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1.
传统基于地震背景噪声互相关的层析成像技术,主要利用了互相关函数的相位信息,即利用走时来反演地球介质的速度和各向异性特征.最近,开始有研究人员利用互相关函数的振幅信息提取介质的衰减.主要是将二维弹性情形下,互相关函数正比于第一类零阶贝塞尔函数J_0(k_0r)这一结论,通过引入指数衰减系数,直接推广到衰减介质情形,令衰减介质中背景噪声互相关函数类比于J_0(k_0r)·e~(-α(ω)r),以此来反演介质的衰减系数α.然而,在衰减介质中,互相关受源的方位平均的影响,这种简单的推广,可能无法提取可靠的衰减系数.本文基于平面波的叠加模型,研究不同的互相关定义和坐标选择下,衰减介质中两点间互相关函数的理论表达式.结果表明,在平面波叠加模型下,互相关函数的表达形式随着坐标原点的选择,并因而随着源分布的变化而变化,对不同的归一化因子,表达式也不尽相同.利用J_0(k_0r)·e~(-α(ω)r)的形式拟合背景噪声的观测数据得到的衰减比实际值偏小. 相似文献
2.
近年来,基于地震背景噪声互相关函数的地震层析成像技术,在研究地球深浅部结构中获得了广泛应用.目前,绝大多数的背景噪声成像仅仅利用了互相关函数的相位信息,即利用走时来反演地球介质的速度和各向异性特征.利用互相关函数的振幅信息提取介质的衰减仍在研究之中.从背景噪声场中提取的衰减信息可以从非弹性的角度更好地约束地壳和上地幔的精细结构,为地球动力学解释提供更多证据.利用背景噪声提取介质衰减,有两种基本的方法:(1)基于时间域噪声互相关函数的相对振幅随台间距变化,即衰减介质中的地震干涉方法;(2)基于频率域空间相干曲线的拟合,即考虑衰减的空间自相关(SPAC)方法.这两种衰减提取的方法在原理上是一致的.本文分别评述这两种方法的理论发展和处理过程,介绍背景噪声互相关技术提取衰减的应用成果.背景噪声互相关函数幅度受噪声源分布,固有衰减、散射、聚焦和散焦等因素的共同影响,文中对此做了评述.利用背景噪声场提取衰减时,需要谨慎对待这些因素的影响.最后对背景噪声衰减提取和今后的发展前景进行了展望.随着密集台阵的布设和衰减提取方法的不断完善,噪声互相关幅度信息的研究将会获得更为广泛的应用. 相似文献
3.
在时间域中,利用地震记录中的振幅与上升时间信息可以计算出岩石介质的品质因子Q值.由于震源能量难以测量,本文通过共炮点道集相邻道循环对比的方法,消除了震源对计算过程的影响,推导出时间域相邻道振幅与上升时间衰减成像的计算公式,并在振幅衰减成像的计算过程中,去除了非粘滞性衰减成分.为了更全面地综合利用波形信息,并充分利用各种方法的长处,将波速成像、振幅衰减成像、上升时间衰减成像集成到一个处理流程中,通过在岩体结构研究中的实际应用,证明这种综合方法具有灵活、实用、可靠的特点. 相似文献
4.
利用由149个台站记录的中国地震年报、四川和云南区域地震台网观测报告的5897个近震的27530条横波振幅与周期资料，反演得到川滇地区及周边的地壳衰减Q0值（频率为1 Hz时的Q值）空间分布图像、台站的场地响应以及由于介质衰减不同造成的震级偏差.结果表明，川滇及周边地区的地壳横波衰减Q0值在200～600范围内变化，平均值为400，横向变化显著.在川西-滇西北-保山地区、云贵交界-昆明-思茅地区以及海原-祁连、汾渭和东昆仑等活动块体边界带的Q0值明显较低，这些地区地震和构造活动相对活跃；而构造相对稳定的四川盆地、马尔康块体、桂西滇东断块以及鄂尔多斯、秦岭-大别等地区的Q0值则明显较高.此外，川滇地区大多数台站的场地响应都在1附近，仅有少数增益或衰减较大，达到2倍左右，且其分布无明显规律性.该区观测报告给出的大多数地震震级偏差不大于03，但也有少数震级偏差达04，其分布与介质品质因子Q0值分布相关，说明震级测定可能受地壳介质衰减横向变化的影响. 相似文献
5.
