浅析台风对湖州地震台重力、地倾斜观测的扰动

正通过对湖州地震台SSQ-2型石英水平摆倾斜仪、VP型宽频带垂直摆倾斜仪、DZW型重力仪多次台风期间分别记录到潮汐曲线上叠加了连续的"扰动"信号分析表明,这些"扰动"信号来自西太平洋的台风。这种振动传播的可能有两个:一是台风中心过境引起的地表振动像地震波那样通过地壳传播;另一个可能是通过大气层。台风和海浪摩擦可以产生次声波,其     

泰安地震台重力扰动现象研究

利用滤波分析法对山东泰安地震台重力固体潮观测的分析表明,重力观测中存在大量高频扰动信号.通过与气象观测实况资料的对比发现,这些异常扰动信号除了受台风等热带气旋影响外,还明显与“冷空气”过境等区域强对流天气有关. 对泰安台JCZ-1甚宽频带地震仪观测资料的频谱分析和滤波处理进一步表明,区域强对流天气及台风对重力仪的影响频段均在1—8 s范围内,其中2—6 s区间影响最为显著; 强对流天气过程触发的扰动信号范围可以在1—16 s,但8 s后扰动信号对重力仪观测基本不造成影响,即重力仪对高频扰动信号的响应存在8 s的截止周期.JCZ-1甚宽频带地震仪的波谱分析还反映出扰动信号的动态特征,即强对流天气产生的扰动信号在发展、传播过程中,首先出现的信号频率较高,随着时间推移信号逐渐向低频演化,揭示了干扰信号传播的多普勒效应以及扰动信号激发源的移动特性.      

强台风对汶川大地震和昆仑山大地震“震前扰动”影响的分析

2008年8.0级汶川大地震发生前约40 h起,中国地震局测震台网中的宽带地震仪、重力仪和倾斜仪都记录到了明显的低频扰动现象.然而,在此期间西太平洋上空产生了一次强台风Rammasun（威马逊）;与此类似,2001年8.1级昆仑山大地震发生前约60 h起,国家地震局测震台网中的宽带地震仪也记录到了明显的低频扰动现象,在此期间中国南海上空产生了一次强台风LingLing（玲玲）.本文针对这两大地震的“震前扰动”现象进行了研究,旨在探讨其“震前扰动”现象是否与台风引起的巨浪产生的地脉动效应有关.我们的研究结果表明：在中国内陆观测到的异常扰动与台风路径以及台风的强度密切相关.近海台风可在中国大陆内地引起明显的异常扰动;而远离大陆海岸位于深水海域上空的台风,很难在中国大陆内地引起明显的异常地脉动变化.台风LingLing的路径距离中国海岸最近处仅有约700 km,而台风Rammasun距离中国大陆海岸最近处却达1300 km.本文的对比分析研究表明：路径和强度类似于LingLing的台风在中国内陆可引起明显的异常扰动.因此,中国内陆和沿海许多地震台记录到的昆仑山大地震的“震前扰动”源于LingLing地脉动效应的可能性较大;但位于新疆的地震台记录到的扰动信号频率却明显偏低,这一现象值得注意.路径和强度类似于Rammasun的台风很难在中国内陆引起明显的异常扰动,因此汶川大地震的“震前扰动”完全源于台风Rammasun地脉动效应的可能性较小.汶川大地震的“震前扰动”产生的原因和机理值得我们去进行深入的探讨和研究.     

风暴及台风天气引起的微震现象分析

正近年来,随着宽频带地震仪及数字化重力仪、倾斜仪在全国的广泛布设,越来越多的研究显示,宽频带地震仪、重力仪和倾斜仪都能观测到一种连续的地震动信号。国内较早的工作主要将其对应为大地震前的前兆异常或震前慢地震,但随后大量的研究表明,这种连续震动信号与台风和大风天气有关。国际地学界对这种连续震动信号的研究在1950年以后就有了比较明确的认识,一般把这种迭加在地脉动或固体潮观测曲线上、周期在2~20s之间的     

云南测震记录数据对台风登陆过程的响应

针对云南省香格里拉县发生的2次地震的"震前扰动"现象,以及同时期在关岛西南部海面上发生的超强台风Utor活动情况,对云南省部分数字地震台站观测到的异常扰动信号的频谱特征及持续时间进行分析研究,探讨震前低频扰动现象是否与台风引起的巨浪产生的地脉动效应有关。结果显示,"震前扰动"现象确与台风路径以及台风的强度密切相关,异常扰动信号开始时间基本与台风进入大陆架时间一致,台风引起的异常扰动信号的优势频率为0.15~0.3Hz。     

