Moment tensor inversion of near-source broadband data

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声发射矩张量反演

地震矩张量反演是获取震源过程的有效方法.岩石变形过程中的声发射与地震类似,均是弹性应变能快速释放.如假设条件得到满足,矩张量反演方法同样可用于了解声发射震源过程.声发射矩张量反演可使用P波位移进行计算.当样品尺寸远大于声发射波长,且声发射由微破裂产生,声发射源的尺度很小时,P波矩张量反演可采用远场近似.本文首先针对声发射的特点,实现根据远场P波反演声发射矩张量的算法,并通过人工声发射实验对算法的正确性和可靠性进行了检验.最后,用声发射矩张量反演方法对花岗岩单轴压缩实验的声发射源特征进行了分析.结果表明：对于纯剪切破裂模式,声发射矩张量反演可得断层面;对于非纯剪切破裂模式,如纵向挤压导致的横向张性劈裂,由于存在多解性不能得到断层面,但可通过矩张量的迹区分破裂模式.     

Moment magnitude estimation using Iran strong motion data

Journal of Seismology - In this study, seismic moment, moment magnitude, and the corner frequency of Iranian earthquakes were estimated using the Iran Strong Motion Network (ISMN) data. To estimate...     

Moment tensor inversion for focal mechanism of the Beibuwan earthquakes

IntroductionOnDecember31,1994andJanuary10,1995,twoearthquakesoccurredconsecutivelyinBeibuwanarea,China.TheirmagnitudewereMs=6.0andMs=6.1respectively.ThehypocentralparametersoftheseearthquakesarelistedinTable1.Thetimeintervalofthetwoewthquakesis10dandtheirepicentrallocationsareneartoeachotherTheyarethestrongestewthquakesinBeibuwanregiononrecord.Since1980,just12earthquakeshadoccurredinthe50kmrangearoundtheepicentresofthesetwoearthquakes(Wu,etal,1996).Thelargestearthquakeamongthe12earthquake…     

Moment tensor inversion of explosive long period events recorded on Arenal volcano,Costa Rica,constrained by synthetic tests

In order to constrain the moment tensor solution of an explosive seismic event recorded on Arenal volcano, Costa Rica, we perform tests using synthetic data. These data are generated using a 3D model including the topography of the volcano and the best estimation of the velocity model available for Arenal. Solutions for (i) the moment tensor components, and (ii) the moment tensor plus single forces, are analyzed. When noisy data and mislocated sources are used in the inversion, spurious single forces are easily generated in the solution for the moment tensor components plus single forces. Forces also appear when the inversion is performed using an explosive event recorded on Arenal in 2005. Synthetic tests indicate that these forces might be spurious. However the mechanism is correctly retrieved by the inversion in both solutions. The ability to recover the explosive mechanism for the 2005 event combined with the interpretative aids from the synthetics tests will enable us to invert for the large variation in events observed on Arenal.     

Moment tensor inversion of small to moderate earthquakes in the Capital Region in 2004

The moment tensor solutions of 51 small to moderate earthquakes occurred in the Capital Region in the year of 2004 are obtained by inverting the broadband waveform data. Accordingly, other source parameters, such as scalar seismic moments, moment magnitudes, double-couple （DC） components and compensated-linear-vector-dipole （CLVD） components, are determined as well as fault parameters and stress-axis parameters. The inverted results are evaluated by groups of numerical tests.     

区域台网地震矩张量快速反演系统研究

基于美国内华达大学地震实验室的矩张量反演程序,采用JAVA和HTML语言,研发了一套近实时全波形矩张量快速反演系统,用于区域台网地震矩张量的快速产出.该系统由区域地震速报系统触发,能自动实现中等强度地震矩张量的快速反演,同时也包含人机交互模块,可进行人工校正,最终以网页形式对外服务.本文将系统运行以来成功反演的结果与USGS和中国地震局地球物理研究所的计算结果进行对比,验证了该系统的可靠性.      

Moment tensor inversion of the November 6, 1988 M S=7.6, Lancang-Gengma, China, earthquake using long-period body-waves data

Moment tensor inversion was carried out to invert the source mechanism and source time function of the MS=7.6 November 6, 1988, Lancang-Gengma, Yunnan Province, China, earthquake. Waveforms of long-period body-waves recorded by China Digital Seismograph Network (CDSN) were used in the inversion. The inverted result shows one nodal plane of right-lateralstrike-slip faulting and another of left-lateral strike-slip faulting and a simple source time function of a duration of about 15 s and scalar seismic moment of 6.4(1020 N(m. From the geological dataand tectonic settings and also from field observations and epicentral distribution of aftershocks, the nodal plane striking in the azimuth of 313( is preferred as the fault plane. The pressure axis lies almosthorizontally in north-south direction.     

