各向异性ATI介质地震矩张量理论研究

引言地震矩张量描述了地震点源的基本特征,其内容涉及到各类震源(包括剪切位错震源、张裂震源和体积震源)的力学机制、震源辐射、地应力场、震源运动学和强地面运动等地震学中的重要课题。一般认为,浅源构造地震是因断层面间的快速纯剪切错动而辐射地震波,造成在地表的振动,传统上该解释被称为双力偶机制。但实际地震观测和地震矩张量反演结果     

岩石裂纹扩展微观机制声发射定量反演

岩石受载内部微裂纹扩展及其震源机制反演有助于认识宏观裂纹扩展过程的非线性断裂力学行为.借助声发射监测手段,本文建立了仅涉及微裂纹张开/闭合和剪切滑移的位移不连续震源模型,通过各位置处传感器耦合质量标定及点源远场P波矩张量反演获得了含预制裂纹砂岩受载过程的震源机制解及时变响应特征,在全局坐标系下分析了微裂纹的三种断裂力学行为.结果表明:在位移不连续模型中,震源矩张量特征值与试样泊松比之间必须满足特定约束条件,该约束条件下的优化问题可采用拉格朗日乘子和Levenberg-Marquardt迭代法求解;受载砂岩裂纹扩展过程中,声发射震源以剪切滑移机制占优,微裂纹空间取向及运动方向与试样宏观主裂纹夹角平均值分别为40.9°和17.7°;对微裂纹体积分解表明岩体微观破裂机制以沿X方向I型张开为主,而沿Y方向的II型断裂滑移方向与试样全局变形方向相一致,由于试样内部晶粒分布非均质性造成了少量沿Z方向的III型平面外微裂纹滑移行为;受载砂岩裂纹扩展过程中微裂纹模式角与震源极性值变化趋势一致、利用震源震级评估的局部应力降值与实验观测结果相吻合,这两者均表明了位移不连续模型在震源机制定量反演中的适用性.     

2000年姚安MS6.5地震3.0≤ML ＜5.0余震的地震矩张量反演

建立合于云南地区的速度结构模型,对云南数字地震台网记录的2000年姚安Ms6．5地震3．0≤ML〈5．0余震的垂直分量进行频率域内的地震矩张量反演。结果表明：矩张量分解得到纯膨胀（各向同性）分量P、纯剪切（双力偶）分量M0和补偿线性矢量偶极C三部分,其中纯剪切（双力偶）分量帆占主要部分,表明地震的震源破裂过程以剪切破裂为主。从余震震源机制解可知,NW-NWW方位的节面占主导,结合余震分布尺度可以判断发震断裂是北西向的断裂。     

云南禄劝地震部分余震的矩张量反演

利用数字盒式磁带记录加速度仪组成的流动地震台网所记录的三分向近场加速度图,通过矩张量反演确定了1985年4月18日云南禄劝 Ms=6.1地震的部分余震的震源机制.以均匀半无限弹性介质的格林函数解释路径效应,并通过正演计算识别由两次积分得到的位移地震图中的直达 P 波、直达 S 波和 SP 转换波震相,然后用这些震相进行矩张量反演.反演结果表明,在解超定线性方程组时,采用适当的加权系数,可使上述直达波和转换波的理论计算值与观测值拟合得较好.尽管用以反演的三个余震大小不同(震级 ML48,3.2,3.5),震源位置也有差别,但它们的震源机制却非常接近,且与主震的震源机制相当一致.这一特征显示了余震的发生与主震发震构造的内在联系.这些实例说明,由震源球球面上分布适宜的数字地震台网取得的近场加速度资料,借助于即使是简单的介质模型,通过地震矩张量反演,不但可以得出这些地震震源的主要成份————剪切位错源,同时还可得出震源所含的其它成分,如膨胀源和补偿线性向量偶极.      

2022年四川泸定MS6.8地震震源基本特征

2022年9月5日,在四川省甘孜州泸定县发生M_S6.8地震.本研究收集区域台网震相数据、全球地震台网(GSN)、国际数字地震台网联盟(FDSN)与德国地学中心GEOFON台网的宽频带P波数据,利用双差定位、矩心矩张量解反演、有限断层波形反演和视震源时间函数分析等方法,分析了此次地震震源的基本特征.重定位结果显示,余震分布具有丛集性,3个地震丛分别集中在震中附近以及相距30 km左右的东南端和西北端,总体上西北端地震较浅,东南端地震较深.矩心矩张量反演表明,矩心位于29.55°N,102.14°E,深度16 km,释放地震矩1.0068×10¹⁹ N·m,相当于矩震级M_W6.60,双力偶成分占88%,是一次近纯走滑的地震事件.结合余震分布可以断定,地震发生在走向163°、倾角77°(倾向西南),滑动角为-5°的断层面.有限断层反演显示,破裂区主要由两部分构成,破裂起始点及其周围是主要破裂区;另一破裂区位于其东南,总体表现为从西北向东南的单侧破裂,最大滑动量约1.4 m,位于起始破裂点附近.从矩心矩张量反演和有限断层反演得到...     

