Pressure–temperature conditions of ongoing regional metamorphism beneath the Japanese Islands     

S. Omori  S. Kita  S. Maruyama  M. Santosh 《Gondwana Research》2009,16(3-4):458-469

We evaluate the pressure–temperature (P–T) conditions of ongoing regional metamorphism at the top of the oceanic crust of the subducted Pacific and Philippine Sea plates through a combination of phase diagrams and hypocenter distribution and based on the dehydration-induced earthquake hypothesis. The brute-force method was employed to find the best match thermal structure to link the hypocenter distribution and dehydration. The estimated thermal structure varies far from the values obtained from numerical simulation. Our estimates are consistent with the qualitative physical prediction for the variation of temperature in different subduction zones and provide quantitative constraints for the models.In northeastern Japan, the P–T path for the top of the oceanic crust turns to the high-T side at a depth of around 90 km. The depth corresponds to the location of the volcanic front and an active convection of the wedge mantle below this depth is suggested. Our computations also reveal the effect of an exceptional scenario beneath the Kanto region. The temperature in the Kanto region, where the cold lid of the Philippine Sea plate prevents heating by the return-flow of mantle wedge above, is much lower than that of northeastern Japan. The subduction of younger Philippine Sea plate leads to a higher-temperature in the oceanic crust. In the central Shikoku region, the thermal structure exhibits high-T/P nature. Heating by shear deformation can explain the high-T/P path in the depth range from 20 to 35 km. The Kyushu area shows moderate type T/P path reaching up to eclogite facies conditions. In the Kii and central Shikoku region, the thermal structure exhibits high-T/P nature. However, the absolute values for the areas seem to have problem in physical context. Our results has risen the significance of sediment subduction in the southwest Japan and requirement for further improvements in this technique including the aspect of variation of the bulk composition of the subducted material.  相似文献   

找矿假设的提出与验证          下载免费PDF全文

程家柏  赵元艺 《地质找矿论丛》2004,19(2):122-129

矿床的形成不为人所能见,由此决定找矿工作必然采取提出找矿假设和对其验证这种形式.文章在分析国内外一些矿床的发现、发展史的基础上,总结和提炼一些找矿假设的思路和方法,及对其验证时应注意的一些问题.  相似文献   

AN EXPERIMENTAL STUDY ON TEMPORAL AND SPATIAL PROCESSES OF WANDERING-BRAIDED RIAVER CHANNEL EVOLUTION     

Ouyang ZHANG  Desheng JIN  Hao CHEN 《国际泥沙研究》1999,(2)

1INTRODUCTIONErgodichypothesisisoneofthebasicconceptsofmoderngeomorphology.Itsuggeststhatundercertaincircumstancessamplinginspacecanbeequivalenttosamplingthroughtime;andthatspace-timetransformationsarepermissibleasaworkingtool.Thisisbasedontheassumptionthat,whenindividualmembersofapopulationoflandformsarechangingregularlythroughtime,thespatialfrequencyofoccurrenceofgiventypesoflandformsisinverselyproportionaltotheirrateofchange(Chorley,etal.,1985).TheconceptofthecycleofDavis'erosioninwhi…  相似文献   

Impact of Analysis-time Tuning on the Performance of the DRP-4DVar Approach     

ZHAO Juan  WANG Bin  LIU Juanjuan 《大气科学进展》2011,28(1):207-216

In this study we extend the dimension-reduced projection-four dimensional variational data assimilation (DRP-4DVar) approach to allow the analysis time to be tunable, so that the intervals between analysis time and observation times can be shortened. Due to the limits of the perfect-model assumption and the tangentlinear hypothesis, the analysis-time tuning is expected to have the potential to further improve analyses and forecasts. Various sensitivity experiments using the Lorenz-96 model are conducted to test the impact of analysistime tuning on the performance of the new approach under perfect and imperfect model scenarios, respectively. Comparing three DRP-4DVar schemes having the analysis time at the start, middle, and end of the assimilation window, respectively, it is found that the scheme with the analysis time in the middle of the window outperforms the others, on the whole. Moreover, the advantage of this scheme is more pronounced when a longer assimilation window is adopted or more observations are assimilated.  相似文献   

