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.

Detection of Earth's free oscillation excited by the Japan Mw9.0 Earthquake using different tiltmeter and strainmeter

The observatory network of the Crustal Deformation China Seismological Bureau was equipped with vertical pendulum tiltmeter,borehole tiltmeter,tunnel extension meters,multi-component borehole strainmeter,body strainmeter and other tilt and strain observation instruments.All of these instruments have recorded the Earth’s free oscillation excited by the Japan Mw9.0 Earthquake.By analyzing those observations,all of the spheroidal oscillation modes(0S3-0S30)and toroidal oscillation modes(0T3-0T20)excited by the Japan Mw9.0 Earthquake were detected in this paper.In addition,comparing the different observation results which obtained by those instruments,we revealed their capacity to observe different kinds of oscillation and different frequency band modes,and analyzed report the reason.We found that the body strainmeter and the vertical pendulum tiltmeter have better observing results for spheroidal oscillation.Because of high noise in low frequency band,the borehole tiltmeter cannot observe the low-order spheroidal oscillation.In terms of observing the toroidal oscillation,the multi-component borehole strainmeter got a best result.The vertical pendulum tiltmeter observes a few toroidal oscillation modes,and the tunnel extension meters can only observe some low-order modes.

Comparison of VP broadband tiltmeter and VS vertical pendulum tiltmeter

Vertical pendulum(VP) tiltmeter is a kind of earthquake precursor observation equipment,which is used to record the interaction force associated with astronomical tidal tilts caused. Currently, VP broadband tiltmeter and vertical sensor(VS) vertical pendulum tiltmeter are primarily used. In this paper, we compare the two different instruments by using four aspectsdmechanical structure, circuitry, zeroing, and bandwidthdbased on their working principles and applications. We conclude that VP broadband tiltmeter is more superior compared with VS vertical pendulum tiltmeter because of its higher bandwidth and degree of automation.

Simulation of the water level influence on the difference within the water-tube tiltmeter in Shuangyang Lake

This article analyzes the relationship between the water level and the water-tube tilting in Shuangyang lake,based on the differential deformation features reflected by the NS and EW components of the water-tube tiltmeter.The results show a good spatiotemporal consistency between the variation of water level and the NS tilt component,which is considered to be affected by the magnitude and duration of the water level variation in Shuangyang Lake.The article uses Landsat remote sensing image data to extract the water boundary of Shuan-gyang Lake,and takes advantage of the finite element numerical simulation method to build three-dimensional models for different geological structural conditions of the Shuangyang seismostation.The simulation results show that when the underground medium is granite,the effect of water level variation on the vertical displacement of the surface is non-directional.With a 50-m soil layer in Model 2,the simulated NS tilt variation is equivalent to the actual observed water-tube tiltmeter NS component when the water level variation is 0.44 m and 0.8m.When the variation of water level reaches 2.0m,the simulation result of the NS component is 79.6 ms,which is slightly larger than the observed result of 60.32 ms.However,the simulation results show that the variation of the EW component is significantly smaller than that of the NS one.Due to the fact that the Shuan-gyang lake is long in the NS direction and short in the EW direction,the existence of the soil layer tends to generate ground deformation along the NS direction in the vicinity of the lake after the increase of water level,thereby resulting in the difference of the ground deformation in the two directions.

Frequency response of tiltmeters and tidal factor

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The background noise level of vertical pendulum tiltmeter in China

By using the observation data of the vertical pendulum tiltmeter in China,the influence of different sampling rates on the results of power spectral density is studied,and the background noise level of the seismic frequency band(200-600 s)of different stations and different types of instruments is emphatically analyzed.The conclusions are as follows:1.The results of both single station and national statistics show that the noise levels of the two types of pendulum tiltmeter equal in the seismic frequency band;2.There is no obvious regularity in the regional distribution,due to the influence of ocean and active tectonic movement,the noise levels of some stations in coastal areas are relatively high;3,The curves of high noise level instrument are generally not smooth and burr-prone.Except for some stations affected by the ocean,they are mostly caused by the observation environment or the instrument itself.

A new capacitive borehole tiltmeter for crustal deformation measurement and its performance analysis

Borehole inclinometers are important observation instruments used to measure ground tilt movement and monitor crustal deformation of solid tides and geological landslide disasters.They are widely used in oil exploration,mineral resource drilling,well logging,exploration and other fields.There is potential for development of rock stress strain monitoring tools.Many types of tiltmeters have been installed,such as SQ-7,FSQ,VS and JB.However,these tiltmeters are generally installed in a deep cave to avoid the interference of temperature,humidity,and human activities.With the urbanization of human society,suitable installation locations are difficult to find.To solve the problem,a two-component borehole tiltmeter,named the CBT-type tiltmeter,is proposed in this paper.It can be installed in a borehole less than500 m deep to eliminate environmental influences.The tiltmeter is composed of two sophisticated gravitational swing and two capacitive transducers.From preliminary theory and experiment analysis,its linear correlation coefficient is higher than 0.99,its co-seismic response is rapid and its noise level is up to 10 4arc seconds in practice.