利用由149个台站记录的中国地震年报、四川和云南区域地震台网观测报告的5897个近震的27530条横波振幅与周期资料，反演得到川滇地区及周边的地壳衰减Q0值（频率为1 Hz时的Q值）空间分布图像、台站的场地响应以及由于介质衰减不同造成的震级偏差.结果表明，川滇及周边地区的地壳横波衰减Q0值在200～600范围内变化，平均值为400，横向变化显著.在川西-滇西北-保山地区、云贵交界-昆明-思茅地区以及海原-祁连、汾渭和东昆仑等活动块体边界带的Q0值明显较低，这些地区地震和构造活动相对活跃；而构造相对稳定的四川盆地、马尔康块体、桂西滇东断块以及鄂尔多斯、秦岭-大别等地区的Q0值则明显较高.此外，川滇地区大多数台站的场地响应都在1附近，仅有少数增益或衰减较大，达到2倍左右，且其分布无明显规律性.该区观测报告给出的大多数地震震级偏差不大于03，但也有少数震级偏差达04，其分布与介质品质因子Q0值分布相关，说明震级测定可能受地壳介质衰减横向变化的影响. 相似文献
6.
以P_P波时窗和P_SV波时窗的交叉部分作为VTI介质中P_P波、P_SV波联合采集的最佳时窗，在有效时窗内通过基于VTI介质的射线追踪法确定每个反射点的P_P波、P_SV波射线路径和相角，求解Zoeppritz方程得出P_SV波与P_P波反射系数(或透射系数)的比值，并将该比值的绝对值定义为控制因子G. 以G值作为控制VTI介质中P_P波、P_SV波联合采集观测系统设计的主要参数，通过分析G值确定检波器位置的最佳接收时窗，得出优化VTI介质中多分量转换波地震数据采集的接收时窗的方法. 相似文献
7.
摆杆尺度因子（K因子）是反映LaCoste&Romberg航空重力仪线性响应特性的最重要参数. 利用基于地面参考数据的外部标定法和基于交叉点不符值的内部标定法分别对其进行了标定，实测数据分析表明，K因子的内、外部标定结果非常一致，且利用新K因子计算的空中重力扰动，其精度较采用出厂值提高了02～04 mGal. 内部标定法具有较好的实际应用价值. 研究了K因子与滤波尺度的相关性，表明重力仪可能为一非线性响应系统，即K因子的大小与摆杆速度的变化有关. 相似文献
8.
摆杆尺度因子（K因子）是反映LaCoste&Romberg航空重力仪线性响应特性的最重要参数. 利用基于地面参考数据的外部标定法和基于交叉点不符值的内部标定法分别对其进行了标定，实测数据分析表明，K因子的内、外部标定结果非常一致，且利用新K因子计算的空中重力扰动，其精度较采用出厂值提高了02～04 mGal. 内部标定法具有较好的实际应用价值. 研究了K因子与滤波尺度的相关性，表明重力仪可能为一非线性响应系统，即K因子的大小与摆杆速度的变化有关. 相似文献
9.
本文利用中国地磁子午链台站的资料，对1997～1999年期间发生的25次磁暴，用自然正交分量法（NOC）、相关分析和傅里叶分析三种方法，分3个步骤依次分离出依赖于世界时（UT）的暴时变化（Dst）、依赖于地方时（LT）的太阳静日变化（Sq）和太阳扰日变化（SD）.对各种变化时空特征的分析表明：①Dst变化清楚地反映出赤道对称环电流磁扰的空间分布和时间演化特征；②满洲里、北京十三陵和琼中台Sq幅度在多数磁暴主相期间出现极大和极小值，反映了Sq焦点在纬度方向上的移动所产生的地磁效应；③SD变化在主相期间最强，在恢复相期间逐渐减弱；④相关分析和傅里叶分析提供了一种能有效提取Sq和SD变化的方法. 相似文献
10.
利用震源距23 km范围内观测的2000年姚安MS65地震余震记录，计算了震源及近邻区域的尾波规一直达S波在频率15～20 Hz之间的傅里叶谱振幅.结果显示谱振幅随震源距增大而增大， 在对谱振幅进行了震源辐射方向性校正之后, 才出现谱振幅随震源距衰减的现象.由此获得了震源及近邻区域S波的Q(f)值,可表示为QS(f)=89f098其值比由尾波得出的姚安地区的平均QC(f)值低得多，表明了震源破裂带的强烈非均匀性对QS(f)的重大影响. 相似文献
11.
