基于噪声谱比法的福建台网观测台站的场地响应研究

应用噪声谱比法, 收集了福建台网观测台站记录的地脉动噪声数据, 计算分析了85个观测台站的场地响应． 根据场地响应曲线形态将福建台网观测台站分为4类, 并简要分析了影响台站场地响应结果的因素． 计算结果表明, 福建台网观测台站台基情况普遍较好, 在台站观测频带内场地响应曲线平坦, 大部分台站均没有明显的频率放大点． 本文采用H/V谱比法与Moya方法所获得的37个台站的场地响应结果基本一致, 仅有少数台站存在较大差异． 应用场地响应分析结果, 结合计算震级时所量取的周期, 对福建台网观测台站的单台震级校正值进行了估计, 并与统计方法获得的单台震级校正值进行了比对． 结果表明, 两种方法获得的台站震级校正值存在一定的相关性, 但由于考虑的影响因素不同, 具体的台站震级校正值尚存在差别．      

1999年台湾集集地震近断层竖向与水平反应谱比值的研究

选取了1999年9月21日台湾集集7.6级地震主震中68组断层距在20km以内的近断层台站记录和46组断层距在40~70km的东部台站记录,按台站的上下盘位置、场地条件和断层距分组,对其竖向和水平加速度反应谱比值V/H进行了统计分析。研究表明:1)断层的滑动方向和断层破裂的传播方向对断层距在3km以内的台站上的地面运动谱比值V/H有一定影响,且主要体现在中短周期范围内,例如平行断层方向的谱比值要比垂直断层方向的谱比值大。在下盘断层距3~20km的范围内,场地条件对V/H基本没有影响。2)在集集地震中长周期(>3s)部分的谱比值通常>32,且有一个较高的峰值,表明其竖向运动加速度中的长周期分量大于其它地震。3)对于下盘的台站,地面运动在短周期(<0.2s)段的谱比值不随断层距的增加而减少。与中远(>40km)距离的台站相比较,近断层台站的V/H在工程界关心的周期范围内普遍较大。4)场地条件对谱比值V/H的影响在近断层处不显著。在远离断层的东部台站上,硬土场地谱比值V/H在长周期段大于软土场地     

云南测震台网台站场地响应与ML震级测定的讨论

利用2016年云南测震台网记录到的地脉动数据,运用H/V谱比法计算分析了47个测震台站在0.1～20.0Hz频段内的场地响应。选取2012～2016年期间云南测震台网记录到的ML≥2.5地震做单台震级偏差统计分析,挑出受场地放大作用而出现单台震级大于台网平均震级的台站做去场地放大校正,然后重新统计单台震级偏差情况。计算结果显示云南测震台网的台站受台基条件和所处位置等地质构造因素影响,均存在一定程度的场地放大作用,大部分台站场地响应的卓越频率为1～6Hz,放大倍数为2～4倍。受场地放大作用的影响,大姚、芒市等19个台站的单台ML震级大于台网平均震级。在去除场地放大作用后,台站单台震级与台网平均震级的偏差有所减小。     

汶川地震强余震场地非线性反应

采用汶川地震强余震26个强震动台站记录,基于H/V谱比法,计算台站场地的强、弱震作用下场地卓越频率之比R_(fp)和体现强、弱震作用下场地H/V谱比曲线差异程度的DNL,进而识别并分析场地非线性反应特征。结果显示,R_(fp)、DNL与PGA之间存在显著相关性;其中10个台站出现明显的场地非线性反应特征;大部分台站发生场地非线性反应的PGA阈值为100 cm/s~2,部分为50 cm/s~2;实例证明,因某些台站不易通过H/V谱比法识别场地卓越频率,因此采用R_(fp)识别场地非线性反应具有一定局限性。     

安徽省国家强震动台站场地响应及背景噪声分析

利用安徽省部分强震动台站记录的地脉动数据和历史地震数据,采用H/V谱比法和噪声功率谱密度函数法,对比分析台站的场地响应及背景噪声,结果表明:全椒、马鞍山地震台的场地卓越周期小且背景噪声低;沈巷地震台卓越周期大且背景噪声高;三山地震台无明显卓越周期;地震台站背景噪声与场地响应曲线之间不存在一一对应关系。     

竖向地震动特征研究

本文以国内外数十次地震(ML≥5)的近场自由地表加速度记录为基础数据，进行近场加速度峰值比的统计分析，并着重对1999年台湾集集地震竖向地震动反应谱特征进行研究。统计结果表明，竖向与水平向(V／H)加速度峰值比与震源距相关，随震源距增加，比值降低；竖向反应谱及竖向与水平向加速度反应谱比是周期的函数、并与场地条件及震源距相关。     

