2013年前郭MS5.8震群矩张量研究

2013年吉林前郭M_S5.8震群为爆发性震群,目前余震活动仍然在持续.基于吉林、辽宁、黑龙江、内蒙古四省地震台网记录的前郭震群波形资料,利用波形信噪比、震源类型、台站及速度模型组合的指标选择最佳的反演方案,应用矩张量的三种反演模式,对序列中5个M_S≥5.0地震进行矩张量反演研究,获得了全矩张量、偏矩张量和纯双力偶的矩张量.使用F-test对地震的三种模式的矩张量反演结果进行显著性检验来确定最佳反演模式.结果显示,5个地震的最优矩张量解均为全矩张量模式反演获得的结果,其双力偶分量仅有20%~65%,矩心深度位于地下3~4 km处,地震在Hudson震源类型图上的投影远离双力偶震源类型区域.这些结果表明,震源类型并非典型的构造地震,推断前郭地震可能是与人类活动有关的诱发地震.     

用应变地震观测求解震源矩张量的基本原理

震源机制解,即对地震矩张量的推断,对于地震研究具有至关重要的意义.应变地震观测是张量观测,与摆式地震仪的位移矢量观测不同,可以为地震研究提供新的数据源.本文讨论用应变地震观测求解震源矩张量的基本原理.在距离震源足够远的地方,地震波可以看成平面波,其性质决定于震源矩张量.假设平面地震波的应变张量可以由震源矩张量通过坐标变换计算得到,就可以通过观测应变地震波求解震源机制.这个假设至少对于双力偶震源机制是成立的.由此可以证明,在理想的无限介质中,只要有两个以上不同地点的应变地震波观测,就可以解出震源矩张量.这为解决震源机制问题提供了新的方法.目前的地震矩张量求解方法需要两方面的条件:或者需要很多观测点(例如体波反演),或者需要长周期地震波资料(例如面波反演).这些方法只适用于分析比较大的地震.对于小震,因为通常其震中周围不会有足够多的摆式地震仪观测点观测到其地震波,而地震波周期又短,难以利用传统方法给出可靠的震源机制解,所以只需少数观测点就能求解震源矩张量的新方法特别有意义.用应变地震观测求解震源机制,可以给出更为精确的结果.     

On the retrieval of moment tensors from borehole data

The complete moment tensors of seismic sources in homogeneous or vertically inhomogeneous isotropic structures cannot be retrieved using receivers deployed in one vertical borehole. The complete moment tensors can be retrieved from amplitudes of P‐waves, provided that receivers are deployed in at least three boreholes. Using amplitudes of P‐ and S‐waves, two boreholes are, in principle, sufficient. Similar rules also apply to transversely isotropic media with a vertical axis of symmetry. In the case of limited observations, the inversion can be stabilized by imposing the zero‐trace constraint on the moment tensors. However, this constraint is valid only if applied to observations of shear faulting on planar faults in isotropic media, which produces double‐couple mechanisms. For shear faulting on non‐planar faults, for tensile faulting, and for shear faulting in anisotropic media, the zero‐trace constraint is no longer valid and can distort the retrieved moment tensor and bias the fault‐plane solution. Numerical modelling simulating the inversion of the double‐couple mechanism from real data reveals that the errors in the double‐couple and non‐double‐couple percentages of the moment tensors rapidly decrease with increase in the number of boreholes used. For noisy P‐ and S‐wave amplitudes with noise of 15% of the top amplitude at each channel and for a velocity model biased by 10%, the errors in the double‐couple percentage attain 25, 13 and 6% when inverting for the double‐couple mechanism from one, two and three boreholes.     

Decomposition of seismic moment tensors for underground nuclear explosions

Generally the decomposition of a seismic moment tensor is not unique. However, to favorably view the characteristics of a certain seismic source, one must decompose a seismic moment tensor into parts according to assumptions about the properties of the seismic source. Different from natural earthquakes in which the shear dislocation component plays a predominant role in the source process, and the seismic moment tensor can be separated into an isotropic component, a double couple, and a compensated linear vector dipole (CLVD), underground nuclear explosions have three major components in their source process, i.e., the explosion, the tensional spalling, and the tectonic strain release associated with the explosion. In such a situation the conventional moment tensor decomposition for earthquakes is not convenient to estimate the yield of the explosion and to characterize the tectonic strain release. In this paper, an alternative decomposition scheme is proposed to deal with the moment tensor of underground nuclear explosions, which might benefit the approach to study the tectonic strain release induced by underground nuclear detonations.     