Ecohydrologic separation alters interpreted hydrologic stores and fluxes in a headwater mountain catchment   总被引：1，自引：0，他引：1  

Molly R. Cain  Adam S. Ward  Markus Hrachowitz 《水文研究》2019,33(20):2658-2675

Recent studies have demonstrated that compartmentalized pools of water preferentially supply either plant transpiration (poorly mobile water) or streamflow and groundwater (highly mobile water) in some catchments, a phenomenon referred to as ecohydrologic separation. The omission of processes accounting for ecohydrologic separation in standard applications of hydrological models is expected to influence estimates of water residence times and plant water availability. However, few studies have tested this expectation or investigated how ecohydrologic separation alters interpretations of stores and fluxes of water within a catchment. In this study, we compare two rainfall‐runoff models that integrate catchment‐scale representations of transport, one that incorporates ecohydrologic separation and one that does not. The models were developed for a second‐order watershed at the H.J. Andrews Experimental Forest (Oregon, USA), the site where ecohydrologic separation was first observed, and calibrated against multiple years of stream discharge and chloride concentration. Model structural variations caused mixed results for differences in calibrated parameters and differences in storage between reservoirs. However, large differences in catchment storage volumes and fluxes arise when considering only mobile water. These changes influence interpreted residence times for streamflow‐generating water, demonstrating the importance of ecohydrologic separation in catchment‐scale water and solute transport.  相似文献   

Modeling the effect of saltation on surface layer turbulence     

Hao-Jie Huang 《地球表面变化过程与地形》2020,45(15):3943-3954

Particle–turbulence interaction has been a research focus in the field of pneumatic transport, especially in aeolian environments. However, knowledge regarding the effect of saltating particles on the turbulence characteristics is very limited. In this article, a process of sand-laden flow from forming sand streamers to stability is investigated via a coupled mathematical model of wind-blown sand that includes the spatiotemporal development. The variations in the turbulence characteristics, such as the mean velocity and turbulence intensity in clean air or sand-laden flow field, are analyzed. The results show that the splash process of sand grains near the wall decrease the wind speed in the saltation layer and destroy the low-speed streaks. Moreover, the profiles of streamwise turbulence intensity exhibit a transition from ‘decreasing’ to ‘increasing’ and approximately intersect at an ‘intensity focus’, which is presented for the first time. Furthermore, it was found that saltating particles could enhance the Reynolds stress. Meanwhile, it was also noticed that the shear stress at the wall surface is greater than the impact threshold and that there is a tendency towards the impact threshold. Therefore, saltation makes the particle Reynolds number of sand-laden flow higher than that under non-saltation conditions, thus changing the particles’ effect on the turbulence intensity. Gravity-dominated saltation is probably the most essential difference between wind-blown sand and other traditional two-phase flows. © 2020 John Wiley & Sons, Ltd.  相似文献   

强降雨下基于Green-Ampt模型的边坡稳定性分析     

苏永华  李诚诚 《岩土力学》2020,41(2):389-398

降雨入渗分析方法直接影响降雨型滑坡的预测与防范。Green-Ampt（GA）模型物理意义明确、参数较少,在降雨型滑坡分析中逐渐得到了重视,但该方法忽略了湿润层非饱和层的存在以及饱和层渗流而影响计算精度。针对以上不足,基于GA模型,建立了适用于边坡并且能综合考虑湿润层土体含水率分布情况与饱和层内平行于坡面渗流作用的降雨入渗分析（LSGA）模型,并提出了该模型下边坡稳定性系数表达式。结果表明：对于不考虑分层的无限长边坡,LSGA模型可简化为GA模型,说明GA模型是LSGA模型的一个特例;与LSGA模型相比,GA模型在失稳深度和时间上有较大延缓;饱和层渗流作用对湿润层特性影响较小,对边坡稳定性影响较大;相反,坡体长度方向尺寸效应则对湿润层特性影响明显,而对边坡稳定性影响较小;利用LSGA模型和稳定性评价方法得到的结果与模型试验揭示的现象基本吻合,证明了该方法有较好的精确性和可靠性。  相似文献   

