甚宽频带地震计磁屏蔽测试

地球磁场和人工磁场不断变化,会对甚宽频带地震计的簧片产生吸引而降低地震观测数据质量。将甚宽频带地震计分别采用宽背簧和窄拉簧悬挂,放置于赫尔姆霍兹线圈中间,测试地震计所受干扰;使用铍莫合金屏蔽罩罩住地震计,再次测试地震计所受干扰。测试结果表明:地震计垂直分向所受干扰严重,使用宽背簧支撑摆体运动的地震计所受干扰程度较大;铍莫合金屏蔽罩对参与测试地震计所有分向均有一定屏蔽效果。     

溧阳地震台地面与井下地震观测对比分析

为系统总结地面与井下地震观测特性,对溧阳地震台地面GL-S60与井下GL-S60B宽频带地震数据对比分析,结果显示：(1)井下地震计方位角约为176.5°,即东南、西北大致反向,并结合地震P波到时极性分析得以验证。(2)垂直向相关系数优于水平向,受人类活动干扰白天低于夜晚。(3)受台站附近南北向公路影响,地面台基噪声水平向大于垂直向,南北向最大,而井下地震计台基噪声整体较小,且水平向小于垂直向,说明深井观测能有效降低台基噪声,尤其水平向。(4)井下记录的地震信噪比次于地面,地面土层对地震波具有一定放大作用。因此,深井观测虽有效降低噪声水平,但不一定意味着高信噪比数据产出,需结合实际观测资料综合分析。     

温度对甚宽带地震计零点及灵敏度的影响

根据宽频带地震计在北方寒冷地区运行时受温度变化影响的实际情况,针对温度对宽频带地震计的影响做了定量的分析研究,从而总结出温度对地震计影响的具体指标和相应关系曲线,并得出了温度对地震计影响的初步结论,即随环境温度的降低地震计灵敏度逐渐降低,地震计零点电压值在不断升高,尤其垂直向零点随温度的变化率更加明显。为地震计厂家增加温度补偿功能或台站温度环境的改进提供了相应的数据参考。     

地震计自噪声的研究

仪器的固有噪声水平是地震计的关键技术指标。 如何降低仪器的自噪声是地震计设计中需要解决的重要问题。 本文分析了产生地震计自噪声的两个主要噪声源: 布朗热噪声和电子噪声(1/f噪声), 以及它们对地震计传递函数的影响。 分析了三种地震计所记录的地震台台基噪声, 并且通过试验来检验仪器噪声对地震计观测数据的影响。     

地震计低自噪声测量及参数建模

本文提出一种基于对比法测定地震计相对传感参数, 并考虑分向对齐误差计算地震计自噪声, 再利用连续3天以上的自噪声数据提取获得地震计低噪声数据的方法。 通过理论分析和实际数据计算检验表明, 采用这一套方法提取地震计的低噪声数据, 对数据选择的要求大大降低, 有利于客观、 稳定地获取地震计的自噪声数据。 此外, 通过参数建模, 获得地震计自噪声曲线的拟合多项式, 直接计算自噪声参考频点数值, 可以避免在实际曲线上读数时受到的计算误差引起的波动影响, 得到客观、 稳定、 可靠的地震计自噪声参数数据, 有利于地震计性能比较评价。 最后作为实例, 给出了采用本文算法计算出的4种国产地震计的自噪声模型及低自噪声参数。     

西昌流动地震台阵背景噪声特征分析

利用西昌流动地震台阵2013年1月至4月观测的垂直分量的地震连续波形数据,计算了各台站评价环境噪声的功率谱密度概率密度函数,对地震台站环境背景噪声特征进行了分析。计算结果表明,西昌流动地震台阵多数台站环境的噪声水平较低,平均噪声水平在0.01~10 Hz频段低于全球新高噪声模型(NHNM)的参考值,不同台站在0.1~1 Hz频段的噪声水平基本相同,更接近于全球新低噪声模型(NLNM)的参考值。当地震计架设在基岩上并采用密封措施后,可以有效防风和保温,并且降低了气压变化对地震计的干扰。     

内蒙古中部地区形变主要干扰的时频响应特征分析

选取内蒙古中部地区定点形变观测中受降雨、大风、气压干扰以及地震波影响的典型数据,采用S变换,对该地区形变观测中4种主要干扰信号的时频响应特征进行分析与讨论。结果表明,降雨干扰信号主要集中在低频区域,其频率先增大后减小;大风干扰表现为高频干扰,时频域能量强度与观测曲线受风扰影响变化幅度成正比;气压干扰信号的优势频率分布在低频段内;地震波影响中VP垂直摆和JCZ地震计记录的地震波较为相似,但VP垂直摆记录的频段要小于JCZ地震计,VP垂直摆主要记录的是低频地震波。同时,4种干扰信号的时频域频率、能量强度随时间变化趋势与数据观测时域变化趋势相一致。     

