基于连续重力台观测的玛多MS7.4地震的同震重力变化特征

同震重力变化可为位错模型的检验和约束提供新数据。文中利用指数函数和阶跃函数法分析了玛多M_S7.4地震震中距≤800km的5个重力台的同震重力信号。结果显示:观测和位错模型模拟结果的方向一致性好,只是量级存在差异。通过对同震重力变化精度的讨论,同震重力变化和GNSS垂直位移的比较,九寨沟M_S7.0、玛多M_S7.4同震重力变化空间分布的分析,以及漾濞M_S6.4地震对同震重力变化影响的改正,分析认为:震中距为175km的玛沁台记录到(2.9～4.0)×10~(-8)m·s~(-2)的同震重力变化;震中距为763km的中甸台在改正了漾濞地震的影响后记录到1.09×10~(-8)m·s~(-2)的同震重力变化;松潘台记录的9.1×10~(-8)m·s~(-2)的重力变化信号中应包含其他因素的影响;林芝台的负变化规律和位错模型模拟结果方向一致。综合文中的观测结果认为,玛多M_S7.4地震能够在175～800km的远场范围内产生约(0.5～4.0)×10~(-8)m·s~(-2)的同震重力变化信号。该结果可为未来中强地震远场产生的同震重力变化量级的判定提供参考。     

2010玉树M_S7.1地震前后青藏高原东缘绝对重力变化

2010年4月14日青海省玉树发生MS7.1地震后,中国地震局及时组织实施了地震科学考察,其中对玉树、西宁、姑咱和西昌等4个绝对重力点进行复测,通过比对前期成果,分别给出了2007年以来(地震前后)3～4期各测点H=1.0m(距墩面高)和H=0.0m(墩面)处的绝对重力变化(观测精度均优于3.0×10-8 m.s-2).结合已有区域地质构造运动、地震活动机制、形变测量成果等,主要结论或认识有:1)地震前后(含同震)玉树、姑咱、西昌绝对重力变化明显呈上升变化,玉树点和姑咱点尤为突出;2)同震模拟结果表明,地震前后玉树点绝对重力变化(H=1.0m)与同震破裂效应基本相当;3)从重力变化角度检核了玉树地震左旋破裂运动对羌塘块体东流运动和川滇菱形块体的南东-南南东运动具有明显激励作用,川滇菱形块体北段尤为强烈,南段可能因南南东向运动遇到中部贡嘎山隆起的阻挡吸收而有所减弱.     

重复绝对重力测量观测的滇西地区和拉萨点的重力变化及其意义

根据近年来在滇西地区和西藏拉萨绝对重力点上的一些新的绝对重力重复观测结果 ,对1990年以来在这些点上绝对重力重复观测结果进行了分析. 滇西地区的5个绝对重力观测 点的近10年的重复观测结果表明,大部分观测时段没有出现与地球动力学事件有关的重力变 化,只有丽江和洱源2个绝对重力观测点的观测结果显示丽江地震前后有变化. 为了研究该 重力变化的原因,本文正演模拟了出现重力变化期间丽江地震同震位错引起的重力变化,模 拟结果与实际观测结果有较好的一致性. 西藏拉萨近10年以来的重复观测结果给出了拉萨点 的绝对重力值以-1.82±0.9×10-8m·s-2·a-1速率下降,这从重力学 的角度反映出青藏高原的隆升. 对拉萨点的重力变化机制进行了探讨,根据印度板块与欧亚 大陆俯冲模型计算的拉萨点重力变化速率与观测到的重力变化速率较一致,表明现今拉萨地 区重力变化是由于印度板块与欧亚大陆俯冲所引起. 根据印度板块向欧亚大陆俯冲的位错模 型计算的拉萨点的重力变化与地表垂直位移的关系,将重力变化转换为拉萨点的隆升速率为 8.7mm/a.      

陕西重力网优化改造及监测能力评估

陕西重力网监测范围由关中盆地扩大到覆盖了鄂尔多斯块体南缘、关中盆地、秦岭山地及陕南、关中主要活动断裂带,同时与豫西、晋南、宁夏区域重力网实现了联网,测网监测能力由原来只具备对网内5级地震的监测提升到具备对发生在网内6级地震的监测。基于3个绝对重力基准约束下的重力观测平差结果表明,测网单位权中误差为7．7×10^-8 m·s-2,平均点值中误差7．9×10^-8m·s-2,当以2．5倍中误差作为限差时,可以识别发生在监测区域内40×10^-8m·s-2左右的重力相对变化,为研究鄂尔多斯块体南缘重力场变化提供依据。     

