Study on the Recent Tectonic Stress Field in the “Huoshan Seismic Window” Region

The focal mechanisms of 62 moderate-small earthquakes since 1980 in the ＂ Huoshan seismic window＂ region are calculated with the method developed recently by Snoke, combining the use of the first motion of P, SV and SH waves with their amplitude ratios. Based on these abundant focal mechanisms, the mean tectonic stress field in the ＂Huoshan seismic window＂ region is inverted with the average stress tensor method, and the result shows that the ＂Huoshan seismic window＂ region is horizontally compressed in the near EW direction and horizontally dilated in the near NS direction, which is in accord with statistical results of focal mechanism parameters. We estimate the difference （also referred to as consistency parameter 0） between the force axis direction of the focal mechanism solution and the mean stress tensor, then further analyze the variation characteristics of 0 versus time, and the relationship with moderately strong earthquakes in the east China region. The result indicates that 0 in the ＂ Huoshan seismic window＂ region is in good correspondence with moderately strong earthquakes in the East China region. When 0 is lower than the mean value, corresponding moderately strong earthquakes may occur in the East China region.

A DTW distance-based seismic waveform clustering method for layers of varying thickness

Seismic waveform clustering is a useful technique for lithologic identification and reservoir characterization.The current seismic waveform clustering algorithms are predominantly based on a fixed time window,which is applicable for layers of stable thickness.When a layer exhibits variable thickness in the seismic response,a fixed time window cannot provide comprehensive geologic information for the target interval.Therefore,we propose a novel approach for a waveform clustering workfl ow based on a variable time window to enable broader applications.The dynamic time warping(DTW)distance is fi rst introduced to effectively measure the similarities between seismic waveforms with various lengths.We develop a DTW distance-based clustering algorithm to extract centroids,and we then determine the class of all seismic traces according to the DTW distances from centroids.To greatly reduce the computational complexity in seismic data application,we propose a superpixel-based seismic data thinning approach.We further propose an integrated workfl ow that can be applied to practical seismic data by incorporating the DTW distance-based clustering and seismic data thinning algorithms.We evaluated the performance by applying the proposed workfl ow to synthetic seismograms and seismic survey data.Compared with the the traditional waveform clustering method,the synthetic seismogram results demonstrate the enhanced capability of the proposed workfl ow to detect boundaries of diff erent lithologies or lithologic associations with variable thickness.Results from a practical application show that the planar map of seismic waveform clustering obtained by the proposed workfl ow correlates well with the geological characteristics of wells in terms of reservoir thickness.

The Coherence Cube Computing Method with Self-adaptive Time Window Based on Wavelet Transform

The coherence cube technology has become an important technology for the seismic attribute interpretation, which extracts the discontinuities of the events through analyzing the similarities of adjacent seismic channels to identify the fault form. The coherence cube technology which uses constant time window lengths can not balance the shallow layers and the deep layers, because the frequency band of seismic data varies with time. When analyzing the shallow layers, the time window will crossover a lot of events, which will lead to weak focusing ability and failure to delineate the details. While the time window will not be long enough for analyzing deep layers, which will lead to low accuracy because the coherences near the zero points of the events are heavily influenced by noise. For solving the problem, we should make a research on the coherence cube technology with self-adaptive time window. This paper determines the sample points＆#39; time window lengths in real time by computing the instantaneous frequency bands with Wavelet Transformation, which gives a coherence computing method with the self-adaptive time window lengths. The result shows that the coherence cube technology with self-adaptive time window based on Wavelet Transformation improves the accuracy of fault identification, and supresses the noise effectively. The method combines the advantages of long time window method and short time window method.

Comparison of four techniques for estimating temporal change of seismic velocity with passive image interferometry

Passive image interferometry （PII） is becoming a powerful tool for detecting the temporal variations in the Earth＇s structure, which applies coda wave interferometry to the waveforrns from the cross-correlation of seismic ambient noise. There are four techniques for estimating temporal change of seismic velocity with PII： moving-window cross-correlation technique （MWCCT）, moving-window cross-spectrum technique （MWCST）, stretching technique （ST） and moving-window stretching technique （MWST）. In this paper, we use the continuous seismic records from a typical station pair near the Wenchuan Ms8.0 earthquake fault zone and generate three sets of waveforms by stacking cross-correlation function of ambient noise with different numbers of days, and then apply four techniques to processing the three sets of waveforms and compare their results. Our results indicate that the techniques based on moving-window （MWCCT, MWCST and MWST） are superior in detecting the change of seismic velocity, and the MWCST can give a better estimate of velocity change than the other moving-window techniques due to measurement error. We also investigate the clock errors and their influences on measuring velocity change. We find that when the clock errors are not very large, they have limited impact on the estimate of the velocity change with the moving-window techniques.

