河套地震带Pg波速度过渡区的地震空间相关长度幂律变化

基于Pg波速度反演和地震重新定位, 运用单键群算法对Pg波速度过渡带的地震空间相关长度进行了幂律拟合分析． Pg波速度反演结果表明, 其速度的横向变化表现出构造相依的特征, 速度高低与地壳厚度呈正相关, 并在包头—西山嘴凸起和岱海凹陷两个区域形成Pg波速度过渡带． 利用重新定位的地震数据计算了这两个速度过渡区的地震空间相关长度, 结果显示其幂律拟合曲线均呈一定的增长趋势, 表明2008年以来两个Pg波速度过渡区域的应力作用不断集聚、 增强, 断层有逐步进入协同化阶段的可能, 加之速度过渡带通常是地壳运动强烈区域, 未来将成为孕育中强地震的有利场所． 在有效控制定位误差的条件下, 重新定位可以明显减小地震空间相关长度的离散形态, 提高计算精度．      

2013年7月22日岷县漳县6.6级地震前地震相关长度增长现象

利用单健群分析方法研究了2013年7月22日岷县漳县6.6级地震前地震空间相关长度增长现象。结果表明,从2011年下半年开始主震周围区域地震空间相关长度明显增长。利用这种特征对可能的大震危险区进行网格式搜索,至少可以对未来强震发生的地点进行初步预测。     

芦山7.0级地震前地震活动的临界点特征

直接检测大地震之前空间相关长度的增长是一种从观测的地震活动中检测临界点特征的独立的方法.本文研究了2013年4月20日四川芦山7.0级地震前5年震中周围地区中等地震活动的空间相关长度变化.结果表明,从地震前近两年开始,中等地震以上地震的空间相关长度出现明显增长,变化趋势可以用幂次率进行很好的拟合.用该地区没有7级以上强震发生的时段的地震目录采用相同方法进行了计算,没有发现明显的幂次率增长现象,说明强震前中等地震以上地震的空间相关长度的幂次率增长是地震孕育过程中临界点物理特征的表现.     

2011年日本9.0级地震前地震空间相关长度增长现象

使用单键群方法研究了2011年3月11日日本本州东北部海域9.0级地震前地震空间相关长度变化。结果表明,在本次地震发生前约两年,5级以上地震的空间相关长度开始出现明显增长,变化趋势可以用幂次率进行很好的拟合。用没有7级以上强震发生的时段内的地震目录,采用相同方法进行了计算,没有发现明显的幂次率增长现象,说明强震前5级以上地震的空间相关长度的幂次率增长是地震孕育过程中震源区的物理性质特征的表现之一。     

甘肃及邻近地区几次中强地震前地震空间相关长度增长的研究

用单键群分析方法,研究了甘肃及邻区发生的几次中强地震前的空间相关长度增长的现象. 结合震源区不同的情况,分别选取了圆形和沿断层带分布的平行四边形空间窗. 结果表明,所研究的几次中强地震前都观察到相关长度增长的现象.     

汶川8.0级地震前地震空间相关长度变化特征

分析了汶川8.0级地震前的地震空间长度的时空演变。在计算空间相关长度过程中采用长轴与孕震区主要断裂走向一致的椭圆型空间窗,并设计了优化程序。在本次特大地震前观测到了增长的地震空间相关长度。利用合成地震目录对结果进行了显著性检验,结果否定了零假设,表明观察到的模型不是由随机数据干扰造成的,这一观点的置信水平被证实为93.9%。     

银川-河套地震带1970年以来5级以上地震活动特征分析

通过对银川-河套地震带发生5级以上地震的时空强特征分析,认为未来该区域发生5级以上地震的可能性很大,并分析了1970年以来5级以上地震前弱震活动规律,得到了该区域未来发生5级以上地震的可能地点。     

南北地震带地震活动特征

采用数理统计方法探讨了780 BC至今、100°—110°E、22°—35°N（中国南北地震带）区域的中国大陆5.0级及以上天然地震的分布规律。通过GMT软件绘制了南北地震带上地震震中和断裂分布图像,分析了南北地震带地震时空分布与地震活动性的规律。研究表明,该地区的大震与强震几乎全部发生在断裂带上,地震频次高、震中密集,呈现集群性等特征,地震活动性较高。该地震带中、南段相似,与北段存在显著差异。在南北地震带上,地震的活跃幕与平静幕持续时间,与活跃幕强度有关。研究结果对于了解地震的时空分布特征,认识中国南北地震带的发震规律,地震的孕震发震和地震活动周期有参考意义。      

