Application of Ambient Stress Parameters to Short-Term Prediction of the 2004, M_S5.0 Shuangbai, Yunnan Earthquake

Based on the data recorded by the regional digital seismic network of Yunnan and using new methods, the short-term variations of the ambient stress field of Yunnan and its adjacent areas are monitored in real time. With the in-depth analyses of the spatial-temporal evolution of the ambient stress field prior to the 2004, Shuangbai M_S5.0 earthquake, concrete procedures for predicting the three elements of the earthquake are presented.

Characteristics of ambient stress values for micro－earthquake sequences in Western Yunnan Earthquake Prediction Experimental Field

According to the source velocity spectrum model suggested by Chen and Duda (1993), the method of directly measuring the maximum value <Vc (cm)>max of the velocity spectrum from the seismic moment M0 has been studied. The authors have measured the seismic moment M0 and source mechanical parameters of three microearthquake sequences, the Er' yuan, Maidi and Songgui sequences, by use of the digital data of these sequences obtained by near-field observation in the Western Yunnan Earthquake Prediction Experimental Field (WYEPEF). The magnitudes ML of the three micro-earthquake sequences are mostly between 1. 0 and 2. 5, the measured seismic moment M0 is between 10(10)N·m and 10(13)N·m, and the rupture radius a of the source between 90 m and 270 m. The study of the ambient stress parameters τ0 and Δσ shows that the ground motion peak velocity r·v is a function of the ambient stress parameters τ0 and Δσ, while the ambient stresses are related to the seismotectonics and the media states in turn. The values of ambient stress parameters τ0 and Δσ for the three earthquake sequences are between 0. 5-5. 0 MPa for the high stress earthquake swarm (Maidi sequence),between 0. 3-1. 5 MPa for the moderate stress swarm (Songgui sequence), and between 0. 01-0. 5 MPa for the low stress swarm (Er' yuan sequence). We have further discussed the dependence of the high, moderate and low stress states on the tectonics and on the difference in media state. This study can help us to understand deeply the relation that the features of ambient stress states bear with the seismogenic process and the potential earthquake risk zone. Besides, the authors have also found that there is an obvious difference between the moment scaling laws for large and small earthquakes. The scaling law between the peak velocity r·v and the seismic moment M0 is r·v∝M0 0.6 when M0>10(14) N·m, but is r·v∝M0(1/2) when M0<10(14) N·m.

Ambient tectonic shear stress field in Southern California and seismic hazard regions

ccording to the fracture mechanics rupture model of earthquakes put forward by us, several equations to compute tectonic ambient shear stress value τ0 have been derived [equations (1), (2), (3), (5)].τ0 values for intermediate and small earthquakes occurred in Chinese mainland and Southern California have been calculated by use of these equations. The results demonstrate that the level and distribution of τ0 are closely related to the location where large earthquakes will occur, i.e. the region with higher level of τ0 will be prone to occur large earthquakes and the region with lower level will usually occur small earthquakes. According to the spatial distribution of τ0 , the seismic hazard regions or the potential earthquake source regions can in some degree be determined. According to the variation of τ0 with time, the large earthquake occurrence time can be roughly estimated. According to the distribution of τ0 in Southern California and variation with time, three high stress level regions are determined, one (Goldfield area) of them is the present seismic hazard region.

Discrimination between nuclear explosions and earthquakes based on consideration of tectonic ambient shear stress values

On the basis of fracture mechanics earthquake rupture model, the relations between source parameters and (0, the value of tectonic ambient shear stress in the place where the earthquake occurs, have been derived. Thus, we can calculate a large number of values of tectonic ambient shear stress or values of background stress in the place where the earthquake occurs. If nuclear explosions are treated as earthquakes in the calculation, we find that (0 values of nuclear explosions have about 20 MPa, which is obviously higher than average (0 values of earthquakes with the same magnitude. This result can be used to discriminate nuclear explosions from earthquakes.

Dynamic variation of ambient shear stress field before and after three strong earthquakes in Yunnan

A method calculating relative shear stress values in seismic source areas using data of seismic wave is used in thispaper which is introduced by PEI-SHAN CHEN, based on a rupture model studying seismic rupture process fromtheory of fracture mechanics. The shear stress values τ0 in mid-small earthquakes occurred in 1986~June of 1997in Yunnan and its adjacent areas are used to trace the variation process of ambient shear stress field before andafter three strong earthquakes in Yunnan and China-Myanmar border areas. The results show that there exists abackground of high values in ambient shear stress field. In the development process of a strong earthquake, theambient shear stress field in and nearby its potential source area increases obviously, for a long time, experiences aprocess of multiple down - up - down - up. The pattern of dynamic variation of ambient shear stress field hasreflected the multi-source fields of seismogenesis in and nearby Yunnan. There exist multi-increased areas of ambient shear slress fields synchronously in southwest, northwest. west and east of Yunnan, and three strong eathquakes of magnitude about 7 occurred in the most obviously increased areas of ambient shear stress fields.