Seismic design analysis of the country masonry school buildings in the meizoseismal area

Several reinforcing schemes are illustrated that are based on the loading characteristics of typical country masonry school buildings with sparsely spaced transversal walls and large depth. From the seismic damage observed following the Wenchuan Earthquake, the effects of reinforcing schemes, tie-columns and tie-beams on the seismic resistance of masonry buildings are analyzed. The concept of improving the ductility of these types of buildings is presented. Finally, some suggestions are proposed for the design of masonry buildings with sparsely spaced transversal walls and large depth.

Seismic Sequence Characteristics of the March 21,2008,M_S 7. 4 Yutian,Xinjiang Earthquake and Seismological Anomalies before the Earthquake

The parameters, stress field background, geological tectonics and seismic sequence of the March 21, 2008, Ms7.4 Yutian, Xinjiang earthquake are discussed in this paper. The characteristics of seismic activity in the epicenter and its adjacent region before the earthquake are analyzed; and a comparison is made between the Ms7.4 Yutian earthquake sequence, the Wenchuan Ms8.0 earthquake sequence and the Wuqia Ms6.9 earthquake sequence. The results show the Ms7.4 Yutian earthquake occurred in the junction between the Aityn Tagh fault and the western Kunlun fault, resulting perhaps from the tensile fracture of the branch fault located southwest of the Ashikule basin due to left-lateral dislocation of the Aityn Tagh fault; the seismic sequence is of main shock-aftershock type, the strongest aftershock being Ms5.8. The aftershocks attenuated quickly, and occurred in groups; the focal mechanism solutions and epicenter distribution have revealed a unilateral rupture source of this earthquake. Seismic activity shows that there was medium and medium-short term abnormity before the earthquake, but there was not short-imminent abnormity. Seismic activity of this earthquake sequence enhanced before the Ms8. 0 Wenchuan and the Ms6. 9 Wuqia earthquakes, showing the window effect to some extent.

Application of the Common Offset Seismic Reflection Method to Urban Active Fault Surveys

The method and principle of common offset seismic surveys as well as the field data gathering and processing technique were introduced briefly. Through two urban active fault survey examples in Fuzhou and Shenyang, the efficiency and limitation of using the common offset seismic reflection technique to carry out urban active fault surveys were probed. The results show that this technique has the properties of high resolving power, better reconstruction of subsurface structures, and real-time analyzing and interpretation of investigation results on site. This method can be used to quickly locate objects under investigation accurately in the areas with thinner Quaternary overburdens and strong bedrock interface fluctuations.

“霍山地震窗”小震检测及其在地震预测中的应用

安徽霍山地震窗作为地震预测效能评价较好的指标(R>R_(0),R=0.26,R_(0)=0.204),对安徽及邻区震情形势研判具有重要作用。历史震例总结显示,当霍山地震窗3个月内M_(L)≥1.0地震累计频次超过40次时,出现开窗异常,该异常对未来一年内地震窗中心点周边100 km范围内的M_(S)3.5地震、 250 km范围内的M_(S)4.0地震、 500 km范围内的M_(S)5.0地震、 500 km以外的M_(S)6.0及以上地震具有预测意义。自1970年以来,使用该指标漏报地震7次,其中,在2018年河南固始M_(S)3.6地震与2019年湖北应城M_(S)4.9地震发震前,霍山地震窗区域内小震活动增强,并且3个月内ML≥1.0地震累计频次接近异常阈值。霍山地震窗区域内小震密集,可能存在小震波形相互交叠干扰而无法被识别的情况。本研究利用匹配定位(M&L)法对2017年4月与2019年4—9月霍山地震窗区域的小震进行检测,以获取更为完整的地震目录,并重新分析了霍山地震窗的预报效能。研究结果表明,基于小震检测后更为完整的地震目录,霍山地震窗开窗异常未漏报2018年河南固始M_(S)3.6地震与2019年湖北应城M_(S)4.9地震,计算得到R>R_(0)(R=0.30,R_(0)=0.196),该项异常对应地震优势发震时间为开窗后9个月内。本研究说明M&L法在霍山地震窗小震检测中具有实用性,可在后续霍山地震窗跟踪中作为一种常规的处理方法,以期获取更为完整的小震目录,为震情跟踪研判提供数据支撑。

