陕西地磁短周期变化分布特征

为研究陕西地区地磁短周期变化特征,1996年9月从陕西南部石泉至甘肃宁县布设临时测线一条,在测线上进行地磁短周期变化三分量同步观测．在3 min至2 h周期范围内,统计计算了各测点各周期成分的地磁垂直转换函数、水平转换函数及谱成分关系．在数据处理中参考应用了随机数据理论,取得了较好效果．分析指出,该区地磁短周期变化受武功、乾陵之间地下近东西向异常感应电流集中的区域性影响及测点附近局部感应电流影响．其主要分布特征为,垂直分量变化在武功和乾陵之间存在一反向轴,频率响应显示出转换函数在周期约20 min时有最大值．      

涡度相关测定中平均周期参数的确定及其影响分析

应用涡度相关技术估算地-气界面的水、热和CO2交换量的研究越来越普遍.为了获得真实可靠的地表通量数据,在实际应用过程中必须根据每个观测点不同的下垫面条件,对观测数据进行相应的订正,并通过对观测数据的分析来确定相关的技术参数.利用禹城、长白山两个观测站的10Hz原始涡度相关数据,以不同的平均周期(从1~720min)对数据进行了重新计算,并将重新计算的结果与30min平均周期的通量值进行了比较,分析选取不同平均周期参数得到的通量值之间的差异.其中重点分析了在禹城小麦地获取的15d连续观测数据.结果表明:(ⅰ)在禹城,当平均周期取值范围在10~60min变化时,相对30min平均周期的通量值改变小于2%;当平均周期作短于10min变化时,通量的计算结果随平均周期的缩短而明显地降低(最大相对误差为?12%);当平均周期作大于120min变化时,通量的计算结果变得不稳定(最大相对误差为±10%以上).(ⅱ)禹城小麦地通量的计算表明,10min平均周期对研究通量日变化比较好,30min平均周期比较适合于通量的长期观测研究.(ⅲ)提出了一种可以确定涡度相关测定中平均周期参数范围的归一化比值方法.通过对农田和森林不同类型下垫面观测数据的对比分析表明:高大的森林下垫面比相对矮小的作物下垫面在一定范围内增加平均周期长度时有增     

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.     

利用AOK时频变换分析短时气压扰动对分量应变的影响

主要利用自适应最优核时频变换方法,对佘山台四分量钻孔应变3次受气压短时扰动的特征进行了分析,结果显示短时气压扰动27 min周期时影响显著,而且周期越长,应变变化与气压之间的相关程度越高。由此可见,自适应最优核时频变换在前兆资料中有较好的应用前景。     

极移振幅主要周期分量的时变特征

用JPL近年发布的地极坐标序列求得1893―1998年间极移的振幅序列,用最大熵谱分析方法求得了该资料序列包含的一些周期的参数,并利用小波变换方法分析讨论了其中的主要周期的变化.结果表明,极移振幅变化中存在着约6.5年和约40年的主要周期,且它们均具有一定程度的时变性.因此,在研究讨论极移与一些地球物理现象和自然灾害现象的关系时,应特别注意极移振幅中主要周期的时变特征.     

马场体应变气压响应特征分析

以马场体应变为研究对象,经小波分析对马场地震台体应变、气压不同时段相同频段的观测数据进行对比研究,分离观测数据信号,并进行相关性分析。分析结果表明,马场台气压对体应变的影响在周期为16~256 min和32~64 h两个卓越频段内主要表现为线性关系。     

中国大陆M_S≥7.0地震与太阳黑子活动之间关系的统计检验

利用1900—2017年间中国大陆地区64次M_S≥7.0地震资料,根据太阳黑子11年周期变化计算了它们的相位角,分析了它们的相位角分布,利用统计检验方法对它们与太阳黑子11年周期变化之间的关系进行了检验。结果是:中国大陆地区M_S≥7.0地震中约66%发生在太阳黑子11年周期变化的谷值点前2年—后3年的时段内,在α=0.001显著性水平下通过显著性检验。2019年底太阳黑子11年周期变化将达谷值点,因此,2018—2022年为中国大陆地区M_S7.0地震易发时段。     

全球地震活动周期的黄金分割特征

刊用黄金分割对全球及美国西海岸、太平洋西北缘、大洋岛弧、亚欧4条洲际地震带大震活动性进行了研究.研究的主要内容是针对地震活动的能量释放周期、A(b)指数进行的.研究的方法是采取地震活动的几个主要周期相比,若其值约为0.618,则认为它符合黄金分割性.研究表明,全球及各洲际地震活动的主要周期是符合黄金分割的.这项研究可利用地震活动的黄金分割性对全球及各洲际的地震活动高潮作出预测,但为什么地震活动会符合黄金分割性的物理实质的解答尚有一定的困难.文中还利用同样方法对中国华北地区的地震活动性进行了讨论,并对其今后的地震发生作了预测.认为2006年前后华北有发生7级地震的可能性,如不发生,则华北地区就进入长期无大震的平静期.     