非对称地震矩张量时间域反演:理论与方法

本文在对称地震矩张量反演的基础上,进一步研究了非对称地震矩张量时间域反演的理论与方法,结果表明:非对称地震矩张量反演与对称地震矩张量反演类似,只需将对称地震矩张量反演方法略加改动,即增加3个待解参数,便可实现非对称地震矩张量反演.为了判断非对称地震矩张量反演相对于对称地震矩张量反演是否存在过度拟合,运用了AIC准则 (赤池信息准则).为了定量地描述地震矩张量之间的差异,引入了地震矩张量的矢量表示法.通过分析格林函数与地震矩张量各分量之间的关系,得出:在非对称地震矩张量反演时,若仅用垂直向地动位移数据,将无法区分M_xy与M_yx这两个分量, 需要同时运用垂直向与水平向地动位移数据进行联合反演才能区分M_xy与M_yx; 若采用不同的速度结构模型或不同的格林函数计算方法,则需重新评估地震矩张量各分量的分辨度问题.为检验非对称地震矩张量反演方法的可行性, 利用合成地震图进行了一系列数值试验.数值试验结果表明,在非对称地震矩张量反演中,有必要引入S波进行P波与S波联合反演以提高反演的准确性和判定断层面的能力.      

宽频P波反演1988年澜沧地震震源参数

本文改进了Kikuchi P波反演震源时间函数方法,在最小二乘法中引入加权系数,均衡各台资料在求解地震矩中的比例关系,使之推广到不同震中距、不同方位的情况。利用我国CDSN台网长周期和中长周期资料,分别用反射率法和远场广义射线法产生了理论子波,反演出澜沧M_s7.6地震的震源参数和破裂时间过程。结果表明,1988年澜沧大震的断层面走向150°,倾角84°,位错矢量与水平夹角175°,为走滑型震源机制;地震破裂上升时间为4秒,特征时间39秒,宏观尺度130公里,总地震矩达到2.5×10~(21)牛顿·米;地震可分成三个子破裂,由东南向西北扩展,构成了P波的复杂性,基本上能与现场地表迹象和地震宏观参数对应。     

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.     

1997年中国西藏玛尼Mem>Ssub>7.9地震的时空破裂过程l

用中国数字地震台网（CDSN）的长周期波形资料反演了1997年11月8日中国西藏玛尼地区MS7.9地震的地震矩张量,用频率域里反褶积方法从P波和S波震相中分别提取了震源时间函数,并经反演依赖于方位的震源时间函数获取了断层面上破裂随时空变化的图象．矩张量反演结果表明:玛尼地震发震应力场的P轴和T轴均接近于水平,P轴在NNE方向（方位角29,倾角7）,T轴在SEE方向(方位角122,倾角23),断层错动以走滑为主;标量地震矩为3.41020 Nm,矩震级MW=7.6．由矩张量反演得到的震源时间函数显示,这次地震是由一次较小事件和较大事件组成的,较小事件大约持续5 s,较大事件持续约10 s．由余震分布可推断出玛尼地震的发震断层是走向为250、以走滑为主的左旋-逆断层,断层面的倾角比较陡,约88．根据反演结果计算了理论格林函数,然后用反褶积方法提取了震源时间函数．从不同台站的P波和S波中分别提取的震源时间函数一致表明这次地震破裂的时间历史比较简单,可用一宽度约10 s的正弦形的函数近似表示．进一步反演从不同台站上得到的、依赖于方位的P波和S波震源时间函数,获得了断层面上滑动的时空分布图象．从破裂的记忆式快照看,破裂开始于断层的西端,然后向东向下发展,总体上具有单侧破裂的特征．破裂面由3个破裂子区构成．一个在断层西端,深度约10 km(西区);另一个距断层西端约55 km,深度约35 km(东区);第3个距断层西端约30 km,深度约40 km(中区)．３个破裂子区构成约长70 km,宽60 km的破裂面．从破裂的遗忘式快照看,这次地震的破裂过程是相当复杂的,在不同时刻断层面上发生错动的地点并不相同,显示出这次地震的破裂过程具有愈合脉冲的特征,而且在断层面上的某些部位发生了多次错动;另一特征是最先和最后破裂的部位都不是主要的破裂区．根据标量地震矩计算了断层面上静态位错的分布,位错最高的3处（西区、东区和中区）的位错值分别为956 cm,743 cm和1 060 cm．由断层面上位错的分布推知,破裂主要集中在震中以东长约70 km的断层上;从余震的分布看,震中以西余震稀疏而震中以东余震密集．这些都表明这次玛尼MS7.9地震是北东东-南西西向至近东-西向断层向东扩展的结果．      

矩张量反演法在江苏及附近海域的应用

利用江苏区域数字地震台网宽频带地震计记录的Pnl波波形资料,采用TDMT_INV时间域地震矩张量反演方法,尝试反演2009-2011年江苏及附近海域7次中小地震(ML3.5以上,最大震级ML5.3)的地震矩张量解,并通过记录清晰的P波初动在震源球的下半球投影对反演结果进行评价.结果表明:反演结果与初动方向一致较好.由此说明在研究区域用矩张量反演法测定中小地震震源机制解具有一定的可行性.     

