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971.
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海南省“十五”测震台网是集数字化、综合化、自动化技术为一体的大动态、宽频带地震观测系统,在地震速报、预报和地震科学研究中发挥重要的作用。本文通过对海南省测震台站故障情况的分析和总结,介绍地震台站维护的一些经验和方法。 相似文献
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Early Paleozoic subduction of the Paleo-Asian Ocean: Geochronological and geochemical evidence from the Dashizhai basalts,Inner Mongolia 总被引:10,自引:0,他引:10
Zircon U-Pb results of basalt from the Dashizhai Town in Inner Mongolia, NE China, shows that the basaltic lava was erupted
at 439±3 Ma, much older than the “Permian basalts” as previously thought. These rocks show arc-type trace element patterns
(i.e., Nb-Ta depletion and light REE and large ion lithophile element enrichment) and unradiogenic Sr and highly radiogenic
Nd and Hf isotope compositions. They can be subdivided into two petrogenetic groups: Group 1 basalts have relatively high
TiO2, MgO and compatible elements and low Sr and Th, characterized by mid-oceanic ridge basalt (MORB)-type Sr-Nd-Hf isotope compositions
(87Sr/86Sr(i)=0.7028−0.7032, εNd(t)=+9.8−+11.2, εHf(t)=+16.1−+18.4). Group 2 has lower TiO2, MgO and compatible elements and higher Sr and Th, and relatively evolved Sr-Nd-Hf isotope compositions (87Sr/86Sr(i)=0.7037−0.7038, εNd(t)=+5.7−+7.3, εHf(t)=+12.6−+13.0). Both groups were interpreted as melts derived from a metasomatized mantle wedge formed during the subduction
of Paleo-Asian Ocean. The mantle source for Group 1 was probably a highly isotopically depleted oceanic mantle modified by
predominant slab fluids; whereas subducted sediments had an important contribution to the melting source for Group 2. The
petrogenesis of the Dashizhai basalts provides clear evidence for early Paleozoic subduction of the Paleo-Asian Ocean, and
the highly radiogenic Nd and Hf compositions in these rocks suggest that these lavas and their possible intrusive counterparts
were one of the important components for Phanerozoic crustal growth. Our and previous studies on the “Dashizhai Formation”
volcanic rocks yield an unrealistic eruption range of 440-270 Ma for different rock types, we thus advise to disassemble the
previously defined “Dashizhai Formation” into multiple lithologic units and to reinterpret the spatial and temporal distributions
of different volcano-sedimentary associations.
Supported by National Basic Research Program of China (Grant No. 2006CB403504) 相似文献
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1987年1月8日甘肃迭部5.9级地震与地形变特征 总被引:1,自引:0,他引:1
根据1987年1月8日甘肃迭部5.9级地震前,该区域的地壳形变中长期背景和定点台站连续观测资料的震反应异常,分析研究了这此异常的变化特征。 相似文献
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Water quality is often highly variable both in space and time, which poses challenges for modelling the more extreme concentrations. This study developed an alternative approach to predicting water quality quantiles at individual locations. We focused on river water quality data that were collected over 25 years, at 102 catchments across the State of Victoria, Australia. We analysed and modelled spatial patterns of the 10th, 25th, 50th, 75th and 90th percentiles of the concentrations of sediments, nutrients and salt, with six common constituents: total suspended solids (TSS), total phosphorus (TP), filterable reactive phosphorus (FRP), total Kjeldahl nitrogen (TKN), nitrate-nitrite (NOx), and electrical conductivity (EC). To predict the spatial variation of each quantile for each constituent, we developed statistical regression models and exhaustively searched through 50 catchment characteristics to identify the best set of predictors for that quantile. The models predict the spatial variation in individual quantiles of TSS, TKN and EC well (66%–96% spatial variation explained), while those for TP, FRP and NOx have lower performance (37%–73% spatial variation explained). The most common factors that influence the spatial variations of the different constituents and quantiles are: annual temperature, percentage of cropping land area in catchment and channel slope. The statistical models developed can be used to predict how low- and high-concentration quantiles change with landscape characteristics, and thus provide a useful tool for catchment managers to inform planning and policy making with changing climate and land use conditions. 相似文献
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