频率域海洋可控源电磁垂直各向异性三维反演   总被引：1，自引：0，他引：1       下载免费PDF全文

彭荣华  胡祥云  李建慧  刘亚军 《地球物理学报》2019,62(6):2165-2175

地层宏观电性各向异性会对可控源电磁响应产生重要影响.由于海底地层电性结构常表现为电导率各向异性，若仅对海洋可控源电磁（MCSEM）数据进行常规各向同性反演，有可能无法获得准确的反演解释结果，从而削弱MCSEM技术的可靠性.本文实现了电导率垂直各向异性（VTI）条件下频率域海洋可控源电磁数据三维反演算法.其中，三维正演采用基于二次场控制方程的交错网格有限体积法，并利用直接矩阵分解技术来求解离散所得的大型线性方程组，有利于快速计算多场源的响应.反演采用具有近似二次收敛性的高斯牛顿算法对目标函数进行最优化.最后，对具有VTI电性各向异性特征的盐丘构造模型的MCSEM合成数据分别进行了电导率各向同性和垂直各向异性三维反演，结果表明：各向同性三维反演算法无法对受VTI介质影响的MCSEM数据进行正确的反演解释，而垂直各向异性三维反演能够获得更为可靠的地下电阻率结构和异常体分布，展现出对海底电性各向异性结构更为优良的反演解释能力.  相似文献   

CHARACTERISTICS OF SATELLITE GRAVITY FIELD AND SEISMOGENIC MECHANISM IN THE LONGMENSHAN FAULT ZONE          下载免费PDF全文

TANG Jing-tian  YANG Lei  REN Zheng-yong  HU Shuang-gui  XU Zhi-min 《地震地质》2019,41(5):1136-1154

Longmenshan fault zone is a famous orogenic belt and seismic zone in the southeastern Tibetan plateau of China. The Wenchuan M_S8.0 earthquake on May 12, 2008 and the Ya'an M_S7.0 earthquake on April 20, 2013 occurred in the central-southern part of Longmenshan fault zone. Because of its complex geological structures, frequent earthquakes and special geographical locations, it has attracted the attention of many scholars around the world. Satellite gravity field has advantages in studying gravity field and gravity anomaly changes before and after earthquake. It covers wide range, can be updated regularly, without difficulty in terms of geographical restrictions, and is not affected by environmental factors such as weather, terrain and traffic. Therefore, the use of high-precision Earth satellite gravity field data inversion and interpretation of seismic phenomena has become a hot topic in earth science research. In order to understand satellite gravity field characteristics of the Longmenshan earthquake zone in the southeastern Tibetan plateau and its seismogenic mechanism of earthquake disasters, the satellite gravity data was used to present the terrain information of the study area. Then, by solving the regional gravity anomaly of the Moho surface, the crustal thickness of the study area was inverted, and the GPS velocity field data was used to detect the crustal deformation rate and direction of the study area. Combining the tectonic setting of the Longmenshan fault zone and the existing deep seismic sounding results of the previous researchers, the dynamic characteristics of the gravity time-varying field after the earthquake in the Longmenshan earthquake zone was analyzed and the mechanism of the earthquake was explored. The results show that the eastward flow of deep materials in the eastern Tibetan plateau is strongly blocked at the Longmenshan fault zone. The continuous collision and extrusion process result in a "deep drop zone" in the Moho surface, and the long-term stress effect is conducive to the formation of thrust-nappe and strike-slip structures. The Longmenshan earthquake zone was in the large-scale gradient zone of gravity change before the earthquake, the deep plastic fluid material transport velocity differed greatly, the fluid pressure was enhanced, and the rock mechanical strength in the seismic source region was weakened, which contributed to the intrusion of crustal fluid and the upwelling of the asthenosphere. As a result, the continuous accumulation of material and energy eventually led to continuous stress imbalance in the deep part and shear rupture of the deep weak structure, causing the occurrence of the thrust-nappe and strike-slip earthquake.  相似文献   