巴彦岱1号井静水位周期变化主要影响因素研究

本文以巴彦岱1号井静水位为研究对象,分别应用别尔采夫滤波、小波分析与相关分析等方法,研究巴彦岱1号井静水位周期变化主要影响因素。分析结果表明,巴彦岱1号井静水位在日波、半日波频段主要受固体潮的影响;气压影响频段可能为64—256min、32—2048h（1—2个月周期的月波）2个频段,年周期变化与气温变化具有较强的线性相关性。     

利用改进的SRTI法研究中尺度电离层行波扰动

针对现有单站电离层行波扰动指数(Single Receiver TID Index,SRTI)探测中尺度电离层行波扰动时探测周期范围有限的问题,本文提出了一种改进的SRTI方法,以提高探测扰动周期的适用范围.介绍了利用SRTI和改进的SRTI探测中尺度电离层行波扰动的原理,从理论上分析比较了二者探测扰动周期范围的能力,并采用美国加州南部的5个IGS站2012年年积日189的GPS观测数据,对电离层扰动进行了分析.结果显示在21∶30—23∶00LT时,扰动观测序列存在周期为15min和39min的扰动波,但是现有SRTI方法只探测到了前者,而改进的SRTI法很好地探测到了两个周期的扰动波,表明其对短周期和较长周期的扰动均具有较好的灵敏性.利用改进的SRTI法计算的扰动观测序列,应用傅里叶变换相位差分法估计了电离层扰动的传播参数,其结果总体上与前人研究成果一致,这表明改进的SRTI法完全可以应用于电离层行波扰动的研究中,而且由于计算简单,在处理大量数据时具有一定优势.     

Horizontal ground deformation patterns and magma storage during the Puu Oo eruption of Kilauea volcano,Hawaii: episodes 22–42

Horizontal ground deformation measurements were made repeatedly with an electronic distance meter near the Puu Oo eruption site approximately perpendicular to Kilauea's east rift zone (ERZ) before and after eruptive episodes 22–42. Line lengths gradually extended during repose periods and rapidly contracted about the same amount following eruptions. The repeated extension and contraction of the measured lines are best explained by the elastic response of the country rock to the addition and subsequent eruption of magma from a local reservoir. The deformation patterns are modeled to constrain the geometry and location of the local reservoir near Puu Oo. The observed deformation is consistent with deformation patterns that would be produced by the expansion of a shallow, steeply dipping dike just uprift of Puu Oo striking parallel to the trend of the ERZ. The modeled dike is centered about 800 m uprift of Puu Oo. Its top is at a depth of 0.4 km, its bottom at about 2.9 km, and the length is about 1.6 km; the dike strikes N65° E and dips at about 87°SE. The model indicates that the dike expanded by 11 cm during repose periods, for an average volumetric expansion of nearly 500 000 m³. The volume of magma added to the dike during repose periods was variable but correlates positively with the volume of erupted lava of the subsequent eruption and represents about 8% of the new lava extruded. Dike geometry and expansion values are used to estimate the pressure increase near the eruption site due to the accumulation of magma during repose periods. On average, vent pressures increased by about 0.38 MPa during the repose periods, one-third of the pressure increase at the summit. The model indicates that the dikelike body below Puu Oo grew in volume from 3 million cubic meters (Mm³) to about 10–12 Mm³ during the series of eruptions. The width of this body was probably about 2.5–3.0 m. No net long-term deformation was detected along the measured deformation lines.     

Earthquake response of a steel frame building

A study has been made of the response, during the San Fernando earthquake 9 February 1971, of the nine-storey steel frame Building 180, located at the California Institute of Technology, Jet Propulsion Laboratory, Pasadena. The analysis throws light on the actual dynamical properties of the building during the earthquake, and also demonstrates that it is possible, when the ground motion is specified, to make accurate predictions of building motions during moderate earthquakes by using a linear viscously damped model. Methods of evaluating the lower mode periods and damping ratios from the earthquake records are described and the values obtained are compared with results from dynamic testing before and after the earthquake and with the periods computed from computer models of the building. Although no structural damage occurred and computed stresses in the steel frame were less than yield stresses, the periods measured by an ambient vibration test after the earthquake were of the order of 10 per cent higher than the pre-earthquake values. The maximum periods during the earthquake were found to be about 30 per cent higher than the post-earthquake periods.     

