Application of Continuous 222Rn Monitor with Dual Loop System in a Small Lake

To estimate the spatial distribution of groundwater discharge from the bottom of a small lake of Kumamoto in Japan, we applied continuous radon measurements with a dual loop system and verified the results obtained using the radon method by visual diving surveys. Time‐shifting correction in the dual‐loop system is reasonable to obtain the true radon activity in water. Distributions of radon activity and water temperature in the study area reveal the effects on groundwater discharge and mixing situation of lake water. The estimated discharge zone ascertained using the radon method agrees with the groundwater discharge distribution observed through diving surveys. Although the data resolution of the radon method is much greater than the width of observed discharge zones, the general distribution of groundwater discharge is recognizable. The dual loop system of radon measurement is useful for smaller areas.     

Correction: Impact of excessive groundwater pumping on rejuvenation processes in the Bandung basin (Indonesia) as determined by hydrogeochemistry and modeling

In the Bandung basin, Indonesia, excessive groundwater pumping caused by rapid increases in industrialization and population growth has caused subsurface environmental problems, such as excessive groundwater drawdown and land subsidence. In this study, multiple hydrogeochemical techniques and numerical modeling have been applied to evaluate the recharge processes and groundwater age (rejuvenation). Although all the groundwater in the Bandung basin is recharged at the same elevation at the periphery of the basin, the water type and residence time of the shallow and deep groundwater could be clearly differentiated. However, there was significant groundwater drawdown in all the depression areas and there is evidence of groundwater mixing between the shallow and deep groundwater. The groundwater mixing was traced from the high dichlorodifluoromethane (CFC-12) concentrations in some deep groundwater samples and by estimating the rejuvenation ratio (R) in some representative observation wells. The magnitude of CFC-12 concentration, as an indicator of young groundwater, showed a good correlation with R, determined using ¹⁴C activity in samples taken between 2008 and 2012. These correlations were confirmed with the estimation of vertical downward flux from shallower to deeper aquifers using numerical modeling. Furthermore, the change in vertical flux is affected by the change in groundwater pumping. Since the 1970s, the vertical flux increased significantly and reached approximately 15% of the total pumping amount during the 2000s, as it compensated the groundwater pumping. This study clearly revealed the processes of groundwater impact caused by excessive groundwater pumping using a combination of hydrogeochemical methods and modeling.

     

The importance of local mean time in remote sensing for mapping megatidal zones

The local mean time is rarely debated in applied remote sensing, although it is a key parameter, especially for the geological mapping of coastal areas with high tidal ranges. French test sites are used to illustrate the role of this parameter. Depending from location and for an average time of acquisition of 11:00 UTC, the exposed tidal flat ranges from 55% (Baie des Veys), 80% (Mont Saint-Michel) to 100% (Cap-Ferret). Eight multisource satellite images were used in the Mont Saint-Michel Bay to draw the limit of the sea and evaluate the corresponding tidal flat's surfaces for various times of acquisition. The relation emphasizes some geometrical properties of the lower part of the intertidal zone. A NW–SE profile allows one to identify a distal part with a slope of 0.2% and a proximal part with a slope of only 0.06%. JERS 1-OPS and ALOS-AVNIR-2 data have been also compared to evaluate the progression of the halophytic vegetation, covering more than 6 km² between 1992 and 2007. From a methodological point of view, the ALOS-AVNIR-2 acquired on October 2007 is the first satellite data covering the Mont Saint-Michel Bay with a water elevation of only 2.56 m, i.e. a tidal flat free of water over 80% of its surface.     

