基于数值模拟的区域性地下水补给过程实例研究          下载免费PDF全文

黄金柏  魏帆  李德标  王斌  桧谷治 《水文》2014,34(3):24-30

研究主要目的是以数值模拟的方法,再现选定的研究区域20世纪70~90年代地下水位处于较低水平的过程并推求地下水的补给过程。研究区为某流域入海口前10×12km2的矩形区域,基于研究区土层纵断面的物理条件,在平面二维的基础上,考虑含水层垂向水收支成分,利用地下水计算的基本方程式开发地下水准三维数值计算模型,以数值模拟的方法验证模型效率。对地下水位数值模拟的结果表明,模型效率可以达到80%以上。基于1966~2005年的数值计算结果,推求了研究区各含水层的补给过程。研究结果可为区域性地下水数值模拟技术及地下水资源量的评估等研究提供方法上的借鉴。  相似文献   

Eocene volcanism during the incipient stage of Izu–Ogasawara Arc: Geology and petrology of the Mukojima Island Group,the Ogasawara Islands     

Kyoko Kanayama  Susumu Umino  Osamu Ishizuka 《Island Arc》2012,21(4):288-316

The Ogasawara Islands mainly comprise Eocene volcanic strata formed when the Izu–Ogasawara–Mariana Arc began. We present the first detailed volcanic geology, petrography and geochemistry of the Mukojima Island Group, northernmost of the Ogasawara Islands, and show that the volcanic stratigraphy consists of arc tholeiitic rocks, ultra‐depleted boninite‐series rocks, and less‐depleted boninitic andesites, which are correlatable to the Maruberiwan, Asahiyama and Mikazukiyama Formations on the Chichijima Island Group to the south. On Chichijima, a short hiatus is identified between the Maruberiwan (boninite, bronzite andesite, and dacite) and Asahiyama Formation (quartz dacite and rhyolite). In contrast, these lithologies are interbedded on Nakodojima of the Mukojima Island Group. The stratigraphically lower portion of Mukojima is mainly composed of pillow lava, which is overlain by reworked volcaniclastic rocks in the middle, whereas the upper portion is dominated by pyroclastic rocks. This suggests that volcanic activity now preserved in the Mukojima Island Group records growth of one or more volcanoes, beginning with quiet extrusion of lava under relatively deep water followed by volcaniclastic deposition. These then changed into moderately explosive eruptions that took place in shallow water or above sea level. This is consistent with the uplift of the entire Ogasawara Ridge during the Eocene. Boninites from the Mukojima Island Group are divided into three types on the basis of geochemistry. Type 1 boninites have high SiO₂ (>57.0 wt.%) and Zr/Ti (>0.022) and are the most abundant type in both Mukojima and Chichijima Island Groups. Type 2 boninites have low SiO₂ (<57.1 wt.%) and Zr/Ti (<0.014). Type 3 boninites have 57.6–60.7 wt.% SiO₂ and are characterized by high CaO/Al₂O₃ (0.9–1.1). Both type 2 and 3 boninites are common on Mukojima but are rare in the Chichijima Island Group.  相似文献   

Tsunami deposit associated with the 2011 Tohoku‐oki tsunami in the Hasunuma site of the Kujukuri coastal plain,Japan          下载免费PDF全文

Dan Matsumoto  Yuki Sawai  Koichiro Tanigawa  Osamu Fujiwara  Yuichi Namegaya  Masanobu Shishikura  Kyoko Kagohara  Haruo Kimura 《Island Arc》2016,25(5):369-385

We describe the detailed sedimentary characteristics of a tsunami deposit associated with the 2011 Tohoku‐oki tsunami in Hasunuma, a site on the Kujukuri coastal plain, Japan. The thick tsunami deposit was limited to within 350 m from the coastline whereas the inundation area extended about 1 km from the coastline. The tsunami deposit was sampled by excavation at 29 locations along three transects and studied using peels, soft‐X imaging and grain‐size analysis. The deposit covers the pre‐existing soil and reached a maximum measured thickness of 35 cm. It consists mainly of well‐sorted medium to fine sand. On the basis of sedimentary structures and changes in grain size, we divided the tsunami deposit into several sedimentary units, which may correspond to multiple inundation flows. The numbers of units and their sedimentary features vary among the three transects, despite the similar topography. This variation implies a considerable influence of local effects such as elevation, vegetation, microtopography, and distance from footpaths, on the tsunami‐related sedimentation.  相似文献   