Uncertainty of moment tensor determination from surface wave analysis for shallow earthquakes

We treat the problem of the non-uniqueness of the moment tensor inversion for shallow earthquakes from long period surface wave data. We give an existence condition for double couples radiating the same long period surface waves as the deviatoric moment tensor obtained by such inversion. We describe the family of such double couples and show that they may provide better estimates of double couple mechanisms than the traditional “best double-couple” solution. We demonstrate the results of application to four large shallow earthquakes with different source signatures.     

Global seismicity of 1982: centroid-moment tensor solutions for 308 earthquakes

The centroid-moment tensor analysis is applied to digital recordings of 308 moderate and large earthquakes that occurred during 1982 and were recorded by the Global Digital Seismograph Network (GDSN) and International Deployment of Accelerometers (IDA) networks. The tables contain numerical results for all events. A graphical representation of the source geometry is shown for the full moment tensor solution, as well as for the “best double couple”.     

Determining the focal mechanisms and depths of relatively small earthquakes using a few stations by full‐waveform modelling

Determining the focal mechanism of earthquakes helps us to better define faults and understand the stress regime. This technique can be helpful in the oil and gas industry where it can be applied to microseismic events. The objective of this paper is to find double couple focal mechanisms, excluding scalar seismic moments, and the depths of small earthquakes using data from relatively few local stations. This objective is met by generating three‐component synthetic seismograms to match the observed normalized velocity seismograms. We first calculate Green's functions given an initial estimate of the earthquake's hypocentre, the locations of the seismic recording stations and a 1D velocity model of the region for a series of depths. Then, we calculate the moment tensor for different combinations of strikes, dips and rakes for each depth. These moment tensors are combined with the Green's functions and then convolved with a source time function to produce synthetic seismograms. We use a grid search to find the synthetic seismogram with the largest objective function that best fits all three components of the observed velocity seismogram. These parameters define the focal mechanism solution of an earthquake. We tested the method using three earthquakes in Southern California with moment magnitudes of 5.0, 5.1 and 4.4 using the frequency range 0.1–2.0 Hz. The source mechanisms of the events were determined independently using data from a multitude of stations. Our results obtained, from as few as three stations, generally match those obtained by the Southern California Earthquake Data Center. The main advantage of this method is that we use relatively high‐frequency full‐waveforms, including those from short‐period instruments, which makes it possible to find the focal mechanism and depth of earthquakes using as few as three stations when the velocity structure is known.     

用P波波形资料反演中强地震地震矩张量的方法

本文给出了利用不同震中距范围（３°-９０°）的长周期Ｐ波记录资料，通过波形拟合和反演确定地震矩张量的方法．在求解过程中，不引入矩张量的迹为零这一约束条件．有６个独立分量的地震矩张量解可分解成各向同性部分、最佳双力偶和补偿线性矢量偶极．文中给出了发生在中国的５次６级以上地震的地震矩张量反演结果，表明在一些地震的震源过程中存在不可忽略的体积变化．     

基于Langston分解和Hilbert变换约束的区域偏量矩张量反演方法及其应用

本文基于Langston的震源机制分解方法以及Minson和Dreger修正后的近场位移的解析解表达式,给出了一种区域纯偏量矩张量的求解方法,方法使用基于Hilbert变换的波形包络作为增强约束．对该方法进行了数值试验. 试验结果表明,定位准确且速度结构已知的情况下,背景高斯噪声水平达30%时,该方法仍可以得到较稳定的解;使用0.01——0.1 Hz的中长周期频段进行反演,在随机震相到时误差最大plusmn;3 s的情况下,近90%的情况可以得到相对准确的解. 速度结构模型的干扰试验表明,平均模型接近真实地壳结构时,可以得到接近真实的解;模型与真实的地壳结构的误差在10%以内时,得到的解与真实解比较接近;误差接近20%时,矩张量解会出现很大的偏差;地震的定位误差主要影响震源深度的判定,从而导致最终解中出现虚假的非双力偶成分,但在约束为偏量矩张量的情况下,反演得到的断层面参数与真实解偏差不大;在台站方位角覆盖较差(＜60deg;)的情况下,使用平均模型仍可以得到较为准确的解．使用该方法研究了2010年10月24日河南周口太康MW4.7地震的震源机制,结果显示矩张量解与初动符号解较为一致．      