承德地区宽频带倾斜仪与宽频带地震计同震响应融合分析

本文以承德地震台VP型宽频带倾斜仪以及同址BBVS-120型宽频带地震计采集的同震波形为研究对象,利用小波分析和短时傅里叶变换的方法,分析二者记录到的6次地震同震波形的时频特征和频带响应,能量集中在0~0.5 Hz,二者的波形曲线形态、频带响应及功率谱密度均有较高的一致性。利用经验公式拟合出宽频带倾斜仪最大振幅与震级二者之间的关系,拟合度较好,得到承德地区宽频带倾斜仪近震和远震最大振幅转换公式。承德地区宽频带倾斜仪与宽频带地震计地震波的最大振幅有较好的对应关系。利用地震波体波震级计算公式,对宽频带倾斜仪和宽频带地震计记录到的地震选取其中的3次地震波计算体波震级,结果表明在地震波频率小于0.5 Hz时,二者计算出的体波震级对应关系较好。

库尔勒VP型宽频带垂直摆倾斜仪背景噪声水平分析

选取库尔勒台、若羌台、且末台3套VP型宽频带垂直摆倾斜仪观测数据,应用功率谱密度分析方法,分别计算在地震频段的地震噪声水平,并结合台站实际进行对比分析。结果表明:库尔勒台因洞室观测条件优异、洞室周边观测环境干扰小,仪器背景噪声水平较低。3套VP型宽频带垂直摆倾斜仪噪声水平在空间分布上未表现出明显的规律,但表现出NS分量记录优于EW分量的一致性。

山西垂直摆倾斜仪背景噪声分析

利用山西地区垂直摆倾斜仪正常时段的观测数据,计算功率谱密度PSD和噪声水平SNM,对观测的正常背景特征进行分析和讨论。结果表明,未受任何干扰的观测数据每日PSD变化不大,分钟采样观测数据能反映最大为8.3 mHz的PSD分布,秒采样观测数据能反映最大为0.5 Hz的PSD分布。临汾地震台同址VS型、VP型垂直摆观测数据的噪声水平具有一致性;有2套仪器的背景噪声水平偏高,有4套仪器的背景噪声水平较低;低噪声水平仪器观测曲线光滑、固体潮清晰,运行稳定;高噪声水平仪器观测曲线毛刺多、不光滑。该现象除受观测环境影响以外,主要还受仪器自身的影响。

2016年新爱尔兰M_(S)7.8地震前中国大陆水平摆倾斜仪记录异常分析

2016年12月17日新爱尔兰发生M_(S)7.8地震,震前约1小时,我国新疆的库尔勒霍拉山台、石场台、榆树沟台、巴里坤台、阿合奇台、精河台、木垒台和河北的怀来台、丰宁台石英水平摆倾斜仪观测到前驱波(震中距最大为9053 km)。研究发现,该前驱波具有以下特征:①各台站前驱波波动持续时间存在一定差异;②同一台站记录的前驱波振幅和波形,在EW和NS分量上存在差异;③各台站前驱波波动变化的特征周期存在差异,最长周期可达660 s,而同一台站不同分量间的差异也较为明显,前驱波传播上具有不均匀性。选取同一发震构造带上基本同期发生的2次M≥7.8地震,从震源条件、观测条件等方面,与此次地震进行对比分析,认为新爱尔兰M_(S)7.8地震的前驱波现象成因,与震源、不同地质块体区域构造应力场和台站观测条件、观测仪器性能均有密切联系,是一种综合作用结果,现象重复性低。

湖北黄梅宽频带形变观测仪与地震计数据融合分析

本文分析对比了湖北黄梅地震监测站宽频带地倾斜仪、地应变仪和地震计观测的同震响应的频谱和震相特征,结果表明两类定点形变仪对地震波具有高度灵敏性,并且相较于倾斜仪,应变仪的频谱更贴近于地震计。因此尝试利用应变地震波确定地震震级,从而收集了2021—2024年全球震级M≥5.0具有同震响应的共计372次有效地震,并基于中国地震台网中心发布的地震目录,用最小二乘法得到了应变震级公式。

云南燕子岩观测站DSQ水管倾斜仪潮汐扰动现象研究

云南燕子岩观测站DSQ水管倾斜仪各分量频繁记录到高频扰动,表现形式为观测曲线脉动加粗,更换放大盒、线圈、线路、数采等都未能排除此高频扰动。经与实况气象观测资料对比后发现:潮汐扰动与气压波动有一定的同步性。经进一步诊断、排查、分析,确定引起高频扰动的原因为:DSQ水管倾斜仪钵体罩子缺少空气管,导致水管仪两端液面上方各自形成独立空腔,两端液面压力平衡被打破,引起高频扰动。对钵体罩子进行打孔处理后,高频扰动排除。这种高频扰动诊断与排除的过程和方法,对提高DSQ水管倾斜仪固体潮观测质量具有重要意义,对改进、管理同类仪器具有参考和借鉴价值。