基于多尺度窗口生成器网络的抽油机噪声压制

在老油田的勘探开发中,抽油机噪声形成强干扰,严重降低了地震资料的信噪比。为此,提出了一种基于多尺度窗口生成器网络进行抽油机噪声压制的方法。构建的网络主要由双层编码器—解码器组成,结合不同层的特征信息可获得准确的去噪结果;在不同层采用不同尺寸的窗口进行特征提取,可以有效地扩大神经网络的感知范围,并从抽油机噪声中提取更多有用的特征。为了防止网络的退化,编码器和解码器的每个块中都分别使用了残差连接。编码器残差块部分采用了卷积核数量中间大、两端小的反瓶颈设计,可以提取地震数据更多的特征;解码器使用了编码器五分之一的卷积层数,加快了模型训练以及地震数据重建的速度。通过这种方式构建的网络可以有效地利用多尺度语义信息压制地震数据中的抽油机噪声。模拟数据和实际数据实验结果均表明,与DnCNN、GAN和MLGNet相比,所提方法能够获得高质量的去噪结果,并最大程度地保留有效数据。

安徽霍山区域科学台阵背景噪声分析

安徽霍山地区区域科学台阵为“十三五”期间新建台阵,为了评估该台阵各子站背景噪声水平,采用噪声功率谱密度法和功率谱概率密度函数法,进行背景噪声数据分析,结果显示:参照台基分类标准,Ⅰ类台基13个,Ⅱ类台基5个,Ⅲ类台基1个,Ⅳ类台基1个,台基噪声水平整体较低,各子站台基勘选较为合理;CLZ站UD分量背景噪声偏大,需要对观测系统运行进行检查;各子站背景噪声概率密度函数分布结果同功率谱密度结果基本一致,但包含的细节或信息更多,特别是叠加噪声功率谱密度后,包含了背景噪声在时间和频率2个维度上的信息,能够显著显示人类活动、仪器标定等干扰在频率、时间上分布。

自适应时窗多道相关的叠后地震波阻抗反演方法

目前提高反演横向连续性的主要手段仍是基于模型参数先验信息假设的正则化方法,当先验信息与实际情况矛盾时,正则化方法会出现问题。为此,基于多道反演理论和方法,提出一种自适应时窗多道相关的叠后地震波阻抗反演方法。首先,利用主动学习的思想,通过查询原始地震数据筛选地震数据关键特征的位置;其次,根据上述位置将地震数据划分为不同尺度的时窗,有助于断层信息保护以及异常体边界识别;再次,根据点乘计算自适应时窗内地震道之间的相关性;最后,通过“加权求和”地震道得到重构地震道——反演目标泛函的约束条件。所提方法借助主动学习以及地震数据局部相关的思想,较好地反映了自适应时窗内的多道间的相关性,并且可并行化处理。模型测试和实际数据测试表明,所提方法反演结果的横向连续性较好,且可以兼顾特殊构造信息,但计算效率较低,在浅、深层速度差异较大的区域存在一定局限性,适用于具有特殊构造的狭小地区。

