The 1980, 1997 and 1998 Azores earthquakes and some seismo-tectonic implications

We have studied the focal mechanisms of the 1980, 1997 and 1998 earthquakes in the Azores region from body-wave inversion of digital GDSN (Global Digital Seismograph Network) and broadband data. For the 1980 and 1998 shocks, we have obtained strike–slip faulting, with the rupture process made up of two sub-events in both shocks, with total scalar seismic moments of 1.9 × 10¹⁹ Nm (M_w = 6.8) and 1.4 × 10¹⁸ Nm (M_w = 6.0), respectively. For the 1997 shock, we have obtained a normal faulting mechanism, with the rupture process made up of three sub-events, with a total scalar seismic moment of 7.7 × 10¹⁷ Nm (M_w = 5.9). A common characteristic of these three earthquakes was the shallow focal depth, less than 10 km, in agreement with the oceanic-type crust. From the directivity function of Rayleigh (LR) waves, we have identified the NW–SE plane as the rupture plane for the 1980 and 1998 earthquakes with the rupture propagating to the SE. Slow rupture velocity, about of 1.5 km/s, has been estimated from directivity function for the 1980 and 1998 earthquakes. From spectral analysis and body-wave inversion, fault dimensions, stress drop and average slip have been estimated. Focal mechanisms of the three earthquakes we have studied, together with focal mechanisms obtained by other authors, have been used in order to obtain a seismotectonic model for the Azores region. We have found different types of behaviour present along the region. It can be divided into two zones: Zone I, from 30°W to 27°W; Zone II, from 27°W to 23°W, with a change in the seismicity and stress direction from Zone I. In Zone I, the total seismic moment tensor obtained corresponded to left-lateral strike–slip faulting with horizontal pressure and tension axes in the E–W and N–S directions, respectively. In Zone II, the total seismic moment tensor corresponded to normal faulting, with a horizontal tension axis trending NE–SW, normal to the Terceira Ridge. The stress pattern for the whole region corresponds to horizontal extension with an average seismic slip rate of 4.4 mm/yr.     

薄冲积层下开采地表动态移动规律与特征

位于采煤影响区的高压线、输气输油管道、河道等设施对地表动态移动极为敏感。以甘肃某煤矿在金沙河下开采为背景,通过现场地表移动监测,获得薄冲积层条件下综放开采地表动态移动变形规律。研究表明：薄冲积层下综放开采地表具有下沉移动起始期很短、活跃期较长等特点。地表移动活跃期位于工作面前方110 m至工作面后方400 m范围内,历时185 d,期间地表点下沉量可达到该点总下沉量的90.7%;地表移动剧烈期在工作面后方50 m至150 m范围内,但剧烈扰动时间相对较短,历时约60 d。基于测点下沉曲线为S型分布、下沉速度曲线类似为正态分布特点,建立了考虑开采时间和工作面推进速度因素的地表下沉及下沉速度动态模型,并追踪刻画出地表测点往复式下沉与水平运动的轨迹。薄冲积层下开采,地表裂缝更易平行于工作面走向方向发育,并且随工作面的推进,地表裂缝具有前移和密集区向工作面外侧小范围扩大的时空特征。     

四川汶川地震灾害与地质环境安全

根据野外应急调查、遥感解译、历史地质信息等资料,对“5.12”汶川地震引发的地质灾害做出了总体评估。划分了地震区地质灾害的类型,描述了地质灾害的典型实例。基于汶川地震的基本特征,结合美国、日本减轻地震灾害的经验,讨论了地质环境与人类安全的关系。初步认为：地质安全是人类生存安全的最基本层面,其工作目标是探求地质环境安全和地质灾害风险的可接受程度,工作任务是调查评价不同尺度和不同功能区域的地质环境质量、容量,并判断地震、气象（候）和人为活动等多种因素影响下的地质灾害风险。     

地下开采引发地面沉陷的未确知聚类预测方法

对未确知聚类预测法进行优化,并将其应用于开采地面沉陷的预测研究。采用开采地面沉陷的实测数据按最大沉陷量进行分类,利用各分类影响因素的均值表示各分类中心,并确定各影响因素的未确知测度函数。由待测对象指标的综合未确知测度与各分类指标的未确知测度间的距离来确定待预测对象所属等级,给出了预测值的计算公式。经计算验证,该方法的正确率为75％。但在实际应用中,为了保证地表建筑设施等更加安全,允许预测级高判,则正确率可达100％。针对某铁矿一观测点进行预测,并与实测数据比较,结果表明,未确知聚类预测的结果是令人满意的,为开采地面沉陷的预测提供了一种新思路。     

