利用地震台网宽频带地震记录计算福建中等强度地震的震源机制解

2007—2009年福建及邻近地区共发生4级以上地震10次。 这些频繁发生的中等强度地震, 给当地居民的生活带来了不小的影响, 因而有必要加强对这些地震的分析研究。 本文利用BSL开发的矩张量反演程序TDMT_INVC, 使用福建数字地震台网宽频带台站地震波形记录, 对2007—2009年福建地区发生的4次M_L>4.2地震的震源机制解进行反演, 并对反演得到的震源机制解进行分析; 在反演过程中, 利用波形拟合方法确定这4次地震的震源深度。     

Inverse analysis of stochastic moment equations for transient flow in randomly heterogeneous media

We present a nonlinear stochastic inverse algorithm that allows conditioning estimates of transient hydraulic heads, fluxes and their associated uncertainty on information about hydraulic conductivity (K) and hydraulic head (h  ) data collected in a randomly heterogeneous confined aquifer. Our algorithm is based on Laplace-transformed recursive finite-element approximations of exact nonlocal first and second conditional stochastic moment equations of transient flow. It makes it possible to estimate jointly spatial variations in natural log-conductivity (Y=lnK)$(Y=\ln K)$, the parameters of its underlying variogram, and the variance–covariance of these estimates. Log-conductivity is parameterized geostatistically based on measured values at discrete locations and unknown values at discrete “pilot points”. Whereas prior values of Y at pilot point are obtained by generalized kriging, posterior estimates at pilot points are obtained through a maximum likelihood fit of computed and measured transient heads. These posterior estimates are then projected onto the computational grid by kriging. Optionally, the maximum likelihood function may include a regularization term reflecting prior information about Y. The relative weight assigned to this term is evaluated separately from other model parameters to avoid bias and instability. We illustrate and explore our algorithm by means of a synthetic example involving a pumping well. We find that whereas Y and h can be reproduced quite well with parameters estimated on the basis of zero-order mean flow equations, all model quality criteria identify the second-order results as being superior to zero-order results. Identifying the weight of the regularization term and variogram parameters can be done with much lesser ambiguity based on second- than on zero-order results. A second-order model is required to compute predictive error variances of hydraulic head (and flux) a posteriori. Conditioning the inversion jointly on conductivity and hydraulic head data results in lesser predictive uncertainty than conditioning on conductivity or head data alone.     

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.     

Experimental investigation on the effect of spudcan shape on spudcan-footprint interaction

The interaction between a spudcan and an existing footprint is one of the major concerns during jack-up rig installation. The influence of spudcan-footprint interaction has recently been well addressed by a number of researchers. A lack of investigation exists in mitigating spudcan-footprint interaction issues. In the field, stomping and successive repositioning is conventionally used in installing a rig adjacent to an existing footprint. Water jetting and perforation drilling are also sometimes suggested. This paper reports a measure for easing spudcan-footprint interaction issues, with the efficiency of a spudcan with 4 slots tested through model tests carried out at 1 g on the laboratory floor. The soil conditions tested simulate soft to moderate seabed strength profiles close to the mudline, varying the undrained shear strength. The most critical reinstallation locations of 0.5D and 1D (D = spudcan diameter) and existing footprint depths of 0.33D and 0.66D were investigated. By comparing with a conventional spudcan, the spudcan with slots reduced the induced maximum moment, horizontal force, and horizontal sliding distance by up to 80%, 40%, and 98% respectively. Critically, no additional operations, such as stomping/repositioning, perforation drilling, water jetting, are required to be performed offshore.     

2013年9月20日甘肃肃南、青海门源交界5.1级地震的加速释放模型研究

针对2013年9月20日甘肃肃南、青海门源交界5.1级地震,研究了其地震矩加速释放现象。采用不同的空间半径进行了"时-空"扫描计算,结果显示该地震前具有明显的地震矩加速释放现象,随着扫描半径的不同,异常表现为"异常出现—减弱—增强—发震"的特点,因此该方法在实际地震预测中具有一定的实用意义。但由于地震矩加速释放模型的研究较为复杂,影响因素较多,本文也只是针对一个震例进行了研究计算,因此更深入的研究工作需要在后续工作中展开。     

Occurrence probability of a freak wave in a nonlinear wave field

The Edgeworth’s form of a cumulative expansion of the probability density function (PDF) of surface elevation expands the maximum wave height distribution to predict the occurrence probability of freak waves. This study investigated the enhancement of the occurrence probability of freak waves due to the fourth order moment of surface elevation, kurtosis, change and found that the nonlinear effects on the occurrence probability of a freak wave linearly depends on kurtosis for a small number of waves N=250. The statistical theory was compared with field data, and freak waves sometimes appear when not expected by the Rayleigh theory, but they were predicted by the proposed theory.     