天津地区场地响应和震源参数联合反演

根据天津数字地震台网记录的发生在天津地区的中小地震波形资料,采用Moya方法,反演天津地区39个地震的震源谱低频水平、拐角频率和28个台站的场地响应,计算了参与反演的地震矩、拐角频率、应力降和震源半径等参数,并讨论了它们之间的关系.结果表明: 27个井下台的场地响应曲线形态基本一致,低频有不同程度的放大,高频衰减较快;蓟县地表基岩台的场地响应低频基本在1附近变化,高频也有明显衰减.地震矩与震级及震源谱拐角频率的关系密切;拐角频率随震级的增大,有明显的下降;对于3级以上的地震,应力降、震源半径随地震震级的增大有明显的增大.     

地震预警仪观测地脉动差异与评估场地条件的可行性研究

根据台站场地条件进行地震动参数校正,有助于提高地震预警的有效性和准确性。针对我国地震预警台网中部分台址场地条件信息不完整及观测仪器的多样性,通过采用不同灵敏度的力平衡式加速度仪、速度仪和MEMS烈度仪,同时进行大量不同类别场地的地脉动观测,多角度对比分析时、频差别,探讨基于地震预警仪观测地脉动评价场地条件的可行性。结果表明,加速度仪灵敏度越高,H/V谱比卓越频率越易识别;速度仪与力平衡式加速度仪观测的地脉动,三分向傅氏谱和H/V谱比的谱形与卓越频率均一致;与TAG-33M强震仪相比,TMA-53烈度仪观测的地脉动整体幅值略高,波形较差,但随着振幅增大趋于一致;在近80%的场地上,TAG-33M强震仪与TMA-53烈度仪观测的地脉动傅氏谱卓越频率相差＜0.5 Hz;当幅值均方根值＞0.05 Gal时,TAG-33M强震仪与TMA-53烈度仪观测的地脉动竖向和水平向傅氏谱均趋于一致;当幅值均方根值为0.02 Gal～0.05 Gal时,TAG-33M强震仪与TMA-53烈度仪观测的地脉动竖向和水平向傅氏谱谱形均有较高的相似性;当幅值均方根值＜0.02 Gal时,TAG-33M强震仪与TMA-53烈度仪观测的地脉动傅氏谱谱形相差较大,相似性低;依据TAG-33M强震仪观测地脉动H/V谱比的卓越频率判定场地类别,准确率达83.3%;TMA-53烈度仪观测地脉动的H/V谱比过于平坦,大多数场地上卓越频率识别困难。     

震源机制对近场地震动反应谱的影响

将欧洲及其毗邻地区以及美国的部分近场强震记录按照震源机制进行分组,详细的分析了震源机制对水平和竖向分量地震动加速度反应谱放大系数以及竖向与水平向反应谱比值的影响.结果表明震源机制对震级不同的地震动以及地震动不同分量反应谱的影响程度不同;震源机制不仅影响反应谱峰值大小以及峰值位置,还在一定程度上影响反应谱的形状.     

2019年10月28日甘肃夏河5.7级地震强地面运动特征分析

2019年10月28日甘肃省夏河县发生5.7级地震,中国数字强震动台网的18个专业台站在此次地震中触发。本文处理捕获的54条三分向加速度记录,给出近场台站的地震动参数,绘制了震中附近区域峰值加速度等值线图,其长轴呈WN-ES方向展布。将实际观测数据与几种常用地震动衰减关系对比,发现俞言祥^[1]短轴衰减预测模型能更好地反映此次地震的影响场。将振幅较大的62LBL、62BLX台的反应谱与我国抗震设计反应谱比较,采用最小二乘法拟合出不同震中距5个台站各周期谱加速度衰减特性,总结了此次地震的反应谱基本特征。运用H/V谱比法对4个典型台站进行场地地震反应分析,研究了局部场地条件对峰值加速度和峰值速度的影响过程。     