The assessment of environmental pollution caused by mining and metallurgy wastes from highly polluted post-industrial regions in Southern Poland

Stored metallurgy and mining wastes contain relatively high amounts of potentially toxic elements. To monitor the distribution of contaminants originating from dumps, the chemical and physical properties of the wastes must be characterised. In this study, the chemical properties of wastes deposited in two different locations in Southern Poland (Szklary and Zloty Stok) were evaluated. Heaps located in Zloty Stok contain wastes from gold mineralisation comprising arsenic while wastes in Szklary originate from a factory that produced an iron-nickel alloy. In Szklary the total concentrations of Ca, Mg, Fe, Zn, Mn, Cr, Co, Cu, Ni, Tl, Ag, Cd and Pb were determined, while in Zloty Stok also As is an important contaminant. To assess the risk of contamination of the surrounding environment and to select the proper method for removing the contaminants, information on the distribution of elements between operationally defined phases must be obtained. For this purpose, a six-step sequential extraction was used. The mobility of most elements in the wastes from Szklary and Zloty Stok was relatively low; however, the large amount of As, 40–180 mg L^?1, that could be released to environment in case of Zloty Stok was high. The results of fractionation studies indicated that Ag, Cd, Tl, Co, Cu, Cr, Pb, Zn and Mn may be released into environment under low pH and low redox potential conditions, which can be induced by bacterial activity.     

Chlorophyll concentration and surface temperature changes associated with earthquakes

The preparation process of an impending earthquake may leave fingerprints on the earth??s surface. Elastic strain in rocks, formation of micro-cracks, gas releases and other chemical or physical activities in the earth??s crust before and during earthquakes has been reported to cause rises in temperature, surface latent heat flux (SLHF), upwelling index and chlorophyll-a (Chl-a) concentration on the ground or sea surface. Changes in surface temperature can be monitored with thermal infrared sensors such as NOAA-AVHRR and microwave radiometers like AMSR-E/Aqua. SLHF data and upwelling indices are provided by National Centers for Environmental Prediction (NCEP) Reanalysis Project and Pacific Fisheries Environmental Laboratory, respectively. This study examines behaviors of the above four factors prior to the past three oceanic and coastal earthquakes occurred at the Pacific Ocean (Northern California of June 15, 2005, Central California of September 28, 2004, and December 22, 2003). We were successful in detecting pre-earthquake anomalies prior to all three earthquakes. Our detailed analysis revealed 1?C5?°C rises in surface temperature in epicentral areas. Considerable anomalies in Chl-a concentration, 1?C2?weeks before the day of the main earthquakes, were spotted, which are attributed to the rise in upwelling index. Time series of SLHF showed meaningful rises from 1?month to a fortnight before the earthquake events. One problem in our research was the low resolution of the data which makes the graphs that are generated from NCEP database affected by all sources of anomalies, other than seismic activities, within an about 1.8°?C2.5° (200?km) area.     

甘肃省矿山地质灾害及其基本特征

甘肃是矿产资源大省,矿产开发利用规模大、强度高,因而矿山地质环境问题突出,其中矿山地质灾害的危害和威胁尤其严重。本文基于实际调查数据,论述分析了甘肃省矿山地质灾害的主要类型、基本特征及其危害特点。根据调查结果,甘肃省主要发育五类矿山地质灾害:采空地面塌陷、滑坡、崩塌、泥石流和矿坑突水。在这五类灾害中,采空地面塌陷分布最广、造成的直接经济损失最严重,滑坡发生频次高、造成人员伤亡最大,矿坑突水灾害分布范围、发生频次和危害程度相对最低。各类灾害的分布和发育特征受地质环境条件及矿山开采规模和开采方式的控制,灾害的危害特点与其分布和发育特征和活动特点有关。     

煤层开采裂缝的观测与分析

利用彩色电视系统对多个矿区由于地下煤层开采造成的岩体破坏进行了实际观测,了解了覆岩破坏裂缝的分布特征和状态,通过对裂缝分布特征以及裂缝状态的分析,总结出了由于煤矿开采而导致的裂缝分布规律,提高了对破坏裂缝及离层裂缝的认识,为煤矿安全采煤提供了依据。     

Sudden surface collapse disasters caused by shallow partial mining in Datong coalfield,China

Numerous sudden surface collapses induced by shallow partial mining in the Datong Jurassic coal seam have caused fatalities, significant property losses and brought about harmful results to the environment. By introducing efficient pillar widths and using the Voronoi diagram, irregular pillar stability can be estimated rationally. Theoretical analysis and numerical simulation demonstrate that the failure of a single pillar increases the load on surrounding pillars. If the magnitude of the transferred load is sufficiently high, the adjoining pillars will also fail in a chain reaction. This can be interpreted by the merger of inner stress arches combined with the external stress arch. In this paper, the evolution mode of sudden surface collapse caused by shallow partial mining is proposed and has been verified by ‘similar material simulation.’ Finally, the potential of sudden surface collapse is determined and an example of collapse prediction and prevention of surface building damage with relocation is given.     