Moment tensor inversion of very long period seismic signals from Strombolian eruptions of Erebus Volcano

Strombolian eruptions from the long-lived lava lake of Erebus volcano, Ross Island, Antarctica, generate repeating Very Long Period (VLP) signals, containing energy between approximately 30 and 5 s, that persist for several minutes and through the post-eruptive refilling of the lava lake. The initial approximately 10 s of this signal is moderately variable, particularly with respect to its initial polarity, while the following VLP coda has been observed to be stable since the earliest VLP observations were made (1996). To estimate forces and force couples consistent with the Erebus VLP signature, we perform moment tensor inversions for point sources using high signal-to-noise data stacks from the six-station, 18-component broadband seismographic network and Green's function forward calculations that incorporate topography. We infer a shallow (approximate depth of less than 400 m below the lava lake surface) source centroid that underlies the center to the northwestern rim of the main crater, east and north of the lava lake. Integrated M_ii functions over the predominant (180 s) signal duration of VLP events show that the net scalar moments for these events are on the order of 4 × 10¹³ N m (corresponding to a moment magnitude mw ≈ 3) for typical sized VLP events. Moment rate tensors which characterize force couple components are dominated (85–97% of variance) by dilatational components. Approximately 25% of the data variance is attributable to single forces that are attributable to oscillatory reaction forces caused by fluid transport, however, the relative contributions of vertical forces and couples with this sparse network is poorly resolved for these shallow sources. The generally high degree of repeatability in the VLP signal across thousands of eruptions over the past decade indicates that the response of the conduit system to gas slug ascent and subsequent gravitational disequilibrium is stable, consistent with the generally unchanging surface manifestation of the convecting lava lake system, and arguing for a thermally and dynamically stable conduit system beneath the lava lake.     

Moment tensor inversion for the focal mechanism of the Dongfang (Hainan) earthquake swarm

IntroductionOnJanuary4,1992,twoearthquakesoccurredconsecutivelyaroundtheGancheng-BanqiaoatDongfangCounty,HainanProvince.Theirorigintimeandmagnitudewere23:01:24,ML=3.4and23:01:54,ML=3.7,respectively.Theepicentrallocationoftwoearthquakeswere18°46′N,108°42′Eand18°45′N,108°42′E,respectively.Thefocaldepthswereabout10kin.Followingthesetwoearthquakes,alotofsmallearthquakesoccurredinthisregion.ThebiggestearthquakeoccurredonMay26,1992.Itsorigintimewas18f43f25andthemagnitudewasML=4.5.Ac…     

大地电磁相位张量和倾子的三维主轴各向异性反演

地壳和上地幔普遍存在的电性各向异性是大地电磁测深方法在实践应用中的关键和难点问题,而由近地表局部地电异常引起的电流型畸变可进一步加剧各向异性反演的多解性和不确定性.为压制电流型畸变影响,本文实现了一种利用大地电磁相位张量和倾子数据获取地下介质主轴电性各向异性结构的三维反演算法.该算法正演问题的求解采用交错采样有限差分法,反演问题的求解采用非线性共轭梯度法.理论模型测试表明,相位张量和倾子的三维各向异性反演不仅恢复了真实的各向异性异常分布特征,且压制了为拟合电流型畸变出现的假异常.由于相位张量和倾子数据不含幅值信息,先验模型选取对反演模型电阻率值的恢复效果影响较大,但初始模型的改变基本不影响反演结果.为进一步验证该算法的有效性,将其应用于USArray项目在美国西北部采集的109个长周期大地电磁实测数据.反演结果表明,相对于阻抗数据,相位张量和倾子数据的各向异性反演结果对浅层结构的刻画更为准确,与地表地质特征更为吻合.

     

基于协同克里金方法的重力梯度全张量三维约束反演

随着重力梯度全张量测量技术的日趋成熟,重力梯度全张量数据的三维反演技术日益受到重视与关注.全张量数据反演与重力数据反演一样仍然面临着严重的多解性问题.本文将基于地质统计学的协同克里金方法应用于重力梯度全张量数据三维反演,建立了密度约束下的多变量协同克里金联合反演方程,以降低反演的多解性.模型试验表明密度信息的加入能够有效降低反演的多解性,提高反演结果的分辨率,尤其是纵向分辨率能够得到显著提高.最后对美国德克萨斯州一个岩丘区所获得实际资料的应用表明了本文方法的实用性.     