Measurement of evapotranspiration in a winter wheat field

Daily evapotranspiration from a winter wheat field on the North China Plain measured by large‐scale weighing lysimeter was linearly related to that measured by the Bowen ratio energy balance (BREB) technique. Soil evaporation averaged about 23·6% of evapotranspiration from the post‐winter dormancy revival stage to the grain ripening stage in 1999. On clear days during winter dormancy, about half of the net radiation flux R_n was used to warm soil. During the revival stage, conductive heat flux G also used most of the incoming R_n, but the ratio of latent heat flux λE to R_n increased. During the stem‐extension stage, λE was about 50% of R_n; thereafter, λE/R_n increased continually, but G remained less than 10% of R_n. During the ripening stage, λE was almost 90% of R_n. Evaporative fraction (EF) can be expressed as a function of plant status and atmospheric boundary layer conditions. The relationship between EF and available energy under moderate air temperature and vapour pressure deficit conditions was examined for five combinations of aerodynamic and canopy conductance. Although the theoretical relationship indicates that EF should be highly correlated to soil water content, the correlation has been difficult to identify under field conditions. However, we observed that there exists a threshold value of R_n ? G, above which EF is less than 1·0, and that the threshold value is lower under soil‐water deficit conditions than under abundant soil‐water conditions. Copyright © 2002 John Wiley & Sons, Ltd.     

Content of plutonium,thorium and protactinium in sea water and recent coral in the North Pacific

The contents of plutonium isotopes (²³⁹Pu and²³⁸Pu), thorium isotopes (²³²Th,²³⁰Th and²²⁸Th) and protactinium-231 in sea water collected in the North Pacific, the East China Sea and the Japan Sea were determined. These nuclides were sequentially analyzed byα-ray spectrometry after separating them mainly with solvent extraction technique. The contents of²³⁹Pu in surface sea water ranged from 0.6 to 1.6 pCi/10001,²³⁸Pu/²³⁹Pu activity ratios being 0.2～0.7. The²²⁸Th/²³²Th activity ratios for the North Pacific waters varied between 7.6 and 30, whereas the sample from the East China Sea showed the very high value, 65. The contents of²³¹Pa are less than 6 percent of that in equilibrium with its parent²³⁵U. Furthermore, the analysis of plutonium isotopes in recent coral from Yoron Island was carried out and it was confirmed that plutonium isotopes have concentrated in recent coral with the concentration factor of about 1～2×10³.     

Fracture-zone conditions on a recently active fault: insights from mineralogical and geochemical analyses of the Hirabayashi NIED drill core on the Nojima fault, southwest Japan, which ruptured in the 1995 Kobe earthquake

An 1800-m-deep borehole into the Nojima fault zone was drilled at Nojima-Hirabayashi, Japan, after the 1995 Hyogo-ken Nanbu (Kobe) earthquake. Three possible fracture zones were detected at depths of about 1140, 1300, and 1800 m. To assess these fracture zones in this recently active fault, we analyzed the distributions of fault rocks, minerals, and chemical elements in these zones. The central fault plane in the shallowest fracture zone was identified by foliated blue-gray gouge at a depth of 1140 m. The degree of fracturing was evidently greater in the hanging wall than in the footwall. Minerals detected in this zone were quartz, orthoclase, plagioclase, and biotite, as in the parent rock (granodiorite), and also kaolinite, smectite, laumontite, stilbite, calcite, ankerite, and siderite, which are related to hydrothermal alteration. Biotite was absent in both the hanging wall and footwall across the central fault plane, but it was absent over a greater distance from the central fault plane in the hanging wall than in the footwall. Major element compositions across this zone suggested that hydrothermal alteration minerals such as kaolinite and smectite occurred across the central fault plane for a greater distance in the hanging wall than in the footwall. Similarly, H₂O+ and CO₂ had higher concentrations in the hanging wall than in the footwall. This asymmetrical distribution pattern is probably due to the greater degree of wall–rock fracturing and associated alteration in the hanging wall. We attributed the characteristics of this zone to fault activity and fluid–rock interactions. We analyzed the other fracture zones along this fault in the same way. In the fracture zone at about 1300 m depth, we detected the same kinds of hydrothermal alteration minerals as in the shallower zone, but they were in fewer samples. We detected relatively little H₂O+ and CO₂, and little evidence for movement of the major chemical elements, indicating little past fluid–rock interaction. In the fracture zone at about 1800 m depth, H₂O+ and CO₂ were very enriched throughout the interval, as in the fracture zone at about 1140 m depth. However, smectite was absent and chlorite was present, indicating the occurrence of chloritization, which requires a temperature of more than 200 °C. Only smectite can form under the present conditions in these fracture zones. The chloritization probably occurred in the past when the fracture zone was deeper than it is now. These observations suggest that among the three fracture zones, that at about 1140 m depth was the most activated at the time of the 1995 Hyogo-ken Nanbu (Kobe) earthquake.     

