皖南东至兆吉口铅锌矿床成矿时代的厘定及其找矿指示意义

皖南东至兆吉口铅锌矿床是近年来在江南过渡带西段新发现的一个规模达中型的中-低温热液型矿床。目前揭露的铅锌矿体均赋存于东至断裂带及其西侧次级张(扭)性断裂及裂隙中。文章选取了该矿床主要矿石矿物闪锌矿以及与主成矿阶段金属硫化物紧密共生的石英,分别采用流体包裹体Rb-Sr法和40Ar-39Ar法进行同位素地质年龄测定。4件闪锌矿样品获得流体包裹体Rb-Sr等时线年龄为(128±1)Ma;2件石英样品获得流体包裹体40Ar-39Ar坪年龄分别为(128.74±3.02)Ma和(128.19±1.98)Ma,等时线年龄分别为(128.81±5.25)Ma和(128.30±3.47)Ma,反等时线年龄分别为(128.82±5.24)Ma和(128.31±3.47)Ma。同位素地质年龄测试结果基本一致,表明兆吉口铅锌矿床形成于128 Ma左右,成矿时代为早白垩世。该成矿年龄与赋矿闪长玢岩的形成时间((129.0±2.3)Ma~(128.4±2.7)Ma)一致,也与东至断裂燕山晚期的活动年龄((126.3±2.2)Ma)相近,表明该矿床成矿与燕山晚期的构造-岩浆活动密切相关,此时区域构造背景为强烈挤压后的伸展环境。这一矿化事件在成矿时代上明显晚于长江中下游成矿带中的断隆区(如铜陵、安庆-贵池等矿集区)的铜金多金属矿床和皖南成矿带中的钨钼多金属矿床(136 Ma),而与长江中下游成矿带断坳区的玢岩铁矿床的成矿时间(135~127 Ma)相近,指示长江中下游成矿带与皖南成矿带之间的江南过渡带中发育有燕山晚期较晚阶段(128 Ma左右)的铅锌矿化事件,为今后在该区开展铅锌多金属矿床找矿勘探提供了重要依据。     

现有孕震模式的研究及其修正

在国内外现行的主要孕震模式的基础上，得出了一个较为合理的详细阐述孕震过程的模式。该模式由（Ⅰ）弹性变形、（Ⅱ）扩容、（Ⅲ）前兆蠕动、（Ⅳ）地震、（Ⅴ）震后调整等阶段组成，主要强调液体（水）存在；发生大小地震的断层均由积累单元和调整单元组成，余震是大震后构造剪切应力重新调整以及主断层未破裂区和位于它两侧尺度小、长度短的断层未破裂区共同破裂的结果。最后，运用断裂力学理论对该模式的孕震过程进行了比较圆满的解释。     

Seismic Displacement of Gravity Walls by a Two-body Model

Gravity walls retaining dry soil are modeled as a system of two bodies: (a) the gravity wall that slides along the wall-foundation soil boundary and (b) the critical soil wedge in the soil behind the wall. The strength of the system is defined by both the frictional and the cohesional components of resistance. The angle of the prism of the critical soil wedge behind the wall is obtained using the limit equilibrium method. The model accounts for changes in the geometry of the backfill soil behind the wall by considering the displacements at the end of each time step under limit equilibrium. The model shows that the standard (single) block model is over-conservative for the extreme case of critical-to-applied-seismic acceleration ratios less than about 0.30, but works well for cases where this ratio ranges between 0.5 and 0.8. The model is applied to predict the seismic displacement of gravity walls (a) tested in the shaking-table and (b) studied numerically by elaborate elasto–plastic analyses.     

中国大陆活动地块边界带主要断层的强震震间晚期综合判定

由于中国大陆强震主要分布在活动地块边界带上,所以活动地块边界带主要断层成为我国大陆型强震研究的重要目标,各强震孕育阶段的判定是大陆型强震原地复发的动力学过程研究主要内容,而目标断层是否处于震间晚期也是强震时间预测的重要研究基础.虽然地震短临预测仍存在诸多科学难题,但最近20年来全球若干强震相关研究表明,如果放宽预测时间尺度的要求,有些方法也可用于强震震间晚期的判定.本文以中国大陆活动地块边界带的391条断层段为研究目标,利用地震地质的强震破裂空段、大地测量的断层运动闭锁段、地震活动的中小地震稀疏段、数值模拟的库仑应力增强显著段等方法,综合判定中国大陆活动地块边界带可能处于震间晚期的主要断层段.本文结果仅是初步结果,该结果的可靠程度有赖于监测条件,其科学性有赖于大陆型强震孕育发生动力学过程的认识水平,虽然本文尝试给出中国大陆活动地块边界带主要断层的震间晚期判定结果,但其结果可靠程度、精细程度等均存在巨大的改善空间.最后,从断层孕震阶段判定需求的角度,本文尝试给出大陆型震源物理模型的具体基础模型,期望起到抛砖引玉的作用,也期望更多地震学家关注大陆型强震的物理机制及其预测基础研究.

     

地震预警断层参数实时识别方法(FinDer)详解及其性能初步评价

详细阐述了美国加州ShakeAlert地震预警系统中使用的断层破裂参数实时测定方法(FinDer FinDer:Finite Fault Rupture Detector)的技术细节.利用1999年集集Mw7.6级地震、2008年汶川Ms8.0级地震及2013年芦山Ms7.0级地震,以及日本K-NET台网记录的80次中...     