本文以宁夏区域地震台网为例，分析了波形互相关法在判定重复地震中可能存在的问题并讨论了相应的处理方法，通过构建三维非均匀体模型并利用谱元法数值模拟地震波的传播，统计了不同台站观测到的地震对波形互相关系数的分布，进一步研究了互相关系数与非均匀体性质及震源机制解之间的关系。结果表明:针对宁夏区域地震台网，利用波形互相关法判定重复地震比地震定位方法更有效；互相关系数在不同台站的取值与震源附近三维非均匀体强度和直达波与尾波的振幅比有关，对于相同的震源间距，较弱震源、较弱非均匀体或者较强振幅的直达波均会导致波形互相关系数变高，因此应选取更高的互相关系数阀值来判定重复地震。宁夏区域地震台网平均台间距为30—50 km，通过选取直达波较弱的台站或只截取尾波窗口计算互相关系数并设定较高的阀值，利用波形互相关法可有效地判定ML1.0—3.0重复地震，进而为重复地震的监测与研究提供依据。 相似文献
12.
Perspectives of Cross-Correlation in Seismic Monitoring at the International Data Centre 总被引：1，自引：0，他引：1
We demonstrate that several techniques based on waveform cross-correlation are able to significantly reduce the detection threshold of seismic sources worldwide and to improve the reliability of arrivals by a more accurate estimation of their defining parameters. A master event and the events it can find using waveform cross-correlation at array stations of the International Monitoring System (IMS) have to be close. For the purposes of the International Data Centre (IDC), one can use the spatial closeness of the master and slave events in order to construct a new automatic processing pipeline: all qualified arrivals detected using cross-correlation are associated with events matching the current IDC event definition criteria (EDC) in a local association procedure. Considering the repeating character of global seismicity, more than 90 % of events in the reviewed event bulletin (REB) can be built in this automatic processing. Due to the reduced detection threshold, waveform cross-correlation may increase the number of valid REB events by a factor of 1.5–2.0. Therefore, the new pipeline may produce a more comprehensive bulletin than the current pipeline—the goal of seismic monitoring. The analysts’ experience with the cross correlation event list (XSEL) shows that the workload of interactive processing might be reduced by a factor of two or even more. Since cross-correlation produces a comprehensive list of detections for a given master event, no additional arrivals from primary stations are expected to be associated with the XSEL events. The number of false alarms, relative to the number of events rejected from the standard event list 3 (SEL3) in the current interactive processing—can also be reduced by the use of several powerful filters. The principal filter is the difference between the arrival times of the master and newly built events at three or more primary stations, which should lie in a narrow range of a few seconds. In this study, one event at a distance of about 2,000 km from the main shock was formed by three stations, with the stations and both events on the same great circle. Such spurious events are rejected by checking consistency between detections at stations at different back azimuths from the source region. Two additional effective pre-filters are f–k analysis and F prob based on correlation traces instead of original waveforms. Overall, waveform cross-correlation is able to improve the REB completeness, to reduce the workload related to IDC interactive analysis, and to provide a precise tool for quality check for both arrivals and events. Some major improvements in automatic and interactive processing achieved by cross-correlation are illustrated using an aftershock sequence from a large continental earthquake. Exploring this sequence, we describe schematically the next steps for the development of a processing pipeline parallel to the existing IDC one in order to improve the quality of the REB together with the reduction of the magnitude threshold. 相似文献
13.
The accuracy of automatic procedures for locating earthquakes is influenced by several factors such as errors in picking seismic phases, network geometry, modeling errors and velocity model uncertainties. The main purpose of this work is to improve the performances of the automatic procedure employed for the “quasi-real-time” location of seismic events in North Western Italy by developing a procedure based on a waveform similarity analysis and by using only one seismic station.To detect “earthquake families” a cross-correlation technique was applied to a data set of seismic waveforms recorded in the period 1985-2002, in a small test area (1600 km2) located in the South Western Alps (Italy). Normalized cross-correlation matrices were calculated using about 2700 seismic events, selected on the basis of the signal to noise ratio, manually picked and located by using the Hypoellipse code. The waveform similarity analysis, based on the bridging technique, allowed grouping about 65% of the selected events into 80 earthquake families (multiplets) located inside the area considered. For each earthquake family a master event is selected, manually re-picked and re-located by using Hypoellipse code. Having chosen a reference station (STV) on the basis of the completeness of the available data set, an automatic procedure has been developed with the aim of cross-correlating new seismic recordings (automatically picked) to the waveforms of the events belonging to the detected families. If the new event is proved to belong to a family (on the basis of the cross-correlation values), its hypocenter co-ordinates are defined by the location of the master event of the associated family. The performance of the proposed procedure is tested and demonstrated using a data set of 104 selected earthquakes recorded in the period January 2003-June 2004 and located in the test area. The automatic procedure is able to locate, associating events with the multiplets detected by the waveform similarity analysis, about 50% of the test events, almost independently of the accuracy of the automatic phase picker and without the biasing of the network geometry and of the velocity model uncertainties. 相似文献
14.