Fragility curves of concrete bridges retrofitted by column jacketing

The Northridge earthquake inflicted various levels of damage upon a large number of Caltrans’ bridges not retrofitted by column jacketing. In this respect, this study represents results of fragility curve development for two (2) sample bridges typical in southern California, strengthened for seismic retrofit by means of steel jacketing of bridge columns. Monte Carlo simulation is performed to study nonlinear dynamic responses of the bridges before and after column retrofit. Fragility curves in this study are represented by lognormal distribution functions with two parameters and developed as a function of PGA. The sixty (60) ground acceleration time histories for the Los Angeles area developed for the Federal Emergency Management Agcncy (FEMA) SAC (SEAOC-ATC-CUREe) steel project are used for the dynamic analysis of the bridges. The improvement in the fragility with steel jacketing is quantified by comparing fragility curves of the bridge before and after column retrofit. In this first attempt to formulate the problem of fragility enhancement, the quantification is made by comparing the median values of the fragility curves before and after the retrofit. Under the hypothesis that this quantification also applies to empirical fragility curves developed on the basis of Northridge earthquake damage, the enhanced version of the empirical curves is developed for the ensuing analysis to determine the enhancement of transportation network performance due to the retrofit. Supported by: MCEER/FHWA under Contract No.DTFH 61-98-C-00094 and Caltrans under Contract No.59A0304     

Fractionation of azaarenes during oil migration

A comparative study of alkylbenzoquinolines in crude oils and rock extracts (bitumens) from Japan and Sumatra shows that the ratios of nitrogen-masked isomers (NMIs) to nitrogen-exposed isomers (NEIs), and the ratio of higher homologs to lower homologs is higher in crude oils than in corresponding bitumens. Also, a regular increase in the ratios of NMIs to NEIs with increasing migration distance is observed for a series of crude oils from the Sarukawa Oil Field, northeastern Japan. These results are attributed to the preferential migration of NMIs caused by their weak adsorption on clay minerals and/or their low solubility in interstitial water, and the selective removal of lower honologs caused by their irreversible adsorption onto clays during oil migration, which are regarded as geochromatographic phenomena. It is suggested that those ratios can be used to estimate the degree of fractionation of oils during primary and secondary migration.     

Effect of the angle of seismic incidence on the fragility curves of bridges

This study examines the effect of the angle of seismic incidence θ on the fragility curves of bridges. Although currently, fragility curves of bridges are usually expressed only as a function of intensity measure of ground motion (IM) such as peak ground acceleration, peak ground velocity, or S_a(ω₁), in this study they are expressed as a function of IM with θ as a parameter. Lognormal distribution function is used for this purpose with fragility parameters, median c_m and standard deviation ζ to be estimated for each value of θ chosen from 0 < θ < 360°. A nonlinear 3D finite element dynamic analysis is performed, and key response values are calculated as demand on the bridge under a set of acceleration time histories with different IM values representing the seismic hazard in Los Angeles area. This method is applied to typical straight reinforced concrete bridges located in California. The results are validated with existing empirical damage data from the 1994 Northridge earthquake. Even though the sample bridges are regular and symmetric with respect to the longitudinal axis, the results indicate that the weakest direction is neither longitudinal nor transverse. Therefore, if the angle of seismic incidence is not considered, the damageability of a bridge can be underestimated depending on the incidence angle of seismic wave. Because a regional highway transportation network is composed of hundreds or even thousands of bridges, its vulnerability can also be underestimated. Hence, it is prudent to use fragility curves taking the incident angle of seismic waves into consideration as developed here when the seismic performance of a highway network is to be analyzed. Copyright © 2012 John Wiley & Sons, Ltd.