基于Matlab的地震计自噪声计算可视化软件设计

基于Matlab的GUI开发环境,采用三仪器法设计地震计自噪声可视化软件,通过对3台地震计同背景同时段原始波形数据进行去均值、去趋势值等一序列数据处理,并运用Welch平均周期法计算噪声功率谱密度,最终绘制完成自噪声功率谱密度曲线。选取山东省临沂市马陵山比测基地作为软件测试地点,以2组各3套地震计(STS2.5、BBVS-120地震计)观测系统作为测试样本,进行地震计自噪声分析,结果发现,STS2.5和BBVS-120型地震计UD向自噪声功率谱曲线在0.04—2 Hz频带内均低于NLNM,表明地震计噪声性能良好,从而验证了软件的可行性与准确性。     

地震计墩改造对观测数据影响分析

国家烈度速报与预警工程重庆子项目实施过程中,部分台站地震计坑因潮湿渗水,改造为地表摆墩观测。对改造前后的观测数据进行功率谱密度计算,用1/3倍频程滤波器在1～20 Hz频带范围内计算地噪声水平,进而得到台站有效测量动态范围。对比分析台站改造前后数据计算结果,显示改造后台站噪声水平有所增加,其中东西向、南北向最大增加9 dB,垂直向最大增加5 dB,但环境地噪声水平仍符合观测规范要求。鉴于地震计墩改造对观测数据产生影响,本文提出了更为合理的浅式半地下室改造方案。     

宽频带地震计数字反馈技术

反馈式地震计的出现在地震计发展历史上具有划时代意义,大动态、宽频带已经成为当代地震观测的主流技术,数字技术应用是地震计的发展方向。采用模拟反馈技术的宽频带地震计存在低频段自噪声高及系统受环境影响大等问题。实验结果显示,通过引入数字反馈技术,可以优化地震计的长周期噪声,提高系统稳定性,首次实现程控配置地震计的周期。     

基于等效源的重力异常空间导数计算方法及其在川滇地区的应用

在综合分析前人研究成果的基础上, 采用基于贝叶斯准则的等效源模型滤波增强方法来识别地质体边界。 通过理论模型实验讨论了在相同的噪声水平情况下, 不同算法对于计算结果的影响, 模型实验结果表明, 与直接计算和传统高斯滤波增强技术相比, 新算法可以有效消除传统算法中普遍存在的对于噪声的过度敏感问题, 所得到的地质体边界形态失真更小。 随后, 利用此方法对川滇地区的重力数据进行了处理, 并对该地区的重力水平总梯度(THD)、 重力垂直梯度模(AVG)、 重力解析信号模量(AAS)、 重力水平梯度垂向导数(VGHD)应用效果进行了对比分析。 研究结果提供了川滇地区的构造分区信息, 对该地区构造演化、 边界定位及动力学过程分析具有重要的指导意义。     

Shipping noise in a dynamic sea: a case study of grey seals in the Celtic Sea

Shipping noise is a threat to marine wildlife. Grey seals are benthic foragers, and thus experience acoustic noise throughout the water column, which makes them a good model species for a case study of the potential impacts of shipping noise. We used ship track data from the Celtic Sea, seal track data and a coupled ocean-acoustic modelling system to assess the noise exposure of grey seals along their tracks. It was found that the animals experience step changes in sound levels up to ~ 20 dB at a frequency of 125 Hz, and ~ 10 dB on average over 10–1000 Hz when they dive through the thermocline, particularly during summer. Our results showed large seasonal differences in the noise level experienced by the seals. These results reveal the actual noise exposure by the animals and could help in marine spatial planning.     

