哈萨克斯坦斋桑7.3级地震前后的地下流体动力学效应

分析了斋桑地震前后天山地震带不同观测井的地下流体动力学及水文地球化学地震前兆和后效的异常变化特征。认为:地震流体效应具有不可逆性,不同构造带,远距离的异常变化可能与地壳区域块体构造运动有关,强震后效敏感带反映了区域应力场的加强过程,亦可发展成为新的潜在震源区。     

2003年呼和浩特城区流体异常特征及其地震地质意义

通过对2003年3月呼和浩特城区出现流体异常的落实和跟踪监测, 讨论了水温和水汞异常的成因, 并分析了大青山地震带的地震动态。 地下流体和地震地质资料表明, 呼和浩特城区3月中旬出现的地下流体异常是区域地壳活动的结果, 是呼-包盆地地壳活动引起新华广场断裂的活动, 断裂活动破坏了地下浅层的隔水层, 深层热水上涌形成了流体异常。 呼和浩特城区流体异常与6月10日托克托县M_S4.2地震都是岩石圈深部活动在地壳内的反映, 2003年3月以来呼和浩特城区出现的流体异常应该是地震的前兆。 西龙王庙的流体异常还未完全结束。     

地壳中的成矿地质流体体系

本文论述了地质流体研究的学科前缘性．认为地壳中可划分出六大类不同的成矿地质流体体系：（1）与大陆地壳中─酸性岩浆热事件有关的热液流体体系（2）与海底基性火山活动有关的热浪喷流派体体系（3）与海相沉积盆地演化有关的盆地流体体系（4）与区域变质作用有关的变质流体体系（5）与地幔排气过程有关的深部流体体系（6）与大型剪切带的发生演化有关的流体体系并简要讨论了每个成矿流体体系的发生、演化、特征和成矿作用．     

地震触发、震群与余震活动过程中的孔隙压力作用

国际上对地震过程中孔隙压力作用的研究已成为认识和理解地壳流体作用的关键科学问题.普遍认为,孔隙压力作用是地震触发和影响震群与余震活动过程的重要因素之一.许多地震震源附近存在着低波速、高泊松比的异常区域,通常认为该区域赋存流体,存在高孔隙压力.     

地下流体附加力源的研究新思路

提出地下流体储量变化是地震和多种前兆发生的附加力源的新观点，认为多种天然的和人为的因素所引起的地下流体储量变化。是一种附加力源。它通过流体载荷、孔隙压力、动水压力及化学腐蚀等作用，促进地壳的构造变形，并导致多种地震前兆异常的产生；而流体载荷和构造变形，又可促进地震的孕育和发生。对于降水、地表水、开采等因素造成的异常变化，不能简单地当做干扰来加以排除，它本身包含有大量的地震前兆信息。论述了该思路的科     

土壤气与覆盖层下断层及岩性关系的研究

0 引言 众所周知,地壳深部流体,特别是气体,其运动学特征同地壳构造活动密切相关。地球化学动力研究表明,地壳凡有结构面的地方,如块体界面、断层面等,其物质能量交换活跃,化学、物理作用强烈,往往成为地下流体外泄的通道。这使以研究土壤气体的组分含量空间变化来判定隐伏断层的存在及其走向、方位成为可能。地壳构造活动和岩石破裂运动常伴随化学作用和物理作用,因而地下流体成份及其运动形式必然发生相应的变化。在地下温度与压力差的作用下,发生变化的地下流体成份运移到地表而形成气体地球化学的异常带。一般说来,这种异常带与地下断层的存在有关。研究断层气体组分随时间的变化可能捕捉到地震孕育或断层活动的信息,因而对地震监测预报、判定地震危险区有实际意义。近几年来,国内外对断层气、土壤气的研究成为地震地球化学工作者探索地震前兆新方法的重要方向之一。我们在肥东形     

