汤东活动断裂带土壤H2、Rn地球化学特征     

胡宁  马志敏  王明亮  王宇  娄露玲  夏修军  张宝山  王文净  郭德科 《地震》2019,39(2):174-182

为研究汤东断裂带土壤气体地球化学特征及其所反映的构造地球化学背景, 采用野外监测的方法分析了张河村与邢李庄村两条测线的土壤H₂、 Rn分布特征。 结果表明, 张河村H₂浓度、 Rn活度浓度的分布范围分别为0.24×10^-6～174.7×10^-6、 13.3～69.8 kBq·m^-3, 背景值分别为14.26×10^-6, 24.8 kBq·m^-3。 邢李庄测线H₂浓度、 Rn活度浓度的分布范围11.8×10^-6～67.06×10^-6、 43.6～72.6 kBq·m^-3, 背景值分别为37.13×10^-6、 72.6 kBq·m^-3。 张河村测线在90～105 m处, H₂、 Rn出现强烈高值异常, 而120～150 m处出现高值异常。 异常值位于断裂带附近, H₂、 Rn气体测值对断裂位置具有良好的指示作用。 气体异常主要受汤东活动断裂构造控制, 汤东断裂下方的深大断裂和汤阴地堑中下地壳的低速体对深部气体释放有重要作用。  相似文献   

唐山震区上地壳平均波速比分析     

信世民  郭学增  刘静  张蕾  李瑞卿 《地震地磁观测与研究》2019,40(3):15-20

收集河北地震台网记录的唐山震区2012-2016年M_L ≥ 1.0地震，选取震源深度5-10 km、波形信噪比较高的波形数据，拾取直达P波、S波震相到时，利用和达法计算平均波速比，并分析研究区平均波速比水平分布特征与时变特征，结果表明：唐山震区上地壳平均波速比约为1.71，且水平分布呈区域化特征，反映了研究区复杂的地壳结构。研究区内3次M_L ≥ 4.0地震前，波速比曲线均呈较显著的下降-低值-回升形态，表明该区平均波速比变化可能具有一定地球物理异常特征。  相似文献   

华北—东北地区震磁异常与日本强震对应关系     

孙澎涛  任俊峰  焦成丽  孙贵成  张玉林 《地震地磁观测与研究》2019,40(2):45-51

选取2009—2014年华北—东北地区发生的12次中等地震,对该区8个地磁台站记录的地磁Z分量日变幅进行小波分析及合成计算,与日本海沟同期发生的12次M≥6.5强震进行关联性分析,发现日本强震对中国华北—东北地区中等地震活动具有连带作用,表现在:(1)日本强震发生前后,华北或东北地区均有M 4—5地震出现,频次一般为1—3,间隔几天至5个月左右;(2) 2011年3月10日日本M 9.1地震后,华北、东北地区中等地震震级有所升高,其中东北地区由M 4升至M 5,距日本最近的中俄交界甚至出现M 6.1地震,华北地区唐山老震区出现1次M 4.8地震,震级接近5;(3)每次日本强震出现后几天至2个月内,8个地磁台地磁Z分量小波细节6阶合成曲线值均出现2—6个月高值异常,但幅度大小与强震震级无明显规律可循,而华北或东北地区中等地震一般在异常高值出现前后低值附近发生。  相似文献   

Strong variation in weathering of layered rock maintains hillslope‐scale strength under high precipitation          下载免费PDF全文

Jennifer Von Voigtlander  Marin K. Clark  Dimitrios Zekkos  William W. Greenwood  Suzanne P. Anderson  Robert S. Anderson  Jonathan W. Godt 《地球表面变化过程与地形》2018,43(6):1183-1194

The evolution of volcanic landscapes and their landslide potential are both dependent upon the weathering of layered volcanic rock sequences. We characterize critical zone structure using shallow seismic V_p and V_s profiles and vertical exposures of rock across a basaltic climosequence on Kohala peninsula, Hawai’i, and exploit the dramatic gradient in mean annual precipitation (MAP) across the peninsula as a proxy for weathering intensity. Seismic velocity increases rapidly with depth and the velocity–depth gradient is uniform across three sites with 500–600 mm/yr MAP, where the transition to unaltered bedrock occurs at a depth of 4 to 10 m. In contrast, velocity increases with depth less rapidly at wetter sites, but this gradient remains constant across increasing MAP from 1000 to 3000 mm/yr and the transition to unaltered bedrock is near the maximum depth of investigation (15–25 m). In detail, the profiles of seismic velocity and of weathering at wet sites are nowhere monotonic functions of depth. The uniform average velocity gradient and the greater depths of low velocities may be explained by the averaging of velocities over intercalated highly weathered sites with less weathered layers at sites where MAP > 1000 mm/yr. Hence, the main effect of climate is not the progressive deepening of a near‐surface altered layer, but rather the rapid weathering of high permeability zones within rock subjected to precipitation greater than ~1000 mm/yr. Although weathering suggests mechanical weakening, the nearly horizontal orientation of alternating weathered and unweathered horizons with respect to topography also plays a role in the slope stability of these heterogeneous rock masses. We speculate that where steep, rapidly evolving hillslopes exist, the sub‐horizontal orientation of weak/strong horizons allows such sites to remain nearly as strong as their less weathered counterparts at drier sites, as is exemplified by the 50°–60° slopes maintained in the amphitheater canyons on the northwest flank of the island. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