武汉九峰地震台超导重力仪观测分析研究

连续重力观测和GPS的技术结合能够监测到物质迁移和地壳垂直形变之间的量化关系.和相对重力测量以及绝对重力测量技术相比,其避免了时间分辨率和观测精度低,无法精细描述观测周期内的物质迁移过程问题.本文利用武汉九峰地震台超导重力仪SGC053超过13000 h连续重力观测数据;同址观测的绝对重力仪观测结果;气压数据;周边GPS观测结果;GRACE卫星的时变重力场;全球水储量模型等资料,采用同址观测技术、调和分析法、相关分析方法在扣除九峰地震台潮汐、气压、极移和仪器漂移的基础上,利用重力残差时间序列和GPS垂直位移研究物质迁移和地壳垂直形变之间的量化关系.结果表明:在改正连续重力观测数据的潮汐、气压、极移的影响后,不仅准确观测到2009年的夏秋两季由于水负荷引起的约(6~8)×10^-8m·s^-2短期的重力变化.而且在扣除2.18×10^-8(m·s^-2)/a仪器漂移和水负荷的影响后,验证了本地区长短趋势垂直形变和重力变化之间具有一致的负相关性规律.同时长趋势表明该地区地壳处于下沉,重力处于增大过程,增加速率约为1.79×10^-8(m·s^-2)/a.武汉地区重力梯度关系约为-354×10^-8(m·s^-2)/m.     

Microseismic noise in northern European Russia: Seismic recordings in the town of Vorkuta

Microseismic noise was studied in the frequency range 0.5–30 Hz in the conditions prevailing in the town of Vorkuta. A seismic noise model was developed consisting of power spectral densities of ground motion velocity separately for daytime and nighttime in different frequency ranges. The absolute noise level for frequencies of 1–5 Hz in Vorkuta varies between −140 and −150 dB in daytime and from −152 to −158 dB in nighttime, with the ranges for the 8-15 Hz noise being −140 to −155 dB in daytime and −155 to −165 dB in nighttime. Well-pronounced daily variations in noise amplitude were observed in the frequency ranges 1.5–3 Hz and 14–17 Hz. The noise amplitude varies by 7 dB over 24 hours, with the amplitude of horizontal component variation being 5 dB above that of the vertical component. The power spectral densities of ground motion velocity in the microseismic noise involve several spectral peaks, whose central frequencies did not vary by more than 0.15 Hz during the entire period of instrumental observation. The seismic background in the town of Vorkuta contains seismic events due to distant earthquakes and local industrial explosions.     

Year-round variability of ambient noise in temperate freshwater habitats and its implications for fishes

Changes in habitat acoustics over the year can potentially affect fish hearing and orientation to sound, especially in temperate climates. This is the first study where year-round changes in ambient noise in aquatic habitats were assessed. Seven different European freshwater habitats were chosen for this study. Sound pressure level (SPL) and spectral composition of the ambient noise varied in both quiet stagnant habitats (lakes, backwaters) and in flowing habitats (streams, rivers). Linear equivalent SPL (L_{Leq, 60s}) tended to be lower in stagnant habitats (means: 91.6–111.7 dB) than in flowing habitats (means: 111.2–133.4 dB). The changes in SPL were smallest in the river (means: 4.2–4.4 dB, maxima: 8.5–10.1 dB), whereas significantly higher values were measured in stagnant habitats and the stream (means: 9.9–14.9 dB, maxima: 25.1–30.9 dB). The spectral compositions of the ambient noise determined at different times of the year were highly correlated to each other at the river sites (mean cross-correlation coefficients: 0.85 and 0.94) and were weaker or not correlated at the other study sites (means: 0.24–0.76). The changes in ambient noise spectra were negatively correlated to changes in SPL, indicating that large changes in SPLs were accompanied by large changes in spectral composition and vice versa. Comparison of these eco-acoustical data with a preceding study (Amoser and Ladich in J Exp Biol 208:3533–3542, 2005) indicates that the auditory sensitivity in hearing specialists is affected by changes in ambient noise levels and spectra throughout a year and that this effect tends to be more pronounced in stagnant waters and the stream than at river sites. On the other hand, absolute noise levels result in a higher degree of masking in flowing waters.     

延时参数对地震信号信噪比的改善

当测区噪声很强,采用组合震源工作仍然不能得到高质量地震数据,为进一步提高地震信号的信噪比,引入能形成定向地震波的相控震源.相控震源产生的地震波方向可由延时参数控制,因此延时参数是影响相控地震效果的重要参数.理论分析表明,定向地震波技术可提高反射波信号信噪比,以含3个激震器的相控震源为例,信噪比可提高6.53~9.54 dB.针对延时参数分别为0,0.802,0.384,0.241,0.174,0.123 ms的情况,完成了野外地震实验.根据原始地震记录,得到了反射波信号功率谱,在此基础上定量地计算了不同延时参数下目标层反射信号的信噪比.结果表明,与单震源情况相比,在6种延时参数下,反射波信噪比分别提高了3.3150,8.0150,6.0547,5.0278,4.5383,4.0364 dB;与组合震源情况相比,信噪比分别提高了0,4.7000,2.7397,1.7128,1.2233,0.7214 dB.综合理论分析及野外实验结果,我们可以得到这样的结论：定向地震波技术能够提高反射波信号信噪比,延时参数变化对信噪比有很大影响,采用合理的延时参数能得到更高的信噪比.     