松辽盆地德惠断陷白垩系火石岭组凝灰岩储层预测及成藏主控因素

基于钻井岩心分析、测井曲线、地震等资料,运用模型正演、多参数反演体融合技术等,对松辽盆地德惠断陷白垩系火石岭组凝灰岩储层分布特征及油气富集条件进行了研究,预测了优质储层分布。研究结果表明:(1)松辽盆地德惠断陷白垩系火石岭组凝灰岩为裂隙式喷发形成的火山碎屑岩,主要为含角砾熔结凝灰岩、含角砾晶屑凝灰岩和沉凝灰岩。地震反射特征总体表现为低频、差连续、中强振幅或弱振幅,多参数反演体融合体技术预测的凝灰岩储层“甜点”分布与钻井证实结果的符合率高,凝灰岩储层平均钻遇率达92.8%,气层平均钻遇率为81.0%,其中12口井获得了工业气流;华家构造带与郭家断阶带储层岩性分别以含角砾熔结凝灰岩和含角砾晶屑凝灰岩为主,断裂发育,是2个优质储层发育区。(2)研究区凝灰岩的测井和地震相特征相匹配形成的岩性-岩相模板可有效指导凝灰岩的地震相识别,振幅属性刻画出的火山口相、近火山岩相为有利岩性分布区。(3)研究区发育火石岭组、沙河子组、营城组3套优质烃源岩厚度均超过300 m,TOC值分别为0.26%~5.08%,0.10%~5.55%,0.10%~9.74%,S1+S2分别为0.24~8.23 mg/g,0.12~18.15 mg/g,0.25~2.86 mg/g,Ro分别为0.6%~1.3%,1.1%~1.6%,1.0%~2.2%,具有丰度高,成熟度中等的特征,为大规模成藏奠定了良好的物质基础。(4)研究区凝灰岩气藏是一套源储侧向对接、高位富集的致密气藏,成藏主要受构造样式、断裂发育程度和供烃窗口控制,其中拉张和伸展作用形成的叠瓦状断弯褶皱控制了油气富集程度,断裂发育程度及供烃窗口的大小决定了气藏规模。

装配式建筑转角飘窗结构性能分析

文中利用数值仿真软件对装配式建筑转角飘窗地震作用下层间位移角、最大位移以及损伤程度进行分析。结果表明,随着楼层数的增加,X向层间位移角先增加、再降低、最后保持稳定,当地震波加载的终止时间从25 s增至55 s,再增加至70 s时,X向最大的层间位移增加幅度基本为3.62%。随着楼层数的增加,Y向层间位移角呈现先增加后降低的变化规律,装配式建筑结构各层X和Y向最大位移同样呈现不断增加的趋势。装配式住宅楼转角窗位置处的楼板混凝土出现一定的受拉损伤,但并不严重,证明本工程转角窗具有良好的抗震效果。

基于位移窗口自注意力网络和迁移学习的地震面波分离

反射地震资料中的面波也携带了丰富的地质信息,充分利用这类面波解决地质问题的前提条件是将其完整地分离出来。针对现有深度学习方法没有充分利用面波与体波表现在时空域图像中的分布位置和纹理细节等问题,提出一种基于深度学习的地震面波分离方法。通过融合位移窗口自注意力机制和U-net主干网络,构建出面波智能分离网络,并使用数据增广后的模拟数据与实际数据构建面波数据集来提升神经网络的泛化性;在充分利用面波全局数据特征的同时,为避免波场分离过程中的面波损伤问题,提出一种对边界、结构和纹理信息敏感的混合损失函数以进一步提高面波分离的质量。通过数值模拟地震记录测试了本文方法的正确性,进而将该方法应用于实际地震资料处理。研究结果表明,在模拟地震记录训练的模型基础上进行迁移学习,可进一步提升神经网络的泛化性;相较于低通滤波法和去噪卷积神经网络方法,本文方法分离的面波更为完整,能大幅度提高能量混叠区域的面波分离质量。

安徽霍山窗重复地震尾波Q_c值变化研究

本文用波形互相关方法识别霍山窗重复地震对，进一步在重复地震对中搜索重复地震序列．人工挑选了一条时间在上覆盖2009年且时间分布相对理想的由8个重复地震组成的重复地震序列（RepeatingEarthquakeSeries，RES）．挑选1个重复地震作为参考对象，使用前人提出的滑动窗口谱振幅比方法计算其它7个重复地震与该地震的尾波Qi。值的变化量△Qc-1，结果发现在2009年的3次重复地震尾波Qc-1值的变化量△Qc-1比2008年和2010年有明显增大，即尾波Qc从2009年开始出现明显降低，2010年后恢复；若换算成Qc值的变化其增幅可达11％～21％．然而在2009年霍山窗及附近地区并未发生中强地震，而是伴随尾波Qc值增加出现了小震活动增强的现象．结合地球动力学知识和前人对中国大陆东西部中强地震活动特征及时间关系的研究结果，认为霍山窗重复地震尾波Qc值的变化与前人研究的震前地震孕育导致的尾波Qc值变化有所不同，前者可能是受到大陆西部物质东移和应力向东传递这种外部因素的影响导致霍山地区地壳应力的变化，因而引起尾波Qc值的变化．