地壳深部稳定性——震源体破裂机制和摩擦滑动机制的综合研究

本文通过地壳应力测量结果和地震资料的综合分析,对深部应力状态与断层运动的关系作了讨论:进而应用库仑准则,推导了三维应力作用下完整岩体和已有的任意空间方向断层面的失稳条件及其滑动方式的解析表达式.通过建立描述岩体和已有断层稳定性的两个函数————破裂函数 Fm 和摩擦函数 Ff,给出了应用破裂机制和摩擦滑动机制综合分析地壳稳定性和失稳性态的方法:根据这种分析方法并结合华北平原区的水压致裂应力测量资料,以及孔隙压力、大地热流等观测结果,定量研究了本区地壳的稳定问题,计算并图示了地壳内破裂函数沿深度的分布,以及各种走向和倾向断层面上的摩擦函数和剪应力分布;计算中以 Byerlee 定律作为断层运动的约束条件,并考虑了地壳密度纵向非均匀性导致的垂直应力沿深度的非线性增长以及深部超静水压力的异常孔隙压力作用.结果表明,华北平原区地壳失稳性态主要表现为已有断层的滑动;伴有高剪应力降的断层运动的深度范围在8至2.0多公里之间:陡断层稳定性低于缓断层,其运动方式以走滑为主;本区 NNE-NE 走向的陡断层是一组易震断层,其震时错动为右旋走滑;孔隙压力的增长对地壳稳定性有显著的影响;华北平原区深部高异常孔隙压力是地震活动的一种重要背景.      

华北强震前地下流体长趋势变化特征及其产生机理的研究

分析了华北地区自1976年以来MS≥6.0地震前地下流体长趋势变化的形态、演化特征。结果表明:地下流体长趋势变化出现时间早、范围广,具有协调性、重复性、迁移性等特性,主要沿构造带迁移,迁移方向为外围向内迁移或内部向外迁移;形态主要为趋势转折、破年变、加速等,其中绝对大多数为趋势转折变化;地下水位分析表明长趋势变化绝大部分呈现为缓慢上升或下降减缓的走势。对比研究了地壳形变与地下流体长趋势变化,发现地壳形变长趋势时间早于地下流体;形变出现张压变化与水位变化有比较密切的关系,即形变绝大部分出现缓慢压性变化或张性减缓变化,水位绝大部分出现缓慢上升或下降减缓变化。最后讨论了强震前地下流体长趋势变化产生的机理:在地震孕育过程初(早)期,构造应力的缓慢增强将使岩体所含裂缝闭合,地壳发生变形,从而改变岩体的空隙率及相应的孔隙压力和渗透率,引起诸如地下流体长趋势动态异常变化;构造应力缓慢增强并向未来震中聚集,造成地下流体长趋势动态异常变化向震中迁移;而深部物质的不断上涌和影响范围增大致使地下流体长趋势动态异常变化向外围迁移。     

地壳深部稳定性——震源体破裂机制和摩擦滑动机制的综合研究

本文通过地壳应力测量结果和地震资料的综合分析,对深部应力状态与断层运动的关系作了讨论:进而应用库仑准则,推导了三维应力作用下完整岩体和已有的任意空间方向断层面的失稳条件及其滑动方式的解析表达式.通过建立描述岩体和已有断层稳定性的两个函数——破裂函数 F_m 和摩擦函数 F_f,给出了应用破裂机制和摩擦滑动机制综合分析地壳稳定性和失稳性态的方法:根据这种分析方法并结合华北平原区的水压致裂应力测量资料,以及孔隙压力、大地热流等观测结果,定量研究了本区地壳的稳定问题,计算并图示了地壳内破裂函数沿深度的分布,以及各种走向和倾向断层面上的摩擦函数和剪应力分布;计算中以 Byerlee 定律作为断层运动的约束条件,并考虑了地壳密度纵向非均匀性导致的垂直应力沿深度的非线性增长以及深部超静水压力的异常孔隙压力作用.结果表明,华北平原区地壳失稳性态主要表现为已有断层的滑动;伴有高剪应力降的断层运动的深度范围在8至2.0多公里之间:陡断层稳定性低于缓断层,其运动方式以走滑为主;本区 NNE-NE 走向的陡断层是一组易震断层,其震时错动为右旋走滑;孔隙压力的增长对地壳稳定性有显著的影响;华北平原区深部高异常孔隙压力是地震活动的一种重要背景.     

