中国东南沿海地区钻孔体应变对超强台风“利奇马”的响应特征与机制

依据超强台风"利奇马"的强度和时空演变特征,本文采用经验模态分解等方法系统地分析并揭示了该台风对我国东南沿海地区钻孔体应变影响的全貌,并在此基础上对台风扰动的机制进行了初步探讨。结果表明:①台风演变过程中漏斗状的长周期气压波动,是造成钻孔体应变大幅张性变化的物理成因,且体应变对台风低压系统具有即时的线弹性响应特征,其变化形态与气压漏斗高度相似,弹性变形的持续时间与气压波动的历时较一致;②在周期为103 h时,-18.2 hPa的气压变幅便可在地下62 m深处产生高达-112.1×10^-9的体应变,该频点的气压影响系数为6.2×10^-9/hPa;③在空间上,台风中心在980 km以外便能影响体应变观测,且随着台风的不断逼近或远离,其影响程度也相应地逐渐增强或减弱。     

钻孔体应变对气压和固体潮响应的传递函数——以陕西地区为例

如何厘清钻孔体应变信号中的气压和固体潮频响效应,一直是地球动力学研究中的一大难点.区别于国内现有研究,本文尝试采用传递函数对陕西地区的4个体应变台进行了系统诊断.结果表明:(1)低频带(0.1～0.5 cpd)气压响应的稳定性和可靠性较好,高频带(8～30 cpd)次之,中频带(0.5～8 cpd)最差;(2)不同频带...     

西太平洋台风对上海地区钻孔应变的低频扰动特征分析

基于上海佘山台四分量钻孔应变仪在6次西太平洋台风期间的观测记录,利用小波分解、优势振动方向等处理方法提取出台风所激发的显著低频扰动信号,并详细分析扰动信号在时频域及空间域的表现特性.结果显示:在低频区间,台风激发的扰动信号优势周期为2～4 min,信号能量随台风进程而变化,并主要与台风量级、台风中心的位置(海上或陆域)...     

合肥地震台钻孔体应变干扰分析

分析合肥地震台钻孔体应变观测资料干扰因素及特征,发现水位和气压等因素对TJ-Ⅱ型钻孔应变仪影响显著.在该地震台观测优化改造期间,钻孔体应变受到临近钻孔灌水的影响,而降雨和灌水导致的水位变化,对体应变干扰程度不同.     

青岛钻孔体应变短时畸变分析

在分析青岛钻孔体应变干扰的基础上,对青岛钻孔体应变出现的短时畸变进行了统计分析.结果表明,青岛钻孔体应变短时畸变可能是钻孔岩壁岩块掉落引起的张性异常,不是地震前兆异常;短时畸变与气压短时突变波动引起的信号均包含有2 min～5 min周期信号,比正常时多了5 min 的周期信号,两者的高频信号幅值相同,约为正常的1.5倍;气压的短时突变可引起青岛体应变观测出现固体潮同步波动畸变和曲线加粗变化.     

佘山台四分量钻孔应变仪记录的台风扰动特征分析

通过对佘山台四分量钻孔应变仪在台风“浣熊”(Neoguri)和“海葵” (Haikui)经过期间所记录的信号进行小波分解、连续频谱分析以及优势振动方向计算,监测到台风对近岸造成显著低频扰动,并分析了扰动信号在时间空间频率域的影响特征,在此基础上探讨了扰动的激发机制.分析结果显示:在台风发育过程中,覆盖周期为2—16分钟的3个频段能量呈现显著的上升—峰值—下降规律,且这种升降变化与台风中心到台站之间的距离具有良好的相关性,其中周期2—4分钟为扰动的优势频段,能量幅值则随周期的增大而不断减弱.四分量钻孔应变仪在两次台风逼近期间的优势振动方向均为160°左右.通过对比风速数据,结合海岸地形,认为风对陆地的作用并不是引起低频扰动的主要原因,更可能是台风以海浪为介质,通过不断与呈光滑凹形形态的杭州湾北部海岸线的反射作用,进而激发自由振荡频段的低频扰动信号.      