1994年9月16日台湾海峡地震及其构造背景研究

采用宽频带Ｐ波波形资料，利用全局反演方法，推断了１９９４年９月１６日发生在台湾海峡的一次强烈地震的地震矩张量；并采用随机加权方法进行误差分析．结果表明，这次地震的矩张量解以双力偶成分为主，是断层面为ＥＷ走向的正倾错动．震源机制的张应力轴接近水平，ＳＮ走向；压应力轴几乎竖直．地震矩值为０．９８×１０１９Ｎｍ．震源过程的持续时间仅有４ｓ，震源时间函数显示了均匀的单一破裂事件．通过对台湾东南到吕宋岛以北地震带的震源性质分析，探讨了该地区产生ＳＮ向水平拉张应力状态的原因．     

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．     

由地震释放的地震矩叠加推导平均应力场

文中给出了根据地震释放的总地震矩求解平均应力场的方法,并使用加入随机误差的人工合成震源机制解数据和唐山余震区震源机制解数据对其进行检验。由检验结果可知,该方法可以应用于区域平均应力场的求解。使用的震源机制解资料越多,所得结果越稳定,且更接近真实的区域应力场。该方法的优点是: 用每个地震的震级作为权重,能够较好地反映出大小地震在应力场反演中的不同贡献; 并且在计算过程中不需要知道震源机制解2个节面中哪个节面为地震断层面。     

On the observability of isotropic seismic sources: The July 31, 1970 Colombian earthquake

Theoretical calculations are made to study the observability of isotropic components of seismic sources. In particular we consider the 1970 deep Colombian earthquake, for which a precursory isotropic component was previously reported by Gilbert and Dziewonski.We compare an ultra-long period vertical record at Pasadena of the 1970 event to synthetic seismograms calculated both for Gilbert and Dziewonski's source model and for the pure double-couple source of Furumoto and Fukao, and obtain better overall agreement for the latter. The amplitude of the long-period synthetic for the isotropic source is about 5–15 times smaller than the synthetic for the deviatoric source, suggesting that the data may be relatively insensitive to the presence of a small isotropic source. When this possibility was tested, the overall agreement was found to be almost completely insensitive to the presence of even a reasonably large isotropic component.However, the isotropic source was derived from multi-station moment tensor inversion, rather than from single-station studies. A numerical experiment on the effect of lateral heterogeneity of eigenfrequencies and of Q on the inversion for the moment tensor shows that even relatively small amounts of heterogeneity can produce spurious isotropic sources from moment tensor inversion.     

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 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.     

Optimum size and density of surface grid arrays for retrieving accurate shear-tensile fracturing of microearthquakes

Surface arrays became an important tool for monitoring the induced seismicity in hydraulic fracturing experiments and for assessing the impact of fluid injection on the fracturing process of microearthquakes. The layout of sensors plays a key role in this task because it controls the accuracy of event locations and retrieved seismic moment tensors. We simulate various configurations of grid sensor arrays characterized by a different number of sensors, array span, sensor spacing, depth of sources and various shear/tensile source mechanisms of events. The moment tensor inversion is carried out using synthetically calculated P-wave amplitudes with added random noise. A bias in the solutions is evaluated by errors in the double-couple percentage of inverted moment tensors because the double-couple errors inform us about the sensitivity of the network to detect the shear/tensile fracturing mode of induced microearthquakes. The results show that the accuracy of the double-couple percentage is mostly controlled by the offset-to-depth ratio R defined as the ratio of half of the network size to the event depth. The optimum value of R is in the range of 0.75–1.5 irrespective of the type of the focal mechanism. If 121 (11 × 11) sensors are distributed in a regular grid and recorded data are characterized by a 10% random noise, the double-couple error is less than 6%. This error increases, if R is not optimum or if the number of sensors is reduced. However, even sparse arrays with 49 (7 × 7) or 16 (4 × 4) sensors can yield a reasonable accuracy, provided the surface grid arrays are designed to have an optimum size.     

Moment tensor inversion and source rupture process of the September 27, 2003 M_S=7.9 earthquake occurred in the border area of China, Russia and Mongolia

IntroductionOn September 27, 2003, an earthquake of MS=7.9 struck the border area of China, Russia and Mongolia. According to the field investigation from the Earthquake Administration of XinjiangAutonomous Region, the whole northern Tianshan region felt the hit. Buildings and structures within six counties and one city in Altay region, which is total about 0.11×106 km2 area, were damaged to different extent and caused certain economic losses. The epicenter determined by China National …