典型强震动加速度仪一致性检验

针对两种典型强震动加速度仪,ETNA与MR2002,利用汶川地震强余震流动观测进行了两仪器的一致性检验.通过架设在同一仪器墩上的2种强震动加速度仪在5次余震事件中所获取加速度记录的波形、峰值、傅里叶振幅谱及反应谱的对比分析可知,ETNA仪器记录的峰值加速度与MR2002仪器记录的峰值加速度间的最大相对误差达23.6％,且南北向峰值加速度差异大于东西向和竖向,竖向明显小于两水平向;反应谱及傅里叶谱变化趋势基本相同,只是幅值存在些微差异,且竖向谱值相差最小,明显小于两水平向,反应谱最大相对误差近5％,相对于低频反应谱,高频反应谱差异较大;此外,亦存在两仪器记录时程曲线反向、记录时间长度不等、触发点不同等差异.经分析认为,这些差异主要是由于两种不同仪器性能上的微差异、仪器参数设置不同、以及触发滤波算法不同等因素引起的.     

碟形弹簧竖向减震体系的分析与研究

对碟形弹簧竖向减震体系利用时程分析方法对其进行动力分析，并输入不同场地、不同频谱的地震波考察其减震效果，验证了碟形弹簧在合理控制其刚度的前提下可以起到有效减小竖向地震的作用。     

Field testing of modular borehole monitoring with simultaneous distributed acoustic sensing and geophone vertical seismic profiles at Citronelle,Alabama

A modular borehole monitoring concept has been implemented to provide a suite of well‐based monitoring tools that can be deployed cost effectively in a flexible and robust package. The initial modular borehole monitoring system was deployed as part of a CO₂ injection test operated by the Southeast Regional Carbon Sequestration Partnership near Citronelle, Alabama. The Citronelle modular monitoring system transmits electrical power and signals, fibre‐optic light pulses, and fluids between the surface and a reservoir. Additionally, a separate multi‐conductor tubing‐encapsulated line was used for borehole geophones, including a specialized clamp for casing clamping with tubing deployment. The deployment of geophones and fibre‐optic cables allowed comparison testing of distributed acoustic sensing. We designed a large source effort (>64 sweeps per source point) to test fibre‐optic vertical seismic profile and acquired data in 2013. The native measurement in the specific distributed acoustic sensing unit used (an iDAS from Silixa Ltd) is described as a localized strain rate. Following a processing flow of adaptive noise reduction and rebalancing the signal to dimensionless strain, improvement from repeated stacking of the source was observed. Conversion of the rebalanced strain signal to equivalent velocity units, via a scaling by local apparent velocity, allows quantitative comparison of distributed acoustic sensing and geophone data in units of velocity. We see a very good match of uncorrelated time series in both amplitude and phase, demonstrating that velocity‐converted distributed acoustic sensing data can be analyzed equivalent to vertical geophones. We show that distributed acoustic sensing data, when averaged over an interval comparable to typical geophone spacing, can obtain signal‐to‐noise ratios of 18 dB to 24 dB below clamped geophones, a result that is variable with noise spectral amplitude because the noise characteristics are not identical. With vertical seismic profile processing, we demonstrate the effectiveness of downgoing deconvolution from the large spatial sampling of distributed acoustic sensing data, along with improved upgoing reflection quality. We conclude that the extra source effort currently needed for tubing‐deployed distributed acoustic sensing vertical seismic profile, as part of a modular monitoring system, is well compensated by the extra spatial sampling and lower deployment cost as compared with conventional borehole geophones.     

摩擦-碟簧三维复合隔震支座的性能试验研究

对适用于大跨结构的摩擦-碟簧三维复合隔震支座进行了振动台试验研究,该支座在水平向和竖向分别采用摩擦滑移装置和碟型弹簧隔震。在水平向,试验重点测试了简谐激励和地震动激励下支座的滞回性能,考察了竖向荷载变化及地震动强度对隔震性能的影响,以期为建立水平隔震理论模型提供依据;在竖向,对碟型弹簧的等效阻尼比和等效刚度进行了测试,研究了竖向预压荷载和动力荷载对竖向滞回性能的影响。结果表明,复合隔震支座在水平向和竖向均具有较好的滞回性能,竖向等效阻尼比在0.10～0.15间,且随着预压荷载的增加而增大。