The Principle and Method for Delineation of Potential Seismic Sources in Northwest Yunnan

Based on the collection and analysis of achievements of other scholars, and by consulting the results of seismic safety evaluation of engineering sites and field surveys of recent years, the seismotectonic indicators are determined for northwest Yunnan and its vicinity, and then potential seismic sources are further delineated. In practice, the following principles are applied: for areas with strong historical earthquakes, the recurrence principle is used to determine the upper bound magnitude; for areas with distinct seismogenic structure but no historical strong earthquake records, the tectonic analogy principle is used in the light of the size and activity behavior of the structure; for areas where the segmentation of the active fault is well studied, the potential sources will be demarcated more precisely; and for areas with buried fault, the seismicity pattern and geophysical abnormity are used to determine the direction of the major axis of the potential seismic source.

Demarcation of potential seismic sources on integration of genetic algorithm and BP algorithm

In this paper potential seismic sources in coastal region of South China are identified by integration of genetic algorithm (GA) and back propagation (BP algorithm). GA is used for finding the best parameter combination rapidly in an infinite solution space for artificial neural networks (ANN). The results show that the distribution of potential seismic sources with different upper magnitude demarcated by this classifier is mostly satisfied the intrinsic relationship between seismic environment and earthquake occurrence, with less effect from subjective judgment of human being.

The Principles and Methods of Division of Potential Seismic Regions for Moderately Strong Earthquakes in Northeast and North China

The uncertainty of potential seismic regions for moderately strong earthquakes has a great effect on the results of seismic hazard analysis in weak seismicity regions,so it is the basement of seismic zoning and seismic hazard assessment for engineering sites by correctly dividing the potential seismic regions for moderately strong earthquakes.By taking Northeast and North China as examples,the authors compiled and systematically analyzed a large amount of basic data and then suggest the principles and methods of potential seismic regions for moderately strong earthquakes based on a great number of case studies.The practical division of potential seismic regions in the Changchun and Jilin areas shows that these principles and methods show better suitability.Moreover,the authors also discuss in this paper the progress obtained and put forward some problems that should be solved in the future.

Study of the Non-Uniform Distribution of Earthquake Risk Within Potential Sources

Potential sources are aggregates of probable future epicenters.In this area,for source models currently,in common use for seismic risk analysis in China,the mean area of each potential source is about 3000-4000 km2.It is assumed that seismic risk has a uniform distribution within the range of each potential source,but studies have shown that the uniform distribution model to a large extent may give an underestimation of the seismic risk.In this paper,the relative distribution of historical epicenters in space within potential sources is discussed,a method is proposed to quantitatively describe the non-uniform distribution of strong earthquakes within potential sources,and some preliminary results are given.By using the results of this paper,seismic risk analysis and seismic zonation can be made more scientific and more reasonable.

Delineation of Potential Seismic Source Regions of Moderately Strong Earthquakes Without Seismogenic Tectonics

In this paper,approaches are developed to delineate the potential seismic source regions of moderately strong earthquakes that do not have clear seismotectonic settings.Based on comprehensive analysis of regional tectonic backgrounds and seismicity,the data,such as isoseisrnals,spatial distribution of after shocks,regional tectonic stress field,and focal mechanisms,are employed for the delineation of the potential seismic source regions.The reliability of such potential seismic source regions is also discussed.

Artificial Neural Network Method Based on Expert Knowledge and Its Application to Quantitative Identification of Potential Seismic Sources

In this paper,an approach is developed to optimize the quality of the training samples in the conventional Artificial Neural Network(ANN)by incorporating expert knowledge in the means of constructing expert-rule samples from rules in an expert system,and through training by using these samples,an ANN based on expert-knowledge is further developed.The method is introduced into the field of quantitative identification of potential seismic sources on the basis of the rules in an expert system.Then it is applied to the quantitative identification of the potential seismic sources in Beijing and its adjacent area.The result indicates that the expert rule based on ANN method can well incorporate and represent the expert knowledge in the rules in an expert system,and the quality of the samples and the efficiency of training and the accuracy of the result are optimized.

Application of Characteristics of Seismogenic Structures in the Determination of Parameter of Potential Seismic Source Areas

The characteristics of seismogenic structures are an important basis for delineating the potential seismic source areas and determining the annual occurrence rate of earthquakes. The potential seismic source area does not only have the intension that “this area has the possibility for destructive earthquakes to occur in the future" but also means that earthquakes of high magnitude interval have the characteristics of similar recurrence. When determining the seismic activity parameters of a statistical unit, some active tectonic blocks in the unit may have different background earthquakes. In order to better reflect the heterogeneity in space of seismic activities, it is necessary to divide the potential seismic source areas into three orders. By analyzing the recurrence characteristics of earthquakes of high magnitude interval in the potential source area and calculating the occurrence probability of earthquakes of high magnitude interval in the potential seismic source area in the time window for prediction, the average annual occurrence rate of earthquakes can be obtained by the method of probability equivalent conversion in the time window for prediction. This would be helpful for considering the recurrence characteristics of strong earthquakes in potential source areas within the framework of seismic risk analysis of China. Besides, the insufficient frequency of characteristic earthquakes of the next high magnitude interval in the potential source area and the heterogeneity of strong earthquakes on seismogenic structures are analyzed to see their application in seismic risk analysis.