Distribution of nitrous oxide dissolved in water masses in the eastern subtropical North Pacific and its origin inferred from isotopomer analysis     

Ayako Fujii  Sakae Toyoda  Osamu Yoshida  Shuichi Watanabe  Ken’ichi Sasaki  Naohiro Yoshida 《Journal of Oceanography》2013,69(2):147-157

N₂O concentration and its isotopomer ratios were measured over a wide area from San Diego to Honolulu in the eastern subtropical North Pacific (ESNP). Waters in the study area had an N₂O maximum (38.2–50.5 nmol kg^?1) at 600–1000 m depth, which is similar to the profiles obtained previously in other areas in the North Pacific. We separated the seawater into five water masses (two for the surface layer, two for the middle layer, and one for the deep layer) and deduced N₂O production–consumption mechanisms in each water body by use of N₂O isotopomer ratios. The results showed that the mechanisms differ slightly among water masses. In the “coastal” surface layer, N₂O is produced by nitrification (NH₂OH oxidation). In the “open ocean” surface layer, it is produced mainly by nitrifier denitrification and to a lesser extent by nitrification under substrate-limited conditions. In both “upwelling” and “open ocean” middle layers it is produced mainly by denitrification and to a lesser extent by nitrifier denitrification. It is also partly reduced. In the deep layer, it is produced predominantly by denitrification with partial reduction. In this way, isotopomers aid elucidation of production–consumption mechanisms of N₂O in the sea even though the mechanisms cannot always be ascertained.  相似文献   

The temporal record and sources of atmospherically deposited fly-ash particles in Lake Akagi-konuma,a Japanese mountain lake     

Osamu Nagafuchi  Neil L. Rose  Akira Hoshika  Kenichi Satake 《Journal of Paleolimnology》2009,42(3):359-371

Fly-ash particles comprising spheroidal carbonaceous particles (SCP) and inorganic ash spheres (IAS), produced from industrial fossil-fuel combustion, are found in lake sediments throughout the world where they provide an historical record of atmospheric pollutant deposition. These particles have been widely used to assess the temporal and spatial distribution of industrial atmospheric pollution in both freshwater and terrestrial environments in Europe and the USA. However, there have been very few palaeolimnological fly-ash studies undertaken in Japan and none in Japanese mountain lakes. Here, we present the historical SCP and IAS records from a radiometrically dated sediment core taken from Lake Akagi-konuma (36°31′ 54″N, 139°11′ 32″E; elevation 1,470 m) located 100 km north-west of Tokyo. Meteorological data and back trajectory analyses confirm potential sources both within Japan and further afield in China and South Korea. SCP contamination began in the 1950s and increased rapidly to a peak in the mid-1980s. It is thought this represents contamination of Japanese origin, principally oil-fired power stations within 150 km of the lake. The profile of IAS, almost solely coal-derived, shows a rapid increase in the 1970s, in contrast to the record of coal consumption in Japan. The IAS record is therefore thought to reflect long-range transport from coal combustion sources in eastern China which started to expand in the 1970s. This raises concerns over the potential impact on Japanese mountain areas from recent rapid increases in, and predicted acceleration of, emissions from this industrial process. The scale of SCP contamination recorded in Lake Akagi-konuma is equivalent to moderately impacted mountain lakes in Europe, but is at the upper end of the range for remote lakes in the western United States.  相似文献   

Frequency–Magnitude Distribution of −3.7 ≤ M W  ≤ 1 Mining-Induced Earthquakes Around a Mining Front and b Value Invariance with Post-Blast Time     

Makoto Naoi  Masao Nakatani  Shigeki Horiuchi  Yasuo Yabe  Joachim Philipp  Thabang Kgarume  Gilbert Morema  Sifiso Khambule  Thabang Masakale  Luiz Ribeiro  Koji Miyakawa  Atsushi Watanabe  Kenshiro Otsuki  Hirokazu Moriya  Osamu Murakami  Hironori Kawakata  Nana Yoshimitsu  Anthony Ward  Ray Durrheim  Hiroshi Ogasawara 《Pure and Applied Geophysics》2014,171(10):2665-2684

