南黄海OBS数据转换横波分析及其地质意义

多分量地震勘探在减小地球物理反演问题多解性的同时提供了更丰富的地下信息,可以从量化的意义上真正实现岩性勘探.由于地壳结构的复杂性及转换横波的特殊性,南黄海地壳结构研究中基本未涉及横波.本文使用南黄海OBS数据,在不同剖面上对比分析纵横波走时、视速度以及质点运动轨迹,基于纵波理论模型对转换横波震相进行射线追踪和走时试算,识别并拟合了来自不同地层的转换横波震相.研究表明,北部坳陷中主要发生了PPS转换,转换界面为陆相沉积层底界面.千里岩隆起区除了发生转换界面为陆相沉积底界面的PPS转换还有转换界面为海底的PSS转换.断层活动引起岩石破碎,高波速比特征的断层边界为胶莱盆地在海上部分的边界圈定再添证据.千里岩地区高速地层成分含有花岗岩,其纵横波速比为1.67~1.68;推测北部坳陷中的海相沉积北-南地层不同,依次为碳酸盐岩及砂岩两类地层.     

基于长时间序列ERA-Interim再分析资料的广东沿海波浪能资源分布特征分析

波浪能的开发利用作为海洋可再生能源发展的重要组成部分,持续受到社会和学界的广泛关注。广东省波浪能资源的开发利用具有得天独厚的优势,但其发展水平还处于探索阶段,亟须进一步加强。本文利用长达40年(1979—2018年)的ERA-Interim再分析波浪资料,从总体分布特征上分析了广东沿海波浪能资源及其长期变化趋势。粤东-珠江口-粤西沿岸一线,波浪能资源呈现"低-高-低-高-低"的分布特征,具有显著的季节变化特征;长期变化趋势上呈现显著的逐年线性递增特征,递增速率为0.054 3 kW/(m·a),其中1979—1994年变化较为快速,2001—2018年变化较为平缓。     

基于植被物候特征的互花米草提取方法研究——以长三角湿地为例

互花米草自1979年引进我国以来迅速增长,呈现外来物种入侵势态,严重影响了滨海湿地生态系统平衡。通过遥感手段监测可以获取互花米草的时空扩展规律,为互花米草治理提供参考和依据。本文选取长三角地区3个主要湿地区域为研究区,依托Google Earth Engine (GEE)平台选取了2014—2019年Landsat 8 OLI时间序列数据,提出了一种基于物候特征的互花米草提取方法。首先,通过归一化差异湿度指数(NDMI)、归一化差异植被指数(NDVI)和归一化差异水体指数(NDWI)提取互花米草生长的高湿度区域;然后,通过植被指数构建表征植被物候特征的时间序列曲线,确定互花米草与其他植被的物候特征差异时相;最后,基于物候特征差异时相数据构建决策树提取互花米草。通过与现有的互花米草决策树提取方法和支持向量机(SVM)方法对比发现,本文方法在3个研究区的提取结果均为最优提取结果,表明本文的方法对提取互花米草具有较好的适用性。     

利用湖泊内源性饵料饲喂中华绒螯蟹(Eriocheir sinensis)的养殖与净水效应

在东太湖网围养殖区进行不同放养密度(3000、6000、9000只/hm²)饲喂太湖水草与螺蛳的中华绒螯蟹(Eriocheir sinensis)养殖实验,各处理组均设投喂鱼肉与玉米等外源性饵料的对照,以获得不同养殖模式对中华绒螯蟹生长、品质及养殖水环境的影响,以及利用浅水草型湖泊内源性饵料养殖中华绒螯蟹的适宜放养密度.结果表明,规格和增肉倍数虽然均显著小于相同养殖密度下投喂外源性饵料的对照组,但是各实验组商品蟹体重均能达到150 g;低密度养殖组(3000只/hm²)的产量与对照组无显著差异,其余两组显著低于对照组;而低密度养殖组的河蟹回捕率显著低于对照组,其余两组则无显著差异.实验养殖区水质状况优于投喂外源性饵料的对照区,其TP含量显著低于对照区,投喂外源性饵料会增加水体N、P含量,导致水体富营养化.投喂太湖水草与螺蛳等内源性饵料进行中华绒螯蟹养殖不但可以有效地抑制浅水湖泊水草的疯长,还可通过中华绒螯蟹收获从水体输出N、P营养盐,起到净化水质的作用.不同密度养殖的生态与经济效益对比结果显示,利用草型湖泊内源性饵料养殖中华绒螯蟹的适宜放养密度为6000只/hm²左右.     