缅甸7.2级地震对云南地下流体的影响

对2011年3月缅甸Ms7.2地震前云南地下流体前兆异常进行系统研究,结果表明,距震中540 km范围内共有14测点17个测项异常;异常时空特征表明,异常演化具有明显的阶段性,地震前5个月开始异常逐月增多,并有向震中收缩发展的迹象.     

Spectral study of the Bouguer anomaly map of a rift valley and adjacent areas in Central India

The spectral study of the Bouguer anomally map of Central India suggests an uplifted crust-mantle interface under the Mahandi graben. This study has delineated three subsurface levels of anomalous masses at the respective depths of 23 km, 8 km, and 2 km apparently representing the Moho, an intermediate discontinuity in the sialic part of the crust and the basement, respectively. Model study of the Bouguer anomaly along a profile suggests a typical continental graben type subsurface structure with a low density depression in the sialic part of the crust between 8 and 18 km supported by an elevated upper mantle of intermediate density (3.4 g/cm³) varying in depth from 25 km to 55 km. The depths of the inferred interfaces in case of Bundelkhand granite are 32 km, 11 km, and 1.5 km, which might represent the Moho, the base of intruded granite massif, and some shallow compositional variation. Similar studies in case of Vindhyan basin have brought out three discontinuities at the respective depths of 16 km, 6–4.5 km, and 2.4 km. The first horizon at the depth of 16 km probably represents the interface between the granitic and the basaltic part of the crust. The 6–4.5 km is the depth of the basement, with the 2.4 km interface separating Bijawar rocks from Vindhyans wherever they are present. A generalized inversion of a profile across a positive belt of Bouguer anomaly representing the subsurface Bijawar rocks support the above result.     

内蒙古锡林浩特-东乌旗剖面壳幔电性结构研究

为研究二连-东乌旗贺根山一带成矿构造环境,提供矿产资源勘查、预测、评价的地质背景依据,跨贺根山和锡林浩特板块缝合带一线布设了26个超宽频带长周期大地电磁测深点,点距3～6 km,剖面长度100 km,在对获取的资料采用Robust变换、互参考处理的基础上,定性分析了视电阻率和相位曲线、二维偏离度、电性主轴,并采用二维共...     

三河-平谷8.0级地震区地壳结构和活动断裂研究——利用单次覆盖深反射和浅层地震剖面

跨1679年三河-平谷8.0级地震区完成的单次覆盖深地震反射剖面和浅层地震反射剖面,揭示了三河-平谷地震区的地壳结构和断裂的深、浅构造特征.结果表明,该区地壳以TWT6～7 s左右的强反射带为界分为上地壳和下地壳,上地壳厚约18～21 km,下地壳厚约13～15 km.剖面揭示的地壳深断裂和浅部活动断裂具有上下一致的对...     