Expected magnitude and distance of potential source area and the estimating method

Magnitude and distance of major potential source are needed in order to determine duration time of artificial ground motion and to determine the type of response spectrum (near field or far field) when using the seismic intensity zonation map. The magnitude probabilistic distribution function of seismic belt and the magnitude and space joint distribution function for given intensity of the site in a potential Source are provided. Then the basicformula of calculating expected magnitude and expected distance are developed. Several examples for calculating expected magnitude and expected distance in northern China are discussed. These results show that expected magnitude and expected distance are related not only to geometry of potential source and magnitude but also to the intensity of the site with certain exceeding probability.

Interrelation between seismicity parameters and delimiting potential seismic sources in a seismic statistical region and its influence on seismic risk estimation

In the paper, we have discovered the abnormal area distribution features of maximum variation values of ground motion parameter uncertainty with different probabilities of exceedance in 50 years within the range of 100°-120°E, 29°-42°N for the purpose to solve the problem that abnormal areas of maximum variation values of ground motion parameter uncertainties emerge in a certain cities and towns caused by seismicity parameter uncertainty in a seismic statistical region in an inhomogeneous distribution model that considers tempo-spatial nonuniformity of seismic activity. And we have also approached the interrelation between the risk estimation uncertainty of a site caused by seismicity parameter uncertainty in a seismic statistical region and the delimitation of potential sources, as well as the reasons for forming abnormal areas. The results from the research indicate that the seismicity parameter uncertainty has unequal influence on the uncertainty of risk estimation at each site in a statistical region in the inhomogeneous distribution model, which relates to the scheme for delimiting potential sources. Abnormal areas of maximum variation values of ground motion parameter uncertainty often emerge in the potential sources of Mu greater than or equal 8 (Mu is upper limit of a potential source) and their vicinity. However, this kind of influence is equal in the homogeneous distribution model. The uncertainty of risk estimation of each site depends on its seat. Generally speaking, the sites located in the middle part of a statistical region are only related to the seismicity parameter uncertainty of the region, while the sites situated in or near the juncture of two or three statistical regions might be subject to the synthetic influences of seismicity parameter uncertainties of several statistical regions.

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.

Potential rupture surface model and its ap-plication on probabilistic seismic hazard analysis

Potential sources are simplified as point sources or linear sources in current probabilistic seismic hazard analysis （PSHA） methods. Focus size of large earthquakes is considerable, and fault rupture attitudes may have great influence upon the seismic hazard of a site which is near the source. Under this circumstance, it is unreasonable to use the simplified potential source models in the PSHA, so a potential rupture surface model is proposed in this paper. Adopting this model, we analyze the seismic hazard near the Chelungpu fault that generated the Chi-Chi （Jiji） earthquake with magnitude 7.6 and the following conclusions are reached. （1） This model is reasonable on the base of focal mechanism, especially for sites near potential earthquakes with large magnitude; （2） The attitudes of potential rupture surfaces have great influence on the results of probabilistic seismic hazard analysis and seismic zoning.

Complex of general seismic zoning maps OSR-2017 of Uzbekistan

The quantitative assessment of seismic hazard of Uzbekistan has been examined,and new maps of seismic zoning has been developed.Quasihomogeneous seismological areas and seism-generating zones are considered as seismic sources,based on the analysis of seismotectonic data.The seismological parametrization of seismic sources has been carried out,including determination of parameters of earthquake’s reoccurrence for different power levels,seismic potential and a predominant type motion in the source of occurring earthquakes.The reoccurrence parameters of seismic sources were both determined by directly from Gutenberg-Richter dependence law and using summation and distribution methods.Setting were conducted separately for a sample of strong(M≥5)and weak(M<5)earthquakes.The seismic potential Mmax of seismic active zones was determined by seismological and seismotectonic methods.The predominant type of movement in the faulting for each seismic source is reverse fault.Regional regularities of seismic intensity attenuation with distance of different power levels are determined.The seismic hazard is expressed in points of a macro seismic scale,in velocities and accelerations of ground motions,and it is characterized by calculated seismic intensity with the set probability(P=0.9,P=0.95,P=0.98 and P=0.99)not exceed within 50 years in the constructed maps.In seismic zoning map,the seismic intensity was in average soil conditions.The developed complex of maps considers a number of uncertainties of the input parameters in relation to both incompleteness of initial seismological and seismotectonic data,as well the probabilistic nature of seismic process and seismic intensity.The factors of uncertainty of the input parameters are taken into account by constructing a logic tree.The constructed maps of the general seismic zoning are intended for imple menting antiseismic actions in Uzbekistan.