We investigated frequency-magnitude distribution (FMD) of acoustic emissions (AE) occurring near an active mining front in a South African gold mine, using a catalog developed from an AE network, which is capable of detecting AEs down to M _W  ?5. When records of blasts were removed, FMDs of AEs obeyed a Gutenberg?Richter law with similar b values, not depending on post-blasting time from the initial 1-min interval through more than 30 h. This result denies a suggestion in a previous study (Richardson and Jordan Bull Seismol Soc Am, 92:1766–1782, 2002) that new fractures generated by blasting disturb the size distribution of background events, which they interpreted as slip events on existing weak planes. Our AE catalog showed that the GR law with b ～ 1.2 was valid between M _W  ?3.7 and 0 for AEs around the mining front. Further, using the mine’s seismic catalog, which covers a longer time period of the same area, we could extend the validity range of the GR law with the same b value up to M _W 1.  相似文献   

Two contrasting magmatic types coexist after the cessation of back-arc spreading   总被引：7，自引：0，他引：7  

Osamu Ishizuka  Makoto Yuasa  Rex N. Taylor  Izumi Sakamoto 《Chemical Geology》2009,266(3-4):283-305

Amongst island arcs, Izu–Bonin is remarkable as it has widespread, voluminous and long-lived volcanism behind the volcanic front. In the central part of the arc this volcanism is represented by a series of seamount chains which extend nearly 300 km into the back-arc from the volcanic front. These back-arc seamount chains were active between 17 and 3 Ma, which is the period between the cessation of spreading in the Shikoku Basin and the initiation of currently active rifting just behind the Quaternary volcanic front. In this paper we present new age, chemical and isotopic data from the hitherto unexplored seamounts which formed furthest from the active volcanic front. Some of the samples come from volcanoes at the western limit of the back-arc seamount chains. Others are collected from seamounts of various sizes which lie on the Shikoku Basin crust (East Shikoku Basin seamounts). The westernmost magmatism we have sampled is manifested as a series of volcanic edifices that trace the extinct spreading centre of the Shikoku Basin known as the Kinan Seamount Chain (KSC).Chemically, enrichment in fluid-mobile elements and depletion in HFSE relative to MORB indicates that the back-arc seamount chains and the East Shikoku Basin seamounts have a significant contribution of slab-derived material. In this context these volcanoes can be regarded as a manifestation of arc magmatism and distinct from the MORB-like lavas of the Shikoku back-arc basin. ⁴⁰Ar/³⁹Ar ages range from 15.7 to 9.6 Ma for the East Shikoku Basin seamounts, indicating this arc magmatism started immediately after the Shikoku Basin stopped spreading.Although the KSC volcanoes are found to be contemporaneous with the seamount chains and East Shikoku Basin seamounts, their chemical characteristics are very different. Unlike the calc-alkaline seamount chains, the KSC lavas range from medium-K to shoshonitic alkaline basalt. Their trace element characteristics indicate the absence of a subduction influence and their radiogenic isotope systematics reflect a mantle source combining a Philippine Sea MORB composition and an enriched mantle component (EM-1). One of the most remarkable features of the KSC is that their geochemistry has a distinct temporal variation. Element ratios such as Nb/Zr and concentrations of incompatible elements such as K₂O increase with decreasing age and reach a maximum at ca. 7 Ma when the KSC ceased activity.Based on the chemical and temporal information from all the data across the back-arc region, we have identified two contrasting yet contemporaneous magmatic provinces. These share a tectonic platform, but have separate magmatic roots; one stemming from subduction flux and the other from post-spreading asthenospheric melting.  相似文献   

