地球主磁场的能量密度谱及其长期变化

根据BJ地磁场模型和第8代国际地磁参考场(IGRF)模型，计算并分折了1690～2000年期间地球表面主磁场和分量的能量密度谱及其长期变化。结果表明1690～2000年期间主磁场的能量密度谱一直在减小，其主要原因是由于偶板子磁场的衰减产生的，而非偶板子磁场的能量密度谱在1690～1780年期间减小，1780～1890年增大，1890年以后快速增大。在地磁场总能谱的变化中，Z分量的贡献起主要作用。能量密度随谐波阶数的变化在半对数坐标中近似线性，非偶板子场的等效磁源深度位于核幔边界附近，n＝1，2谐波项的等效磁源位于地球内核边缘，其位置随时间变化。1780和1890年前后是地磁场变化的转折时期。能量密度谱的长期变化存在大约60a的周期规律。     

1945－1995地磁场功率谱及其长期变化

本文根据最新修正的国际地磁参考场模型，研究了１９４５－１９９５地磁场中心偶极矩变化，地磁总场及其分量Ｘ、Ｙ、Ｚ的空间功率谱，地磁场长期变化谱的经向漂移和纬向漂移的功率谱和西向漂移速度。研究中发现最近５０年偶极矩仍在继续衰减，空间功率谱的变化也呈减小趋势。在经向谱的漂移中观察到１９７０年出现最小值，而在纬向漂移变化中１９７０年出现最大值，西向漂移速度的变化也在１９７０年出现最大值，这种现象正是１９７０年发生的地磁长期变化的突变，称作地磁＂Ｊｅｒｋ＂。     

大同—阳高中强地震的地磁短期异常空间演变特征再研究

本文通过对１９８８至１９９３年首都圈部２９个测点的地磁差值ΔＦ及其年变率ΔＦ变化的全面分析，获得了２次大同－阳高中强地震的比较清晰完整的地磁短期异常空间演变图象。研究表明是一次以磁报震探索和震磁关系研究较好的近场前兆震例。     

基于10ka尺度的区域非偶极子磁场变化的研究

我们利用千年时间尺度的全球地磁模式CLAS10K.1b和CALS3K.4计算和分析了公元前10000年(10000 BC)至公元1900年(1900AD)中国大陆非偶极子(ND)磁场的时空变化,还考察了ND场和ND场Z分量的功率谱.以地磁ND场垂直分量Z为例,结果显示10000 BC—1900 AD期间,ND场有三个主要的变化期.10000 BC—2500 BC期间,正值区几乎占据了整个大陆;在2500 BC—1500 AD期间,正值区域变成负值区域.1500 AD—1900 AD,负向区域变为正值区域.东亚地区ND场的磁异常最早出现在1682 AD,其极值强度在研究期间总共增加了18128.73 nT,自1682年以来,极值位置一直向东南移动.ND场Z分量的平均年变率也可分为3个阶段,随时间共增加了56.45 nT/a.球谐阶数截断至N=3时东亚ND场磁异常区已基本形成,N>5时磁异常极值位置基本固定在44°N和103°E,强度随阶数增加而不断增强.功率谱表明,ND场的功率变化主要受Z分量功率的影响.     

唐山M 4.8地震地磁谐波振幅比变化

针对2012年5月28日河北唐山M 4.8地震,采用地磁谐波振幅比方法,分析昌黎、静海、红山及承德地磁台2007年1月至2015年12月地磁观测数据,结果显示：各台站10 min周期的计算结果波动性明显,其他周期形态较为一致;距震中最近的昌黎地磁台Y_ZHx（NS）测向的10-40 min周期地磁谐波在下降至极低值后,开始转折时发生地震,而Y_ZHy（EW）测向未出现明显转折现象;位于河北平原地震带中部的静海地磁台对此次地震反应显著,2个测向在震前均出现下降-转折-上升的变化特征。通过对比位于不同地区的4个地磁台站地磁谐波振幅比变化,发现受大范围整体构造应力场作用的影响,计算结果具有相似的趋势性变化特征,具体到局部地区或断裂带内部,各台站之间显示出一定差异。     

1945—1995地磁场功率谱及其长期变化

本文根据最新修正的国际地磁参考场模型，研究了１９４５－１９９５地磁场中心偶极矩变化，地磁总场及其分量Ｘ，Ｙ，Ｚ的空间功率谱，地磁场长期变化谱的经向漂移和纬向漂移的功率谱和西向漂移速度。研究中发现最近５０年偶极矩仍在继续衰减，空间功率谱的变化也呈减小趋势。     