应用微动H/V谱比法和台阵技术探测场地响应和浅层速度结构

为了快速而且廉价地获取北京市详细的场地响应和浅层速度结构,应用于地震动模拟和地震灾害预防,我们开展了微动观测技术和处理方法研究.本文利用2007年夏季北京五棵松地区进行的几个微动观测实验数据,使用单台H/V谱比法分析场地的卓越频率及其对应的放大系数,并对比了不同地震仪和观测时间对H/V曲线的影响;应用高分辨率F-K频谱分析方法从微动台阵数据中得到Rayleigh波的频散曲线并使用邻域算法反演出浅层速度结构.H/V结果表明该地区卓越频率在2.1～2.2 Hz之间,对应的放大系数下限约为3;利用微动H/V方法得到的场地卓越频率具有较高的稳定性.微动台阵反演结果给出了比较合理的波阻抗界面深度和层平均速度结构,认为地下80多米处的波阻抗界面是决定场地卓越频率和其场地放大系数的主要界面.本研究表明微动技术应用于评估城市地震场地响应和浅层速度结构是可行且易于实施的.     

张家口地震台和兴隆地震台地脉动信号初步分析

选取河北省张家口和兴隆2个台站的数字化地震仪连续1年,每日02～03时的地脉动记录,计算功率谱和自相关函数。结果发现兴隆台脉动谱中有4个比较突出的峰值,分别为0．3Hz、3Hz、8Hz、15Hz,张家口台只有3个峰值0．3Hz、3Hz、15Hz。兴隆台UD向的自相关函数呈现出一种比较典型的“红噪声”形态,EW向则呈现出负相关特征,认为可能是只作用于水平向的倾斜脉动的影响。小幅度的仪器干扰信号无论从脉冲标定还是地震波形中都很难发现的,而对脉动进行谱分析则很容易分辨。兴隆台和张家口台地脉动卓越周期时间曲线,基本集中在0．3秒,比较稳定。     

P- and S-Wave Site Response of the Seismic Network RESNOM Determined from Earthquakes of Northern Baja California, Mexico

—We determined the response to P- and S-wave incidence of the permanent stations of the seismic network of Baja California (RESNOM) using two independent methods. We selected 65 events with magnitudes between 2.2 and 4.8 and hypocentral distances ranging between 5 and 330 km. The site response of the ten stations analyzed was first estimated using average spectral ratios between the horizontal and the vertical components of motion (H/V ratios). As a second approach we performed a simultaneous inversion for source and site. In order to invert the spectral records to determine the site response, we made an independent estimate of the attenuation for two different source-station path regions. Then we corrected the spectral records for the attenuation effect before we made the inversion. Although the average H/V ratio of many sites is inside the error bars of the site response estimated with the spectral inversion, the spectral inversion tends to give higher values. For the S wave some sites show similar frequency of predominant peak when comparing the responses obtained with both methods. In contrast, for the P waves the H/V ratios disagree with the results of the inversion. In general, the site response of the stations is strongly frequency dependent for both P and S waves. We also found that the natural frequency of resonance of the sites is near 0.5 Hz for P and near 0.8 Hz for the S waves.     

汶川地震远场地震动场地相关性与分析方法评价

为考查远场地震动的场地相关性并评价一些场地特性分析方法的适用性,采用不同方法对汶川地震山东省12个远场台站的强震记录进行了分析.选取台站分别位于按建筑抗震设计规范(CBC)场地划分中的Ⅰ—Ⅲ类场地上.地震动记录的分析方法包括傅里叶幅值谱法,地震反应谱法,水平与竖向谱比率法,参考点谱比率法,以及尾波分析等.结果表明,按傅里叶幅值谱法,地震反应谱法,水平与竖向谱比法计算得到的卓越周期均远大于台站场地的卓越周期,不同方法得到的结果之间也有较大差别,且主要反映长周期地震动的卓越频率;参考点谱比率法的结果未反映地震动的卓越周期,也与场地的卓越周期差别较大;对完整记录尾波分析所得的结果比较接近场地的卓越周期.希望本文能为考虑远场地震作用时设计谱的建立,以及场地特性估计时地震动分析方法的选取提供参考依据.     

安徽强震动台站场地响应研究

采用H/V谱比法,利用安徽强震台网记录的波形数据,计算了3个强震台的场地响应。结果表明,当台站场地为基岩或覆盖层较薄时,由地脉动和S波数据分别计算出的谱比曲线一致性很好。当覆盖层大于30.5 m的时候,两者的放大因子有差异,即用S波计算的场地放大响应要明显大于用脉动计算的场地响应。     