Fault－weakening effect of reservoir temperature of hot spring and its influence on seismic activities

In this paper, the reservoir temperatures of 14 hot spring samples collected from the northern segment of theRed River Fault are calculated by using the mixing-model of SiO2-geothermometer. Based on the features ofreservoir temperatures and densities of hot springs, the northern segment of the Red River Fault is furtherdivided into 4 sub-segments. The influence of weakening effect of water on seismic activities is discussed fromthe view point of fault-weakening effect of water. It is suggested that the difference in seismic activity between various sub-segments is principally caused by the difference in intensity of the fault-weakening effect ofwater of these sub-segments. The Eryuan sub-segment where the reservoir temperatures are high and the hotsprings are dense corresponds to a slipped region, however, the Jianchuan and Midu sub-segments where thereservoir temperatures are lower and the hot springs are fewer as well as the Dan sub-segment where the hotspring are very few all correspond to locked regions. It is suggested that Dan sub-segment is the riskiest region for strong earthquake preparation, while the possibility for strong earthquake preparation is very little inthe Eryuan sub-segment.

Seismotectonic Zonation of the Longmengshan and Chengdu Region

The principle of three-level delineation is adopted in determination of a potential seismic source for the new National Seismic Ground Motion Parameters Zoning Map of China,to embody the inhomogeneity of the spatial distribution of background seismic activity and induct a uniform seismotectonic model for each seismotectonic region. Based on achievements of determining potential seismic sources in southwestern China,this paper introduces the basic characteristics, historical earthquakes magnitude and frequency distribution,identification of deformation mechanism of main active tectonic structures for the Longmenshan and Chengdu seismotectonic region in the Longmenshan seismic region,establishes the seismogenic model for each seismotectonic region,and identifies the upper limit of background earthquakes. A simple method is also put forward for calculating the spatial distribution function of a background seismic source.

Methods for Estimating Mean Annual Rate of Earthquakes in Moderate and Low Seismicity Regions

Two kinds of methods for determining seismic parameters are presented,that is,the potential seismic source zoning method and grid-spatially smoothing method. The Gaussian smoothing method and the modified Gaussian smoothing method are described in detail, and a comprehensive analysis of the advantages and disadvantages of these methods is made. Then,we take central China as the study region,and use the Gaussian smoothing method and potential seismic source zoning method to build seismic models to calculate the mean annual seismic rate. Seismic hazard is calculated using the probabilistic seismic hazard analysis method to construct the ground motion acceleration zoning maps. The differences between the maps and these models are discussed and the causes are investigated. The results show that the spatial smoothing method is suitable for estimating the seismic hazard over the moderate and low seismicity regions or the hazard caused by background seismicity; while the potential seismic source zoning method is suitable for estimating the seismic hazard in well-defined seismotectonics. Combining the spatial smoothing method and the potential seismic source zoning method with an integrated account of the seismicity and known seismotectonics is a feasible approach to estimate the seismic hazard in moderate and low seismicity regions.

Research on the Probability of Earthquake Occurrence in the Daduhe Drainage Area

This paper applies the Seismic Hazard Analysis method for the cities of China to research on the probability of earthquake occurrence in the Daduhe drainage area,where the cascade dam system is located.This research is based on the potential seismic source scheme of the Seismic Ground Motion Parameter Zonation Map of China(2001),and uses Poisson distribution as an earthquake occurrence model.Earthquake magnitude obeys truncated exponential distribution.The spatial distribution function of the potential seismic source zone is taken as the first-class spatial probability distribution,and the homogeneous probability distribution in the potential seismic source zone as the second-class spatial probability distribution.Considering the seismic intensity attenuation relationship of western China,we compute the occurrence probability of an earthquake around magnitude 6.0(5.5～6.5),7.0(6.5～7.5)and over 7.5 in the Daduhe drainage area,where 22 series cascade dams will be built.The results can be used for hydropower plant planning,hydropower dam site selection and seismic fortification.