TECTONIC INDICATIONS OF OCCURRENCE OF MODERATE-TO-STRONG EARTHQUAKES IN CHAOHU-TONGLING AREA,ANHUI PROVINCE

The Chaohu-Tongling area in Anhui Province is a typical moderate-to-strong earthquake active area in the mainland of China. Four earthquakes occurred in this area, displayed as a NNE-trending zonal distribution, including the 1585 M5(3/4) Chaoxian earthquake and the 1654 M5(1/4) Lujiang earthquake, which formed a striking moderate-to-strong seismic activity zone. Field survey, shallow geophysical prospecting, drilling data, collection and dating of chronology samples and comprehensive analysis of fault activity indicate that the Fanshan, Xiajialing and Langcun faults are not active since Quaternary. The NNE-trending Tongling Fault is a buried middle-Pleistocene fault, but it can produce moderate-to-strong earthquakes and control the evolution and development of three en echelon geologic structures. The intensity of the four earthquakes is characterized by southward progressive decrease, which is in accordance with the characteristics that the subsidence range of Wuwei Basin is obviously larger than that of Guichi Basin to its south since late Cenozoic. In terms of deep structure, the characteristics of spatial distribution of Tongling Fault indicate that it corresponds to a NNE-striking Bouguer gravity anomaly gradient belt. So there is a spatial correspondence between the middle-Pleistocene Tongling Fault, the en echelon structures, the differential movement of the neotectonics, the Bouguer gravity anomaly gradient belt and the moderate-to-strong seismic activity belt in the Chaohu-Tongling area, indicating that they should be the tectonic indications of occurrence for moderate-to-strong earthquakes.     

STUDY FOR ABNORMAL VARIATIONS OF UNDERGROUND FLUID IN LIJIANG AREA,YUNNAN PROVINCE BEFORE LUDIAN MS6.5 EARTHQUAKE IN 2014

The study is based on the underground fluid observation data in Lijiang area, northwest Yunnan Province. The data include the water level and temperature in Dangxiao well and Jinjia well, and the ion measurements in Ganze spring. Combining with the data of regional hydrogeology, rainfall, well structures, and the geothermal gradient, we analyzed the variations of each measurement item before the Ludian M_S6.5 earthquake on August 3, 2014 and discussed the possible mechanism for the abnormal variations. The water levels of both Dangxiao well and Jinjia well are influenced by local rainfall, but the former shows hysteresis according to rainy seasons and is the long trend influence; while the latter shows synchronization between high water level and rainy season, indicating good connection between well water and shallow aquifer. The recharge water for Dangxiao well is in relatively low temperature, and the temperature sensor is located at the major connecting section between the well water and the aquifer; the water temperature variation is mainly affected by the discharge status and variation of water level. The Jinjia well is always in static level, and the temperature sensor is below the major connecting section between the well water and aquifer, so the water temperature is affected little by water level variations and in smooth fluctuation. The recharge source for Ganze spring can generally increase the contents of calcium and magnesium ions, so does the conductivity. The water level data of Dangxiao well since 2012 are decomposed with wavelet technique. The results, excluding such high-frequency components as the noise and the semidiurnal and daily wave components influenced by earth tide, are further processed with difference method in order to eliminate the trend effect. The results show that the relative change of water level is enhanced and in relatively rapid increase before the Ludian M_S6.5 earthquake; the corresponding water temperature values are high. The tendency of water level in Jinjia well displays descending, while the corresponding water temperature shows ascending. The content of calcium ion, magnesium ion, bicarbonate ion, and conductivity of Ganze spring are descending, while the content of fluoride ion is ascending. The abnormal variations of underground fluid in Lijiang area appeared in turns and were accompanied with minor earthquakes before Ludian M_S6.5 earthquake, which indicates enhancing of regional stress and increasing of fluid activity.     

Modeling lateral circulation and its influence on the along-channel flow in a branched estuary

