na under moderate levels of salinity, suggesting that P. alba is a good candidate for phytoremediating salinized soil.     

Nitrate-nitrogen isotopic patterns in surface waters of the western and central equatorial pacific

To understand the processes transporting nitrate to the surface layer of the western and central equatorial Pacific, we measured the nitrogen isotopic ratio of nitrate (δ ¹⁵NO ₃ ⁻ ), which is a very useful tracer of the source of nitrate, above 200 m depth in this region in December 1999. δ ¹⁵NO ₃ ⁻ is higher (about 13.0‰) in the surface water than in the subsurface water (where it is about 6.5‰) due to isotopic fractionation during nitrate uptake by phytoplankton. The δ ¹⁵NO ₃ ⁻ value has a roughly linear relationship with the natural logarithm of nitrate concentration (ln[NO ₃ ⁻ ]). However, for values above 150 m depth, the intercept of this linear relationship varies with position from east to west. On the other hand, the data at 200 m depth at all observation stations are concentrated around a single point (ln[NO ₃ ⁻ ] = 2.5 and δ ¹⁵NO ₃ ⁻ = 6.5‰) and do not fit the linear relationships for the shallower values. To examine the meaning of the observed distributions of δ ¹⁵NO ₃ ⁻ and nitrate concentration we developed a box model including nitrogen and nitrogen isotopic cycles. By reproducing the observed relationship between δ ¹⁵NO ₃ ⁻ and nitrate concentration using this model we found that most nitrate is transported horizontally from the eastern equatorial Pacific. We also conducted case studies and investigated the effects of differences in pathways of nitrate transport on the distributions of δ ¹⁵NO ₃ ⁻ and nitrate concentration. From these studies we concluded that the observed linear relationships between δ ¹⁵NO ₃ ⁻ and ln[NO ₃ ⁻ ], having a common slope around 6‰ but different intercepts at each station, are evidence of the significant horizontal transport of nitrate to the surface water in this area.     

Compression mechanism and amorphization of portlandite, Ca(OH)2: structural refinement under pressure

In order to investigate compression mechanism and the pressure-induced amorphization of portlandite, Ca(OH)₂, the crystal structure has been refined up to 9.7?GPa using Rietveld analysis. Angular-dispersive synchrotron X-ray powder diffraction experiments were performed using a diamond anvil cell and an imaging plate at BL-18C in the Photon Factory at KEK, Japan. Compression behavior is highly anisotropic and the c axis is approximately 2.5 times as compressible as the a axis (β_a=0.004, β_c=0.011?GPa^?1). Because the refined fractional coordinate, z, of the O atom increases linearly with pressure, compression along the c axis is due to the shortening of the interlayer spacing. The compression mechanism shows no change up to the amorphization pressure and is basically the same as that of brucite, Mg(OH)₂, observed below 10 GPa. The octahedral regularity of CaO₆ approaches a regular configuration with pressure. The interlayer O…O distance is expected to be about 2.75 Å at the amorphization pressure and should affect hydrogen bonding.     

Influence of export rain ratio changes on atmospheric CO<Subscript>2</Subscript> and sedimentary calcite preservation

The responses of atmospheric pCO₂ and sediment calcite content to changes in the export rain ratio of calcium carbonate to organic carbon are examined using a diffusion-advection ocean biogeochemical model coupled to a one-dimensional sediment geochemistry model. Our model shows that a 25% reduction in rain ratio decreases atmospheric pCO₂ by 59 ppm. This is caused by alkalinity redistribution by a weakened carbonate pump and an alkalinity increase in the whole ocean via carbonate compensation with decreasing calcite burial. The steady state responses of sedimentary calcite content and calcite preservation efficiency are rather insensitive to the deepening of the saturation horizon of 1.9 km. This insensitivity is a result of the reduced deposition flux that decreases calcite burial, counteracting the saturation horizon deepening that increases calcite burial. However, in the first 10,000 years the effect of reduced calcite deposition on the burial change is more prominent; while after 10,000 years, the effect of saturation horizon deepening is more dominant. The lowering of sediment calcite content for the first 10,000 years is effectively decoupled from the 1.9 km downward shift of the saturation horizon. Our results are in part a consequence of the more dominant role that respiration CO₂ plays in sediment calcite dissolution over bottom water chemistry in our control run and support the decoupling of calcite lysocline depth and saturation horizon shifts, as suggested originally by Archer and Maier-Reimer (1994) and Archer et al. (2000).     

O<Subscript>2</Subscript> consumption rate and its isotopic fractionation factor in the deep water of the Philippine Sea

Concentration and stable isotopic compositions (δ ¹⁸O) of dissolved O₂ were measured in seawater samples collected from the Philippine Sea in June 2006. The in-situ O₂ consumption rate and the isotopic fractionation factor (α _r ) during dissolved O₂ consumption were obtained from field observations by applying a vertical one-dimensional advection diffusion model to the deep water mass of about 1000–4000 m. The average O₂ consumption rate and α _r were, respectively, 0.11 ± 0.07 μmol kg⁻¹yr⁻¹ and 0.990 ± 0.001. These estimated values agree well with values from earlier estimations of Pacific deep water. The in-situ O₂ consumption rates are two or more times higher north of 20°N, although the value of α _r was not significantly different between the north and south. Its levels varied rapidly in the water mass of less about 2000 m depth. These results suggest that organic matter from the continent imparts a meaningful contribution to the upper water in the northern part of the area; it might produce the strong O₂ minimum that is evident in the water mass from about 1000–2000 m in the northern part of the Philippine Sea.     