新增玉屏潜源对湘黔边界地区峰值加速度影响的研究

本文收集了怀化西部新增玉屏潜在震源区相关资料,对研究区域1′×1′的空间格点进行了地震危险性概率分析,主要讨论了在新增该潜源前、后对湘黔边界地区的峰值加速度的变化,并根据Ⅱ类场地峰值加速度绘制等值线并进行分区。地震危险性分析结果表明,新增玉屏潜源对其内部与附近约20 km范围的地震动峰值加速度影响很大,而当震源深度取10 km时,玉屏潜源范围内50年10%的峰值加速度由35~40 cm/s^(2)增加至80~95 cm/s^(2),约增加2.3~2.4倍,潜源内新晃、芷江等局部区域基本烈度可达Ⅶ度,潜源外部峰值加速度也从35 cm/s^(2)逐渐增加至80 cm/s^(2);当地震带的震源深度取15 km时,新晃、芷江等地区基本烈度仍为Ⅵ度。文中还结合怀化西部新晃、芷江不同类型房屋的抗震能力进行了初步分析,在后续防震减灾工作中需特别加以关注。

Interrelation among several important links in seismic risk analysis

In order to further reveal the interrelation among division of seismic statistical regions, delimitation of potential seismic sources and estimation of seismicity parameters, we select 21 representative sites located in different places within the range of 100°-120°E, 29°-42°N to study the influences of seismicity parameter uncertainties of statistical regions on seismic risk estimations of these sites in the inhomogeneous and homogeneous distribution models. Combining the results from this study and previous ones, we can see that different schemes for dividing seismic statistical regions can change the seismic data in a statistical region. The uncertain data and additional uncertainty in selecting time intervals for seismic statistics will result in uncertainty of seismicity parameters estimation in a statistical region. For the homogeneous model, the larger the variation of this uncertainty is, the greater the uncertain influence on the seismic risk estimation of a site will be, which means that the division of seismic statistical regions makes a major contribution. In a seismic statistical region, the delimitation of potential sources and variant weight assignment of spatial distribution functions can raise the estimated values of ground motion parameters in the place where great earthquake might occur and its vicinity. In these places, the influence of uncertainty in potential source delimitation is very obvious, especially on the absolute magnitude of ground motion parameters （e.g., intensity）, which means that the link of potential source delimitation makes a major effect. Generally speaking, the link of potential source delimitation affects mainly the sites located in the potential sources with the highest and second-high upper-limit earthquake magnitudes or in the vicinity of those with the highest upper-limit magnitude. While for the sites located in the potential sources with low upper-imit magnitudes, the uncertainty influence of statistical region division is larger than that of potential source delimitation.

融合三维断层源和二维潜在震源区的随机抽样概率地震危险性分析算法研发

文中采用蒙特卡罗随机抽样方法,研发了一套融合传统二维潜在震源区(下文简称“潜源”)和三维断层源的概率地震危险性算法。该算法不仅适用于传统的区域面源,同时还能考虑地震的破裂尺度并兼容三维断层源的概率地震危险性计算。文中研发的算法可高效实现断层源地震事件集的三维模拟,并将地震破裂尺度引入到概率地震危险性计算中,显著提高了近断层地区地震危险性计算的合理性。为了提高程序的执行效率,算法采用预先在平面潜源中充填网格点的方式随机模拟地震事件在潜源内的均匀分布。对于椭圆衰减的地震危险性计算,算法采用了预先构建不同震级、距离及不同场点与潜源长轴方向夹角下的短轴距的三维矩阵,通过查表和插值方式直接获得相应场点的短轴距,避免了循环迭代逼近短轴距计算效率低下的问题。分别利用五代图的概率地震危险性程序和文中研发的算法,计算了湖南长-株-潭(长沙-株洲-湘潭)城市群所处的中强地震活动环境的区域地震危险性以及近断层源的常德、株洲2个场点在不同概率水平下(重现期分别为50a、 475a和2 475a)的地震危险性。比较研究表明,五代图的程序低估了三维断层源附近的地震危险性,且随着概率水平的降低,低估的程度越来越高。最后,利用太平洋地震工程中心(Pacific Earthquake Engineering Research Center, PEER)验证概率地震危险性程序的算例(数据集1案例10)验证了文中算法的可靠性。

基于地震灾害风险普查的概率地震危险性分析--以从化区为例

为了厘定概率地震危险性分析方法在地震灾害风险调查与评估工作中的适用性,针对从化区,以中国地震动参数区划图(GB18306-2015)提供的信息为依托,给出其周边的潜在震源区划分、地震活动性参数及地震动衰减关系,基于地震灾害风险普查资料,利用概率地震危险性分析(CPSHA)方法对其进行地震危险性分析。确定了对从化区地震动峰值加速度起主要贡献的几个潜在震源区及贡献值,计算了从化区未来50年超越概率63%、10%、2%和100年超越概率1%的PGA分布,基于地理信息系统(Geographic Information System,GIS)平台绘制了从化区4种概率下的基岩及地表地震动峰值加速度值分布图。结果表明:背景源(17)、广州、佛冈、河源、担杆岛、珠海和东莞潜在震源区对计算区内PGA起主要贡献;区内50年超越概率10%地表地震动分布中间高两边低。