A global analysis of urbanization effects on amphibian richness: Patterns and drivers     

《Global Environmental Change》2022

Urbanization presents an unplanned and highly replicated global experiment to understand biotic responses to global changes. Here we conducted a global analysis on patterns and drivers of urbanization effects on biodiversity using the global amphibian richness dataset along with background climate and the continuous rural-urban gradients. We, for the first time, empirically generalized the urbanizational gradients of amphibian richness at the global scale and in different climate zones despite the substantial differences in history, ecological context, and socioeconomic conditions across large geospatial extents. We found a positive imprint of urbanization on amphibian richness in cool and climate zones whereas the presence of urban thermal stress in high temperature climate zones. Anthropogenic forces behind the urbanization gradients entangled with environmental variables directly and indirectly drove the patterns as revealed by the structural equation modeling (SEM). The urbanizational diversity gradient (UDG) found in this study might signify the existence of another general principle in ecology analogous to well-known latitudinal and elevational diversity gradients. We proposed the heat-and-threat balance (HATB) hypothesis to explain UDG: urbanization-induced heat would promote biodiversity if the ambient temperatures are cooler than their optima. Alternatively, it may put threats on biodiversity when the ambient temperatures are close to their optima. There is an urgent need to advance the knowledge on UDG in an urbanizing planet by additional studies from diverse taxa, various geographical locations, and at different scales.  相似文献   

Spatiotemporal shifts in key hydrological variables and dominant factors over China     

Shanlei Sun  Zaoying Bi  Shujia Zhou  Hongzhou Wang  Qingqing Li  Yi Liu  Guojie Wang  Shijie Li  Haishan Chen  Yang Zhou 《水文研究》2021,35(8):e14319

Quantitatively and physically understanding changes in land surface hydrology is a hot topic in the hydro-meteorological research, especially over China with high population density but uneven distribution of water resources. Therefore, the spatiotemporal dynamics (i.e., the 1980s [1981–1990] and 1990s [1991–2000] relative to the baseline of 1961–1980) in evapotranspiration (ET) and streamflow/runoff (Q) were examined across 426 hydrological divisions (HDs) of China. Both the 1980s and 1990s ET decreased over roughly 50% HDs mainly in the central and southeast parts of China, while the 1980s (1990s) Q decreased over slightly higher than 50% (63%) HDs generally in north and southwest China (the central and north parts of China). Relative to the 1980s, more HDs had strong changes in ET and Q in 1990s. Based on the separated contributions of precipitation (P), reference ET and Budyko-type equation parameter n (an integrated variable of catchment property) to ET and Q changes, we found that in 1980s and 1990s, n dominated ET changes over about 60% HDs mainly in the south, with the dominant of P around 35% HDs generally in the north and northeast, while for Q changes, nearly 60% (slightly less than 40%) HDs were dominated by n (P). Moreover, the dominants for ET (Q) changes have shifted from 1980s to 1990s over 36% (45%) HDs, mainly changing from P to n. This study provides a framework for quantitatively understanding land surface hydrological dynamics from the perspectives of climatic and physiographic controls over regions.  相似文献   

GPS测量技术在假设坐标系中的应用探讨     

胡捍东  臧峰 《测绘与空间地理信息》2009,32(1)

目前,GPS全球定位系统已广泛应用于大地测量、工程测量、航空摄影测量、地形测量及变形观测等各个方面.小范围内的工程测量常采用假设坐标系,本文将以两个勘测项目为例,叙述GPS测量系统在假设坐标系中的应用.  相似文献