大同－阳高中强地震的地磁短期异常空间演变特征再研究

本文通过对１９８８至１９９３年首都圈西部２９个测点的地磁差值△Ｆ及其年变率△Ｆ变化的全面分析，获得了２次大同－阳高中强地震的比较清晰完整的地磁短期异常空间演变图象。研究表明是一次以磁报震探索和震磁关系研究较好的近场前兆震例。     

地磁低点位移与地磁场等效电流体系关系的初步研究

利用地磁内外源场分离的方法,反演得到了1997年11月8日玛尼地震和1998年１月10日张北地震前地下和空间等效电流体系的演化图象,并分析研究了地磁低点位移出现前后等效电流体系变化特征．结果表明,内、外场等效电流体系的变化与地震ldquo;低点位移rdquo;异常现象有着内在的联系,等效电流体系变化可能是地磁低点位移异常现象产生的原因之一。随着我国地磁台站的加密建设,势必可以得到更为精确的地磁场等效电流体系的演化特征,更有利于地震预测的研究。      

航磁梯度数据曲化平分析

航磁梯度表征空间磁场的变化率,主要反映磁场的高频信息,较航磁总场随高度增加而衰减更快,其受地形起伏或飞行高度变化的影响更为严重,曲化平研究对航磁梯度数据的应用具有重要意义.本文在分析航磁梯度特点的基础上,针对航磁梯度数据的曲化平问题,采用等效源技术及位场物性反演方法实现了航磁梯度曲化平.讨论了等效源的设置问题,等效源采用单层向下延伸的长方体,延伸长度通常为其宽度的5~20倍,避免了多层等效源反演结果中物性分布趋近于地表,从而导致曲化平误差较大的问题,并节省了计算时间.理论模型计算与实际资料处理表明该曲化平方法可靠,具有实用性.     

淮南深地地磁总场连续观测与时变特征

深地实验室具有电磁干扰小的“超净”地磁观测优势,已成为地磁观测的新平台和研究热点.为了评估淮南深地实验室地磁环境、认识地磁总场时变特征及地下与地面耦合性,我们于2022年在地下巷道(-848 m)和地表(+22 m)同步实施了地磁总场长期连续观测,对观测数据进行了功率谱、小波谱、地磁总场变化特征的分析及与附近的蒙城地磁台比对.研究结果表明：(1)地下无(或弱)磁干扰点位的地磁环境较优越,与蒙城地磁台相媲美,适用于地磁场变化的高精度、长期连续观测;(2)地下地磁观测可有效过滤地表上由工业与人类活动等的电磁干扰,其记录的地磁总场变化与蒙城地磁台具有较好的耦合性;(3)地下磁测可清晰记录地磁总场的平静变化、不同周期磁暴、地磁脉冲等丰富的时变信息,可为地球系统科学研究提供地磁学依据.     

广西南丹大厂矿区震源参数研究

利用广西南丹县大厂矿区地震监测台网记录的地震波资料,采用Brune（1970）模型,将速度记录谱归算为震源位移谱,使用遗传算法计算拐角频率及零频极限,然后计算地震矩、应力降等小震震源参数,并系统分析各种参数之间的关系。大厂矿区38次较大地震的震源参数计算结果为：地震矩范围在2.18×1011~7.89×1012 N·m之间;震源破裂半径78~439m;地震应力降在0.01~1.79 MPa之间。表明：地震矩与震级、震源半径、拐角频率之间呈线性关系,而应力降不依赖于地震矩,分布较为离散。大厂矿区应力降值明显偏低,这可能与该区域背景应力低有关。     

行波效应对大跨度空间结构随机地震响应的影响

深入研究了行波效应对大跨度空间结构随机地震响应的影响,进一步完善了大跨度空间结构随机地震响应分析理论。推导了双支座、单自由度体系地震响应功率谱密度函数的解析表达式,研究了不同频率体系的响应峰值随地面视波速的变化规律,分析了多支撑点、多自由度体系的地震响应功率谱矩阵的特点,发现多自由度体系地震响应随地面视波速的变化规律与单自由度体系相似。数值模拟了某体育馆网壳结构在不同地面视波速情况下的随机地震响应,结果表明,考虑地震动行波效应后,结构地震响应随地面视波速的变化而显著变化,当视波速较低时其变化规律很复杂;且支撑点附近、受拟静力位移影响较大的部分杆件的地震响应明显增大,远离支撑点处、受拟静力位移影响较小的部分杆件的地震响应稍有减小。由此得出结论,对于大跨度空间结构的随机地震响应分析,必须考虑地震动的行波效应,尤其当受拟静力位移影响较大的部分杆件对结构抗震设计起控制作用时;且应对可能出现的地面视波速进行全面分析,作为结构抗震设计依据。     