华东地区钻孔体应变对飑线天气过程响应的特征与机制

2018年3月4日华东地区爆发了一次强飑线天气过程,为揭示过境区域钻孔体应变对该飑线生命史期间的响应特征与机制,本文结合多普勒天气雷达和地面气象站数据,系统分析了南昌、黄山、湖州和岱山等4个钻孔体应变台的观测记录。结果表明：(1)飑线过境时的气压突变是引起体应变显著变化的主因,由此引起最大的体应变量为16.2×10^-9;(2)气压涌升幅度与体应变的弹性压缩量具有较好的线性关系,两者变化的周期较一致,为26～74 min,而气压影响系数高达5.0×10^-9/hPa;(3)各台对飑线的响应能力较好,而且在时间、空间和强度上,体应变变化能较好地呈现飑线的演变过程和传播特征。以上结果,不仅有助于科学识别飑线所引起单台或多台体应变异常变化的物理本质;还能为短周期气压效应的改正模型提供实证依据。     

荷载对钻孔应变观测影响的实例分析

在对比分析地表集中荷载模型和三维有限线段荷载模型的基础上,结合张家口台钻孔体应变2012年1~5月短期异常变化时段受工程影响的实例,采用三维有限线段荷载模型定量计算清水河清淤和蓄水阶段对张家口体应变影响的理论值。结果表明:计算得到的张家口体应变理论值为-3.12×10-9、4.07×10-9,而实际扣除线性漂移后短期异常为-1.58×10-7、2.30×10-7,理论值远小于实测应变值,因此该项异常变化不能仅归结为工程建设造成的荷载变化所引起,可能存在其他干扰因素或地壳应变变化的共同作用。荷载对钻孔应变观测影响的定量计算,在钻孔应变资料异常分析判定中能起到一定的辅助作用。     

小波方法对钻孔应变数据初步分析——以牡丹江台为例

牡丹江台钻孔应变仪自安装以来,受到很强烈的外界干扰,记录情况一直不好,没有取得理想的记录效果,仪器也没有发挥应有的功效。本文用小波方法对钻孔应变记录到的数据进行分析处理,查找原因,并提取有价值的信息,在现有情况下充分利用记录数据,为进一步对地震监测分析做准备。     

福建省钻孔体应变同震响应分析

通过福建省4个钻孔体应变仪对印尼强震的同震响应波对比分析,研究了福建省体应变变化特征,得出体应变幅度与震级成正比、响应延迟时间与震中距成正比的结论,进一步探讨了福建省各台站对印尼远强震的体应变变化特征及其与断层性质的关系。     

利用体应变观测智利8.8级大地震激发的地球球型自由振荡

用河北省体应变的数字化观测资料,利用功率谱密度估计方法,在没有对资料进行处理的情况下,准确获得了2010年2月27日智利8.8级大地震激发的0S5-0S35摹频球型自由振荡,并与地球初步参考模型(PREM)的理论自由振荡频率进行对比,发现实测振荡频率与PREM预测的振荡频率基本符合.河北省体应变的数字化观测资料的确可以...     

苏北平原井下摆观测效果的讨论

文章以江苏省大丰台、盐城台、淮阴台、海安台，射阳台井下摆观测为例。比较它们的观测结果，分析认为井下摆的观测效果不仅与地面复盖层的厚度有关，而且与井下摆周围的环境干扰，观测用井的质量有关。为了提高井下摆观测效果，应尽量减少环境干扰，并注意井的垂直度和固井，文章还指出，沿海地区井下摆受海浪干扰相当显著的。     

