华北平原沉降地区重力场变化分析   总被引：2，自引：1，他引：2  

陈素改  陈绍绪  李光振  姚玉致 《华北地震科学》1996,14(1):27-35

华北平原沉降带相对于西部太行山区,近几年观测到的重力值相对1989年同期呈上升状态、其中某些地区累计上升量相当大,比如,沧州地区达143×10~(-8)m/s~2,任丘地区103×10~(-8)m/s~2,巨鹿—南宫为(89—103)×10~(-8)m/s~2.对某些地区的重力变化量进行地下水下降量和地面沉降量校正,其校正量可达到变化量的1/3—1/2.校正后的重力值变化幅度减小,但有些异常依然存在.这种较大的剩余变化量,可能含有两个因素:其一可能与华北平原沉降带的继承性下降及某些地区构造断裂活动有关;其二可能是实际地面沉降量比推测的沉降量大.  相似文献   

Oxygen isotopic distribution in an amoeboid olivine aggregate from the Allende CV chondrite: Primary and secondary processes     

Hajime Imai  Hisayoshi Yurimoto 《Geochimica et cosmochimica acta》2003,67(4):765-772

The oxygen isotopic distribution in an amoeboid olivine aggregate (AOA), TTA1-02, from the Allende CV3 chondrite has been determined by secondary ion mass spectrometry. The irregular shaped TTA1- 02 (5×3mm) consists mostly of olivine grains of ca. 5μm in diameter. Olivine grains of Mg-rich (Fo₉₅) and Fe-rich (Fo₆₀) composition are in direct contact with each other, with a sharp compositional boundary. Oxygen isotopic compositions of Fe-rich olivine grains are ¹⁶O-poor (Δ¹⁷O ≅ −5‰), whereas Mg-rich olivine is ¹⁶O-rich (Δ¹⁷O ≅ −25‰). Several Al-rich inclusions (<ca. 500 μm in diameter) are enclosed by olivine grains in the AOA. Oxygen isotopic compositions of spinel and fassaite in Al-rich inclusions are ¹⁶O-rich (Δ¹⁷O ≅ −20‰), whereas those of anorthite, nepheline and phyllosilicate are ¹⁶O-poor (Δ¹⁷O ≅ −5‰). We propose the following sequence of events during the formation of AOAs in the Allende meteorite: 1) Formation of Al-rich inclusions with ¹⁶O-rich oxygen isotopic composition; 2) Accretion of Mg-rich olivine grains with ¹⁶O-rich oxygen isotopic composition around Al-rich inclusions; 3) Accretion into parent body; and 4) Aqueous alteration in the parent body, which led to crystallization of ¹⁶O-poor minerals, Fe-rich olivine, anorthite, nepheline, and phyllosilicate. This is reflecting reactions among primary ¹⁶O-rich AOA minerals and aqueous fluid having ¹⁶O-poor oxygen isotopic composition. Fe-rich olivine grains precipitated from aqueous fluids, which partially dissolved pre-existing Mg-rich olivine grains. Sintering and Mg-Fe diffusion occurred during thermal metamorphism. Anorthite, nepheline and phyllosilicate in Al-rich inclusions replaced primary anorthite or melilite during the aqueous alteration stage.  相似文献   

Study on hydraulic characteristics of sabo dam with a flap structure for debris flow     

Yeonjoong Kim  Hajime Nakagawa  Kenji Kawaike  Hao Zhang 《国际泥沙研究》2017,32(3)

The front part of the flow is very important and complex in the case of debris flow where there is an accumulation of large boulders. It is important to control or dampen the energy of the frontal part of a debris flow for the safety of the downstream area because the impact pressure of debris flow is much greater than that of clear fluid. The main objective of this study is to analyze the hydraulic characteristics of the proposed dam (i.e. closed-type dam with flap). The vertical pressure distribution of this type is compared with conventional dam types. In the experiments, the total pressure associated with major debris flows was recorded in real time by a system consisting of four dynamic pressure sensors installed on different types of dam. The results from experimental data clearly show that the dam with the flap has advantages of capturing the debris flow with large boulders and controls the total pressure by flow circulation due to presence of the flap structure compared to a closed-type dam without flap. Further-more, the empirical coefficients of hydrodynamic and solid collision models were proposed and com-pared with available coefficients.  相似文献   