双阳水管NS分量异常分析及其预报效能评估

利用中国地震局《震情会商技术方法业务应用推荐清单(2022)》中列装的异常判定方法,对双阳台DSQ型水管倾斜仪NS分量2008-2023年观测数据进行处理,整理归纳出现的异常,利用R值评分对该测项预报效能进行评估,结果显示:速率分析法R值为0.6,且通过R值检验,可以用于该测项的预测预报工作;破年变分析法和趋势转折法虽未通过R值检验,但都是对应率高、漏报率和虚报率低,也为该测项的预测预报工作提供了参考。

PCA优化CEEMD的DSQ水管倾斜仪信号随机噪声压制方法

提出一种基于主成分分析(PCA)优化完备集合经验模态分解(CEEMD)的DSQ水管倾斜仪信号随机噪声压制方法CEEMD-PCA。该方法融合了相关系数、分布熵、MSE、R^(2)、SSE、RMSE、MAE、MAPE等8个IMF分量质量评价指标,借助PCA实施指标值矩阵的降维压缩,将其转化为一个能代表全部不同类型指标特点的新参数,并构建IMF分量质量综合评价函数,根据分数排名结果完成原始含噪信号的线性重构。仿真信号和实测信号去噪实验结果皆表明,CEEMD-PCA模型优于卡尔曼滤波、70阶低通FIR滤波等经典模型,能提高原始信号的信噪比,精准完成信号重构,更好地保留有效成分。

2022年11月19日红河M_(S)5.0地震前石屏水平摆倾斜仪数据异常及预报效能回溯分析

2022年11月19日红河发生M_(S)5.0地震,采用形态分析和速率差分方法,对石屏站水平摆倾斜仪震前数据进行处理,分析结果显示:此次地震发生前,石屏水平摆测项中长期异常显著,主要表现为年变幅度减小、趋势加速下降、速率差分跃变等异常特征。通过地震预报效能回溯分析,该异常与石屏站周边中强震存在较好的相关性,表明石屏水平摆测项映震效果较好。该异常指标对于地震发生时间尺度的预测偏向于中长期。

巴彦浩特石英水平摆倾斜仪地震地球物理短临异常分析

收集并整理2015-2022年巴彦浩特地震台石英水平摆倾斜仪观测资料,选取典型震例,结合观测区域内地震孕育特点,运用小波分析理论方法,系统分析该台地震地球物理短临异常。结果表明,在地震发生前一段时间内,巴彦浩特地震台石英水平摆倾斜仪NS分量固体潮出现倾斜、阶变、突跳、畸变、扰动变化特征,表明石英水平摆倾斜仪观测数据短临异常映震效果较好,异常持续时间、大小与震级和震中距大小具有相关性,可对阿拉善盟及周边地区形变观测仪器震前短临异常分析提供有效参考。

腾冲地震台老洋河观测站水管倾斜仪干扰分析

腾冲地震台老洋河观测站DSQ型水管倾斜仪观测曲线南北向和东西向自2023年1月底以来偶尔出现小幅台阶。通过对此异常出现的干扰因素进行排查,认为此类台阶是由水管倾斜仪钵体内胶水脱落部分溶解于水造成。此类异常特点主要表现为:异常前期水管倾斜仪观测曲线偶尔出现小幅台阶;异常中后期台阶幅度和出现频率都逐渐增加。通过清理水体杂质能减少台阶出现频率,但不能根本解决,清洗钵体后更换水体才能彻底消除台阶。

内蒙古VP型垂直摆倾斜仪背景噪声特征分析

选取内蒙古地区5套VP型垂直摆倾斜仪2020-03~2021-02秒采样连续观测数据,计算加速度功率谱密度(PSD),对比分析不同台站、不同频率下VP型垂直摆背景噪声的时空变化特征。结果表明,VP型垂直摆背景噪声水平基本符合全球地震背景噪声模型频率特性;次微震频段背景噪声水平秋冬强、夏季最弱,季节性变化显著,未呈现出明显的空间分布特征;主微震频段背景噪声水平秋冬略大于春夏,春夏噪声水平相当,存在一定的季节性变化,不同台站背景噪声水平差异明显;在长周期频段,通常情况下四季噪声水平相近,无明显的季节性变化规律。若仪器受自然环境干扰,背景噪声水平也呈现秋冬高于春夏的季节性变化特征。此外,良好的洞体条件可有效降低长周期频段的背景噪声水平。

DSQ水管倾斜仪信号随机噪声压制研究

基于自适应噪声完备集合经验模态分解CEEMDAN和小波去噪,提出一种DSQ水管倾斜仪信号随机噪声压制方法。首先将信号进行CEEMDAN分解,得到若干个本征模态函数IMF,分解数量随不同信号噪声动态变化;然后计算每条IMF和原信号的相关性系数,对处于系数阈值范围内的IMF作小波变换处理;最后执行线性重构,得到去噪后的信号。仿真和实际去噪实验结果表明,随机噪声压制效果明显,信号有效成分保留比率较高,优于其他同类方法。