用长周期体波反演地震矩张量及其实际意义

介绍了地震矩张量的性质和用长周期体波反演地震矩张量的方法。用地震矩张量表示震源，能够使震源参数线性化，从而实现由观测资料快速。

巴颜喀拉块体东部及邻区块体边界断裂变形特征及其强震危险性分析

在对巴颜喀拉块体东部及其邻区活动块体划分的基础上,基于刚性块体运动模型,利用1999—2007年GPS数据反演得到巴颜喀拉块体东部及邻区活动块体边界断裂带的长期滑动速率,并且利用一维弹性位错模型反演了各活动块体边界断裂的闭锁深度。根据反演得到的滑动速率和闭锁深度,结合GIS平台上获取的各边界断裂的几何长度得到各边界断裂的主要地震矩累积,并通过对比各断裂带上历史强震目录估算的地震矩释放分析各边界断裂带上的地震矩亏损量,进而分析各活动块体边界断裂的强震背景,以期为区域强震的中长期地震危险性分析和防震减灾策略的制定提供资料。

丽江7.0级地震的余震环境应力τ_0值研究

利用 1996年丽江 7 0级余震序列资料 ,通过波谱分析 ,求出了余震的地震矩M0 ,以断裂力学和地震标定律的新观点 ,导出了用峰值速度νp 求震源处环境应力的关系 ,估算了环境应力τ0 值。震源参数测定的结果给出 ,震级ML2 0～ 3 5之间求出的地震矩M0 在 10 19～ 10 2 2 (dyne·cm)之间 ,每次地震平均环境应力 τ0 值在 1 0～ 9 0MPa的范围内变化 ,绝大多数为 2 0～ 5 0MPa。高τ0 值主要分布在 7 0级主震断裂构造及几次 5 0～ 6 0级强余震的周围地区。其次 ,本文研究的另一个重要结果是 ,发现场地放大对地震波记录影响十分明显 ,通过基岩台站与沉积层台站记录的数字地震波谱场地影响分析 ,结果给出频率f在 1 0～ 3 0Hz的范围内 ,沉积层水平向放大约为基岩的 3 5倍 ,理论关系给出二种场地测定的τ0 值沉积场地比基岩场地大1 5倍 ,本文用峰值速度实测求出的震源环境应力τ0 值也相应增大约 1 3倍 ,与理论关系结果基本一致。由此 ,本文详细研究了丽江峡谷的场地放大对震源应力参数测定的影响。

Influence of the liquefied soil layer distribution on the seismic response of rectangular tunnel

In order to obtain the seismic responses of the soil-rectangular tunnel structure,based on the PL-Finn constitutive model,four different conditions,namely,the liquefied soil around the rectangular tunnel,the liquefied soil below the rectangular tunnel,the liquefied soil on either side of the tunnel and the structure on non-liquefied soil,are compared.In accordance to the time at which a large deformation occurs,the possibility of destruction from hard to easy follows a descending order:the liquefied soil all around the structure,the liquefied soil on the bottom of the structure,and the liquefied soil on the two sides of the structure.The area of large deformation is mostly beneath the two arch angles of the tunnel floor.The soil on the two sides,especially close to the structure,is the hardest to liquefy and deform.The large deformation of soil caused by the liquefaction appears after the peak seismic value occurs.The higher the input seismic value is,the easier a large deformation can take place.With the same input of peak ground motion,the total displacement vector of the structure and differential displacement of the side-wall are in accordance with an order from large to small in the three situations:when the saturated sand is on two sides,all around the structure,and on the bottom of the structure.

Scaling of Reduced Energy or Apparent Stress and Its Seismological Significance

Comparison between the NEIC broadband radiated energy catalogue and the Harvard CMT catalogue provides information about apparent stress. In spite of its significant uncertainties and limited reliability, the clues obtained from this comparison seem interesting in the physics of earthquakes. Scaling of apparent stress provides information about the dynamic friction along an earthquake fault. Relation between reduced energy and seismic moment implies that for strike-slip earthquakes, velocity-dependent friction plays a predominant role, while for non-strike-slip earthquakes, slip-dependent friction is predominant. It is also found that strike-slip events with extremely low apparent stress tend to occur “in single”, which is applied to the prediction of the seismic tendency following the 2001 Qinghai-Xizang (Tibet) border M W7.8 earthquake.

