2019年9月16日张掖5.0级地震前多尺度电磁异常现象

2019年9月16日甘肃张掖发生5.0级地震，地震发生前既有空间范围跨度较大的地磁低点位移异常，也有单台电磁扰动异常；既有震前2年开始出现的山丹台视电阻率的年变形态畸变，也有震前3个月之内出现的高台钻孔应变和高台大庄低频电磁扰动异常。本次地震震级不高却记录到丰富的电磁场的异常信号，表明该地区处于地震电磁异常的敏感区。高台钻孔应变在震前观测到同步的异常变化，揭示孕震区应力状态发生了显著的变化。     

西昆仑东段震源机制和构造应力场特征

本文利用新疆测震台网记录的宽频带波形数据，采用CAP方法反演西昆仑东段2010年1月—2018年12月M_S≥3.0地震震源机制，并结合研究区早期的震源机制数据分区反演构造应力场。结果表明:研究区地震破裂类型以逆断型和走滑型为主，其次为正断型，过渡型最少；震源机制节面在NWW向存在明显优势分布且倾角较陡，压应力P轴在NNE向有优势分布且倾角较小，张应力T轴在NW-SE向有优势分布且倾角较小，说明研究区总体上主要以NNE向的水平挤压和NW-SE向水平拉张作用为主；西南区域应力结构为走滑型，东北区域应力结构为逆断型，最大主应力轴σ₁方位的最优解都呈NNE向，但西南区域更偏东，东北区域水平作用更明显。东北区域的应力形因子R值较小，体现该区域的物质隆升相对于西南区域物质隆升分量大。     

Stress tensor analysis of the 1998–1999 tectonic swarm of northern Quito related to the volcanic swarm of Guagua Pichincha volcano, Ecuador

The phreatic activity and the subsequent dacitic dome growth in 1998–1999 at Guagua Pichincha volcano, Ecuador, were associated with two seismic swarms: one located in the northern part of Quito (population: 1,500,000) and another one, just below the active volcano, about 15–20 km SW from the first one. Quito swarm tectonic events have high frequencies (from 1 to 10–15 Hz). We registered more than 3200 events (among which 2354 events of 1.4≤M_L≤4.2) between June 1998 and December 1999 at the −2- and −17-km depth. The volcanic events below the Guagua Pichincha caldera have high (from 1 to 10–15 Hz) and low (less than 3 Hz) frequencies. Approximately, 130,000 events were registered between September 1998 and December 1999 at the +2.4- and −3.5-km depth. Here, we study the stress tensors of these two swarms deduced from the polarities of P first motions and compare them to the regional stress tensor deduced from CMT Harvard focal mechanisms. The Quito swarm stress tensor is relatively close to the regional stress tensor (the σ₁ axis was oriented N117°E close to the N102°E direction of the plate motion found by the GPS measurement, and σ₃ is nearly vertical). The difference may be due to the action of the closely active Guagua Pichincha volcano. The Guagua Pichincha stress tensor is very different from the regional tectonic one. The σ₁ axis of the volcano is oriented N214°E, almost perpendicular to the σ₁ of the swarm of Quito and σ₃ is almost horizontal. Even if these two tensors are different, they can be explained in a more general tectonic scheme. The almost horizontal direction of σ₃ just below the volcano is compatible with an extensional horizontal direction that may be expected in the shallow extrados part of a compressional region and consistent with an opening of the top of the Guagua Pichincha volcano. The movement of the fluids (magma, gas and/or groundwater) produced by the closely active Guagua Pichincha volcano seems to have an influence in the acceleration of the generation of seismic events.     

