K‐Th‐Ti systematics and new three‐component mixing model of HED meteorites: Prospective study for interpretation of gamma‐ray and neutron spectra for the Dawn mission

Abstract– The Dawn spacecraft carries a gamma‐ray and neutron detector (GRaND), which will measure and map the abundances of selected elements on the surface of asteroid 4 Vesta. We compare the variability of moderately volatile/refractory incompatible element ratios (K/Th and K/Ti) in howardite, eucrite, and diogenite (HED) meteorites with those in other achondrite suites that represent asteroidal crusts, because these ratios may be accurately measured by GRaND and likely reflect initial chemical compositions of the HED parent body. The K/Th and K/Ti variations can differentiate HED meteorites from angrites and some unique eucrite‐like lithologies. The results suggest that K, Th, and Ti abundances determined from GRaND data could not only confirm that Vesta is the parent body of HED meteorites but might also allow recognition of as‐yet unsampled compositional terranes on Vesta. Besides the K‐Th‐Ti systematics study, we propose a new three‐component mixing model for interpretation of GRaND spectra, required because the spatial resolution of GRaND is coarser than the spectral (compositional) heterogeneity of Vesta’s surface. The mixing model uses abundances of K, Ti, Fe, and Mg that will be analyzed more accurately than other prospective GRaND‐analyzed elements. We examine propagated errors due to GRaND analytical uncertainties and intrinsic errors that stem from an assumption introduced into the mixing model. The error investigation suggests that the mixing model can adequately estimate not only the diogenite/eucrite mixing ratio but also the abundances of most major and minor elements within the GRaND propagated errors.     

Tidal Mixing in the Kuril Straits and Its Impact on Ventilation in the North Pacific Ocean

A numerical study using a 3-D nonhydrostatic model has been applied to baroclinic processes generated by the K ₁ tidal flow in and around the Kuril Straits. The result shows that large-amplitude unsteady lee waves are generated and cause intense diapycnal mixing all along the Kuril Island Chain to levels of a maximum diapycnal diffusivity exceeding 10³ cm²s⁻¹. Significant water transformation by the vigorous mixing in shallow regions produces the distinct density and potential vorticity (PV) fronts along the Island Chain. The pinched-off eddies that arise and move away from the fronts have the ability to transport a large amount of mixed water (∼14 Sv) to the offshore regions, roughly half being directed to the North Pacific. These features are consistent with recent satellite imagery and in-situ observations, suggesting that diapycnal mixing within the vicinity of the Kuril Islands has a greater impact than was previously supposed on the Okhotsk Sea and the North Pacific. To examine this influence of tidal processes at the Kurils on circulations in the neighboring two basins, another numerical experiment was conducted using an ocean general circulation model with inclusion of tidal mixing along the islands, which gives a better representation of the Okhotsk Sea Mode Water than in the case without the tidal mixing. This is mainly attributed to the added effect of a significant upward salt flux into the surface layer due to tidal mixing in the Kuril Straits, which is subsequently transported to the interior region of the Okhotsk Sea. With a saline flux into the surface layer, cooling in winter in the northern part of the Okhotsk Sea can produce heavier water and thus enhance subduction, which is capable of reproducing a realistic Okhotsk Sea Mode Water. The associated low PV flux from the Kuril Straits to the open North Pacific excites the 2nd baroclinic-mode Kelvin and Rossby waves in addition to the 1st mode. Interestingly, the meridional overturning in the North Pacific is strengthened as a result of the dynamical adjustment caused by these waves, leading to a more realistic reproduction of the North Pacific Intermediate Water (NPIW) than in the case without tidal mixing. Accordingly, the joint effect of tidally-induced transport and transformation dominating in the Kuril Straits and subsequent eddy-transport is considered to play an important role in the ventilation of both the Okhotsk Sea and the North Pacific Ocean. This revised version was published online in July 2006 with corrections to the Cover Date.     