5·12汶川地震地表破裂基本参数的再论证及其构造内涵分析

地震地表破裂基本参数是反演地震破裂过程的基本约束条件和预测其他活动断层地震危险性不可缺少的物理量.以野外地表破裂带重要观测点全站仪或差分GPS仪实测数据为基础,结合高分辨率遥感资料解译、先存断层陡坎构造地貌标志的识别、以及地形测绘资料的考证等,重新论证了5·12汶川地震地表破裂带展布样式、长度、最大同震位移值等基本参数.结果表明,地震地表破裂带长度可达240 km,最大垂直位移为6.5±0.5 m,最大右旋走滑位移4.9 m,基于倾角向下变缓逆断层模型推测汶川地震在龙门山推覆构造带中段产生了最大~7 m的地壳缩短量,说明青藏高原东缘横向逆断层为将高原内部东向水平运动转换为高原隆升的转换构造,这一研究结果有助于深化认识青藏高原东缘隆升机理.     

THE APPLICATION OF MINIATURE UNMANNED AERIAL VEHICLE IN 25 NOVEMBER 2016 ARKETAO MW6.6 EARTHQUAKE

In order to complete the field investigation to the 25 November 2016 Arketao M_W6.6 earthquake, ultra-low altitude remote-sensing data were obtained from miniature unmanned aerial vehicle. The surface rupture surveying has important significance for earthquake research. This paper selects the macro-epicenter of Arketao as the study area. The pictures were obtained with DJI Phantom 3 professional input into the software, the Digital Elevation Model (DEM), Digital Orthophoto Map (DOM) were acquired based on photogrammetry method using the overlapped optical remote-sensing images of UAV. Using these data, we can identify surface ruptures that have vertical dislocation. We selected six feature points and drew the elevation profile. In the elevation profile map, we chose smooth part of the surface rupture sides and obtained the trend line. A stable point in the surface rupture was selected and the abscissa of the point was taken into the equation of two straight lines. Then subtracting the results of the two equations, we can get the vertical dislocation of the surface rupture. On this basis, we chose six feature points and determined their vertical dislocation, which are between 4.4cm and 10.4cm. What's more, taking Bulungkou Xiang in Xinjiang Uygur Autonomous Region for example, we speculated some surface ruptures that have vertical dislocation. It can provide a new method for identifying surface rupture in the field. In addition, we get DEM data of the Bulunkou area where ambient conditions are very poor, by using miniature unmanned aerial vehicle and taking 255 photos. Putting those photos into the EasyUAV software, we got the area digital elevation of 2cm resolution. Comparing these data with RTK data, we summarized some practical problems and solutions in the practical operation and evaluated the accuracy of miniature unmanned aerial vehicle data. The Pearson Correlation Coefficient is 0.996 6. In terms of absolute elevation, the average result of UAV and RTK differs by 156.96m. In terms of relative elevation, the average result of UAV and RTK differs by 9.74m. Compared with the previous test of Pishan County, there is a notable divergence in the results. It shows that the data accuracy will be affected to some extent in the cold weather in high elevations. The specific impact needs further exploration.     

2019年四川长宁MS6.0地震前破裂区内视应力和b值的变化

视应力和b值都可以反映地壳应力变化。当应力增加时,视应力会增加,而b值降低。因此,应力变化将导致视应力和b值之间呈负相关关系,即,根据视应力和b值之间的负相关关系可以研究地壳构造应力的变化。本文利用2000年1月—2019年12月长宁M_S6.0地震破裂区内3.0≤M_L≤3.6地震的视应力和2.0≤M_L≤4.3地震目录,研究了视应力和b值随时间的变化,发现:2013年2月—2017年3月间,视应力呈趋势上升变化,历时约4年,在震前两年时间内,视应力仍维持在较高水平。在视应力呈趋势上升变化期间,b值则呈趋势下降变化。当视应力维持在较高水平时,b值则维持在较低水平。即,长宁M_S6.0地震发生前,破裂区内视应力增加,同时b值下降。这表明,2019年长宁M_S6.0地震发生前破裂区内存在明显的构造应力增加过程,对地震孕育过程的认识和地震预测研究都具有启示意义。      

水对受力岩石变形破坏宏观力学效应的实验研究

为了了解水对受力岩石的宏观力学效应,在MTS电液伺服材料试验系统上,对不同饱水度的砂岩、花岗闪长岩、灰岩和大理岩进行了单轴压缩试验,取得了这几种岩石的单轴抗压强度和弹性模量随饱水度变化的定量结果.结果表明,水对受力岩石的力学效应与岩石中的含水状态是密切相关的,自然状态的砂岩、花岗闪长岩浸水后,其峰值强度和弹性模量随饱水度的增加而迅速衰减,当饱水度达到某一定值时,这两种岩石的峰值强度和弹性模量基本稳定下来;文中用函数Y=Aexp（-Bx）+C对实验结果进行了最小二乘法拟合.实验中求得水饱和状态和自然状态砂岩的泊松比并没有明显差异,说明在宏观上水对该种岩石受力变形的作用是各向同性的.通过10^-5/s和10^-4/s两种不同应变率试验,发现水对受力岩石的力学效应具有时间依赖性,这一特点说明仅从有效应力原理来考虑水对受力岩石的力学效应是不够的,而应考虑应力腐蚀这样复杂的过程.此外,大理岩的试验结果表明,水对受力的碳酸盐类岩石的作用机理是一个值得进一步探讨的问题,它与水对受力的含SiO₂类岩石相比,可能存在差异.