Estimation of debris flow discharge coefficient considering sediment concentration     

Namgyun Kim  Hajime Nakagawa  Kenji Kawaike  Hao Zhang 《国际泥沙研究》2019,34(1):1-7

A sabo dam has a purpose to block the path of debris flow. However, when overflow occurs, a sabo dam works as a weir, a vertical obstruction, where the fluid must flow over. Many empirical formulas and discharge coefficients for weirs relating flow depth to discharge have been proposed to calculate overflow discharges. However, only a few studies about overflow discharge coefficients are available in the case of debris flow. In this paper, experiments and numerical simulations were done to estimate debris flow discharge coefficients by considering the sediment concentration. In the numerical simulation, a complete overflow equation and a free overfall equation were implemented to calculate debris overflow discharges at a sabo dam. To determine the discharge coefficients for each equation, single factor regression analysis was used. Laboratory experiments were done to calibrate and to compare with the simulation. Study results showed that the discharge coefficients increase as the sediment concentration increases. This finding suggests debris flow discharge coefficients are derived to calculate the debris overflow discharges at a sabo dam.  相似文献   

Wave set-up in the storm surge along open coasts during Typhoon Anita     

Soo Youl Kim  Tomohiro Yasuda  Hajime Mase 《Coastal Engineering》2010

Wave set-up in storm surges is studied using a numerical model for coasts in Tosa Bay, Japan, open to the Pacific Ocean. Simulation models employing only atmospheric pressures and winds as external forces are unable to properly simulate open coast storm surge heights, such as those due to Typhoon Anita (1970). However, the present study shows that a numerical model incorporating wave-induced radiation stresses, as well as wind stresses and pressure gradients, is able to account for the open coast surge heights. There is a maximum contribution of 40% by the radiation stresses to the peak sea level rises. This study also evaluates the effects of the tides; including the tides improves the agreement between the predicted water surface elevations and the observations. The difference in predictions between one-way coupling from wave to surge models and two-way coupling of the surge and wave models is found to be small.  相似文献   

Relationship between sinking organic matter and minerals in the shallow zone of the western Subarctic Pacific     

Masahito Shigemitsu  Yutaka W. Watanabe  Yasuhiro Yamanaka  Hajime Kawakami  Makio C. Honda 《Journal of Oceanography》2010,66(5):697-708

We used time-series sediment trap data for four major components, organic matter and ballast minerals (CaCO₃, opal, and lithogenic matter) from 150, 540, and 1000 m in the western subarctic Pacific (WSAP), where opal is the predominant mineral in sinking particles, to develop four simple models for settling particles, including the “ballast model”. The ballast model is based on the concept that most of the organic matter “rain” in the deep sea is carried by the minerals. These four models are designed to simultaneously reproduce the flux of each major component of settling particles at 540 and 1000 m by using the data for each component at 150 m as initial values. Among the four models, the ballast model, which considers the sinking velocity increase with depth, was identified as the best using the Akaike information criterion as a measure of the model fit to data. This model successfully reproduced the flux of organic matter at 540 and 1000 m, indicating that the ballast model concept works well in the shallow zone of the WSAP on a seasonal timescale. This also suggests that ballast minerals not only physically protect the organic matter from degradation during the settling process but also enhance the sinking velocity and reduce the degree of decomposition.  相似文献   

Measurements of air-ice drag coefficient over the ice-covered Sea of Okhotsk   总被引：1，自引：0，他引：1  

Ayumi Fujisaki  Hajime Yamaguchi  Takenobu Toyota  Akio Futatsudera  Masaru Miyanaga 《Journal of Oceanography》2009,65(4):487-498

The air-ice drag coefficient under neutral stratification C _DN was measured with the eddy correlation method in the southern Sea of Okhotsk. The disturbance of the wind field caused by the ship’s structure was evaluated by computational fluid dynamics (CFD), and two types of correction methods were applied to estimate the error span of C _DN : one is based on the results of CFD, and the other is based on the parameterization of C _DN over open water suggested by Taylor and Yelland (2001). The C _DN × 10³ values finally obtained ranged from 1.9 to 5.4 with a mean value of 2.7 by the CFD correction and from 1.5 to 5.0 with a mean value of 3.1 by the other method. This is somewhat larger than the value of 2.5 suggested by Shirasawa (1981), and in the same range as 2.2–4.0 over rough ice and 3.1–5.0 over very rough ice, values which were complied by Guest and Davidson (1991) for first year ice. Most of the ice conditions were characterized by broken floes with a diameter less than 100 m and raised rims, which made the surface rougher than flat, level ice. The relation between C _DN and ice concentration was not clear, mainly because the contribution of the form drag caused at the freeboard was undetectable due to the great variation of ice surface condition. The roughness length z _M was also evaluated using the model developed for snow covered ice in a previous study.  相似文献   