Moment tensors of earthquakes in and near the Tibetan Plateau and their scaling law

Moment tensors of eleven major earthquakes in the Tibetan Plateau and its surrounding region from 1966 to 1980 are estimated by generalized inverse technique. The seismic source time function and focal depth are immediately determined in the inversion. The results show that moment tensors of some events differ significantly from double couple, the deviation increases with decreasing plunge angle of null axis. All these events occurred in the upper crust, much shallower than those reported so far, for example, in NEIS Bulletin. Focal mechanism solution obtained from the moment tensors are consistent with the idea that the Indian plate collides northwards with the Eurasian plate and that an eastward spreading exists in the crust of the Tibetan Plateau. The stress drops for earthquakes of intraplate are systematically higher than those of earthquakes in suture zone. The source process duration becomes longer with seismic moment, but for the same seismic moment, the process duration for earthquakes in suture zone is about 1.4 times of those for intraplate event, these results suggest that the earthquakes near suture zone may be of a special characteristics in source process differently from those in intraplate. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,14, 423 – 434, 1992.     

Moment tensor inversion of near-source broadband data

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Discrimination of induced seismicity by full moment tensor inversion and decomposition

Human activities, including operations related to mining and reservoir exploitation, may induce seismicity and pose a risk for population and infrastructures. While different observations are commonly used to assess the origin of earthquakes, there is a lack of rules and methods for the discrimination between natural and induced seismicity. The inversion and decomposition of the full moment tensor and the observation of relevant deviation from a pure double couple (DC) model may be an indicator for induced seismicity. We establish here a common procedure to analyse a set of natural and induced events of similar magnitude, which occurred in Germany and neighbouring regions. The procedure is based on an inversion method and on a consistent velocity model and recording network. Induced seismicity is recorded during different mining and/or reservoir exploitations. Moment tensors are inverted using a multi-step inversion approach. This method, which was successfully applied in previous studies at regional and teleseismic distances, is further developed here to account for full moment tensor analysis. We first find a best DC solution and then perform a full moment tensor inversion, fitting full waveforms amplitude spectra at regional distances. The moment tensor solution is decomposed into DC, compensated linear vector dipole and isotropic terms. The discrimination problem is then investigated through the evaluation of distributions of non-DC source components for natural and induced data sets. Results illustrate the potential of the inversion and discrimination approach. Additional detailed analyses are carried out for the two most significant induced earthquakes, and rupture models are compared with the full moment tensor solutions.     

Moment tensors and source processes of three deep Sea of Okhotsk earthquakes

Three large deep earthquakes beneath the Sea of Okhotsk are studied using the relative amplitudes of the direct P phase and the surface reflections pP and sP observed on teleseismic long-period WWSSN seismograms. Use of this comprehensive dataset provides a redundancy of information which allows possible deviation of the source mechanism from the double couple model to be studied over a large part of the focal sphere, in a region where previous workers have postulated complex source mechanisms including implosive precursors and multiple events. Focal mechanism solutions derived from the relative amplitudes are used to create synthetic seismograms which further assist the modelling of the source processes of these earthquakes. One of the three earthquakes occurred close to a sequence of complex earthquakes in 1970–1971 and comprises a number of discrete but related subevents, the two main subevents with similar source mechanism orientations, and the latter subevent probably triggered by the first. The other two earthquakes, which occurred further southwest, are similar to each other and their seismograms display features characteristic of the finite size and rupture propagation of the source which enable the source size, geometry and rupture velocity to be estimated. The source moment tensors of all three earthquakes show no significant deviation from a simple double couple and show no evidence of a volumetric component.     

Source parameters determination for earthquakes in Kushiro,Japan considering source time function

This paper applies a new formulation to do moment tensor inversion for earthquakes in the Kushiro area of Japan. Comparing with conventional moment tensor inversion method, the new one takes the effect of source time function into consideration. For the inversion, best solution is obtained by minimizing the difference between the observed seismograms and the synthetic ones. And the best-fitting focal depth is determined from the variance reduction. The results indicate that half duration of source time function is proportional to the magnitude of earthquakes. Large earthquakes have long half duration, whereas that of moderate-small earthquakes is comparatively shorter. The focal mechanisms of all three earthquakes are of thrust fault type, which is mainly ascribed to the collision of the North American plate with the Eurasia plate in the late Cretaceous or Paleogene.     