Shield-like upper mantle velocity structure below the Indo-Gangetic Plains: Inferences drawn from long-period surface wave dispersion studies

Shield-like upper mantle velocity structure has been inferred to exist below the Indo-Gangetic Plains from a study of mantle Rayleigh and Love wave group and phase velocities for periods extending to 200 seconds. The investigations have been carried out for the path between the World Wide Standard Seismic Network Stations at Chiengmai (CHG), Thailand, and New Delhi (NDI), India, for an earthquake with its epicenter in the New Hebrides Islands. Application of improved frequency time analysis has permitted measurement of regional surface wave dispersion for periods extending to several minutes; previous results for this region were for periods no greater than about one minute.     

Preliminary Map of Soil's Predominant Periods in Barcelona Using Microtremors

—?In order to evaluate soil effects in the urban area of Barcelona, the Nakamura's technique has been used to estimate the predominant periods of soils. Noise measurements for 195 sites were performed using a strong motion accelerograph and a velocimeter. In this work, the resulting preliminary map of predominant periods is presented. The obtained predominant periods are coherent with the geological and geotechnical features of the area. The analysis of the information has allowed the distinctions among several types of soil and underlying materials. A predominant period of about 0.06?s is evaluated for sites located over outcrop Paleozoic rock in the Tibidabo-Collserola Mountains. For sites consisting of material named tricycle, that is the most extensive and also the most heterogeneous zone, predominant period range from 0.10?s up to 2.0?s depending on the thickness of the surface materials and the kind and thickness of the underlying materials. In the Besós river two zones are observed: the riverside with periods between 0.50?s and 0.83?s and a second area with periods between 1.0 and 2.1?s. In the Llobregat river delta the obtained periods are quite homogeneous with values around 0.72?s. Other predominant periods are found in some tertiary rock outcrop.     

Evaluation of building period formulas for seismic design

Building period formulas in seismic design code are evaluated with over 800 apparent building periods from 191 building stations and 67 earthquake events. The evaluation is carried out with the formulas in ASCE 7‐05 for steel and RC moment‐resisting frames, shear wall buildings, braced frames, and other structural types. Qualitative comparison of measured periods and periods calculated from the code formulas shows that the formula for steel moment‐resisting frames generally predicts well the lower bound of the measured periods for all building heights. But the differences between the periods from code formula and measured periods of low‐ to‐medium rise buildings are relatively high. In addition, the periods of essential buildings designed with the importance factor are about 40% shorter than the periods of non‐essential buildings. The code formula for RC moment‐resisting frames describes well the lower bound of measured periods. The formula for braced frames accurately predicts the lower bound periods of low‐to‐medium rise buildings. The formula for shear wall buildings overestimates periods for all building heights. For buildings that are classified as other structural types, the measured building periods can be much shorter than the periods calculated with the code formula. Based on these observations, it is suggested to use C_r factor of 0.015 for shear walls and other structural types. Copyright © 2010 John Wiley & Sons, Ltd.     

太湖定振波的初步研究

初步分析研究了太湖定振波的变化规律,结果表明:(1)东、西太湖有各自的振动周期,东太湖变化范围在181—292min,平均为243min;西太湖在120—540min,平均为400min。(2)观测到的最大振幅(1/2波高)为120—130mm。(3)用差分法对定振波的特征值进行了近似估算,其周期误差为20min。(4)定振波引起的湖流相当大,当振幅为100mm时,最大流速可达±20cm/s。(5)定振波振幅的突变与气压场、风场和降水分布不均匀并在短期内发生突变有关。     

福建省数字化形变资料的异常分析

为了提取中短期地震前兆信息,对福建省2006～2008年数字化形变观测整点值资料进行了二进小波多分辨率分析,结果表明：小波分析结果的细节部分dn主要包含周期为2n-2a＋1小时的信号,而近似部分‰包含所有周期大于2n＋1小时的信号;在此期间,福建省及其邻近地区的中强地震发生前,多数形变观测台站或测项同步接收到了周期大约为21～43d幅度较大的异常信号,这些信号可能是地震前兆。     

The amplitude-frequency function of pressure variations: Steam-water mixture in the Verkhne-Mutnovskii hydrothermal system

The mathematical methods of direct spectral analysis were employed for the database that was drawn from the monitoring of well # 30 during 2004 in order to obtain the amplitude-frequency function of steam-water mixture pressure in the Verkhne-Mutnovskii hydrothermal system (the depth at which pressure was measured was 950 m, the time interval between measurements was 2 min, resulting in a total of about 250000 determinations). We identified large-scale and small-scale types of pressure variability. The large-scale variability reflects the low-frequency component of the variation and is seen as macro-fluctuations involving considerable (as large as 2 bars), sudden or gradual pressure changes. The small-scale variability consists of both irregular and regular oscillations. Medium-frequency and high-frequency components can be identified in the latter variability. The medium-frequency component consists of gradual fluctuations with periods of about 20 min (a frequency of 0.00083 Hz), with the maximum pressure changes between measurements being 0.7 bars. The high-frequency component consists of sudden pressure changes (drops, rises, or spikes), as well as of fluctuations with periods below 5 min.