Seismic capacity of retrofitted beam–column connections in high‐rise steel frames when subjected to long‐period ground motions

The seismic capacity of beam‐to‐column connections in steel high‐rise frames is a matter of concern, particularly when they are subjected to long‐period ground motions. A previous full‐scale shaking table test conducted at the E‐Defense National Research Institute for Earth Science and Disaster Prevention in Japan disclosed cracks and fractures in such beam‐to‐column connections. This paper examines the effects of three types of beam‐to‐column connection retrofit: supplemental welds, wing plates, and a haunch. Quasi‐static member tests and a series of shaking table tests applied to a full‐scale specimen are conducted to quantify the respective performances of the retrofit schemes. The performance of a total of 28 connections tested by the member and shaking table tests is evaluated together with that of an additional 12 unretrofitted connections tested in the previous test. When the supplemental welds are applied only to the shear tab to the web, the connection fractures at the same instant as the connection without retrofit. The corresponding cumulative plastic rotation is not improved. When the supplement welds are further applied to the web‐to‐column connection, strain concentration at the bottom flange, primarily promoted by the presence of the RC floor slab, is significantly reduced, and the cumulative plastic rotation capacity is increased to eight times that of the connection without retrofit. For the wing plate connection and haunch connection, the critical section is moved from the beam end to the beam cross‐section corresponding to the tip of the wing plates or haunch, resulting in an improvement of ductility by eight times that of the unretrofitted connection. Copyright © 2011 John Wiley & Sons, Ltd.     

Effects of bedrock groundwater discharge on spatial variability of dissolved carbon,nitrogen, and phosphorous concentrations in stream water within a forest headwater catchment

The quantitative evaluation of the effects of bedrock groundwater discharge on spatial variability of stream dissolved organic carbon (DOC), dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorous (DIP) concentrations has still been insufficient. We examined the relationships between stream DOC, DIN and DIP concentrations and bedrock groundwater contribution to stream water in forest headwater catchments in warm-humid climate zones. We sampled stream water and bedrock springs at multiple points in September and December 2013 in a 5 km² forest headwater catchment in Japan and sampled groundwater in soil layer in small hillslopes. We assumed that stream water consisted of four end members, groundwater in soil layer and three types of bedrock groundwater, and calculated the contributions of each end member to stream water from mineral-derived solute concentrations. DOC, DIN and DIP concentrations in stream water were compared with the calculated bedrock groundwater contribution. The bedrock groundwater contribution had significant negative linear correlation with stream DOC concentration, no significant correlation with stream DIN concentration, and significant positive linear correlation with stream DIP concentration. These results highlighted the importance of bedrock groundwater discharge in establishing stream DOC and DIP concentrations. In addition, stream DOC and DIP concentrations were higher and lower, respectively, than those expected from end member mixing of groundwater in soil layer and bedrock springs. Spatial heterogeneity of DOC and DIP concentrations in groundwater and/or in-stream DOC production and DIP uptake were the probable reasons for these discrepancies. Our results indicate that the relationships between spatial variability of stream DOC, DIN and DIP concentrations and bedrock groundwater contribution are useful for comparing the processes that affect stream DOC, DIN and DIP concentrations among catchments beyond the spatial heterogeneity of hydrological and biogeochemical processes within a catchment.     

Wind-Tunnel and Numerical Simulations of the Coastal Thermal Internal Boundary Layer

Wind-tunnel experiments in a thermally stratified wind tunnel and direct numerical simulations were performed to simulate the thermal internal boundary layer (TIBL) that developed over a coastal area in a sea-breeze flow. The results of the simulations were analyzed to investigate turbulence structure in the TIBL. To study the effects of the atmospheric stability over the sea on the TIBL, two vertical profiles of temperature were created in the upstream portion of the wind-tunnel experiment and the direct numerical simulation. Turbulence statistics of the TIBL changed significantly according to the temperature profile over the sea, indicating that the stability of the flow over the sea has a significant effect on the structure and turbulence characteristics of the TIBL. Furthermore, the TIBL heights were estimated from the vertical profiles of the local Richardson number. The estimated TIBL heights agreed with those predicted by a pre-existing relation, suggesting that both the wind-tunnel experiment and the direct numerical simulation accurately reproduced the growth of the TIBL.     