西藏日喀则拉堆-乃东与毕定-甲舍拉断裂的活动性分析研究          下载免费PDF全文

雷生学  李振海  张文朋  陈宇坤  郭巍  谢静博  高也  高锦瑞 《地震工程学报》2018,40(4):785-793

综合采用地质地貌调查、探槽开挖及OSL测年等,对离日喀则市最近的拉堆—乃东和毕定—甲舍拉断裂的活动性进行研究,结果表明:拉堆—乃东断裂在距今约3万年前停止了活动,毕定—甲舍拉断裂则至少在5万年前停止了活动,即二者自晚更新世晚期已不再活动——不属于全新世活动断裂,这与部分学者认为拉堆—乃东断裂为全新世活动断裂的结论不同。研究获得的最新断层活动资料可为该地区的地震预测提供科学依据。  相似文献   

基于高通量测序方法分析荣成月湖潮间带趋磁细菌多样性     

张文燕  潘红苗  董逸  杜海舰  陈一然  吴龙飞  肖天 《海洋科学》2019,43(3):1-10

荣成月湖是一个典型天然潟湖,潮间带沉积物中存在多种形态趋磁细菌。通过Roche454高通量测序平台,对沉积物样品(B_S)和磁收样品(B_M)进行16SrRNA基因高通量测序,认识荣成潮间带沉积物的细菌群落结构,并了解趋磁细菌多样性及系统进化地位。研究结果表明沉积物样品中主要的细菌类群为δ-变形菌纲,占总细菌数的26.4%,其次是γ-变形菌纲和α-变形菌纲;而磁收样品中细菌多样性和种类明显降低,以α-变形菌纲占绝对优势,相对比例达72.6%。在磁收样品和沉积物样品分别发现了1 612条和186条reads与趋磁细菌相关,分别占细菌总数的5.76%和0.85%,磁收样品中趋磁细菌数是沉积物样品的6.8倍。对两个样品中获得的趋磁细菌序列进行系统进化分析,发现这些序列多数属于变形菌门的α-变形菌纲,以趋磁球菌占绝对优势,少数属于δ-变形菌纲,与多细胞趋磁原核生物亲缘关系最近。海洋趋磁螺菌属仅在B_M样品中检出,趋磁弧菌属在B_M样品优势度高于B_S样品,而多细胞趋磁原核生物和趋磁螺菌属在B_S样品中优势度更高。通过分析样品间的差异OTUs,认为荣成潮间带沉积物中可能存在大量未知的趋磁细菌新类群。研究结果为下一步培养和开发趋磁细菌这一功能菌群,发现趋磁细菌新类群及趋磁细菌生态功能提供了基础资料。  相似文献   

长江三角洲蓝图重绘的基础科学问题:进展与未来研究     

汪亚平  贾建军  杨阳  周亮  冯威  高建华  魏稳  李占海  史本伟  高抒 《海洋科学》2019,43(10):2-12

在全球气候变化和人类活动影响加剧的背景下,作为河口海岸重要子系统的三角洲正在发生快速变化。长江三角洲地处长江入东海交汇处,是中国最重要的经济核心区之一,对邻近区域乃至整个长江经济带经济社会发展都起着重要作用。由于全球变暖、海面上升和强烈人类活动引发了三角洲系统状态转换,因此以往基于恒定系统状态而获得的有关长江三角洲的认识已不能满足未来需求,迫切需要对未来海面变化、极端事件、流域与河口工程影响下的三角洲物质循环条件、物理过程、地貌冲淤演化、源-汇格局调整等科学问题进行深入研究。在三角洲系统行为、未来演化趋势的预测能力建设中,应重视从海面到海底的综合立体观测系统的发展,以获取关键数据;基于三角洲系统的时、空演化特征,建立三角洲本征态和衍生态的谱系理论。未来需针对系统状态转换而调整原先的经济社会发展模式,以便保护自然资源、重建生态系统,更好地支撑长江经济带发展,重绘长江三角洲发展蓝图。  相似文献   

Estimating groundwater recharge for a freshwater lens in an arid region: Formative and stability assessment     