广西平果2013年震群震源参数特征

使用广西数字地震台网记录的2013年6月-7月广西平果ML1.0-3.0震群162次地震波形资料,采用Brune（1970）模型,通过几何扩散校正、介质衰减校正、仪器校正等,将速度记录谱归算为震源位移谱,利用遗传算法计算拐角频率及零频极限,然后计算地震矩、应力降等小震震源参数,系统分析各参数之间的关系.研究表明：近震震级、地震矩、震源破裂半径、拐角频率、应力降等之间可以拟合为对数或半对数的线性关系;地震应力降、视应力与震源破裂半径没有明显的依赖关系,但与地震矩成正相关关系;与其他地区的同类研究结果基本一致,获得各参数的定标关系相近,尤其是通过最小二乘法拟合应力降与地震矩之间的关系后,与浙江珊溪水库地区的应力降与地震矩之间的关系有很强的一致性;与其他地区的应力降及视应力降相比较,本研究区属于低应力释放地区,但由于此次研究的地震事件时间跨度较短,且时间段比较集中,对该地区的应力释放水平还需跟踪研究.     

中国的地震烈度衰减率分区

本文采用1900年至1980年发生在中国的198个地震的等震线图,用公式 lnIi/I0=a——blnRi——cRi计算了烈度随距离的衰减率。式中I0为震中烈度,Ri为某烈度Ii等震线昕围面积的等效半径。按上式结果可将中国分成12个区,对于等震线明显受构造控制的地区,用上式分别计算了沿等震线长、短轴方向上不同的衰减率。在近场区,采用了一个与深度有关的修正量（深度因子）D,将上式改写为 ln（Ii/I0）=a——bln（Ri+D）——cRi得出了更适用的结果。对所得的分区结果和上两式中各量的意义进行了某些研究。      

浙江珊溪水库地震震源参数特征研究

利用2014年1月-2015年12月浙江省区域数字地震台网记录的1 360次珊溪水库M_L0.5-4.4地震资料,采用Brune模式,将台站获取的速度记录进行几何扩散校正、介质衰减校正及仪器校正后得到速度谱,对速度谱在频率域进行傅里叶积分得到震源位移谱,之后使用遗传算法计算得到拐角频率和震源位移谱零频极限值,进而计算出该区的地震矩为1010-1014 N·m,震源破裂半径为33-550 m,拐角频率为2.4-39.7 Hz,地震应力降为0.04-6.74 MPa,视应力为0-2.75 MPa.在此基础上,对各参数特征及其关系进行系统性分析,结果表明:各震源参数之间表现出一定的对数线性或半对数线性关系;空间上,应力降和拐角频率在库区西北段较高,东南段较低;应力降与地震矩在空间上呈反向关系,拐角频率与破裂半径在空间上呈负相关.      

A study on variations of non-dipole magnetic field over Chinese mainland during 2000 BC to 1990 AD

We calculated and analyzed variation of the non-dipole(ND)magnetic field at the millennium scale over the Chinese mainland during 2000 BC–1900 AD using the newest global geomagnetic model,CALS3K.4(3K.4).The newest-generation IGRF(IGRF11)was used to verify the results.Taking component Z for example,we calculated and analyzed the distribution and annual change rates of the ND field during 1900–1990 AD every 5 yr,using two models.To thoroughly analyze the contributions of field sources,quadrupole and octupole fields,and others within the ND field at the surface and core-mantle boundary(CMB)were investigated.Results show that there were three main variation phases of the field during the period 2000BC–1900 AD.The mean amplitude roughly reflected the ND field because of the distribution and variation of that field,corresponding somewhat to the mean amplitude change.A magnetic anomaly of the ND field over East Asia(EA)first emerged in 1682 AD,and its extreme intensity had increased a total of 15276.95 nT by 1900 AD.Its location moved continuously southeastward after 1690 AD.The asymmetry between location and intensity of extreme points over EA,particularly during1740–1760 AD,indicates irregularity of fluid motion inside the outer core.Mean annual changes of Z are generally divided into four phases,which first oscillated between 2000 and 800 BC,then increased,decreased and increased in the periods 800BC–300 AD,300–900 AD and 900–1900 AD,respectively.The intensity of mean annual change increased a total of 22.87nT/yr.Anomaly extreme locations based on 3K.4 and IGRF11 over EA centered around 44°N and 103°E for degree(n)greater than 5,and intensities continuously increased with n.During 2000 BC–1990 AD,ND energy of Z at the surface and CMB had decreased in total by 18.29%and 23.23%,respectively.The field source of 26–210 pole fields are more or less affected by the lithospheric field.Energies of higher degree at the surface attenuate by almost 99%compared with CMB,but mean attenuation speeds of the low-degree ND field are faster than high-degree,which implies that the low-degree ND field has a deeper source.     