A numerical modeling study of the influence of the lateral flow on the estuarine exchange flow was conducted in the north passage of the Changjiang estuary. The lateral flows show substantial variabilities within a flood-ebb tidal cycle. The strong lateral flow occurring during flood tide is caused primarily by the unique cross-shoal flow that induces a strong northward (looking upstream) barotropic force near the surface and advects saltier water toward the northern part of the channel, resulting in a southward baroclinic force caused by the lateral density gradient. Thus, a two-layer structure of lateral flows is produced during the flood tide. The lateral flows are vigorous near the flood slack and the magnitude can exceed that of the along-channel tidal flow during that period. The strong vertical shear of the lateral flows and the salinity gradient in lateral direction generate lateral tidal straining, which are out of phase with the along-channel tidal straining. Consequently, stratification is enhanced at the early stage of the ebb tide. In contrast, strong along-channel straining is apparent during the late ebb tide. The vertical mixing disrupts the vertical density gradient, thus suppressing stratification. The impact of lateral straining on stratification during spring tide is more pronounced than that of along-channel straining during late flood and early ebb tides. The momentum balance along the estuary suggests that lateral flow can augment the residual exchange flow. The advection of lateral flows brings low-energy water from the shoal to the deep channel during the flood tide, whereas the energetic water is moved to the shoal via lateral advection during the ebb tide. The impact of lateral flow on estuarine circulation of this multiple-channel estuary is different from single-channel estuary. A model simulation by blocking the cross-shoal flow shows that the magnitudes of lateral flows and tidal straining are reduced. Moreover, the reduced lateral tidal straining results in a decrease in vertical stratification from the late flood to early ebb tides during the spring tide. By contrast, the along-channel tidal straining becomes dominant. The model results illustrate the important dynamic linkage between lateral flows and estuarine dynamics in the Changjiang estuary.     

走滑断层地震地表破裂带分布影响因素数值模拟研究——以1973年炉霍MS7.6地震为例

地震后在断层两侧的强变形与破裂带是地震灾害最严重的区域.为系统、定量研究同震地表变形带特征及其影响因素,本研究建立了走滑断层的三维有限元模型,分别探讨了断层位错量、断层倾角、错动方式、上覆松散层厚度、沉积层土性等因素的影响规律.模拟结果显示：走滑断层同震地表变形表现为以断层为中心的近似对称单峰分布,强地表变形集中在断层两侧各50 m宽度范围,地表变形量峰值随位错量增加而增大,破裂带宽度也随位错量增加而增大,但增量逐渐减小,并趋于一个渐近值;断层倾角对地表变形与破裂带宽度影响表现为随倾角减小变形量峰值点向上盘小距离偏移;走滑兼正断位错引起的变形量峰值最大,但地表破裂带宽度最小,走滑兼逆断引起的变形量峰值最小,但地表破裂带宽度最大,直立纯走滑断层的两参量都居中;走滑断层地表变形量峰值随上覆松散层厚度增大而减小,但随厚度减小的速率逐渐变小,松散层厚度从5 m增加到20 m时,破裂带宽度随厚度增加而缓慢增加,但自厚度大于20 m时,破裂带宽度开始随厚度增加而逐渐下降;当不同土性覆盖层（粗砂、粉砂、黏土）厚度相同时,地震引起的地表变形量峰值自粗砂、粉砂、黏土逐次增大,当粗砂厚度为60 m以上时,3.6 m的同震水平位错已不能形成地表破裂,而粉砂的厚度为70 m以上,黏土的厚度则为75 m以上.     

遥感数据产品真实性检验不确定性分析研究进展

不确定性分析是遥感产品真实性检验最重要的部分,本文以叶面积指数LAI为例,从测量、模型以及蕴含在测量和模型中的尺度效应3个方面分析产品真实性检验过程的不确定性来源,并针对问题提出减小其不确定性的办法。对于相对均一的地表,地面测量的空间代表性比较好,可不考虑地表空间代表性引起的尺度效应和蕴含在模型中的尺度效应引起的不确定性。针对异质性地表,分为两种情况:若模型是线性的,蕴含在模型中的尺度效应可以忽略,只需要考虑测量的不确定性、模型本身的不确定性、以及地面测量的空间代表性引起的尺度效应;若模型是非线性的,则测量、模型和蕴含在测量和模型中的尺度效应引起的不确定性都需要考虑。     

河西走廊张掖绿洲土地利用/土地覆盖变化特征

Taking two false color composite Landsat 5 TM(Thematic Mapper)images of band 4,3,2taken in 1995 and 2000 as data resources,this paper carried out study on LUCC of Zhanye oasis in recent five years by interpretation according to land resources classification system of 1∶00,000 Resources and Environmental Database of the Chinese Academy of sciences.The results show that great changes have taken place in landuse/landcover in Zhangye oasis since 1995:(1)Changes of landuse structure show that cropland and land for urban construction and built-up area increased,on the contrary,water area and grassland decreased.These changes reflect the deterionration of arrangement of water and land resources between the upper and lower reaches of the Heihe River.(2)Regional differences of landuse/landcover are evident,characterized by following aspects:in Sunan County located in Qilian Mountain area,unused land and grassland decreased,but cropland and land for urban construction and built-up area inreased.In Minle and Shandan counties located in foothills,unused land,warer area and cropland decreased,but grassland and land for urban construction and built-up area increased.In Zhangye City,Linze County and Gaotai County located in plain area of the middle reaches of the Heihe River,unused land,warer area and grassland decreased,while woodland,cropland and land for urban construction and buile-up area increased.