Assessment of visual impact induced by surface mining with reference to a case study located in Sardinia (Italy)

Surface mining and quarrying typically generate a considerable number of environmental impacts among which landscape alteration remains one of the most significant. Although landscape alteration does not directly affect public health, it may produce an adverse reaction among potential observers and compromise the use and potential growth of the surrounding territory. In order to assess the impact produced by surface excavation, some aspects of landscape modification can be objectively measured, such as the extent of the visible alteration, its shape and the chromatic contrast with the surroundings. With reference to a case study located in Sardinia, this article discusses the implementation of two different visual impact assessment methods, one defined by the EC decision 272/02 (Commission Decision 2002), the other previously proposed by the authors of the present article and based on the estimation of the impact indicator Lvi (level of visual impact). The comparison of the results proves that the method established by the EC decision leads to the underestimation of the visual impact for alterations which are significantly wider than their height. On the other hand, the implementation of the Lvi method clearly shows how the indicator is affected by the quarry’s lateral extent and suggests the possibility of calculating a global impact factor LVI to be associated to a given route, considering the variability of the visual impact with the curvilinear abscissa of the route itself.     

东昆仑、玉树、汶川地震的发生规律和形成机理:兼论大陆地震成因与预测

青藏高原东北部东昆仑、汶川、玉树等强震的同震地表破裂不对称发育,伴随余震有规律地分别向东、南东和北北东方向迁移,很可能是源于恒河盆地流经亚东、当雄、安多、库赛湖、治多、玉树、甘孜、汶川的弧形下地壳“热河”的流速和流向变化形成的,下地壳热流物质正在向云南及邻区汇聚形成下地壳“热海”,导致长时间跨季度构造热干旱,其影响超过大气环流的作用。地表破裂不一定受断层控制,震源也不在断层面上,下地壳流动导致中地壳发震并进一步影响上地壳形成同震脆性破裂系统。大陆板内盆山过渡带地震密集,大陆板内地震是在下地壳层流的热动力作用下导致活动地壳分层变形的产物。在大陆盆山耦合、圈层耦合的非线性开放系统中,从大洋底部的软流圈层流进入大陆底部使得地幔软流圈加厚,底辟上升为大陆下地壳流动,为地震活动提供了巨量热能;热软化的下地壳缓慢的韧性流动孕育了大陆板内地震;中地壳韧 脆性剪切带易于积累能量,发生热能与应变能的转化,产生地震,形成震源层;上地壳脆性断层活动和地表破裂是地震释放深部能量的载体和方式之一。地壳稳定性评价的依据应当是地壳的活动性而不是断层的活动性。大陆活动构造区地震活跃期与平静期交替实际上是下地壳地震能量的聚散过程,体现在下地壳热主导的韧性流动构造与上地壳应力主导的脆性破裂构造之间的相互作用。下地壳热软化物质流动过程中流速、流向等突然改变触发地震,并产生共振波。大陆下地壳流层在厚度、温度、粘度、流速、流向上的变化产生一定程度的温度异常、流体异常及与其相关的大气层、电场、磁场、重力场、地球化学场、应力场、应变场、生物场等异常。合理布置天空网、地面网、地下网,综合立体监测有效的地震前兆,系统地开展长期、中期和短临地震预测,能够不断地提高地震预测水平。     

采矿地表沉陷的神经网络预测

矿山开采引起的地表沉陷受地质条件和采矿条件等诸多因素的影响,这些因素又具有非线性关系,很难用数学模型加以描述,因而在求解问题时遇到困难.利用神经网络系统对求解非线性问题的优点,对地表沉陷问题进行预测,其结果和实测值基本一致,从而证明了它对地表沉陷预测的可行性和实用性.     

孕震空区和逼近地震在台湾地震中的应用

本文应用陆远忠等人提出的孕震空区和逼近地震方法 ,分析了台湾及其东部海域所有资料较完整的 6 0级以上的地震。结果表明该区普遍存在孕震空区和逼近地震。在判定是否为孕震空区时 ,采用同样的三个标志。用所得到的数据计算经验公式。最后得出 5点初步结论