Geophysical survey of the proposed Tsenkher impact structure,Gobi Altai,Mongolia

Abstract– We have performed forward magnetic and gravity modeling of data obtained during the 2007 expedition to the 3.7 km in diameter, circular, Tsenkher structure, Mongolia, in order to evaluate the cause of its formation. Extensive occurrences of brecciated rocks, mainly in the form of an ejecta blanket outside the elevated rim of the structure, support an explosive origin (e.g., cosmic impact, explosive volcanism). The host rocks in the area are mainly weakly magnetic, silica‐rich sandstones, and siltstones. A near absence of surface exposures of volcanic rocks makes any major volcanic structures (e.g., caldera) unlikely. Likewise, the magnetic models exclude any large, subsurface, intrusive body. This is supported by an 8 mGal gravity low over the structure indicating a subsurface low density body. Instead, the best fit is achieved for a bowl‐shaped structure with a slight central rise as expected for an impact crater of this size in mainly sedimentary target. The structure can be either root‐less (i.e., impact crater) or rooted with a narrow feeder dyke with relatively higher magnetic susceptibility and density (i.e., volcanic maar crater). The geophysical signature, the solitary appearance, the predominantly sedimentary setting, and the comparably large size of the Tsenkher structure favor the impact crater alternative. However, until mineralogical/geochemical evidence for an impact is presented, the maar alternative remains plausible although exceptional as it would make the Tsenkher structure one of the largest in the world in an unusual setting for maar craters.     

Geological evolution of Ares Vallis on Mars: Formation by multiple events of catastrophic flooding, glacial and periglacial processes

Ares Vallis is one of the greatest outflow channels of Mars. Using high-resolution images of recent missions to Mars (MGS, 2001 Odyssey, and Mars Express), we investigated Ares Vallis and its valley arms, taking advantage of 3-dimensional analysis performed using the high-resolution stereo capability of the Mars Express High Resolution Stereo Camera (HRSC). In our view, Ares Vallis is characterized by catastrophic flood landscapes partially superimposed by ice-related morphologies. Catastrophic flood landforms include erosional terraces, grooved terrains, streamlined uplands, giant bars, pendant bars, and cataract-like features. Ice-related morphologies include probable kame features, thermokarstic depressions, and patterned grounds. Our investigations outline that throughout the Hesperian age, Ares Vallis and its valley arms had been sculpted by several, time-scattered, catastrophic floods, originating from Iani, Hydaspis and Aram Chaos. Geomorphological evidence suggests that catastrophic floods were ice-covered, and that climatic conditions of Mars at this time were similar to those of the present day. At the end of each catastrophic flood, ice masses grounded, forming a thick stagnant dead-ice body. Each catastrophic flood was followed by a relatively brief period of warmer-wetter climatic conditions, originated as a consequence of catastrophic flooding. During such periods thermokarstic depressions originated, liquid water formed meandering channels, and ice-contact deposits were emplaced by ice-walled streams. Finally, the climate turned into cold-dry conditions similar to the present-day ones, and ice masses sublimated.     

Causes of large-scale landslides in the Lesser Himalaya of central Nepal

Geologically and tectonically active Himalayan Range is characterized by highly elevated mountains and deep river valleys. Because of steep mountain slopes, and dynamic geological conditions, large-scale landslides are very common in Lesser and Higher Himalayan zones of Nepal Himalaya. Slopes along the major highways of central Nepal namely Prithvi Highway, Narayangadh-Mugling Road and Tribhuvan Highway are considered in this study of large-scale landslides. Geologically, the highways in consideration pass through crushed and jointed Kathmandu Nappe affected by numerous faults and folds. The relict large-scale landslides have been contributing to debris flows and slides along the highways. Most of the slope failures are mainly bechanced in geological formations consisting phyllite, schist and gneiss. Laboratory test on the soil samples collected from the failure zones and field investigation suggested significant hydrothermal alteration in the area. The substantial hydrothermal alteration in the Lesser Himalaya during advancement of the Main Central Thrust (MCT) and thereby clay mineralization in sliding zones of large-scale landslide are the main causes of large-scale landslides in the highways of central Nepal. This research also suggests that large-scale landslides are the major cause of slope failure during monsoon in the Lesser Himalaya of Nepal. Similarly, hydrothermal alteration is also significant in failure zone of the large-scale landslides. For the sustainable road maintenance in Nepal, it is of utmost importance to study the nature of sliding zones of large-scale landslides along the highways and their role to cause debris flows and slides during monsoon period.