三峡库区秭归与巴东交界Ms4.0地震矩张量及应力环境研究

三峡库区湖北秭归与巴东交界地区2013年以来发生5次Ms4.0以上地震.本文基于湖北、重庆等省属13个测震台站宽频带波形数据,采用kiwi软件包和rapidinv12程序反演了这些地震的全矩张量解,结果显示所有地震双力偶解均为走滑兼逆断性质,两个节面走向、倾角、滑动角与P、T轴走向和倾俯角的一致性均较好,主压应力P轴N...     

Modelling short-period crustal phases at regional distances for the seismic source parameter inversion

Waveforms of short-period crustal phases observed at regional distances are modelled in an attempt to retrieve the source parameters of small earthquakes. For a simple shield type crustal structure, the synthetic seismograms calculated for elementary source mechanisms show that the waveforms of crustal phases are quite distinct for different source mechanisms, and suggest that these features can be used to constrain the source mechanisms. Waveforms of the crustal phases are also strongly affected even by small variations in the crustal thickness as well as in the focal depth.A generalized, linearized waveform inversion technique is used to invert the regional crustal phases for a deviatoric moment tensor source. The inversion technique is applied to regional short-period records from a small earthquake in central Sweden for determining its source parameters. The waveform inversion, which mainly used Lg waves, produced a satisfactory fit between the observed and synthetic records, suggesting that the source mechanism and focal depth estimates were reasonable. The focal depth of 40 km obtained for the event studied suggests the occurrence of a deep crustal earthquake and demonstrates the usefulness of crustal phases in studying small intraplate earthquakes.     

2011年云南腾冲5.2级双震发震机理

本研究联合使用观测震相到时和波形互相关数据,采用双差法对2011年6月20日与8月9日发生在云南腾冲的5.2级双震及其余震序列进行重定位,并采用gCAP(generalized Cut and Paste)方法反演了该双震全矩张量解.结果显示,双震震中位于龙川江断裂的西侧,余震序列在深度上为一个倾斜的柱状体,且倾向腾冲火山区;6月20日和8月9日5.2级地震均表现为体积缩小的闭合型破裂,包含有显著的非双力偶成分,但后者包含的非双力偶成分相对明显减小.这些结果表明,云南腾冲5.2级双震及余震活动可能与火山下方的地壳岩浆作用密切相关,龙川江断裂为热物质向上运移提供了通道,而双震型地震的发生可能与首次地震的破裂体积缩小挤出的流体作用于断裂密切相关.     

The relative amplitude moment tensor method applied to the IASPEI deep earthquakes

The relative amplitude moment tensor method is used to determine the source types and source orientations of the four deep earthquakes from those selected for discussion at the 1985 General Assembly of IASPEI. Source types show no direct evidence of deviation from a double couple, and the well-constrained orientations of this source type can be derived since solutions are tightly constrained by a few important relative amplitudes, mostly involving nodal observations. These solutions are compared with the results of other methods and agree favourably with the USGS first motion solutions. The Harvard CMT solutions, however, often predict P, pP and sP relative amplitudes inconsistent with those observed, and therefore tend to be at variance with the solutions obtained here.     

断层厚度的地震效应和非对称地震矩张量

本文导出了具有厚度和滑动弱化区域的断层的非对称地震矩张量表示式,指出要求地震矩张量具有对称性不是一个绝对必要的限制.在非对称地震矩张量中,位错项对应于对称地震矩张量,拉力项对应于非对称地震矩张量.由于拉力项等效于单力偶,所以在非对称地震矩张量解的两个节面上,沿滑动矢量方向的力偶强度不再相同,与较大力偶相联系的节面为断层面,与较小力偶相联系的节面为辅助面.这一性质可用以从两个正交的节面中判断哪一个节面是断层面.如果忽略拉力项,会高估与位错对应的标量地震矩.只有满足相应的约束条件的非对称地震矩张量才能表示具有厚度和滑动弱化区域的断层模型,并从中分离出与位错和拉力对应的地震矩张量.     

基于密集台阵研究2019辽宁抚顺M2.4矿震震源参数

分析矿震破裂机制及微震的时空分布能够为矿区灾害评估提供更多的有效信息.本研究基于密集台阵观测对2019 年11 月12 日辽宁抚顺2.4 级矿震开展震源参数研究,震源机制解显示地震破裂包含明显的非双力偶分量,表现为体积压缩的塌陷机制,且震源深度较浅,最佳拟合矩心深度为0.6 km.同时,对 11 月3 日—25 日记录...