风暴及台风天气引起的微震现象分析

本文主要利用时频分析法,基于2016年以来山东省泰安台重力仪及宽频带地震仪观测到的资料,对风暴天气和台风天气引起的微震现象进行研究. 结果表明:这两种天气过程产生的微震信号的频率基本分布在2—20 s之间,能量集中在5—7 s,15 s附近存在一个能量平稳加强的频段;风暴天气产生的微震信号具有由高频向低频演化的动态特征;两种天气条件下产生的微震信号均具有连续、高频及持续时间长的性质,反映了微震信号激发源的移动特征。 结合泰安台微震与风暴和台风天气的一一对应情况,认为微震是一种与近海风暴或远海台风活动有关的微震动过程,而不是与地震有关的前兆异常。      

重力仪高频信息和地脉动的观测研究

本文介绍了应用电磁反馈零位检测技术改装的重力仪进行高频信息的观测。阐述重力仪高频信息频谱分布特征、数据采集、数字计算和随机信息的处理方法。利用高频信息可以很好地观测和研究地脉动,给出北京香山地震台利用重力仪高频信息观测所得的地脉动功率谱。分析了地脉动特征及其与台风过程的关系;讨论了某些大地震前所出现的地脉动异常现象。得出北京地区正常地脉动频率分布范围为0.13-0.32Hz,优势频率为0.2Hz,相应的卓越周期为5s的脉动频率异常,也可能在地脉动的正常频率处（0.2Hz左右）,出现幅度很大的脉动幅度异常,后者又往往与台风引起的幅度异常相混淆。     

由泰安地震台形变资料看固体潮数字化观测运行

泰安地震台为全国形变一类观测台。现有除重力仪、井下竖直摆外的几乎所有形变固体潮数字化观测仪器。通过对山东泰安台固体潮形变观测的数字化与模拟资料的一致性、精度和格值的对比研究,以及对数字化资料连续性、稳定性的综合统计分析,对各套仪器的运行状况进行了评价和论证。认为数字化与模拟观测资料的固体潮形态、观测精度、方差及均值无显著性差异。在数字化倾斜仪中,水管倾斜仪的稳定性及精度较高,石英摆存在一定程度的漂移,垂直摆倾斜仪的漂移较大、资料内精度较低。伸缩仪资料也存在精度较低的情况;压容及体应变仪资料内精度较高,但压容仪漂移较大,仪器稳定性不及体应变仪。     

震前重力扰动与背景噪声时空变化特征——以玛多MS7.4与漾濞MS6.4地震为例

2021年5月21—22日,云南漾濞、青海玛多先后发生了M_S6.4和M_S7.4地震。为检测震前是否存在重力扰动与重力仪背景噪声异常信号,文中基于中国连续重力台网中15台重力仪的秒采样数据,成功提取了震前重力扰动信号,并计算了排列熵(PE)及重力仪在地震频段(200～600s)的背景噪声等级(SNM)。结果表明：1)大地震发生前多数台站在2021年5月15—18日存在1组重力扰动信号,其中沿海台站同时还存在其他2组扰动信号,扰动幅度为±(10～100)μGal,扰动频率集中在0.15～0.25Hz。沿海台站的扰动幅度普遍大于内陆台站,震中距与扰动幅度无明显相关性,沿海台站扰动幅度较大及产生其他2组扰动的原因可能与海浪脉动或局部降雨有关;2)不需要对原始重力序列作任何预处理,PE能够快速检测到数据中的突变信号,PE时间序列中持续显著下降的信号对应震前扰动信号,PE瞬时向下的脉冲信号对应地震波引起的颤动信号;3)多个台站的SNM时变曲线显示,震前2个月(2021年3月初)直至主震发生时背景噪声水平显著升高,SNM的空间分布表明,震前1～2个月,位于...     

海南井水位对热带气旋响应特征的分析

大量观测资料及实验研究证实,地下水对地壳应力-应变的响应频率较宽,可记录到地震波中的瑞利波(10～20 s)、潮汐波动(1/3～1/2 d)、气压波动(儿小时至几十天)等.在文献中,已见热带气旋引起地震仪的震颤波,倾斜仪和重力仪的“脉动加粗”等方面研究成果,但井水位对大气环流、雷暴高压、热带气旋等的响应,则未见报导.     

安徽六安井下地震计与地表地震计观测质量对比

将安徽六安2015年安装的2台GL-S60B井下地震计记录数据,分别与在各自井口架设的BBVS-60地表地震计记录数据进行对比,得到了噪声有效值、频谱特征和有效动态范围等,初步获得了井下地震计在六安的运行情况。研究表明,井下地震计观测效果明显优于地面地震计,这对于未来地震台站选址、仪器选型等具有参考意义。     

Correlations of three-component ground motions from the 23 June 2010 Val-des-Bois, Québec, earthquake