利用GRACE数据反演日本Mw9.0地震区域黏滞性

利用CSR(Center for Space Research)发布的GRACE RL05月重力场模型数据,通过水文模型GLDAS(Global Land Data Assimilation System)和CPC(Climate Prediction Center)扣除土壤水和雪水的影响,根据冰川模型扣除GIA(Global Isostatic Adjustment)的影响,采用P3M6去相关滤波和300 km扇形滤波,基于最小二乘拟合的方法得到日本M_W 9.0地震的同震及断层上下盘两个特征点重力变化时间序列,利用PSGRN/PSCMP模型对日本M_W 9.0地震区域黏滞性进行了反演,并计算了同震及震后5年研究区域重力变化的空间分布.结果表明,扣除土壤水和冰川均衡调整因素的影响,同震重力变化为-5.2×10~(-8)～2.9×10~(-8) ms~(-2);两个特征点在震后5年重力均增加,下盘重力增加较大;日本M_W 9.0地震区域黏滞性横向差异较明显,断层上下盘的地幔黏滞系数分别为2.5×10~(18) Pa·s、5.0×10~(17) Pa·s时,与GRACE观测值较接近,综合考虑断层上下盘的震后重力变化,区域黏滞系数大约为1.5×10~(18) Pa·s.     

泸定M6.8地震同震重力与形变效应模拟研究——闭锁剪力孕震模式的新证据

2022年泸定M6.8地震为近期川滇地区显著强震。本文基于Okubo平面矩形弹性位错理论,采用已有的由地震波反演获得的同震破裂模型,模拟研究了泸定M6.8地震产生的地表同震重力变化、垂直位移和水平位移。结果表明:(1)同震重力变化图像具有以发震断层为界,呈正、负四象限对称分布特征,与震前(2019年9月—2020年9月)实测重力变化图像和发震断层左旋走滑特征具有一致性,说明其孕震过程可用闭锁剪力模型来解释;(2)在远场区域,同震垂直位移图像与重力变化图像类似,位错引起的介质密度变化效应大于地表垂直位移效应,而近场地表垂直位移效应大于介质密度变化效应,显示出负相关性;(3)同震水平位移图像具有对称的四象限特征,与GNSS实测结果显示的变形特性一致。该结果可为地震前后重力、形变观测结果的解释提供依据,同时为强震孕育的机理研究提供线索,尤其为闭锁剪力孕震模式的进一步完善提供了新的实例依据。     

汶川大地震震后重力变化和形变的黏弹分层模拟

基于有限矩形位错理论及陈运泰等、JiChen等通过地震波反演的断层模型,结合研究区地壳——上地幔平均波速分层结构,利用PSGRN/PSCMP软件模拟计算了黏弹分层半空间中汶川地震（Ms8.0）产生的同震及其震后地表形变和重力变化,同时给出了震后形变和重力变化的年变化率．模拟结果表明,同震形变和重力变化显示出发震断层倾滑逆冲兼具右旋走滑综合特征;其变化主要发生于断层在地表的投影区附近,震后地表重力变化和形变量均不断增大,影响的范围也不断扩张;震后50a间近场年均形变量可达10mm,年均重力变化量可达2times;10-8m/s2,而远场年均形变量一般低于2mm,年均重力变化量一般低于0.4times;10-8m/s2;形变和重力变化在震后200a内变化较为显著,变化率逐渐减小,水平位移在400a后基本稳定不变,垂直位移、重力变化和大地水准面变化在800a后基本稳定不变．      

利用震后黏弹性位错理论研究苏门答腊地震(M_w9.3)的震后重力变化

本文利用2003—2011年的GRACE RL05数据提取了苏门答腊地震(Mw9.3)引起的震后重力变化,发现断层两侧震后重力变化速率存在明显差异,断层下盘总体变化率为0.55μGal/yr,断层上盘为0.16μGal/yr.基于子断层叠加的编程思想,本文将Tanaka的黏弹球体位错理论配套计算程序(简称黏弹位错程序)加以改造,克服了其近场计算精度不足(甚至错误)的缺陷,可用来研究大地震引起的近场震后位移与重力变化.本文利用改造后的黏弹位错程序计算了2004年苏门答腊地震(Mw9.3)产生的同震重力变化,计算结果在空间分布和量级上均与利用弹性位错程序计算获得的结果一致,验证了我们对黏弹位错程序进行改造的正确性.最后,结合GRACE卫星观测数据,本文利用Tanaka的黏弹位错理论研究了苏门答腊地区的地幔黏性因子.结果表明,该地区地幔黏滞性具有显著的横向差异,当发震断层上下两盘的地幔黏滞性系数分别取8×1018 Pa·s和1×1018 Pa·s时,模拟的震后重力变化在总体空间分布和变化趋势上与GRACE卫星观测结果更接近.     

关于地球横向不均匀结构对同震重力变化的影响研究

以Molodenskiy的三维不均匀潮汐理论以及孙文科等的球对称地球模型位错理论为基础,本研究借助互换定律和扰动方法,推导出一整套计算公式,用来高精度计算三维不均匀地球模型中地震位错引起的地表以及空间同定点同震重力变化.     