Dynamic Method of Seismic Casualty Assessment

The concept of Initial Casualty Matrix is introduced. Using some probability distribution functions, the initial casualty matrix of masonry is determined. The dynamic method of seismic casualty assessment is established and then applied to the Tangshan earthquake data, with some conclusions drawn.

Preliminary Study on Characteristics of Source Parameters of Earthquakes in the Nuozhadu Reservoir Area,Yunnan Province

We computed source parameters for 143 earthquakes with M_L≥ 1. 0 occurring from January,2011 to March,2014 using waveform data recorded by the Nuozhadu and Jinghong Reservoir Seismic Networks. Then,the variation of seismic activity and the characteristics of source parameters before and after the impoundment of the reservoir were investigated. The results show that:( 1) the seismic activity increased obviously after the impoundment,especially during the 3- 4 months after impoundment;( 2) the focal depths of the earthquakes occurring in the reservoir area are shallower than the earthquakes occurring outside the reservoir area in the initial stage of impoundment,but after a time,the difference was gradually reduced;( 3) corner frequency varies with the seismic moment and the log-linear relationship is more obvious after impounding;( 4)stress drop and apparent stress increase with increasing seismic moment,moreover they are lower for the earthquakes occurring in the reservoir area after impounding than those occurring outside the reservoir area or before impounding with the same seismic moment;( 5) the effect of reservoir impoundment on an earthquake can reach a depth of 10 km,and the maximum effect is seen at a depth of 3km- 6km,and the differences of seismic activity and average apparent stress between the inside and outside of the reservoir are significant.

Corresponding Relation Between the Space-time Evolution of Seismic Apparent Strain and the Region of Strong Earthquakes in Yunnan

On the basis of our predecessors' research,we study the distribution and the space-time evolution characteristics of the seismic apparent strain field in Yunnan since the 1970's using the seismic data of Yunnan and its surrounding areas.The result shows that there is a rather strong corresponding relationship between the anomaly region of seismic apparent strain and strong earthquakes.In the nine earthquakes studied,anomaly areas of seismic apparent strain had appeared before eight earthquakes,including five occurring in the anomaly region and three on the edge.Finally,the investigative result is demonstrated primarily.

Focal Mechanism of the Xianyou Earthquake Sequence,Fujian,China

1,209 earthquakes occurred in Xianyou,Fujian from August 4,2010 to October 4,2013.The largest earthquake was M L5. 0 on September 4,2013. In order to study the Xianyou earthquake sequence and understand the causative structure and stress field of Xianyou,the focal mechanism solutions of six earthquakes( M L> 3. 5) in the Xianyou earthquake sequence are calculated using the broadband digital data of the Fujian Seismic Network with the seismic moment tensor inverse method. The results show that the focal faults of the six earthquakes are similar,which are all strike-slip faults striking to the northwest with high dip angles. The direction of the principal compressive stress axes is near SN,which is different from the stress field of Fujian region. The Xianyou earthquake sequence may have been induced by the stress adjustment after the impoundment of Jinzhong reservoir.

Ways of Determining the Focal Mechanisms in the Carpathian Region of Ukraine

The modification to the matrix method for constructing the displacement field on the free surface of an anisotropic layered medium was presented. The source of seismic waves was modelled by a randomly oriented force and seismic tensor. A trial and error method was presented for solving the inverse problem of determining parameters of the earthquake source. A number of analytical and numerical approaches to determining the earthquake source parameters, based on the direct problem solutions, were proposed. The focal mechanisms for the events in the Carpathian region of Ukraine are determined by the graphical method. The theory of determinating the angles of orientation of the fault plane and the earthquake＇s focal mechanism was presented. The focal mechanisms obtained by two different methods were compared.