The use of near-antenna artificial density ducts for increasing the power of VLF radiation in space plasma

We investigate the radiation from an artificial density duct excited by an annular electric current in the VLF frequency range. It is assumed that the duct possesses the form of a quasi-cylindrical density enhancement which smoothly reduces with distance from the source. We have found that the field in the duct is represented with a good accuracy in terms of eigenmodes whose propagation is supported in density enhancements. The radiation field in the background medium arises due to reemission of these eigenmodes from the duct. We calculate the excitation coefficients of eigenmodes and study the characteristics of a radiation field. We show that the presence of a duct with enhanced density can cause a considerable increase in the power radiated from the source. In particular, we study the distribution of radiated power over the spatial spectrum of waves excited in a surrounding magnetoplasma. It is concluded that under certain conditions an appreciable increase in the power radiated into the long wavelength part of the spatial spectrum can be achieved. We give concrete estimations for the conditions appropriate to the Earth's ionosphere.     

Source Characteristics of the 22 January 2003 M w?=?7.5 Tecom��n, Mexico, Earthquake: New Insights

Aftershock locations, source parameters and slip distribution in the coupling zone between the overriding North American and subducted Rivera and Cocos plates were calculated for the 22 January 2003 Tecomán earthquake. Aftershock locations lie north of the El Gordo Graben with a northwest-southeast trend along the coast and superimposed on the rupture areas of the 1932 (M _w?=?8.2) and 1995 (M _w?=?8.0) earthquakes. The Tecomán earthquake ruptured the northwest sector of the Colima gap, however, half of the gap remains unbroken. The aftershock area has a rectangular shape of 42?±?2 by 56?±?2?km with a shallow dip of roughly 12° of the Wadati-Benioff zone. Fault geometry calculated with the Náb??lek (1984) inversion procedure is: (strike, dip, rake)?=?(277°, 27°, 78°). From the teleseimic body wave spectra and assuming a circular fault model, we estimated source duration of 20?±?2?s, a stress drop of 5.4?±?2.5?MPa and a seismic moment of 2.7?±?.7?×?10²⁰?Nm. The spatial slip distribution on the fault plane was estimated using new additional near field strong motion data (54?km from the epicenter). We confirm their main conclusions, however we found four zones of seismic moment release clearly separated. One of them, not well defined before, is located toward the coast down dip. This observation is the result of adding new data in the inversion. We calculated a maximum slip of 3.2?m, a source duration of 30?s and a seismic moment of 1.88?×?10²⁰?Nm.     

NOC model of the earth's main magnetic field

The international geomagnetic reference field (IGRF) is a standard model for describing the spatial structure and temporal variation of the earth抯 main magnetic field[1—3]. The first IGRF model, designated IGRF 1965, was adopted by IAGA in 1968[4]. In l…     

research of source parameters and stress state in shandong segment of tanlu fault zone

In recent years, there have been few researches and analysis published on the seismic activity and stress state in Shandong segment of Tanlu fault zone using digital seismological methods such as seismic apparent stress, focal mechanism solution and so on. In this paper, source parameters such as focal mechanism solutions and apparent stress are calculated using the waveform data of M_L≥1 moderate-small earthquakes in Shandong segment of Tanlu fault zone recorded by Shandong digital seismic network since 2007. According to focal mechanism solutions, a statistical analysis is done on the focal dislocation types in the study area using triangle graphical method, and the results show that the faulting in this area is mainly of strike-slip mechanism, and there are less thrust and normal mechanism. Calculation with the mean stress tensor method illustrates that the direction of mean principle stress of Shandong segment of Tanlu fault zone is NEE-SWW, which is the result of the combined effect of the subduction of West Pacific plate and the extrusion of Indian plate to Eurasian plate; the small dip angle indicates that the mode of action of stress is nearly horizontal, and the direction of principal stress axis is nearly perpendicular to the Tanlu fault zone. Under the action of such compressive stress field, dislocation is not likely to occur and the stress accumulation is enhanced on both sides of the fault. The apparent stress is calculated using the source spectral parameters method. Apparent stress has positive correlation with the magnitude and increases with the increased magnitude. So we get apparent stress difference by subtracting the empirical fitting value from the apparent stress. By removing the impact of magnitude, and according to the temporal-spatial evolution image of apparent stress difference, we found that the apparent stress in Shandong segment of Tanlu fault zone generally has a trend of decrease starting from the Wenchuan earthquake in 2008, and the spatial distribution of apparent stress in the region is very uneven. Combined with the spatial distribution of b values, the result shows that high stress is mainly located in Anqiu segment and Tancheng-Juxian segment, especially in Anqiu segment where small magnitude earthquakes appeared accompanying with the high stress. Low b-value means high stress and low frequency means low stress release, which indicates that Anqiu segment might accumulate higher stress and is at the fault locking stage. The research will provide new data for better understanding the present active feature and stress state of the Shandong segment of the Tanlu fault zone.