Three-dimensional inversion of full magnetic gradient tensor data based on hybrid regularization method

Rapid developments in SQUID-based technology make it possible for geophysical exploration to direct measure, inverse and interpret magnetic gradient tensor data. This contribution introduces a novel three-dimensional hybrid regularization method for inversion of magnetic gradient tensor data, which is based on the minimum support functional and total variation functional. Compared to the existing stabilizers, for example, the minimum support stabilizer, the minimum gradient support stabilizer or the total variation stabilizer, our proposed hybrid stabilizer, in association with boundary penalization, improves the revision result greatly, including higher spatial and depth resolution, more clear boundaries, more highlighted images and more evident structure depiction. Moreover, suitable selection of model parameter λ will further improve the image quality of the recovered model. We verify our proposed hybrid method with various synthetic magnetic models. Experiment results prove that this method gives more accurate results, exhibiting advantages of less computational costs even when less prior information of magnetic sources are provided. Comparison of results with different types of magnetic data with and without remanence indicates that our inversion algorithm can obtain more detailed information on the source structure based on rational estimation of total magnetization direction. Finally, we present a case study for inverting SQUID-based magnetic tensor data acquired at Da Hinggan Mountains area, inner Mongolia, China. The result also certifies that the method is reliable and efficient for real cases.     

Moment tensor inversion of some aftershocks of the April 18, 1985 Luquan earthquake of Yunnan Province, China

Based on the three component accelerograms, recorded at near-field distance by a temporary seismic network consisting of digital cassette tape recording accelerographs, the focal mechanisms of three aftershocks of the April 18, 1985, Luquan, Yunnan Province, China, earthquake ofM _S=6.1, are calculated using seismic moment tensor inversion technique. The phases of direct P, S and converted SP waves in the displacement seismograms, produced by twice integrations of the observed accelerograms, are identified via forward calculation using Green’s functions for homogeneous semi-infinite elastic medium, and used in the inversion. The results of inversion show that a better fit of synthetic to the observed seismograms of direct as well as converted phases can be achieved if appropriate weighting functions are used in solving the over definite linear equations. While these aftershocks are of different magnitudes (M _L=4.8, 3.2 and 3.5, respectively) and hypocentral locations, their focal mechanisms are very similar and consistent with that of the main shock. This feature demonstrates the intrinsic correlation between the occurrence of aftershocks and the seismogenic fault of main shock. Our experimentations show that using the near field accelerogram obtained from the digital seismic network with appropriate azimuthal coverage on the focal sphere, with the aid of even simple medium model, not only the shear dislocation source, but also the isotropic part and CLVD (compensated linear vector dipole) can be retrieved by the technique of moment tensor inversion. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 412–419, 1991. This work is supported by the Chinese Joint Seismological Sciences Foundation and the Western Yunnan Earthquake Prediction Test Site (WYEPTS), State Seismological Bureau.     

Higher degree moment tensor inversion of Mani earthquake using far-field broadband recording

Breakthrough point source model, extended earthquake source model is used to calculate more seismic source parameters in this paper. We express seismic source using higher degree moment tensors, to reduce a large number terms originally presenting in higher degree moment tensor representation, Haskell rupture model is used. We inverted the source parameters of Mani earthquake in Tibet using broad-band body wave of 32 stations of Global Seismograph Network (GSN), the results show that it is a strike-slip fault, rupture direction is 75° , rupture duration is 19 s, the fault plan is f =77° , d =88° , l =0° , the auxiliary plane is f =347° , d =90° , l =178° , and the fault dimension is 47 km′ 28 km. These results will give new quantitative data for earth dynamics and have practical meaning for seismic source tomography research.     

Forest-height inversion using repeat-pass spaceborne polInSAR data

Forest-height inversion using airborne double-antenna synthetic aperture radar(SAR)systems has been widely researched,leading to increasing accuracy.Polarimetric SAR Interferometry(PolInSAR)data from spaceborne single-antenna SAR systems,which are influenced by temporal decorrelation,have difficulty inverting forest height.Given the temporal decorrelation effect,the classical random volume over ground(RVoG)model has been proven to invert forest height with significant errors,using repeat-pass PolInSAR data.In consideration of this problem,the temporal decorrelation RVoG(TD-RVoG;based on the RVoG)model was proposed.In this study,an improved TD-RVoG model is presented,with a new temporal decorrelation function.Compared with TD-RVoG,the new model has fewer unknown parameters and can be applied in a three-stage inversion procedure.Validity of the new model is demonstrated by Advanced Land Observing Satellite/Phased Array type L-band SAR(ALOS/PALSAR)data.Results show that the improved TD-RVoG has better accuracy,with inversion error less than 1.5m.     