Development of a New Method of Extraction of Interstitial Water from Low‐Porosity Consolidated Sediments Recovered During Super‐Deep Drilling Projects

During the Integrated Ocean Drilling Program (IODP) Expedition 338, several methods were tested for the extraction of interstitial water in consolidated, low‐porosity deep‐sea sediments from Site C0002 in the Kumano Basin. On the basis of those tests, we propose a modified ground rock interstitial normative determination (GRIND) method of extraction of interstitial water. In separate runs of the new method, sediment samples were ground in a ball mill with either ultrapure water or a solution of HNO₃. The interstitial water was then extracted with a conventional squeezer. Sufficient solution was extracted by this method to analyse most major and a few minor components of interstitial water that were comparable to those previously reported for samples extracted by the conventional squeezing method. The new method requires much smaller amounts of sediment than that of the conventional method and will be useful for analysis of samples recovered during super‐deep drilling programmes.     

Estimation of sub-annual inter-catchment groundwater flow using short-term water balance method

Predicting inter-catchment groundwater flow (IGF) is essential because IGF greatly affects stream water discharge and water chemistry. However, methods for estimating sub-annual IGF and clarifying its mechanisms using minimal data are limited. Thus, we quantified the sub-annual IGF and elucidated its driving factors using the short-term water balance method (STWB) for three forest headwater catchments in Japan (named here catchment A, B and As). Our previous study using the chloride mass balance indicated that annual IGF of catchment A (49.0 ha) can be negligible. Therefore, we calculated the daily evapotranspiration (ET) rate using the Priestley–Taylor expression and the 5-year water balance in catchment A (2010–2014). The sub-annual IGF of the three catchments was then calculated by subtracting the ET rate from the difference between rainfall and stream discharge during the sub-annual water balance periods selected using the STWB. The IGF rates of catchment B (7.0 ha), which is adjacent to catchment A, were positive in most cases, indicating that more groundwater flowed out of the catchment than into it, and exhibited positive linear relationships with rainfall and stream discharge. This suggested that as the catchments became wetter, more groundwater flowed out of catchment B. Conversely, the IGF rates of catchment As (5.3 ha), included in catchment A, were negative in most cases, indicating that more groundwater flowed into the catchment than out from it, and exhibited negative linear relationships with rainfall and stream discharge. Given the topography of the catchments studied, infiltration into the bedrock was the probable reason for the IGF outflow from catchment B. We hypothesized that in catchment As, the discrepancy between the actual hydrological boundary and the surface topographic boundary could have caused an IGF inflow. This study provides a useful tool for determining an IGF model structure to be incorporated into rainfall-runoff models.     

Virtual velocity of sand transport in water

Using the 160‐m‐long flume at Tsukuba University we undertook an experiment to provide a first estimate of the virtual velocity of sand in the size range 0.5–2.0 mm. For the flow velocity used in our experiment this sediment‐size range would conventionally be regarded as suspended sediment. The virtual velocity was found to be 37–41% of the flow velocity. Paradoxically, virtual velocity decreases as particle size decreases. Such a lower virtual velocity of finer sediment is not inconceivable. First, trapping of the sediment appears to be a function of bed roughness, and there is a probable relationship between bed roughness and trapping efficiency for particles of different sizes. Second, finer particles are more likely to find sheltered positions on a rough bed and thus experience lower mobility, relative to the more exposed coarser grains, as observed for bedload transport. Third, the virtual velocity of particles undergoing bedload transport has been found, in some instances, to be lower for finer clasts. We combine our data with previous studies of virtual velocity of bedload to develop, for the first time, a hypothesis for a holistic analysis of sediment movement in rivers. Copyright © 2017 John Wiley & Sons, Ltd.     

Kizawa tunnel cracked on 23 October 2004 Mid-Niigata earthquake: An example of earthquake-induced damage to tunnels in active-folding zones

Earthquakes in active-folding zones often trigger long-lasting landform changes. Since an underground structure closely follows the motion of its surrounding soils and rocks even after it was damaged in an intense earthquake, experts in charge of reconstruction have to wait until they are convinced that the soils and rocks have been stabilized. Kizawa tunnel was seriously cracked during the 23 October 2004 Mid-Niigata Earthquake. The upper half of the tunnel's cross-section near the north mouth shifted about 0.5 m sideways. Since a ring-shaped cross-section of a tunnel sustains the surrounding soil pressure, this crack pattern seemed to be serious. The authors collaborated with the Nagaoka Regional Development Bureau, Niigata Prefectural Government, in investigating the causes of the damage and in conducting long-term observation of the soils and rocks. This paper summarizes some findings for rational rehabilitations through the investigations.