周至深井水震波数字化记录与地震波记录的对比研究

介绍了周至深井井孔概况和水位观测的仪器设备配置，通过对2000年10月6日日本本州7．3级地震的水震波数字化记录的频谱分析，与陕西数字地震台网同一地震事件进行对比研究，结果表明，周至深井可以记录到周期大于2s的水震波，对地动位移的放大倍率约为200倍，带宽大于DK-1地震仪和FBS-3地震计，相当于一台深井宽带地震仪。     

井下、地表地震计记录波形对比——以松原地震台为例

分析了相邻井下、地表地震计记录的背景噪声及近震、远震波形特征,以及相关的振幅谱及近震、远震接收函数波形特征。结果表明,井下地震计记录的背景噪声比地表地震计小1个数量级,其近震、远震波形记录较清晰、简洁;井下、地表地震计记录的远震振幅谱和径向接收函数具有较好的一致性,但背景噪声、近震振幅谱、近震接收函数、远震切向接收函数波形存在一定差异;由地表地震计得到的近震震级比井下地震计的大0.12,地表地震计到井下地震计之间的P波速度约为2 km/s。     

Simulating and mapping the risk of surge floods in multiple typhoon scenarios: a case study of Yuhuan County,Zhejiang Province,China

We propose a scenario-based method for simulating and mapping the risk of surge floods for use by local authorities concerned with public safety and urban planning in coastal areas. Focusing on the triad of hazard, vulnerability and adaptation capability, we estimate the comprehensive risk and display its spatial distribution using the raster calculation tool in ArcGIS. The detailed methodology is introduced via a case study of Yuhuan, an island county in Zhejiang Province, China, which is frequently affected by typhoon storm surges. First, we designed 24 typhoon scenarios and modeled the flood process in each scenario using the hydrodynamic module of MIKE 21. Second, flood depth and area were used for hazard assessment; an authorized indicator system of land use categories and a survey of emergency shelters were used for vulnerability and adaptation capability assessment, respectively; and a quantified model was used for assessment of the comprehensive risk. Lastly, we used the GIS raster calculation tool for mapping the risk of storm surges in multiple typhoon scenarios. Our principal findings are as follows: (1) Seawalls are more likely to be overtopped or destroyed by more severe storm surges with increasing typhoon intensity. (2) Most of the residential areas with inadequate emergency shelters are highly vulnerable to flood events. (3) As projected in the risk mapping, if an exceptional typhoon with a central pressure of 915 or 925 hPa made a landfall in Yuhuan, a wide range of areas would be flooded and at high risk. (4) Determining optimal strategies based on identification of risk-inducing factors is the most effective way of promoting safe and sustainable development in coastal cities.     

Ferrospinels and petromagnetism of Siberian traps: A case study of traps drilled by the Norilsk borehole

Magnetic characteristics and compositions of ferromagnetic species of trap samples from the Norilsk borehole are studied; the borehole penetrated the complete section of a trappean rock sequence (nearly 3 km) represented by eight magmatic formations. The lowest (Ivakinskian) formation consists of rocks of the subalkalic type, and the remaining formations generally belong to the tholeiitic series. Primary ferromagnetic phases are represented by titanomagnetites with various ulvospinel concentrations in a solid solution. Three modes characterized by TiO₂ concentrations of 14.6, 18, and 23.9 wt % are revealed. The Ivakinskian rocks are most magnetized, and magnetization is low in core samples from depths of 1700–2500 m. Various magnetic characteristics have polymodal distributions of their values. Plateau basalt samples of the Ivakinskian Formation from other regions of Siberia, the Lory Plateau (Armenia), and Kamchatka are additionally studied. On the whole, titanomagnetites of plateau basalts were crystallized under the quartz-fayalite-magnetite (QFM) buffer conditions.     