Rapid Determination of the Centroid Moment Tensor of the 2014 M_S7.3 Yutian,Xinjiang Earthquake

We successfully employ an automatic centroid moment tensor(CMT) inversion system to infer the CMT solutions of the February 12,2014 MS7.3 Yutian,Xinjiang earthquake using near-field seismic waveforms(4° < △ < 12°) observed by the virtual China seismic networks,which have been recently set up.The results indicate that this event occurred on a rupture plane(strike 243°,dip 70°,and rake-18°),showing left-lateral strike-slip faulting with a minor normal-faulting component.The centroid in the horizontal direction is located nearly 13 km east of the epicenter(36.123° N,82.499° E),and the best-fitting centroid depth is around 10 km.The total scalar moment,M0,is retrieved with an average value of 3.05 × 1019N·m,corresponding to moment magnitude MW6.92.Most of the energy is released within about 14 s.Moreover,we discuss about the potential application of this system in earthquake disaster decision.

Seismic Hazard Matrix of Buildings in Yunnan

Seismologists have begun to investigate the earthquake damage and assess the economic losses on the spot in the Yunnan area since the earthquakes with M_S6.7 and M_S6.9 that occurred on the boundary between China and Myanmar west of Menglian county,Yunnan Province,on April 23,1992.From 1992 to 2003,50 destructive earthquakes occurred in Yunnan,and large amounts of data on seismic hazard have been accumulated.With focus on the major building structures,the paper makes statistical analysis on the earthquake damage ratio,loss ratio and seismic hazard index in the areas with different seismic intensity of the 50 events,and presents the seismic hazard matrix of buildings for the Yunnan area.

Applications of texture attribute analysis to seismic interpretation

The first generation coherence algorithm(namely C1 algorithm) is based on the statistical cross-correlation theory, which calculates the coherency of seismic data along both in-line and cross-line. The work, based on texture technique, makes full use of seismic information in different directions and the difference of multi-traces, and proposes a novel methodology named the texture coherence algorithm for seismic reservoir characterization, for short TEC algorithm. Besides, in-line and cross-line directions, it also calculates seismic coherency in 45° and 135° directions deviating from in-line. First, we clearly propose an optimization method and a criterion which structure graylevel co-occurrence matrix parameters in TEC algorithm. Furthermore, the matrix to measure the difference between multi-traces is constructed by texture technique, resulting in horizontal constraints of texture coherence attribute. Compared with the C1 algorithm, the TEC algorithm based on graylevel matrix is of the feature that is multi-direction information fusion and keeps the simplicity and high speed, even it is of multi-trace horizontal constraint, leading to significantly improved resolution. The practical application of the TEC algorithm shows that the TEC attribute is superior to both the C1 attribute and amplitude attribute in identifying faults and channels, and it is as successful as the third generation coherence.

Using Long-Period Body Wave to Inverse Moment Tensors of the M_S6.8 Jiashi,Xinjiang Earthquake in 2003 and the Moderate and Small Earthquakes before and after It

An M_S6.8 strong earthquake took place in Jiashi,Xinjiang on February 24 of 2003.The digital wave form data recorded in Kashi and Wushi stations are selected to inverse the moment tensor solutions for the strong earthquake and the moderate and small earthquakes before and after it(108 earthquakes in 2001～2004).67 focal mechanism solutions have been calculated,and the results agree with those from Harvard University and USGS.The analysis reveals that before the strong earthquake,the moderate and small earthquake distribution was dispersed,and after the event the distribution was mainly concentrated around the strong earthquake.Before the strong earthquake,the seismic faults of the mid and small events had the character of strike-slip and normal faulting,and after the event,they exhibit strike-slip and thrust faulting.The region is dominated by near-NS horizontal compression from the southern block after the strong earthquake.