ELECTROMAGNETIC ANOMALOUS PULSES BEFORE AND AFTER EARTHQUAKES(M>6.0) IN CHINA CONTINENT IN 2008

In this paper,we provided the electromagnetic anomaly phenomena prior to five earthquakes with magnitude M_W>6.0 occurring in China continent in 2008.The electromagnetic data in frequency bands 800~0.1Hz are recorded at two stations located in Urumqi,Xinjiang Uygur Autonomous Region (URQ) and Tonghai,Yunnan Province (TH).The time series of four horizontal components of the electromagnetic field at the stations are converted to the spectra using Fast Fourier Transform.The relationship between the electromagnetic anomalous phenomena and the earthquake events is studied through analyzing the temporal variation of electromagnetic spectra and comparing them with earthquake events.This study provides the new examples for electromagnetic anomaly phenomena before the earthquakes.The following features can be found.①The obvious anomalous power spectrum density (PSD) of electromagnetic fields in frequency band of 128~0.5Hz appeared before earthquakes.The anomalous PSD is related to the earthquake magnitude and the epicenter distance.The anomaly size of magnetic PSD is about 1-3 orders of magnitude bigger than the background field before Wenchuan M_S8.0 earthquake.② The changes of parameters are also related with frequency of the signal;The ELF signal strength observed at seismic stations is significantly related with distance between the stations or the measured magnetic and electrical field components and the source of earthquake.We also found that the field strength attenuated faster in area closer to the source than in far area.It is clear that the magnetic signals have higher signal noise ratio than the electric data.③ The amplitudes are also related with the azimuth of the earthquake to station and with the frequency of the data.④ The anomalous pulses showed cluster phenomenon in time.     

阿拉善左旗5.8级地震前地脉动信号特征分析

本文针对2015年4月15日发生在南北地震带北端的阿拉善左旗5.8级地震,利用乌海台、东升庙台、石嘴山台的连续数字地震波形资料,采用快速傅里叶变换对三个台站的2015年4月1日00时—4月15日23时波形数据进行分析,并持续跟踪0~0.25 Hz包络幅值极大值的变化形态。结果显示:(1)在5.8级地震前,震中附近的乌海地震台、东升庙地震台、石嘴山地震台记录的地震波形均出现频谱向低频偏移的现象;(2)三个台站出现低频异常的包络幅值极大值跟踪形态不一致,其中只有乌海台在震前出现明显的持续不稳定异常,异常持续时间约120h;(3)三个台站距离震中由近及远包络幅值极大值的跟踪形态差异明显。     

Low‐frequency passive seismic experiments in Abu Dhabi,United Arab Emirates: implications for hydrocarbon detection

Low‐frequency passive seismic experiments utilizing arrays of 3‐component broadband seismometers were conducted over two sites in the emirate of Abu Dhabi in the United Arab Emirates. The experiments were conducted in the vicinity of a producing oilfield and around a dry exploration well to better understand the characteristics and origins of microtremor signals (1–6 Hz), which had been reported as occurring exclusively above several hydrocarbon reservoirs in the region. The results of the experiments revealed that a strong correlation exists between the recorded ambient noise and observed meteorological and anthropogenic noises. In the frequency range of 0.15–0.4 Hz, the dominant feature is a double‐frequency microseism peak generated by the non‐linear interactions of storm induced surface waves in the Arabian Sea. We observed that the double‐frequency microseism displays a high variability in spectral amplitude, with the strongest amplitude occurring when Cyclone Gonu was battering the eastern coast of Oman; this noise was present at both sites and so is not a hydrocarbon indicator. Moreover, this study found that very strong microtremor signals in the frequency range of 2–3 Hz were present in all of the locations surveyed, both within and outside of the reservoir boundary and surrounding the dry exploration well. This microtremor signal has no clear correlation with the microseism signals but significant variations in the characteristics of the signals were observed between daytime and nighttime recording periods that clearly correlate with human activity. High‐resolution frequency‐wavenumber (f‐k) spectral analyses were performed on the recorded data to determine apparent velocities and azimuths of the wavefronts for the microseism and microtremor events. The f‐k analyses confirmed that the double‐frequency microseism originates from wave activity in the Arabian Sea, while the microtremor events have an azimuth pointing towards the nearest motorways, indicating that they are probably being excited by traffic noise. Results drawn from particle motion studies confirm these observations. The vertical‐to‐horizontal spectral ratios of the data acquired in both experiments show peaks around 2.5–3 Hz with no dependence on the presence or absence of subsurface hydrocarbons. Therefore, this method should not be used as a direct hydrocarbon indicator in these environments. Furthermore, the analyses provide no direct evidence to indicate that earthquakes are capable of stimulating the hydrocarbon reservoir in a way that could modify the spectral amplitude of the microtremor signal.