THE 3-D VELOCITY STRUCTURE OF CRUST AND UPPERMOST MANTLE AND ITS TECTONIC IMPLICATIONS IN FUJIAN PROVINCE

It is important to detect the fine velocity structures of the crust and uppermost mantle to understand the regional tectonic evolution, earthquake generation processes, and to conduct earthquake risk assessment. The inversion of uppermost mantle velocity and Moho depth are strongly influenced by crustal velocity heterogeneity. In this study, we collected first arrivals of Pg and Pn and secondary arrivals of Pg wave from the seismograms recorded at Fujian provincial seismic network stations. New 3-D P-wave velocities were inverted by multi-phase joint inversion method in Fujian Province. Our results show that the fault zones in Fujian Province have various velocity patterns. The shallow crust is characterized by high velocity that represents mountains, while the mid-lower crust shows low velocities. The anomalous velocities are correlated closely with tectonic faults in Fujian Province. Velocity anomalies mainly show NE-trending distribution, especially in the mid-lower crust and uppermost mantle, which is consistent with the NE-trending of the regional main fault zones. Meanwhile, a part of velocity patterns show NW trending, which is related to the secondary NW-oriented faults. Such velocity distribution also shows a geological structural pattern of "zoning in east-west direction and blocking in north-south direction" in Fujian area. In the crust, a low velocity zone is found along Zhenghe-Dapu fault zone as mentioned by previous study, however our result shows the low velocity exists at depth of 20~30km in mid-lower crust. Compared with previous study, this low velocity zone is larger and deeper both in range and depth. The crustal thickness of 28~35km from our joint inversion is similar to the results from the receiver functions of previous studies. The thinnest crust(28km)is observed at offshore in the north of Quanzhou; while the thickest crust(35km)is located west of Zhangzhou near the Zhenghe-Dapu fault zone. Generally, thinner crustal thickness is found in offshore of Fujian Province, and thicker crustal thickness is in the mainland. However, we also found that crustal thickness becomes thinner along the east side of Yongan-Jinjiang Fault. The values of Pn velocities in the region vary from 7.71 to 8.26km/s. The velocity distribution of the uppermost mantle presents a large inhomogeneity, which is correlated with the distribution of the fault zone. High Pn velocity anomalies are found mainly along the west side of the Zhenghe-Dapu fault zone(F₂), and the east side of the Shaowu-Heyuan fault zone(F₁), which is strip-shaped throughout the central part of Fujian. Low Pn velocity anomalies are observed along the coast and Taiwan Straits, including the Changle-Zhaoan fault zone, the coastal fault zone, and the Fuzhou Basin. We also found a low Pn velocity anomaly zone, which extends to the coast, in the Shaowu-Heyuan fault zone at the junction of the Fujian, Guangdong and Jiangxi Provinces. In the west of Taiwan Straits, both high and low Pn velocity anomalies are observed. Our results show that the historical strong earthquakes(larger than magnitude 6.0) are mainly distributed between positive and negative anomaly zones at different depth profiles of the crust, and similar anomalies distribution also exists at the uppermost mantle, suggesting that the occurrence of strong earthquakes in the region is not only related to the anomalous crustal velocity structure, but also affected by the velocity anomaly structure from the uppermost mantle.     

The 3D magnetic structure beneath the continental margin of the northeastern South China Sea

Understanding the continental margin of the Northeastern South China Sea is critical to the study of deep structures, tectonic evolution, and dynamics of the region. One set of important data for this endeavor is the total-field magnetic data. Given the challenges associated with the magnetic data at low latitudes and with remanent magnetism in this area, we combine the equivalent-source technique and magnetic amplitude inversion to recover 3D subsurface magnetic structures. The inversion results show that this area is characterized by a north-south block division and east-west zonation. Magnetic regions strike in EW, NE and NW direction and are consistent with major tectonic trends in the region. The highly magnetic zone recovered from inversion in the continental margin differs visibly from that of the magnetically quiet zones to the south. The magnetic anomaly zone strikes in NE direction, covering an area of about 500 km × 60 km, and extending downward to a depth of 25 km or more. In combination with other geophysical data, we suggest that this strongly magnetic zone was produced by deep underplating of magma associated with plate subduction in Mesozoic period. The magnetically quiet zone in the south is an EW trending unit underlain by broad and gentle magnetic layers of lower crust. Its magnetic structure bears a clear resemblance to oceanic crust, assumed to be related to the presence of ancient oceanic crust there.     

断层带流体对断层强度和强震孕育的影响

大量研究表明,流体在断层弱化中起着非常重要的作用.在地壳浅部脆性域,自由水通过流体孔隙压力减小断层有效正压力,从而降低断层摩擦强度;在地壳深部,矿物中的微量结构水弱化岩石流变强度.另外,流体-岩石相互作用等化学过程,如长石水解反应,对断层强度的影响也非常显著.断层深部流体通过物理作用与化学作用影响着岩石的变形机制,从而影响断层力学性质与地震孕育和发生.断层内部流体孔隙压力周期性变化是断层带脆-塑性转化、裂缝张开与愈合等的直接体现,这种变化控制着断层强度与强震周期性发生现象.     