In this paper, we investigate the characteristics of three-component ground motions recorded during the $M_\text{w}\,5.2$ Val-des-Bois (Québec) earthquake, which occurred on the 23 June 2010. The earthquake is the largest recorded event in eastern Canada within the last decade. The records analyzed were provided by a strong motion monitoring network, comprising accelerometers located at sites with different soil conditions. The two orthogonal horizontal components and one vertical component at each recording station are uncorrelated to determine their principal directions, and the results obtained are used to characterize intensity ratios between the three uncorrelated components. A new hodograph representation is proposed to highlight the correlation between accelerations and displacement trajectories along various time increments at each recording station. The principal components are discussed in light of seismographic data, local site conditions, and trajectories. Time–frequency analyses of the uncorrelated records are also conducted to compare the distribution of spectral amplitudes and frequency content along the three principal components during the shaking. The results of this work shed more light on the characteristics of three-component ground motions from an important Eastern North America earthquake, and could be used to calibrate simulated multicomponent ground motions in this region.     

兰州形变台水管倾斜仪映震能力的分析研究

以兰州形变台FSQ水管倾斜仪1987年以来的观测资料为研究对象,从非潮汐和潮汐两个方面,利用形态分析法、曲线拟合、残差分析、潮汐因子动态分析、半日波大潮椭圆以及潮汐偏角分析等方法对数据进行了系统分析,研究了观测异常与地震的关系。结果表明该台的水管倾斜仪对邻区的中强地震有很好的中、短期响应。     

十堰市地震台测震系统运行问题及解决措施

受供电和数据传输方式的影响,十堰地震台测震系统数据断记时间较长,数据质量较差。为此,采用3路交流供电自动切换辅助2路直流供电方式,为仪器运行提供稳定的电力供给,并采用一主一备有线光纤传输解决微波单线传输的弊端。为验证解决措施的有效性,选取该台2009—2020年测震记录,统计SEED格式波形记录数据断记时长,结果发现,在2013年进行整改以来,数据断记现象减少,断记时长明显缩短。选取该台2015—2021年测震系统仪器更换以来的数据记录,分析地方震、近震、远震和极远震震相特征,发现该台记录地震波形清晰、可靠。可见,该台数据断记整改措施得到有效检验,测震系统运行质量得到提升,可为国内同类测震台站提供参考。     

Joint observation of long period tremor signals with broadband seismometer,tiltmeter and gravimeter

We report here the observation result of joint observation of long period tremor signals with broadband seismome-ter,tiltmeter and gravimeter at the HUST(Huazhong University of Science and Technology)station.The observed data were compared and analyzed.Since 2005,the several tens of abnormal tremor signals which are weak,com-plex and duration of 2 to 3 days have been synchronously recorded by the different instruments.The tremor signals have the periodic domain in the range of 3 to 5 minutes,20 to 30 minutes and even more than 1 hour.The observa-tion shows such tremors are a physical existence.The analysis indicates that a part of the tremors caused by the typhoon from the western Pacific Ocean.These tremors have a close relationship with wind velocity of typhoon and distance between the typhoon center and the station.Except these,the cause of others is still unclear.     

Tsunamis on the Pacific Coast of Canada Recorded in 1994–2007

In the last 15 years there have been 16 tsunami events recorded at tide stations on the Pacific Coast of Canada. Eleven of these events were from distant sources covering almost all regions of the Pacific, as well as the December 26, 2004 Sumatra tsunami in the Indian Ocean. Three tsunamis were generated by local or regional earthquakes and two were meteorological tsunamis. The earliest four events, which occurred in the period 1994–1996, were recorded on analogue recorders; these tsunami records were recently re-examined, digitized and thoroughly analysed. The other 12 tsunami events were recorded using digital high-quality instruments, with 1-min sampling interval, installed on the coast of British Columbia (B.C.) in 1998. All 16 tsunami events were recorded at Tofino on the outer B.C. coast, and some of the tsunamis were recorded at eight or more stations. The tide station at Tofino has been in operation for 100 years and these recent observations add to the dataset of tsunami events compiled previously by S.O. Wigen (1983) for the period 1906–1980. For each of the tsunami records statistical analysis was carried out to determine essential tsunami characteristics for all events (arrival times, maximum amplitudes, frequencies and wave-train structure). The analysis of the records indicated that significant background noise at Langara, a key northern B.C. Tsunami Warning station located near the northern end of the Queen Charlotte Islands, creates serious problems in detecting tsunami waves. That station has now been moved to a new location with better tsunami response. The number of tsunami events observed in the past 15 years also justified re-establishing a tide gauge at Port Alberni, where large tsunami wave amplitudes were measured in March 1964. The two meteorological events are the first ever recorded on the B.C. coast. Also, there have been landslide generated tsunami events which, although not recorded on any coastal tide gauges, demonstrate, along with the recent investigation of a historical catastrophic event, the significant risk that landslide generated tsunami pose to coastal and inland regions of B.C.     