稀疏台网反演区域地震偏量矩张量解的稳定性

使用区域地震台网的波形资料,研究了2010年2月26日台湾以东海域Mw5.4地震的偏量矩张量,所得结果与Havard CMT目录给出的解之间的Kagan角为9.5°,两者较为一致;反演得到这次地震的震源深度为41 km,接近USGS给出的定位结果,可能更接近真实的震源深度.选择不同的台站组合,分析了台站布局对矩张量解的影响.结果显示,3个台站的组合基本上都可以较为准确地得到矩张量解,台站方位覆盖越好,反演得到的解的偏差越小;在合适的情况下,两个台站的组合也可以得到较为可靠的解.     

基于卡尔曼滤波的自然电场数据时序反演

自然电场法常用于环境与工程等领域的监测作业,但各时刻观测数据往往单独反演解释.为了充分利用时序数据间的关联信息,提高监测数据的反演解释可靠性,提出基于卡尔曼滤波的自然电场监测数据时序反演方法.根据达西定律和阿尔奇公式建立污染物在孔隙介质中的运动扩散的动态地电模型,作为用于构建卡尔曼滤波的状态模型.而卡尔曼滤波的观测模型则通过常规的自然电场法正演获得.在建立状态模型和观测模型的基础上,构建起卡尔曼滤波递归,将地电模型演化信息与自然电场观测数据进行信息融合,实现自然电场监测数据的时序反演.加入噪声的自然电场模拟数据测试表明时序反演算法具有较好的鲁棒性,对噪声不敏感.沙槽物理实验监测数据的计算测试也同样证明时序反演能有效处理监测数据,实现对动态模型的准确重构.

     

Locating microseismic events using borehole data

Constraining microseismic hypocentres in and around hydrocarbon reservoirs and their overburdens is essential for the monitoring of deformation related to hydraulic fracturing, production and injection and the assessment of reservoir security for CO₂ and wastewater storage. Microseismic monitoring in hydrocarbon reservoirs can be achieved via a variety of surface and subsurface acquisition geometries. In this study we use data from a single, subsurface, vertical array of sensors. We test an existing technique that uses a 1D velocity model to constrain locations by minimizing differential S‐to‐P arrival times for individual sensors. We show that small errors in either arrival time picks or the velocity model can lead to large errors in depth, especially near velocity model discontinuities where events tend to cluster. To address this issue we develop two methods that use all available arrival times simultaneously in the inversion, thus maximizing the number of potential constraints from to N, where N is the number of phase picks. The first approach minimizes all available arrival time pairs whilst the second approach, the equal distance time (EDT) method defines the hypocentre as the point where the maximum number of arrival time surfaces intersect. We test and compare the new location procedures with locations using differential S‐to‐P times at each individual sensor on a microseismic data set recorded by a vertical array of sensors at the Ekofisk reservoir in the North Sea. Specifically, we test each procedure's sensitivity to perturbations in measured arrival times and the velocity model using Monte Carlo analysis. In general, location uncertainties increase with increasing raypath length. We show that errors in velocity model estimates are the most significant source of uncertainty in source location with these experiments. Our tests show that hypocentres determined by the new procedures are less sensitive to erroneous measurements and velocity model uncertainties thus reducing the potential for misinterpretation of the results.     

地震密度反演及地层孔隙度估计

地层密度直接与孔隙度、孔隙流体类型、饱和度和骨架矿物成分有关.本文通过理论分析和计算,讨论了油气藏储层物性参数变化引起的密度变化及密度变化对地震波速度、阻抗和振幅的影响,提出了基于完全纵波方程的全波形地震密度反演和孔隙度估计方法,克服了常规地震密度反演对地震数据更多处理引起的信号畸变,提高了地震密度反演和地层孔隙度估计的精度.该方法采用波场导数的时间积分和多炮求和,对地震数据中的噪声具有比较强的压制作用.理论模型研究表明该方法是可行的.通过对我国西部某气田实际数据处理、分析和反演,获得了地层密度和孔隙度,结果与测井基本吻合,证明了预测结果的准确性和方法的有效性,从而为后续的有效储层预测和储量计算提供了可靠的数据.