Insight into the Crustal Structure of the Eastern Marmara Region, NW Turkey

In order to investigate crustal structure beneath the eastern Marmara region, a seismic refraction survey was conducted across the North Anatolian Fault (NAF) zone in north west Turkey. Two reversed profiles across two strands of the NAF zone were recorded in the Armutlu Highland where a tectonically active region was formed by different continents. We used land explosions in boreholes and quarry blasts as seismic sources. A reliable crustal velocity and depth model is obtained from the inversion of first arrival travel times. The velocity-depth model will improve the positioning of the earthquake activities in this active portion of the NAF. A high velocity anomaly (5.6–5.8 km s⁻¹) in the central highland of Armutlu block and the low velocity (4.90 km s⁻¹) pattern north of Iznik Lake are the two dominant features. The crustal thickness is about 26 ± 2 km in the north and increases to about 32 ± 2 km beneath the central Armutlu block in the south. P-wave velocities are about 3.95 km s⁻¹ to 4.70 km s⁻¹ for the depth range between about 1 km and 5 km in the upper crust. The eastern Marmara region has different units of upper crust with velocities varying with depth to almost 8 km. The high upper crust velocities are associated with Armutlu metamorphic rocks, while the low velocity anomalies are due to unconsolidated sedimentary sequences. The western side of Armutlu block has complex tectonics and is well known for geothermal sources. If these sources are continuous throughout the portions of the crust, it may be associated with a granitic intrusion and deformation along the NAF zone. That is, the geothermal sources associated with the low velocity may be due to the occurrence of widespread shear heating, even shear melting. The presence of shear melting may indicate the presence of crustal fluid imposed by two blocks of the NAF system.     

Poroelasticity: Finite element modelling of anomalous tilt and pore pressure caused by pumping in a sedimentary half space with fault

Extraction of groundwater or hydrocarbons causes pore pressure gradients and soil deformation due to poroelastic coupling. Recent studies show that high-resolution engineering tiltmeters installed at shallow depth between 2 and 10 m resolve this deformation. Models using poroelasticity can describe the relationship between fluid extraction, pore pressure gradients and induced tilt for homogeneous and layered sedimentary half spaces. Faults intersecting a stack of sedimentary layers, for example in the Lower-Rhine-Embayment, are of fundamental impact to the groundwater flow system of an area. However, the fault’s hydromechanical effect on pump induced tilt and the pore pressure regime is still poorly investigated. We chose a comparatively simple approach to quantify anomalous pump induced tilt and pore pressure observed near a fault and close to the surface in a sedimentary subsoil. A PC-based Finite Element software is used to model poroelastic deformation, i.e. modelling vertical tilt and excess pore pressure in response to fluid extraction through a singular well. We compare numerical solutions for models with and without faults and show that a fault can modify symmetry and amplitude of the deformation field by more than a magnitude. We conclude that tilt and pore pressure measurements also at shallow depth can thus be biased by large subsurface structures like faults. Vice versa, these measurements may provide means to quantify hydromechanical effects caused by subsurface structures. However, depending on the geological setting, i.e. if pathways are established by a fault, the anomaly caused by the fault can also be small and hard to detect. Therefore, faults and geological structures like material boundaries have to be considered in poroelastic models carefully. For tilt surveys with a limited number of instruments in geologically well constrained areas these models allow the preselection of potential positions for tiltmeters where prominent field anomalies are expected.     

太行山断裂带东南缘地壳三维P波速度结构成像

应用多年地震台网观测数据,使用多震相走时成像方法获得了太行山断裂带东南缘地壳的三维P波速度结构模型。结果表明:速度结构图像在浅部较好地反映了地表地形、地质构造的特征,深部显示地壳速度具有明显的横向变化特征。12km深度以上显示研究区北部太行山隆起区地壳主要呈现为高速区,南部沉降区为低速区,而12km深度以下具有反转的特点。整体显示速度异常的走向大致与邻近活动断裂走向一致。垂直速度剖面显示研究区地壳具有分层特征,上地壳厚约10km,速度横向变化较小;中、下地壳的界面呈现局部上隆或凹陷状,横向起伏变化较大。通过分析速度、断裂与中强地震发生的关系推测研究区具备发生中强震的深部孕震条件。