Comparative analysis of strong motion (SM) records from the July 2017 Ohrid seismic sequence

During the months of June–July 2017, the Lake Ohrid area in the southwestern Macedonia experienced a series of small to intermediate earthquakes. More than a thousand earthquakes occurred in that period, all in the epicentral area about 10 km east-northeast from Ohrid city center. The earthquakes showed characteristics of a swarm with 50 of them having magnitudes of 3 or greater and the strongest reaching magnitude M5.0. The earthquakes caused concern among the people in Ohrid and neighboring cities and villages and prompted the installation of two networks of temporary stations. One network was deployed in the epicentral area to determine in more detail the earthquakes’ depth and source parameters. The other urban network of instruments was installed to monitor the influence of the ground on the amplification of shaking and the dynamics of structures in the city of Ohrid. In this study, a selection of the urban network strong motion (SM) records was analyzed for the first time. Accelerograph records from a magnitude M3.1 earthquake recorded at eight places in the city and from the two earthquakes with magnitudes M4.2 and M5.0 recorded at the permanent seismological station Ohrid (code OHR) were used. The results of the behavior of the instrumented building were also compared with the findings of previous experiments. The differences in the spectral values on the SM records from the stations were investigated in respect to the ground conditions and location where the instruments were installed, i.e., bedrock and sediments at the sites. The power spectra and the H/V ratio of the earthquake records from the 2017 seismic sequence in the Ohrid area were also viewed in respect to the Eurocode-8. In addition to being used as part of standard engineering practice, this information about the local soil conditions can be of interest to geophysicists in seismic and geotechnical investigations, as well as in seismic risk-assessment applications.     

基于小波方法分析汶川地震近断层地震动的速度脉冲特性

选取断层距小于200 km的64组强震记录数据,基于小波方法分析汶川地震近断层速度脉冲的地震动特性,并将此次地震中获取到的速度脉冲周期和幅值参数与Chi-Chi 地震和Northridge地震进行了比较,统计分析地震震级、距离对速度脉冲的周期和幅值参数的影响.研究表明:(1)汶川地震近断层速度脉冲具有周期长、幅值小的特点.速度脉冲周期主要分布在6~14 s之间,其中51MZQ台沿平行断层的分量脉冲周期最大为14.2 s,速度脉冲幅值与Chi-Chi 地震和Northridge地震相比明显偏小.(2) 速度脉冲记录出现在沿着地震断层破裂传播的方向上,且与地表断裂的距离都在30 km以内,这些长周期速度脉冲的形成可能主要由破裂传播的向前方向性效应引起.(3)速度脉冲的周期随矩震级呈对数线性增大,且随断层距增大有减小趋势.在矩震级小于M_w7.5时,观测到的地震动脉冲幅值为50~150 cm/s之间,与100 cm/s的典型断层滑动速率非常接近;而震级大于M_w7.5时,断层距10km范围内脉冲的幅值已经超过100 cm/s,个别记录的脉冲幅值甚至达到200 cm/s,远超过前人给出的饱和值,这可能与大的永久形变或该处土层介质条件有关.     

泰安台固体潮平行观测一致性分析及对异常判定的意义

对山东省泰安基准台固体潮形变观测各分量的曲线形态、潮汐参数等进行了对比分析,认为各分量观测中不同类型仪器之间有较好的同比性,相关性较高。结合仪器频响特征,对几次突出变化的异常性质进行了综合分析,认为均与仪器或局部环境变化有关,不是地震异常。表明在台基良好的条件下,平行观测在异常识别中有重要意义。     

2001年11月14日昆仑山大地震震前扰动信号的再研究

研究了2001年11月14日昆仑山M_S8.1大地震前新疆地区宽频带地震仪记录到的异常扰动事件.新疆地震台网在发生强震的前三天记录到了强烈的扰动信号.由于新疆地震台距离昆仑山大地震的震中很近,因此该震前扰动的成因备受关注,一直被认为可能是与大地震相关的慢地震事件,可能是大地震的某种前兆现象.本研究扩大了观测异常扰动事件的范围,分析了欧亚大陆187个宽频带地震仪在2001年11月的观测记录,发现这些地震仪在11月10—12日期间都记录到了时频特征类似的强扰动信号,其中最强的扰动信号出现在挪威台站KONO.调查研究发现挪威海域在11月10—12日期间出现了一次超强北极风暴,我们对扰动源位置初步定位后发现大地震前欧亚大陆各台站记录的最大扰动信号主要来源于挪威西南海岸.本文的研究结果确认昆仑山大地震前新疆台网记录到的强烈震前扰动信号不是与大地震相关的慢地震事件,而是挪威海域北极风暴激发的微地震（地脉动）.本文进一步研究表明北极风暴激发的地脉动可显著影响中国大陆的地震和重力观测.在分析中国大陆地震台网记录的强扰动信号时,北极风暴的影响不能忽视.