2019年甘肃夏河Ms5.7地震前重力场变化

本文对2017年以来中国地震局在南北地震带采集到的5期相对重力测网数据进行了平差计算,简要分析了甘东南研究区内测点平差精度,进而分析了2019年10月28日甘肃夏河Ms5.7地震前的区域重力场变化.结果表明:①研究区内90％测点平差后重力值精度小于10×10-8 m·s-2,与绝对重力观测结果符合性也较好,表明观测质量...     

SCIENCE CHINA Earth Sciences SUBJECT INDEX TO VOLUME 57(2014)

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Distribution of throughfall and stemflow in multi‐strata agroforestry,perennial monoculture,fallow and primary forest in central Amazonia,Brazil

The partitioning of rain water into throughfall, stemflow and interception loss when passing through plant canopies depends on properties of the respective plant species, such as leaf area and branch angles. In heterogeneous vegetation, such as tropical forest or polycultural systems, the presence of different plant species may consequently result in a mosaic of situations with respect to quantity and quality of water inputs into the soil. As these processes influence not only the water availability for the plants, but also water infiltration and nutrient leaching, the understanding of plant effects on the repartitioning of rain water may help in the optimization of land use systems and management practices. We measured throughfall and stemflow in a perennial polyculture (multi‐strata agroforestry), monocultures of peach palm (Bactris gasipaes) for fruit and for palmito, a monoculture of cupuaçu (Theobroma grandiflorum), spontaneous fallow and primary forest during one year in central Amazonia, Brazil. The effect on rain water partitioning was measured separately for four useful tree species in the polyculture and for two tree species in the primary forest. Throughfall at two stem distances, and stemflow, differed significantly between tree species, resulting in pronounced spatial patterns of water input into the soil in the polyculture system. For two tree species, peach palm for fruit (Bactris gasipaes) and Brazil nut trees (Bertholletia excelsa), the water input into the soil near the stem was significantly higher than the open‐area rainfall. This could lead to increased nutrient leaching when fertilizer is applied close to the stem of these trees. In the primary forest, such spatial patterns could also be detected, with significantly higher water input near a palm (Oenocarpus bacaba) than near a dicotyledonous tree species (Eschweilera sp.). Interception losses were 6·4% in the polyculture, 13·9 and 12·3% in the peach palm monocultures for fruit and for palmito, respectively, 0·5% in the cupuaçu monoculture and 3·1% in the fallow. With more than 20% of the open‐area rainfall, the highest stemflow contributions to the water input into the soil were measured in the palm monocultures and in the fallow. Copyright © 1999 John Wiley & Sons, Ltd.     

A Monte Carlo study of rainfall forecasting with a stochastic model

A procedure for short-term rainfall forecasting in real-time is developed and a study of the role of sampling on forecast ability is conducted. Ground level rainfall fields are forecasted using a stochastic space-time rainfall model in state-space form. Updating of the rainfall field in real-time is accomplished using a distributed parameter Kalman filter to optimally combine measurement information and forecast model estimates. The influence of sampling density on forecast accuracy is evaluated using a series of a simulated rainfall events generated with the same stochastic rainfall model. Sampling was conducted at five different network spatial densities. The results quantify the influence of sampling network density on real-time rainfall field forecasting. Statistical analyses of the rainfall field residuals illustrate improvement in one hour lead time forecasts at higher measurement densities.     

Anthropogenic Eutrophication and Red Tide Outbreak in Lacustrine Systems of the Kashmir Himalaya

Red tide, a recurrent phenomenon has become conspicuous in several Kashmir lake ecosystems since 1991. The responsible organism (Euglena pedunculata), a rare flagellate rediscovered in the Kashmir Himalaya (Khan 1993) caused first and unprecedented red tide outbreak, constituting a maximum of 96% of resident numerical phytoplankton density in Dal Lake. At present, conflicting hypotheses exist on the generation of causal assemblage(s) imparting redness to waters: Jeeji Bai (1991) linked its origin to acid precipitation – a fallout of burning oil‐fields during the Gulf War – whilst Khan (1993) holds local factor(s) responsible. Field/experimental studies support the latter contention that the influx of untreated sewage, in unison with warm temperatures, high levels of PhAR, iron and interruption to hydrological flow‐pattern together with absence/or reduction in grazing activity created conducive environmental milieu for red tide outbreak. Dal Lake “red tide” drifted the bloom‐inoculum to other waters, including Lake Wular, where additional ecological niches were carved out, threatening the aesthetic value and biological diversity of Kashmir lakes. Ecological monitoring indicates frequent seasonal red tide occurrence in Dal Lake (including summer‐autumn event of 1998) which testifies its unabated eutrophication status. Further studies are needed on ecological adaptability and biogeographic distribution of this rare and unique red tide‐causing flagellate.