单台地震自动定位网格搜索法及其MATLAB试验 总被引：3，自引：3，他引：0
提出了一种利用单个地震台站三分向数字地震波形记录进行单台地震自动定位的网格搜索法。该方法以台站为中心,建立辐射状网格,按可变震中距步长和方位角步长进行搜索。对一个检测到的地震事件记录波形,对每个震中距,计算预测波形特征函数与记录波形特征函数的互相关函数值,选其最大值对应的震中距;对每个方位角,合成沿径向和沿横向的波形分量,并计算P波段的径向绝对积分值与横向绝对积分值之差,选其最大值对应的方位。对于选定的方位,如果合成的径向分量与记录垂直分量乘积在P波段的积分值为负,则取该方位角为震中相对于台站的方位角,否则该角要加上180°。在MATLAB环境中对该方法的基本步骤进行了试验,初步结果表明该方法是可行的。 相似文献
15.
In this paper, we use the double difference location method based on waveform cross-correlation algorithm for precise positioning of the Three Gorges Reservoir (TGR) earthquakes and analysis of seismic activity. First, we use the bi-spectrum cross-correlation method to analyze the seismic waveform data of TGR encrypted networks from March, 2009 to December, 2010, and evaluate the quality of waveform cross-correlation analysis. Combined with the waveform cross-correlation of data obtained, we use the double difference method to relocate the earthquake position. The results show that location precision using bi-spectrum verified waveform cross-correlation data is higher than that by using other types of data, and the mean 2 sig-error in EW, NS and UD are 3.2m, 3.9m and 6.2m, respectively. For the relocation of the Three Gorges Reservoir earthquakes, the results show that the micro-earthquakes along the Shenlongxi river in the Badong reservoir area obviously show the characteristics of three linear zones with nearly east-west direction, which is in accordance with the small faults and carbonate strata line of the neo-tectonic period, revealing the reservoir water main along the underground rivers or caves permeated and induced seismic activity.The stronger earthquakes may have resulted from small earthquakes through the active layers. 相似文献
16.
结合波形互相关的双差定位方法在三峡水库地震中的应用 总被引：1，自引：1，他引：0
本文采用基于波形互相关算法的双差定位方法对三峡水库地震进行精定位和地震活动性分析。首先使用双谱互相关方法分析了三峡库区加密台网于2009年3月至2010年12月观测到的地震波形数据，并对波形互相关分析的结果进行了评价。基于结合获得的波形互相关数据使用双差定位方法对地震事件进行精定位研究，结果表明使用双谱法验证的波形互相关数据的定位精度要高于其他数据的结果，其东西向震源位置平均误差为3.2m、南北向为3.9m、垂直向为6.2m。重定位震中结果显示巴东神龙溪两岸微震分布明显呈现出3条近东西向的线性条带状，与地表小规模断裂和碳酸盐岩地层走向一致，揭示了库水主要沿着溶洞或者地下暗河渗透进而诱发地震活动，较强地震可能是微小地震贯穿活动面的结果。 相似文献
17.
利用国家测震台网数据备份中心时间跨度超过7年的连续波形资料, 设定至少三个台站记录的垂直分量波形互相关系数大于0.8的地震对为一组重复地震, 通过波形互相关分析, 识别出龙门山断裂带周缘波形相关意义上的“重复地震”2790次, 构成2907组重复地震。 沿用Schaff和Richards的研究结果, 假定“重复地震”间距很小(小于1 km), 地震目录记录的重复地震对位置之差主要为地震台网的定位误差所致, 基于此误差给出了龙门山断裂带周缘地震台网的定位精度估计: 台网的水平定位精度较高, 水平定位误差约为2.8 km(2倍标准差), 且西南段台网的水平定位精度优于中北段; 垂直定位精度较差, 垂直定位误差约为10 km(2倍标准差), 现有地震定位方法对震源深度的测定有待改善。 相似文献
18.