Mosaed S. Alrashidi  Ryan T. Bailey 《水文研究》2020,34(4):1063-1080

The formation of subsurface freshwater lenses on top of brackish groundwater is a fascinating hydrologic phenomenon that creates groundwater supplies of great potential value in arid regions. Information on the recharge quantity and mechanism of these lenses is both scarce and uncertain. This study examines the formation and macroscale stability of the Rawdatain freshwater lens in Kuwait, for which significant pre-development data are available. The Rawdatain is a large (150 million m³) subsurface freshwater lens overlying brackish groundwater compared to the other freshwater lenses in the Arabian Peninsula. In this study, a three-dimensional (3D) density-dependent groundwater flow model is tested against the following data targets to estimate long-term diffuse and focused groundwater recharge: (i) groundwater head, (ii) total dissolved solids (TDS) groundwater concentration, (iii) volume and vertical thickness of stored groundwater of three different water quality TDS ranges (0–700, 700–1000 and 1000–2000 mg/L) and (iv) geometrical shape features of the lens along cross-sections. To better represent the spatial variation in TDS, six different recharge zones were assigned to allocate diffuse and focused recharge conditions. Twelve recharge rate scenarios, encompassing a wide range of feasible long-term average annual recharge values (200,000–5,000,000 m³/year), were tested against the multiple targets and compared with the groundwater age of the Rawdatain lens. Based on comparison with data targets, the long-term average annual recharge is estimated to be 500,000 m³/year. Scenarios of reduced recharge, which may occur due to changes in land-use or climate, demonstrate the extremely slow response of the lens, which is in agreement with the slow development and formation of the lens (>2,000 years). Within a 100-year time frame, a 50% reduction in annual recharge reduces the lens volumes by 21, 17 and 9% for the three water quality categories, respectively. This study demonstrates the stability of freshwater lenses in arid regions and also provides methodology for similar focused rainfall recharge freshwater lenses.  相似文献   

Satellite-based monitoring and statistics for raft and cage aquaculture in China’s offshore waters     

《International Journal of Applied Earth Observation and Geoinformation》2020

Based on Landsat 8 remote sensing images, a combination of an unsupervised classification algorithm and artificial review was used to extract areas for Chinese offshore raft and cage aquaculture in 2018. The results of the extraction showed that China’s 2018 coastal zone raft aquaculture area comprised 194,110 ha, of which the province having the largest raft aquaculture area was Jiangsu (28.77 %), followed by Fujian (20.42 %) and Shandong (13.11 %). The cage aquaculture area covered 57,847,799 square meters, of which the provinces with the largest cage aquaculture area were Fujian (64.81 %), Guangdong (17.45 %), and Liaoning (5.63 %). In addition, by combining high-resolution remote sensing image visual interpretation and field investigation, the classification of 1200 sample points in four regions was determined, and the accuracy of the aquaculture area extraction was found to be 87.35 %. The extraction results can be used not only to evaluate China’s aquaculture production but also offer significant reference value for scientific planning related to sea use, ecological environmental protection, and marine disaster prevention and mitigation.  相似文献   

Seismic fracture evaluation of diaphragm joints in welded beam-to-box column moment connections     

Ching-Yi Tsai  Keh-Chyuan Tsai  Chao-Hsien Li  Chung-Che Wu  Ker-Chun Lin  Sheng-Jhih Jhuang 《地震工程与结构动力学》2020,49(13):1344-1362

Steel box columns are widely used in steel building structures in Taiwan due to their dual strong axes. To transfer the beam-end moment to the column, diaphragm plates of the same thickness and elevations as the beam flanges are usually welded inside the box column. The electro-slag welding (ESW) process is widely used to connect the diaphragms to the column flanges in Taiwan because of its convenience and efficiency. However, ESW may increase the hardness of the welds and heat-affected zones (HAZs), while reducing the Charpy-V notch strength in the HAZ. This situation can cause premature fracture of the diaphragm-to-column flange welds before a large plastic rotation is developed in the beam-to-box column joints. To quantify the critical eccentricity and the effectiveness of fracture prediction, this study uses fracture prediction models and finite element model (FEM) analysis to correlate the test results. In this study, two beam-to-box column connection subassembly tests are conducted with different loading protocols and ESW chamber shapes. To implement a fracture prediction model, the material parameters are established from circumferential notched tensile tests and FEM analysis. Test results indicate that the fracture instances can be predicted on the basis of the cumulative plastic deformation in the HAZs. Analytical results indicate that fracture instances and locations are sensitive to the relative locations of the ESW joints and beam flange. Tests also confirm that the possible fracture of the diaphragm-to-column flange joints can be mitigated by enlarging the chamber of the ESW joint.  相似文献