The dependence of response spectrum on the tectonic ambient shear stress field

It has been analyzed the influence of the tectonic ambient shear stress value on response spectrum based on the previous theory. Based on the prediction equation BJF94 presented by the famous American researchers, CLB20, a new prediction formula is proposed by us, where it is introduced the influence of tectonic ambient shear stress value on response spectrum. BJF94 is the prediction equation, which mainly depends on strong ground motion data from western USA, while the prediction equation SEA99 is based on the strong ground motion data from exten-sional region all over the world. Comparing these two prediction equations in detail, it is found that after BJF94′s prediction value lg(Y) minus 0.16 logarithmic units, the value is very close to SEA99′s one. This case demonstrates that lg(Y) in extensional region is smaller; the differences of prediction equation are mainly owe to the differences of tectonic ambient shear stress value. If the factor of tectonic ambient shear stress value is included into the pre-diction equation, and the magnitude is used seismic moment magnitude to express, which is universal used around the world, and the distance is used the distance of fault project, which commonly used by many people, then re-gional differences of prediction equation will become much less, even vanish, and it can be constructed the uni-versal prediction equation proper to all over the world. The error in the earthquake-resistant design in China will be small if we directly use the results of response spectrum of USA (e.g. BJF94 or SEA99).

A comparison of tectonic ambient shear stress value in China with that in western USA

A method is proposed to estimate average tectonic ambient shear stress value for a region. Thus the average stress values of 19 regions in western USA, and 43 regions (each region is 1010) in Chinese mainland and its surroundings have been obtained. The data of 15 993 earthquakes are from the Internet Centroid Moment Tensor solution made by Harvard University from 1997 to 1999. The results demonstrate that there are highest average stress values in the regions of south California of USA and its off coast sea, reach to 12.0 MPa and 13.7 MPa respectively, then gradually decrease toward north, south, and east. The lowest value is 8.7 MPa and 63% of highest value. The average stress values in northern Xinjiang and in the Chayu region of Tibet are 17.2 and 12.9 MPa respectively. They are highest values in China and higher than USAs. The average stress value in North China, Yunnan, Sichuan, Taiwan is similar to south California of USA. The average stress value in South-North seismic zone is about 13 MPa, a little higher than south California. The distribution of average stress value for two important regions provides basic data for geology. These results are useful to research earthquake activity background and attenuation relation of strong ground motion parameters (e.g. peak acceleration and response spectra).

风积沙的压实特性与循环荷载下变形性状的试验研究

在对风积沙压实特性进行分析的基础上 ,探讨了含水量对风积沙压实影响的机理。通过动三轴试验 ,得到了影响循环荷载下风积沙变形特性的主要因素为压实含水量。

循环荷载作用下水泥复合土变形性状试验研究

通过复合土体的动三轴试验 ,研究了循环荷载作用下循环应力比、加荷周数和围压对复合土体轴向应变的影响。

前震特征及其识别研究

分析了中国大陆地区1970年以来117次中强地震(东部MS≥5.5, 西部MS≥6.0), 其中有直接前震的地震11次, 占9%; 有广义前震的地震63次, 占51%. 直接前震与主震的时间间隔优势分布在30天以内, 空间距离50 km以内, 震级差在1级以上. 利用辽宁数字地震资料, 得到了1999年11月29日和2000年1月15日岫岩MS5.6和5.1地震前的直接前震具有较高的剪应力背景.

中国强地震动速度衰减研究

在研究构造环境应力场特征的过程中，发现构造环境剪应力场量值、对峰值地震动速度PGV有很大影响.用公式定量地把、值引入到PGV的预测方程中，得到了新的预测方程CLB97V；并用观测资料证明了所得方程在震中距＝5──250km范围内，对美国大地震和中国大地震均适用．本文还考虑了大、中、小地震的速度具有不同的优势频率：大震较低，小震较高，因此，小震的PGV衰减较快．这样，CLB97V不仅适用于大震，也适用于中、小地震．如果考虑了世界各地不同的构造区域具有不同的构造环境应力场以后，预测方程可以适用于世界各地．

“霍山地震窗”小震序列运动学参数时变特征研究

利用安徽及邻近地区的数字化地震资料,详细研究了“霍山地震窗口”小震序列的构造环境背景应力和视应力变化特征。结果表明,环境应力值和视应力值不仅能反映震“源”区的应力背景强弱,在距未来强震震中比较远的特殊构造部位,即素有“地震活动穴位”的地震窗口的小地震,同样能较客观反映出孕震区附近应力环境的信息,在华东中强地震前后应力状态的差异性是显著的。