The Applicability of Modern Methods of Earthquake Location 总被引：7，自引：0，他引：7
Paul G. Richards Felix Waldhauser David Schaff Won-Young Kim 《Pure and Applied Geophysics》2006,163(2-3):351-372
We compare traditional methods of seismic event location, based on phase pick data and analysis of events one-at-a-time, with
a modern method based on cross-correlation measurements and joint analysis of numerous events. In application to four different
regions representing different types of seismicity and monitored with networks of different station density, we present preliminary
results indicating what fraction of seismic events may be amenable to analysis with modern methods. The latter can supply
locations ten to a hundred times more precise than traditional methods. Since good locations of seismic sources are needed
as the starting point for so many user communities, and potentially can be provided due to current improvements in easily-accessible
computational capability, we advocate wide-scale application of modern methods in the routine production of bulletins of seismicity.
This effort requires access to waveform archives from well-calibrated stations that have long operated at the same location. 相似文献
19.
The study of the stress-strain state of a medium in seismically quiet areas is difficult because of the absence of strong events. Under such circumstances, each earthquake, even relatively weak, is of high importance. In this case, all possible information on tectonic stresses and their dynamics, e.g., information on time, location, and magnitude of aftershocks, should be obtained from available seismic data. The earthquake near the town of Mariupol which occurred on August 7, 2016, had a body wave magnitude of 4.5–4.9 from the data of the different seismological centers. We detected 12 aftershocks that occurred within 5 days after the main shock using two seismic arrays (AKASG and BRTR) and one three-component station (KBZ) of the International Monitoring System, as well as two array stations of the Institute of Geosphere Dynamics, Russian Academy of Sciences. For six aftershocks, signals were found at three or more stations. The other aftershocks were detected from the data at two out of three nearest stations. Signal detection and association with aftershocks of the main shock, as well as estimation of magnitude and relative location of the found aftershocks, were carried out using the method of waveform cross-correlation (WFCC). The signals from the main shock that acted as the only master event (ME) for the WFCC method were used as waveform templates. To increase the signal-to-noise ratio and to determine the exact onset time of regular seismic waves from aftershocks, we used waveform templates of different length, from 10 to 180 s depending on the wave type and distance to the station, as well as band filtering in narrow frequency bands. The highest sensitivity of the detector and accuracy of the P-wave onset time estimates were reached when a waveform template included all regular waves from P to L g . Association of signals with aftershocks was based on back projection of signal arrival times to origin times using the travel time from a master event to the station, which was measured with a very low error, being equal to almost half of the digitization step length. To develop a seismic event hypothesis, the origin times at two or more stations should be spaced within a 2-s interval. 相似文献
20.
Real-time envelope cross-correlation detector: application to induced seismicity in the Insheim and Landau deep geothermal reservoirs 总被引：1，自引：0，他引：1
Margarete Vasterling Ulrich Wegler Jan Becker Andrea Brüstle Monika Bischoff 《Journal of Seismology》2017,21(1):193-208
We develop and test a real-time envelope cross-correlation detector for use in seismic response plans to mitigate hazard of induced seismicity. The incoming seismological data are cross-correlated in real-time with a set of previously recorded master events. For robustness against small changes in the earthquake source locations or in the focal mechanisms we cross-correlate the envelopes of the seismograms rather than the seismograms themselves. Two sequenced detection conditions are implemented: After passing a single trace cross-correlation condition, a network cross-correlation is calculated taking amplitude ratios between stations into account. Besides detecting the earthquake and assigning it to the respective reservoir, real-time magnitudes are important for seismic response plans. We estimate the magnitudes of induced microseismicity using the relative amplitudes between master event and detected event. The real-time detector is implemented as a SeisComP3 module. We carry out offline and online performance tests using seismic monitoring data of the Insheim and Landau geothermal power plants (Upper Rhine Graben, Germany), also including blasts from a nearby quarry. The comparison of the automatic real-time catalogue with a manually processed catalogue shows, that with the implemented parameters events are always correctly assigned to the respective reservoir (4 km distance between reservoirs) or the quarry (8 km and 10 km distance, respectively, from the reservoirs). The real-time catalogue achieves a magnitude of completeness around 0.0. Four per cent of the events assigned to the Insheim reservoir and zero per cent of the Landau events are misdetections. All wrong detections are local tectonic events, whereas none are caused by seismic noise. 相似文献