欧亚地震带地震活动和中国大陆地震

欧亚地震带及其与中国大陆相邻地域的地震活动和中国大陆地震之间存在有多种相关关系，这些相关关系对预测中国大陆地震活动趋势有一定的作用     

河套地震带的b值时空变化特征分析

本文以b值作为研究对象,在b值由应力状态和介质性质共同决定的理论框架下,开展了河套地震带的b值时空变化特征分析。选取1970年发生在河套地震带的ML≥1.5地震作为考察对象,运用EMR方法定量检测了最小完整性震级Mc的时序非均匀变化,并根据研究区地震活动实况,确定b值的起算震级为ML2.0。运用最小二乘法进行了b值时间扫描计算,结果显示,b值时序变化较好地对应了研究时段内的中强地震活动、台网分布和余震剔除等变化因素。运用极大似然法进行了b值空间扫描计算,结果显示,河套地震带的b值空间差异可能由地壳介质体性质和应力环境共同引起,相对来讲,b值的构造相依特征更为明显。此外,满足各震级档有足够多的地震样本依然是提高b值计算精度的关键环节。     

analyzing the variation characteristics of stress field in hetao seismic belt using focal mechanism data

Based on analysis of background of geological tectonic movement and strong earthquake activity, we first obtained the focal mechanism solutions using amplitude ratio and CAP method, then determined the characteristic of average stress field of the study area by inversion of the stress field. On this basis, we selected the source mechanism consistency parameter as the inspection index to obtain the latest changes of stress field in Hetao seismic zone based on its temporal and spatial analysis. Two methods were used in the stress field inversion for comparison and analysis, which are average stress axis tensor and LSIB(Linear stress inversion bootstrap, LSIB). According to the geological tectonic movement and focal mechanism solutions of M_S≥4.0 earthquakes from 1970, we judge that the stress field evolution process of Hetao seismic belt is controlled jointly by vertical difference movement and horizontal shear movement, resulting in that the normal fault and strike-slip fault mechanisms are dominating.Taking into account the station layout of the study area, and in order to ensure the accuracy of calculation, we calculated 224 earthquakes focal mechanism solutions by using amplitude ratio and CAP method, including 164 earthquakes with 2.8≤M_L<3.5, 42 earthquakes with 3.5≤M_L<4.0, and 18 earthquakes with M_L≥4.0; The statistical results on type of focal mechanisms show that, there are 142 strike-slip earthquakes(63.4%), 50 normal fault earthquakes(22.3%)and 32 thrust fault earthquakes(14.3%). In this study period(from 2001 to 2012), most earthquakes had a strike-slip mechanism in Hetao seismic belt, this is one of the inherent characteristics of the stress field.The result of average stress axis tensor and LSIB shows that, the azimuth of maximum compressional stress is 47°～52°, direction is NE-SW; The azimuth of minimum compressional stress is 313°～322°, direction is NW-SE; This indicates that, the stress field characteristics of Hetao seismic belt and its sub-block are not completely consistent. Linhe Basin exhibits coordinated stress field characteristics with Hetao seismic belt, but Hubao Basin exhibits regional differences, direction of compressive stress has clockwise deflection in Baotou area, and the compressive stress direction is NEE. This heteropical character of stress field is also confirmed by horizontal projection distribution of stress axis of historical strong earthquakes and recent moderate and small earthquakes. Since 2003, the temporal sequence curve of consistency parameter of Hetao seismic belt had a downward trend, this change was caused by focal mechanism consistency parameter of Linhe to Wuhai area, which indicates that this structural position is possible to be a priority area for stress accumulation and accelerated release in future.     

Discussion about the relationship between seismic belt and seismic statistical zone

This paper makes a summary of status of delimitation of seismic zones and belts of China firstly in aspects of studying history,purpose,usage,delimiting principles,various presenting forms and main spectialties.Then the viewpoints are emphasized,making geographical divisions by seismicity is just the most important purpose of delimiting seismic belts and the concept of seismic belt is also quite different from that of seismic statistical zone used in CPSHA method.The concept of seismic statistical zone and its history of evolvement are introduced too.Large differences between these two concepts exist separately in their statistical property,actual meaning,gradation,required scale,and property of refusing to overlap each other,aim and usage of delimitation.But in current engineering practice,these two concepts are confused.On the one hand,it causes no fit theory for delimiting seismic statistical zone in PSHA to be set up;on the other hand,researches about delimitation of seismic belts with purposes of seismicity zoning and studying on structural environment,mechanism of earthquake generating also paues to go abead.Major conclusions are given in the end of this paper,that seismic statistical zone bases on the result of seismic belt delimiting,it only arises in and can be used in the especial PSHA method of China with considering spatially and termporally inhomogeneous seismic activities,and its concept should be clearly differentiated from the comcept of seismic belt.     

