峰值速度和加速度对环境剪应力的依赖性

从导出的地震定标律和地震破裂过程的断裂力学模式出发,得到了震源平均位移、速度和加速度谱的表达式,进而又推导出震源的峰值位移d_m,速度v_m和加速度a_m的表达式:d_m=k_dM_0~2/~3τ_0~(2/3),v=k_vM_0~(1/3)τ_0~(4/3),a_m=k_aτ_0~2式中M_0是地震矩,τ_0是环境剪应力值,k_d,k_v,k_a为适当的常数.我们选用了66个地震的观测资料,这些地震的矩震级范围包括了从1级左右的极微震,3-5级的小震,直到6-7级的大震;地震矩从10~9-10~(20)Nm,跨越了10个数量级,并用这些地震检验了上述公式. 令所有地震的平均应力为5MPa,定出常数k_d,k_v,k_a,进而由速度和加速度观测资料求得66个地震的环境剪应力τ_0值,这些数值相当稳定.多数极微震的τ_0值在2-4MPa之间;小震的τ_0值多数在4-8MPa左右;大震的τ_0值为10MPa左右。τ_0值对震源深度和断层类型有明显的依赖性.一般深度很浅的小震和极微震,τ_0值很低;正断层地震的τ_0值相对较低;逆断层地震的τ_0值较高;走滑断层地震的τ_0值则居中.     

Cluster analysis of seismic moment tensor orientations

This paper demonstrates that well-known methods of cluster analysis and multivariate data analysis are useful for geodynamic interpretation of seismic moment tensors. To use these methods, moment tensors are expressed as vectors in a 6-D space. These are vectors in a rigorous sense, rather than an arbitrary set of ordered numbers, because a dot product can be defined that is independent of the coordinate system. In this vector space, non-isotropic moment tensors are a 5-D linear subspace and normalized moment tensors are unit vectors, or points on a unit sphere. Distance along a great circle of the unit sphere satisfies reasonable requirements for any measure of the difference between normalized moment tensors. In regions with a few isolated sets of orientations, cluster analysis based on the great circle distance identifies the same groups of earthquakes that a seismologist would. Figures based on principal component analysis and discriminant analysis illustrate orientation clustering better than equal area projections of moment tensor principal axes. In one case where clusters have been claimed to exist, orientations appear to be continuously distributed and no evidence is found for separate populations of moment tensors.     

用混合源模型研究矿山地震震源机制

本文讨论了矿山地震的混合源机制问题，并根据内源矩张量分解的特点提出了一种较合理的点源混合机制以及拟合求解方法。这相当于利用Ｐ波初动振幅进行相对矩张量反演，对于区分双力偶事件和非双力偶事件是有意义的。在简化情况下，对１９８７年发生在门头沟煤矿的１５次事件进行了讨论，发现它们大多属于剪切事件。     

四阶矩准正态分布和三阶矩剪切近似的验证

本文利用近地面层大气湍流量的观测资料对四阶矩的准正态分布假定和三阶矩的剪切近似进行了实验验证。结果表明，四阶矩能够较好地符合准正态分布假定；三阶矩不仅完全满足剪切近似，甚至还可以对剪切程度进一步加强，并且得到了一系列剪切近似的加强修正系数。     

Moment tensor inversion of near-source broadband data

Ｍｏｍｅｎｔ　ｔｅｎｓｏｒ　ｉｎｖｅｒｓｉｏｎ　ｏｆ　ｎｅａｒ－ｓｏｕｒｃｅ　ｂｒｏａｄｂａｎｄ　ｄａｔａ（吴忠良）（陈运泰（倪江川）（王培德）（王鸣）Ｍｏｍｅｎｔｔｅｎｓｏｒｉｎｖｅｒｓｉｏｎｏｆｎｅａｒ－ｓｏｕｒｃｅｂｒｏａｄｂａｎｄｄａｔａ￥Ｚ...     

Seismotectonics of the Median Tectonic Line in southwest Japan: Implications for coupling among major fault systems

The relationship between the slip activity and occurrence of historical earthquakes along the Median Tectonic Line (MTL), together with that of the fault systems extending eastward has been examined. The MTL is divided into three segments, each containing diagnostic active faults. No historical earthquakes have been recorded along the central segment, although the segment has faster Quaternary slip rates compared with the other segments that have generated historical earthquakes. This discrepancy between earthquake generation and slip rate can be explained by a microplate model of southwest Japan. The microplate model also provides spatial and temporal coupling of slip on adjacent fault systems. In the context of this model, slip on adjacent faults reduces the normal stress on the MTL. Historical data and paleoseismic evidence indicate that slip on this segment occurs without significant strong ground motion. We interpret this as indicating anomalously slow seismic slip or aseismic slip. Slip on the central segment of the MTL creates transpressional regions at the eastern and western segments where historical earthquakes were recorded. Alternatively, the earthquakes at the eastern and western segments were triggered and concentrated shear stress at the edge of the segments resulted in postseismic slip along the central segment. The sequence of historical events suggests that the MTL characteristically does not produce great earthquakes. The microplate model also provides a tectonic framework for coupling of events among the MTL, the adjacent fault systems and the Nankai trough.     

用P波波形资料反演中强地震地震矩张量的方法

本文给出了利用不同震中距范围（３°-９０°）的长周期Ｐ波记录资料，通过波形拟合和反演确定地震矩张量的方法．在求解过程中，不引入矩张量的迹为零这一约束条件．有６个独立分量的地震矩张量解可分解成各向同性部分、最佳双力偶和补偿线性矢量偶极．文中给出了发生在中国的５次６级以上地震的地震矩张量反演结果，表明在一些地震的震源过程中存在不可忽略的体积变化．     

Large-magnitude Central American earthquakes, 1898–1994

We have collected and re-examined macroseismic information for large Central American earthquakes since the beginning of the period of instrumental recording about one hundred years ago, and combined this with a reassessment of early instrumental information to produce a catalogue of 51 events that, we believe includes ail those with magnitudes ( Ms ) greater than 7.0. We have reassessed surface-wave magnitudes by consulting station bulletins and we have derived a correction that gives an equivalent Ms for events of intermediate depth. We have also developed a regional relationship between Ms and seismic moment, which enables us to estimate the seismic slip rate across the Middle American Trench. Our best estimates give an average slip rate several times smaller than suggested convergence rates, but with the seismic slip in the central segment of the trench almost an order of magnitude smaller than that in the segments on either side. The low seismic slip rate may indicate aseismic crustal deformation