“霍山地震窗”小震序列运动学参数时变特征研究

利用安徽及邻近地区的数字化地震资料,详细研究了“霍山地震窗口”小震序列的构造环境背景应力和视应力变化特征。结果表明,环境应力值和视应力值不仅能反映震“源”区的应力背景强弱,在距未来强震震中比较远的特殊构造部位,即素有“地震活动穴位”的地震窗口的小地震,同样能较客观反映出孕震区附近应力环境的信息,在华东中强地震前后应力状态的差异性是显著的。

“霍山窗”地区现代构造应力场研究

应用Snoke于2009年提出的利用P、SV和SH波的初动和振幅比联合计算震源机制解的方法,得到"霍山窗"地区1980年以来62次中小地震的震源机制解。基于大量的震源机制解资料,根据应力张量平均法反演得到"霍山窗"地区的平均构造应力场;结果表明,其与震源机制参数统计结果一致,表现为近EW向的水平挤压和近NS向的水平拉张作用。计算单个震源机制解力轴与平均应力场主应力轴的差异,即震源机制的一致性参数θ,进而分析θ随时间变化特征及其与华东地区中强震的关系;结果表明,"霍山窗"地区震源机制的一致性参数θ对华东地区相应中强震似有一定的指示意义。

东大别山构造带六安—英山地磁剖面观测与地震研究

本文以东大别构造带内六安—英山地磁剖面磁异常数据为基础,结合研究区域地质学和地震学研究成果,反演给出研究区域居里面埋深及地下介质磁性结构模型.通过对磁异常变化特征曲线、介质磁性结构模型分析发现:东大别构造带北部磁异常较强且波动较大、地下磁性结构特征相对复杂,北淮阳地区磁异常较弱、地下介质结构成叠瓦状形态分布,合肥盆地磁异常曲线变化平缓、埋深较深,为连续均匀的磁性基底,结果较好地反应了合肥盆地、北淮阳、东大别构造带北部之间的差异;"霍山地震窗"地壳下方6～12km处存在显著地磁性差异,结合东大别构造带内70年代以来地震和历史强震,对"霍山地震窗"地震活动性与地下构造、场源关系进行了研究,初步探讨了其动力学成因.

“霍山震情窗”动力学背景及预测意义分析

安徽"霍山震情窗"作为华东地区的应力敏感部位,能够以微震、小震活动的形式反映区域应力场的变化。本文基于应变能释放方法对"霍山震情窗"的动力学背景进行了研究,结果表明该震情窗易受青藏块体强震活动的影响,从而出现开窗异常,其异常变幅相对较大;此外,震情窗所处区域应力场的波动变化也会导致开窗异常,其异常变幅则相对较小。上述2种动力学背景的开窗异常对华东地区中强地震均具有较好的预测意义。此外,在实际应用中应关注多种动力学背景的共同影响可能导致的开窗异常。

安徽“霍山窗”中小地震的地震波衰减特征研究

利用安徽合肥台、六安台和豹子崖台记录到的2001—2010年安徽"霍山窗"发生的ML≥2.0地震的波形资料,计算了其振幅衰减系数K值和卓越频率衰减系数a值,分析研究了K值和a值的时空变化特征,并讨论了其与华东地区中强地震的对应关系及与Qc值的相关性.结果表明,3个台站均记录到了明显的变化特征:①"霍山窗"ML4.0地震、江西九江MS5.7地震及河南太康ML5.0地震前6个月左右时间内,K值和a值均呈现持续下降的异常低值状态,平均下降幅度K值为20%—35%,a值为45%—51%,并于上升的过程中发震,震后趋于正常;②K值的平面分布特征显示,K值异常地震主要位于断裂带交汇区附近,并沿断裂带方向分布;③K值、a值与Qc值基本呈负相关.上述特征为进一步了解该区域的地壳介质状态和研究中强震前后Qc的变化特征提供了一定的依据.该研究结果可能对中长期地震预报和震后趋势判断有一定的指示意义.