Intensified mid-Holocene Asian monsoon recorded in corals from Kikai Island, subtropical northwestern Pacific     

Maki Morimoto  Hajime Kayanne  Malcolm T. McCulloch 《Quaternary Research》2007,67(2):204-214

Coupled records of Sr/Ca and oxygen isotope ratios (δ¹⁸O) of coral skeletons have been used to produce quantitative estimates of paleo-sea surface temperature (SST) and δ¹⁸O of surface seawater that can in some cases be converted to sea surface salinity (SSS). Two fossil corals from Kikai Island in the subtropical northwestern Pacific, a location affected by East Asian summer and winter monsoons, were analyzed to investigate differences between mid-Holocene and present-day SST and SSS. At 6180 cal yr BP, SSTs were roughly the same as today, both in summer and winter; δ¹⁸O_seawater and SSS values were higher both in summer (+ 0.5‰, +1.1 psu) and in winter (+ 0.2‰, + 0.6 psu) than modern values. At 7010 cal yr BP, SSTs were slightly cooler both in summer and winter (−0.8 and −0.6 °C), whereas δ¹⁸O_seawater and SSS had higher values in summer (+ 0.3‰, + 0.6 psu) and in winter (+ 0.8‰, + 1.9 psu) than present-day values. These results are consistent with other marine records for the mid-Holocene of the low and midlatitudes in the northwestern Pacific. Such regional conditions indicate that the East Asian summer and winter monsoons were more intense in the mid-Holocene, which was likely a function of the mid-Holocene insolation regime.  相似文献   

Ultraviolet-background-induced bifurcation of galactic morphology     

Hajime Susa  Masayuki Umemura 《Monthly notices of the Royal Astronomical Society》2000,316(2):L17-L20

Based upon a novel paradigm of galaxy formation under the influence of an ultraviolet background, the evolutionary bifurcation of pre-galactic clouds is compared with observations of elliptical and spiral galaxies. The theory predicts that the dichotomy between dissipational and dissipationless galaxy formation stems from the degree of self-shielding from the ultraviolet background radiation. This is demonstrated on a bifurcation diagram of collapse epochs versus masses of pre-galactic clouds. Using the observed properties, the collapse epochs and mass are assessed for each type of galaxy . By direct comparison of the theory with observations, it turns out that the theoretical bifurcation branch successfully discriminates between elliptical and spiral galaxies. This suggests that the ultraviolet background radiation could play a profound role in the differentiation of galactic morphology into the Hubble sequence.  相似文献   

Seasonal variation of bivalve larvae on an exposed sandy beach on Kashima-nada: Tips for the sandy beach recruitment process     

Hideki Sawada  Hajime Saito  Kumiko Adachi  Haruhiko Toyohara 《Journal of Sea Research》2011,65(2):275-283

Bivalves are often the dominant macrobenthos species in exposed sandy beach environments. However, our understanding of their recruitment processes before post-settlement stages on sandy beaches with highly energetic environments is incomplete. To clarify the characteristics of the free-swimming planktonic stage that affects recruitment efficiency in sandy shore ecosystems, we investigated the temporal (weekly–biweekly) variation of bivalve planktonic larval concentration coupled with oceanographic conditions on an exposed sandy shore on the sea of Kashima-nada, Japan, from summer 2003 to autumn 2005. Larvae were observed throughout the year, but the surge of larval concentration composed of sandy beach and sessile bivalves occurred most prominently in summer, from August to September. The peak concentration of larvae during this season was more than 1000 times higher than in other seasons. The larval concentration was positively correlated with water temperature and northward wind velocity and negatively correlated with each of the nutrient concentrations. On the other hand, chlorophyll a concentration and salinity seemed to have little effect on the larval concentration. Based on this fundamental knowledge, further investigations about planktonic larvae in sandy beaches are needed.  相似文献