Influence of uncertainty in delimitation of seismic statistical zone on results of PSHA

The seismic hazard of research area is evaluated by probabilistic analysis method for three different seismic statistical zone scenarios.The influence of uncertainty in seismic statistical zone delimiting on the evaluation result is discussed too.It can be seen that for those local sites along zone‘s border or within areas with vast change of upper bound magnitude among different scenarios the influence on seismic hazard result should not be neglected.     

南北地震带上倾斜潮汐因子的空间分布特征研究

从理论上讲,纬度对潮汐因子造成影响的改正值极小,一般不予考虑.通过对位于中国南北地震带上18个地倾斜观测台站的地倾斜潮汐观测资料进行调和分析,研究倾斜固体潮潮汐振幅较大的两个潮波O1波和M2波NS、EW分量的空间分布特征,结果发现γO1、γM2的空间分布与该带特殊的地质构造背景之间有一定的相互关系.并对可能存在的其他原因如海潮负荷效应、仪器本身的频率响应差异以及局部负荷效应影响等,进行了初步探讨.     

南北地震带及邻近区域强震时空分布特征

搜集整理南北地震带区域自史料记载（公元前193年）到2012年9月的强震（Ms≥6.0）资料,初步分析南北地震带及附近区域的地震发震构造活动性和时空分布规律.结果表明,地震一般发生在断层带上,具有空间分布的集群性特征和时间群集性质.研究发现,地震带南段发生6.0≤Ms≤7.9地震次数明显高于北段和中段,而发生Ms≥8.0地震的可能性较低,中段与南段较接近,与北段有明显差异;南北地震带存在明显的纬向、经向强震活动迁移现象,纬向尤其明显;1900年以来,南北地震带已经有4次明显的能量释放阶段,并给出Ms≥6.0地震的震级-频度统计关系式.     

南北地震带南北段地震迁移现象

对1990年以来南北地震带南段发生的Ms 5.0以上地震和北段发生的Ms4.5以上地震的迁移现象进行分析.结果表明,在南北地震带南、北段发生的中强地震具有呼应现象,且呈现一定规律,即大致以30°N线为基线对称分布.通过对震源机制的对比分析,发现南段和北段的地震类型不一致,可能与不同的地质构造和作用力有关.     

On temporal and spatial distribution of seismic apparent stresses in Yunnan area

Introduction In recent years the study of the digital seismology has made great progress due to the wide use of the broadband digital records. And many fine results of the focal theory have obtained. The focal theory mainly studies the physical process of the seismic fracture and production of the seismic wave, as well as its traveling process. One of the great progresses is to simulate the fracture process in the active fault. Especially a new concept of the fracture mechanics has been intro…     

Correlation between plate age and layer separation of double seismic zones

Global seismicity catalogs are sufficient for characterizing double seismic zones (DSZs) in subducting slab and facilitate to estimate layer separation without inconsistent uncertainties as local catalogs.Previous studies have shown the correlation between DSZs layer separation and plate age while correlation for those younger than ～60 Ma is suspicious.The lacking of DSZs with layer separation less than 10 km further makes it difficult to precisely estimate such correlation.Thus,we incorporate eight DSZs data determined through local seismicity into globally-determined dataset and reexamine such correlation.The best fitting results show that both a linear model and a square root of plate age can mathematically fit the layer separation well.However,it is difficult to distinguish these two models when plate age is greater than ～20 Ma since their difference is less than 2 km.However,if extrapolation is possible,both models should provide physical information thatDSZs will not form if there is no subducting lithosphere.As a result,the DSZs cannot be produced until the oceanic lithospheric age becomes greater than 0.9 Ma in the square root model while the linear model gives a misleading result.As such the square root model demonstrates the relationship physically better than the linear one,it still needs further test in the future with more available data,nevertheless,our study might also provide evidence for the suggestion that the plate age is a primary control factor of the DSZs geometry as well as the subducting process which disregards any local tectonic stresses.