根据构造环境应力场预测峰值水平加速度

在分析了对峰值加速度 PGA 的影响因素之后,我们发现构造环境剪应力场参数τ_0对 PGA起了重要的作用,将τ_0引入 PGA 的预测公式中,同时考虑了 PGA 对频率的依赖性。大地震的PGA 的优越频率 f_a 较低,小地震的 f_a 较高.因此,小地震的衰减系数较大,PGA 衰减较快。基于上述两点改进,提出了新的 PGA 预测公式。在该公式中,构造环境应力场、震级、距离和场地条件是预测将来强地面运动的重要变量。此公式有很大的适用范围,可以用于大地震(矩震级 M_w=6—7.8),也可以用于较小地震(M_w=3—6)的 PGA 预测;在考虑了世界各个地区不同的构造环境应力值水平以后,新预测公式可以应用于世界不同地区(例如美国加州和中国华北、西南等)。用实际观测资料检验结果表明,预测效果良好。

青岛崂山地区环境应力与视应力变化分析

利用青岛市地震监测中心数字台网的地震波形记录，选取震级下限为ML1．0，计算了2003～2004年崂山地震序列过程中青岛地区地震视应力吼δapp和环境剪应力τ0值的变化，结果表明，崂山地震序列的中等地震发生前相近震级小震所反映出来的应力增强变化并不明显，2003年以来青岛地区背景应力场也不存在明显的趋势性变化。对青岛崂山地震序列中261个小震的数字化波形记录计算分析后发现，环境剪应力τ0值和视应力吼δapp值与震级明显相关，并且相同震级的地震事件所计算出二者的变化与地震序列的活动状态密切相关。

中国强地震动位移衰减关系的研究

根据断裂力学破裂模式，发现峰值地震动加速度（PGA）、速度（PGV）和位移（PGD）均对构造环境剪应力场量值了τ0有强烈的依赖性．本文把了τ0值定量地引入到PGD的预测方程中，并同时考虑得到了PGD的优势频率fd对震级的依赖性.基于以上两点改进，从理论上寻出了PGD的预测方程（CLB98d）．用观测资料验证了此方程可用于震中距△＝10─250km范围内的Mw＝4─7．2地震．世界不同地区的τ0值会有差异，但对PGD的预测方程影响不大．

斑节对虾天门冬氨酸转氨酶基因的克隆及氨氮胁迫条件下的表达分析

为了探索天门冬氨酸转氨酶(AST)在斑节对虾(Penaeus monodon)氨氮(NH3-N)解毒代谢中的作用,该研究利用RACE技术获得了斑节对虾AST基因(PmAST)的cDNA全长序列,进行了相关生物信息学分析,在此基础上采用荧光定量与氨氮胁迫实验的方法研究了PmAST基因在斑节对虾的不同组织以及不同浓度氨氮胁迫过程中差异表达情况。该序列全长1 957 bp,开放阅读框(ORF)为1 242 bp,3'非编码区(UTR)为584 bp,包括含有30个碱基的poly(A)尾,5'非编码区(UTR)为131 bp。ORF可编码413个氨基酸,预测分子量为45.852 kD,理论等电点为8.85。序列含有1个AAT-like超家族结构域、15个磷酸化位点和2个糖基化位点。PmAST的mRNA在斑节对虾各组织中都有表达,在肝胰腺中表达量最高,其次为鳃组织,在胃和脑组织中的表达量最低。96 h氨氮胁迫后荧光定量PCR分析结果表明,PmAST在肝胰腺和鳃组织中都具有不同程度的表达上调,显著高于对照组(P<0.05)。研究结果表明斑节对虾的PmAST基因在氨氮胁迫条件下会出现表达上调,并且氨氮浓度越高其上调幅度也越大,所以PmAST参与了斑节对虾的急性氨氮胁迫应答。

澜沧江流域水电工程地区的环境剪应力及震源参数

使用昆明数字地震台网记录的地震波形资料,研究了1999年1月至2003年12月澜沧江流域地区的震源参数和环境应力τ0值,重点讨论了小湾、漫湾和大朝山三个电站高坝水库地区的应力状态及震源参数,结果表明地面运动峰值速度(r·v)符合M1/20τ0的标度关系,较适合澜沧江流域地区中小地震活动规律;水利枢纽工程地区的环境剪应力τ0平均值为36MPa,明显低于澜沧江流域北东和南西地区,属于低应力地区;发生于该区的地震震源深度多小于10km,震级大部分小于3级。分析认为发生于该区的低应力、浅源、低强度地震,可能与该区库区蓄水压力增加有关。

格尔木地区砾石砂的动力学特性及路堤施工措施研究

通过对格尔木地区砾石砂的动三轴试验 ,得到了影响循环荷载作用下砾石砂变形特性的主要因素为循环应力比和围压 。

汶川8.0级地震环境剪应力特征研究

基于甘肃强震固定台和流动观测记录的汶川8.0级地震主震及余震加速度资料,选用三分向记录均完整的87次地震(震级范围为3.0~8.0级),根据用位错理论二维断裂模式推导的震源峰值加速度与环境剪应力关系式计算汶川地震序列的环境剪应力值,探讨其环境剪应力场特征。结果表明,环境剪应力和矩震级有较好的相关性,3~5级地震对应的应力值多在3~6 MPa,5~6级多在6~9 MPa,6~7级多在9MPa以上,且环境剪应力对震源深度也有较强的依赖性。