Earthquakes in the Eastern Great Lakes Basin from a regional perspective

This paper presents a summary of the seismicity and its relation to stress and geologic structures in the Eastern Great Lakes Basin (EGLB) and compares it with that of other regions in the central and eastern North America (CENA). The earthquakes scattered throughout the EGLB are occurring at a rate somewhat less than that of the Appalachians and along the Atlantic Seaboard. Paleoseismology studies suggest that the lower seismicity rate may be characteristic of the EGLB since the Late Wisconsin. North of the EGLB, earthquakes have primarily thrust mechanisms, while to the south of the EGLB, most earthquakes are strike-slip. Throughout the region, including the EGLB, the average P axes of the earthquakes are oriented NE–SW and are aligned with the direction of the current plate driving stress. On a regional basis, earthquakes are centered primarily in the Precambrian basement beneath the Paleozoic cover. Many of the earthquakes in the EGLB have occurred in areas of preexisting faults, at least some of which may have been active during past episodes of continental rifting. For individual faults that have been studied in some detail, however, it is not clear whether earthquakes represent reactivations of local preexisting structures or nucleation of new ruptures in or near the old fault zones.     

地震剪切破裂的三维断裂力学有限元分析—1966年邢台地震的数值模拟

以往用断裂力学方法研究地震的发生，绝大多数是针对二维问题或三维椭圆盘断层，而真实的断层是三维的。本文运用线性断裂力学理论，以Ｋｏｓｔｒｏｖ的Ｇｒｉｆｆｉｔｈ静肪表面能为断裂准则，对地震剪切破裂进行了三维有限元分析。在断裂面前缘，我们采用了由２０点等参单元退化而成的１５点元，非奇异单元用２０点元，证明了１５点元能反映应力的奇异性，推导了局部会标系下的应力强度因子的有限元解，并编制了大型的三维线弹性断     

东亚大陆的地震迁移（二）——沿地震带的迁移

分析了东亚大陆现代和历史地震地震带顺序的迁移图象，以时空线性度做为迁移图象的判别参数，确定了：（１）２０世纪上半叶帕米尔－贝加尔，苏门答腊－蒙古，喜马拉雅三个地带的大范围巨峰迁移事件，该三带迁移具有同期性和交叉性围绕着青藏高原周边呈三角形图案。迁移速度在５５～１５００ｋｍ／ａ；（２）中国大陆内部区域性地震带的小规模迁移，共１２个地带的２８个迁移序列，有些地带在几百年地内地震曾反复迁移，迁移速度从１     

下辽河盆地现今构造应力场特征

目前研究现今构造应力场的方法很多，如地壳形变测量，震源机制解等方法，本文利用井壁崩落法、套芯法及有限元数值模拟所得结果，研究分析了下辽河盆地现今构造应力的特征。     

爆炸防雹中的云微物理机制的探讨

在综合实验和观测结果的基础上 ,提出了能形成大雹的雹胚 ,在它运行增长中常会有一个下伸到 0℃层以下融化 ,又再进入主上升气流区上升到 0℃层以上再次冻结的过程。发生这一过程的位置是雹云的悬挂回波所在的冰雹胚胎帘区的底部 ,如果在这个位置利用爆炸引起由雹胚融化而形成的液滴破碎 ,会改变大雹的运行轨迹 ,从而抑制大雹的形成。同时还利用数值模式模拟研究了该机制 ,结果表明该机制是合理的。     

华北4次中、强地震前震源区及其附近应力场的变化

使用小震机制解资料 ,分析了 1975年海城 7 3级和 1976年唐山 7 8级强震及 1983年菏泽 5 9级和 1995年苍山 5 2级中强震前 ,震源区及其周围不同构造部位应力场的时、空变化 ,证实震前震源区附近应力场曾有某些异常改变 ,如唐山强震前震源区周围出现长达 4a多的小震机制解主应力轴一致性取向的现象 ,菏泽地震前小震机制解P轴“集中—转向” ,苍山地震前P轴偏转且一致性增强。同时还发现 ,唐山地震前应力场异常变化开始时间可能早于 1972年 ;震源区内的陡河台与源外区的昌黎台小震综合机制解反映出震前的受力差异 ;震源断层附近不同应力区内震源机制解和地震活动有时空动态差异。这些现象一定程度上提供了不同构造条件和应力背景下 ,中、强震前震源区不同构造部位力学状态的改变或地震孕育过程的信息 ,对研究不同地震的孕震过程及差异有一定意义。     

监测网的精度测度与三维应变参数的准则矩阵

本文基于监测网的特点，用变形参数的精度来测度同的质量，讨论了精度标准的不变性，重点根据位移向量与应变参数的关系，构造了三维应变参数的准则矩阵，以供参考。