Study on relationship between features of strain anomaly obtained by borehole strain meter at Wushi station in Xinjiang and strong earthquake: Taking Jiashi MS = 6.8 earthquake as an example

Introduction According to the Seismograph Network of China, an earthquake of MS=6.8 occurred at10:03:42 on February 24, 2003 in Jiashi county, Xinjiang (39.55°N, 77.15°E) with the focal depthof 25.2 km. The macroseismic epicenter located at the boundary of Bachu and Jiashi counties,Xinjiang Uygur Autonomous Region. 248 persons died and 4 853 ones were injured (2 058 ofthem were heavily injured) in the earthquake. 49 656 households (about 205 079 persons) losttheir houses. The Dis…     

Drought analysis of monthly hydrological sequences: a case study of Canadian rivers

Abstract

Two parameters of importance in hydrological droughts viz. the longest duration, L_T and the largest severity, S_T (in standardized form) over a desired return period, T years, have been analysed for monthly flow sequences of Canadian rivers. An important point in the analysis is that monthly sequences are non-stationary (periodic-stochastic) as against annual flows, which fulfil the conditions of stochastic stationarity. The parameters mean, μ, standard deviation, σ (or coefficient of variation), lag1 serial correlation, ρ, and skewness, γ (which is helpful in identifying the probability distribution function) of annual flow sequences, when used in the analytical relationships, are able to predict expected values of the longest duration, E(L_T ) in years and the largest standardized severity, E(S_T ). For monthly flow sequences, there are 12 sets of these parameters and thus the issue is how to involve these parameters to derive the estimates of E(L_T ) and E(S_T ). Moreover, the truncation level (i.e. the monthly mean value) varies from month to month. The analysis in this paper demonstrates that the drought analysis on an annual basis can be extended to monthly droughts simply by standardizing the flows for each month. Thus, the variable truncation levels corresponding to the mean monthly flows were transformed into one unified truncation level equal to zero. The runs of deficits in the standardized sequences are treated as drought episodes and thus the theory of runs forms an essential tool for analysis. Estimates of the above parameters (denoted as μ_av, σ_av, ρ_av, and γ_av) for use in the analytical relationships were obtained by averaging 12 monthly values for each parameter. The product- and L-moment ratio analyses indicated that the monthly flows in the Canadian rivers fit the gamma probability distribution reasonably well, which resulted in the satisfactory prediction of E(L_T ). However, the prediction of E(S_T ) tended to be more satisfactory with the assumption of a Markovian normal model and the relationship E(S_T ) ≈ E(L_T ) was observed to perform better.     

Short‐term variability in isotopic composition of precipitation: A case study from the Midwestern United States

Oxygen and deuterium isotopes in precipitation were analysed to define local isotopic trends in Iowa, US. The area is far inland from an oceanic source and the observed averages of δ¹⁸O and δ D are ? 6·43‰ and ? 41·35‰ for Ames, ? 7·53‰ and ? 51·33‰ for Cedar Falls, and ? 6·01‰ and ? 38·19‰ for Iowa City, respectively. Although these data generally follow global trends, they are different when compared to a semi‐arid mid‐continental location in North Platt, Nebraska. The local meteoric water lines of Iowa are δ D = 7·68 δ¹⁸O + 8·0 for Ames, δ D = 7·62 δ¹⁸O + 6·07 for Cedar Falls, and δ D = 7·78 δ¹⁸O + 8·61 for Iowa City. The current Iowa study compares well with a study conducted in Ames, Iowa, 10 years earlier. The differences between Iowa and Nebraska studies are attributed to a variable climate across the northern Great Plains ranging from sub‐humid in the east to semi‐arid in the west. Iowa being further east in the region is more strongly influenced by a moist sub‐humid to humid climate fed by the tropical air stream from the Gulf of Mexico. The average d‐excess values are 10·06‰ for Ames, 8·92‰ for Cedar Falls and 9·92‰ for Iowa City. Eighty seven percent of the samples are within the global d‐excess range of 0‰ and 20‰. The results are similar to previous studies, including those by National Atmospheric Deposition Programs and International Atomic Energy Agency. It appears that the impact of recycled water or secondary evaporation on δ¹⁸O values of area precipitation is minimal. Copyright © 2008 John Wiley & Sons, Ltd.