花岗岩变形破坏的阶段性模型--应力速度及预存微裂纹密度对断层形成过程的影响   总被引：2，自引：0，他引：2       下载免费PDF全文

雷兴林  佐藤隆司  西泽修 《地震地质》2004,26(3):436-449

依据对具有较高微裂纹密度的筑波花岗岩和极低微裂纹密度的花岗斑岩 2种极端的岩石标本、在等应力速率的快速加载 (约 6MPa/min)和蠕变加载 (轴向应力保持在约 95 %破坏强度 ) 2个极端的加载条件下的实验结果 ,讨论了预存微裂纹密度与加载速度对多晶质结晶岩变形破坏过程的影响。实验中利用高速多通道声发射波形数字记录系统 (每秒可记录多达 5 0 0 0个声发射事件的 32通道波形 ) ,获得了岩石标本破坏前微破裂活动的详细时空分布数据。声发射的发生率、震级 -频度关系中的b值及震源的空间分布揭示出岩石变形破坏过程中微破裂活动具有 3个典型阶段 :初期阶段、第 2阶段和成核阶段。尤其是在成核阶段 ,还观测到发生率和b值有大幅度前兆性起伏。一般而言 ,在相同加载条件下预存微破裂密度越高 ,或对同一岩石加载速度越慢 ,对应的断层成核过程就越长 ,因此最终破坏的可预报性也越高。为了进一步探讨微破裂活动的阶段性特征及其物理本质 ,还利用亚临界破裂扩展模型对声发射数据进行了理论分析  相似文献   

Presence of high nitrate to phosphate ratio subsurface water in the Tsushima Strait during summer     

Taketoshi Kodama  Akihiko Morimoto  Tetsutaro Takikawa  Masashi Ito  Yosuke Igeta  Shoko Abe  Ken-Ichi Fukudome  Naoto Honda  Osamu Katoh 《Journal of Oceanography》2017,73(6):759-769

To identify water with an excess nitrate concentration to phosphate ratio and its potential source, the nutrient concentrations in the Tsushima Strait (TSS) were investigated over ten cruises in August and September 2007–2014, excluding 2010. On the basis of the Redfield ratio, water with an excess nitrate concentration of >1 μM (positive ExNOx water) was identified below the surface mixed layer during four cruises in 2011–2013. Positive ExNOx water was present mainly in less-saline (<34) waters with a density of 22–25 σ _θ , and 25–75 m depth. However, in August 2012, positive ExNOx was detected in dense (25–25.5 σ _θ ) and deep (50–110 m depth) waters near the salinity maximum, although the salinity during this period was significantly lower than that in other years. The horizontal length of positive ExNOx water was >100 km across the TSS during two cruises in August 2012 and September 2013, respectively. According to multi-regression analysis conducted on the silicate concentration, temperature, and salinity, the silicate concentration was increased in the less-saline subsurface water. The required amount of original freshwater was 10^8–9 m³ day^?1 based on the excess nitrate concentration. This evidence indicates that the positive ExNOx water originated from large river waters such as the Changjiang. Thus, discharged water from the rivers of the East Asia is contributing to the increased N:P ratio in the Tsushima Warm Current, southern Japan Sea.  相似文献   

Short-term flow fluctuations in Onagawa Bay,Japan, as revealed by long-term mooring observation     

Daisuke Takahashi  Kenji Kaneko  Yasushi Gomi  Yuki Minegishi  Michihiro Shoji  Hikaru Endo  Akihiro Kijima 《Journal of Oceanography》2017,73(1):67-86

Short-term flow fluctuations in the southern central part of Onagawa Bay were examined using long-term mooring and hydrographic data observed during the period from May 2013 to April 2014. The short-term flow fluctuations were dominant in the periodic bands of 15–27 days and shorter than 10 days. The principal and minor components of these flow fluctuations were respectively along and across the local isobaths, which are almost parallel in the north direction. The northward flow fluctuations along the local isobaths were correlated with the northeastward wind fluctuations in both periodic bands, and these correlations were more evident from fall to winter. On the basis of these results, the northward flows are regarded as wind-induced barotropic coastal jets. On other hand, the eastward flow fluctuations across the local isobaths were related to inflow and outflow via the bay mouth or the Izushima Channel. Inflow and outflow with reverse flow at lower depths formed in summer, but those with vertically uniform flow tended to form in winter. The main summertime inflow and outflow were driven by horizontal gradients in density. These permit us to regard the main summertime inflow and outflow as gravitational circulation. Also, the summertime inflow can be intermittently caused by internal waves.  相似文献