Seismic Health Monitoring of Foundations Using Artificial Neural Networks

Damage identification plays an important role in structural health monitoring systems. Despite variety in damage identification methods, little attention has been paid to the seismic damage identification of foundations. When shear walls serve as the lateral load resistance system of structures, foundations may subject to the high level of concentrated moment and shear forces. Consequently, they can experience severe damage. Since such damage is often internal and not visible, visual inspections cannot identify the location and the severity of damage. Therefore, a robust method is required for damage localization and quantification of foundations. According to the concept of performance-based seismic design of structures, the seismic behavior of foundations is considered as Force-Controlled. Therefore, for damage identification of foundation, internal forces should be estimated during ground motions. In this study, for real-time seismic damage detection of foundations, a method based on artificial neural networks was proposed. A feed-forward multilayer neural network with one hidden layer was selected to map input samples to output parameters. The lateral displacements of stories were considered as the input parameters of the neural network while moment and shear force demands at critical points of foundations were taken into account as the output parameters. In order to prepare well-distributed data sets for training the neural network, several nonlinear time history analyses were carried out. The proposed method was tested on the foundation of a five-story concrete shear wall building. The obtained results revealed that the proposed method was successfully estimated moment and shear force demands at the critical points of the foundation.

Seismic high-resolution processing method based on spectral simulation and total variation regularization constraints

There is little low-and-high frequency information on seismic data in seismic exploration,resulting in narrower bandwidth and lower seismic resolution.It considerably restricts the prediction accuracy of thin reservoirs and thin interbeds.This study proposes a novel method to constrain improving seismic resolution in the time and frequency domain.The expected wavelet spectrum is used in the frequency domain to broaden the seismic spectrum range and increase the octave.In the time domain,the Frobenius vector regularization of the Hessian matrix is used to constrain the horizontal continuity of the seismic data.It eff ectively protects the signal-to-noise ratio of seismic data while the longitudinal seismic resolution is improved.This method is applied to actual post-stack seismic data and pre-stack gathers dividedly.Without abolishing the phase characteristics of the original seismic data,the time resolution is signifi cantly improved,and the structural features are clearer.Compared with the traditional spectral simulation and deconvolution methods,the frequency distribution is more reasonable,and seismic data has higher resolution.

Constraining the focal mechanism of the Lushan earthquake with observations of the Earth's free oscillations

The amplitudes of the Earth＇s free oscillations have a close relationship to earthquake focal mechanisms. Focal mechanisms of large earthquakes can be well analyzed and constrained with observations of long period free oscillations. Although the 2013 Lushan earthquake was only moderately sized, observable spherical normal modes were excited and clearly observed by a su- perconductive gravimeter and a broadband seismometer. We compare observed free oscillations with synthetic normal modes corresponding to four different focal mechanisms for the Lushan earthquake. The results show that source parameters can be analyzed and constrained by spherical normal modes in a 2.3-5 mHz frequency band. The scalar seismic moment M~ has a major influence on the amplitudes of free oscillations; additionally, the strike, dip, rake and depth of the hypocenter have mi- nor influences. We found that the synthetic modes corresponding to the focal mechanism determined by the Global Centroid Moment Tensor show agreement to the observed modes, suggesting that earthquake magnitudes predicted in this way can readily reflect the total energy released by the earthquake. The scalar seismic moment obtained by far-field body wave inver- sion is significantly underestimated. Focal mechanism solutions can be improved by joint inversion of far- and near-field data.

Determination of regional earthquake source parameters in wavelet domain

Investigating source parameters of small and moderate earthquakes plays an important role in seismology research. For small and moderate earthquakes, the mechanisms are usually obtained by first motion of P-Wave, surface wave spectra method in frequency-domain or the waveform inversion in time-domain, based on the regional waveform records. We applied the wavelet domain inversion method to determine mechanism of regional earthquake. Using the wavelet coefficients of different scales can give more information to constrain the inversion. We determined the mechanisms of three earthquakes occurred in California, the United States. They are consistent with the previous results (Harvard Centroid Moment Tensor and United States Geological Service). This proves that the wavelet domain inversion method is an efficient method to determine the source parameters of small and moderate earthquakes, especially the strong aftershocks after a large, disastrous earthquake.