Wave force on vertically submerged circular thin plate in shallow water

The paper presented is a solution of shallow water wave force, using small amplitude linear wave theory on two-dimensional vertically submerged circular thin plates under three different configurations: (1) a surface-piercing circular thin plate, (2) a submerged circular thin plate, and (3) a bottom-standing circular thin plate. Finally Morison's equation is used for the determination of wave force which is based on the linear wave theory. The plate is submerged in water near the shore on uniformly sloping bottom. The solution method is confined in a finite domain, which contains both the region of different depth of water and the plate. Laplace's equation and boundary value problems are solved in a finite domain, by the method of separation of variables and the small amplitude linear wave theory. The variation of horizontal force by single particle, total horizontal force and moment with respect to the wave amplitude are obtained at different depth of water and at different wave period. It is observed that the force and moment are converging with the increase of wave period and the gradients of force and moment with respect to the wave amplitude are extremely high for lower wave period.     

惯量投影椭球在构造变形分析中的意义初探

本文讨论了一种新的数学工具,即惯量投影椭球（和椭圆）,在具有任意形状构造变形体的变形描述与应变分析中的意义。论证了在均匀的递进变形过程中,构造标志体惯量投影椭球的变形与其自身的变形保持一致,两者遵循同样的均匀变形方程。在进行构造变形描述和分析时,构造标志体形状与其惯量投影椭球是等效的。惯量投影椭球具有有限应变椭球相同的性质,可以用来描述任意形状构造标志体的变形,并可以替代具有任意形状构造标志体进行变形分析。先前适用于椭圆形标志体变形分析的方法均可应用于具有任意形状的构造标志体。这将为我们对具有任意形状的构造标志体变形的描述和分析提供方便和有用的数学工具。     

Seismic source mechanism inversion from a linear array of receivers reveals non-double-couple seismic events induced by hydraulic fracturing in sedimentary formation

We developed a new method to invert source mechanisms of seismic events observed from a single (vertical or near vertical) array of receivers. This method was tested on a synthetic dataset and applied to a seismic dataset acquired during hydraulic fracturing of a sedimentary formation. We show that a crack-opening seismic event recorded on a single vertical array can be inverted as a pure shear seismic event, indicating that the best fitting shear mechanisms inverted from seismic data acquired along a vertical borehole provide misleading information. We found that the majority of the analyzed source mechanisms of the induced events are not consistent with pure shear faulting as previously thought. The non-shear source mechanisms are required even when seismic noise, location uncertainty, and uncertainty in the attenuation structural model are considered.     

The 10 June 2012 Fethiye Mw 6.0 aftershock sequence and its relation to the 24–25 April 1957 Ms 6.9–7.1 earthquakes in SW Anatolia,Turkey

The 10 June 2012 M_w 6.0 aftershock sequence in southwestern Anatolia is examined. Centroid moment tensors for 23 earthquakes with moment magnitudes (M_w) between 3.7 and 6.0 are determined by applying a waveform inversion method. The mainshock is a shallow focus strike-slip with reverse component event at a depth of 30 km. The seismic moment (M_o) of the mainshock is estimated as 1.28 × 10¹⁸ Nm and rupture duration of the Fethiye mainshock is 38 s. The focal mechanisms of the aftershocks are mainly strike-slip faulting with a reverse component. The geometry of the focal mechanisms reveals a strike-slip faulting regime with NE–SW trending direction of T-axis in the entire activated region. A stress tensor inversion of focal mechanism data is performed to obtain a more accurate picture of the Fethiye earthquake stress field. The stress tensor inversion results indicate a predominant strike-slip stress regime with a NW–SE oriented maximum horizontal compressive stress (S_H). According to variance of the stress tensor inversion, to first order, the Fethiye earthquake area is characterized by a homogeneous interplate stress field. The Coulomb stress change associated with the mainshock and the largest aftershock are also investigated to evaluate any significant enhancement of stresses along the Gulf of Fethiye and surrounding region. Positive lobes with stress more than 0.4 bars are obtained, indicating that these values are large enough to increase the Coulomb stress failure towards NNW–SSE and E–W directions.