CHARACTERISTICS OF TECTONIC STRESS FIELD OF THE XIAOWAN RESERVOIR BEFORE AND AFTER THE IMPOUNDMENT          下载免费PDF全文

HUANG Hao  FU Hong 《地震地质》2019,41(6):1413-1428

Using the seismic waveform data of Xiaowan seismic network and Yunnan seismic network, we determined the focal mechanisms of 36 earthquakes(M_L ≥ 3.0)from Jun. 2005 to Dec. 2008 and 51 earthquakes(M_L ≥ 2.5)from Jan. 2009 to Dec. 2015 by generalized polarity and amplitude technique. We inverted tectonic stress field of the Xiaowan reservoir before impounding, using the focal mechanisms of 36 earthquakes(M_L ≥ 3.0)from Jun. 2005 to Dec. 2008 and CAP solutions of 58 earthquakes(M_L ≥ 4.0)collected and the solutions in the Global Centroid Moment Tensor(GCMT)catalog; We inverted local stress field of the reservoir-triggered earthquake clustering area, using 51 earthquakes(M_L ≥ 2.5)from Jan. 2009 to Dec. 2015. Focal mechanisms statistics show that, the Weixi-Qiaohou Fault is the seismic fault. Focal mechanisms were strike-slip type in initial stage, but normal fault type in later stage. Focal depths statistics of 51 earthquakes(M_L ≥ 2.5)show that, the average value of focal depths in period Ⅰ, period Ⅱ and period Ⅲ are 8.2km, 7.3km and 7.8km respectively and the standard deviations are 4.3km, 3.5km and 6.0km respectively. The average value of focal depths is basically stable in different period, only the standard deviation is slightly different. Therefore, there is not positive connection between focal depth and deviation of focal mechanisms. What's more, there are 2 earthquakes(number 46 and number 47 in Fig.5 and Table 3)with almost the same magnitude, epicenter and focal depth, but they have different faulting types as normal and strike-slip. The focal mechanism of event No.46 is strike:302°, dip:40° and rake:-97° for plane Ⅰ, however, the focal mechanism of event No.47 is strike:292°, dip:82° and rake:140° for plane Ⅰ. Likewise, earthquake of number 3 and number 18 have similar characteristic. Therefore, the obvious focal mechanism difference of similar earthquake pair indicates the complexity of Weixi-Qiaohou Fault. Considering the quiet-active character of reservoir-triggered earthquakes, we discussed the change of local stress field in different period. The σ₁ of tectonic stress field was in the near-south direction, with a dip angle of 14° before the impoundment, however, the direction of σ₁ of local stress field changed continuously, with the dip angle getting larger after the impoundment. The direction of σ₁ of local stress field of reservoir-triggered earthquake clustering area is close to the strike of Weixi-Qiaohou Fault, and reservoir impoundment increased the shear stress in the fault, so the weakening of fault was beneficial to trigger earthquakes. Comprehensive analysis suggests that fluid permeation and pore pressure diffusion caused by the water impounding, and the weakening of fault caused by local stress field are the key factors to trigger earthquake in the Xiaowan reservoir.  相似文献   

Beerkan multi-runs for characterizing water infiltration and spatial variability of soil hydraulic properties across scales   总被引：1，自引：1，他引：0  

Laurent Lassabatere  Simone Di Prima  Rafael Angulo-Jaramillo  Saskia Keesstra  David Salesa 《水文科学杂志》2019,64(2):165-178

A method is presented for characterizing the spatial variability of water infiltration and soil hydraulic properties at the transect and field scales. The method involves monitoring a set of 10 Beerkan runs distributed over a 1-m length of soil, and running BEST (Beerkan estimation of soil transfer parameters) methods to derive hydraulic parameters. The Beerkan multi-runs (BMR) method provides a significant amount of data at the transect scale, allowing the determination of correlations between water infiltration variables and hydraulic parameters, and the detection of specific runs affected by preferential flow or water repellence. The realization of several BMRs at several transects on the same site allows comparison of the variation between locations (spatial variability at the field scale) and at the transect scale (spatial variability at the metre scale), using analysis of variance. From the results, we determined the spatial variability of water infiltration and hydraulic parameters as well as its characteristic scale (transect versus field).  相似文献   

Magnetic Field Feedback Circuit for Geomagnetic Field Compensation Control     

SHEN Xiaoyu  HU Xingxing  HE Zhaobo 《中国地震研究》2019,33(4):661-675

In the current state of geomagnetic instrument testing, some aspects of geomagnetic instrument performance are difficult to test in the laboratory. If laboratory test results are inadequate, the instrument will have multiple problems while operating in the field, where a geomagnetic instrumentation test platform with a stable natural magnetic field is critical. Here, the magnetic field feedback circuit for geomagnetic field compensation control is studied in detail. That is, the magnetic field measured by the feedback magnetic sensor and the required working magnetic field are compared as input to the system, and the electric signal is transmitted to the feedback coil through an analog circuit to form a closed loop control, which provides compensation to control the magnetic field. Compared with the existing magnetic shielding method, the analog control circuit can achieve the realization of any working magnetic field, and it is not limited to a null magnetic field. The experimental result shows that the system compensates the earth''s magnetic field of 10,000nT with an average error of 10.6nT and average compensation error of 0.106%, providing a high compensation accuracy. The system also shows high sensitivity and excellent stability. The feedback circuit has achieved effective compensation control for the earth''s magnetic field.  相似文献   

双向地震作用下锯末混合土场地动力特性分析          下载免费PDF全文

陈红娟  李小军  闫维明  陈适才  张学明 《地震工程学报》2019,41(4):1017-1025

在北京工业大学振动台台阵系统上开展了一系列锯末混合土地基自由场振动台模型试验,试验中模型箱采用装配式连续体刚性模型箱,试验中输入地震动时程采用El Centro地震动记录、Taft地震动记录和天津地震动记录,地震动输入方向分为水平单向和水平双向。文中,重点考察了双向地震动输入下锯末混合土模型场地的动力特性及其变化规律,主要指标包括模型场地地震动反应的峰值加速度及其动力放大系数、加速度时程及其傅氏谱。试验结果表明:随着输入地震动强度的增大,同一测点反应的峰值加速度总体上在增大,而其加速度动力放大系数总体上呈现减小的趋势,反应的频谱组成从较高频率向较低频率移动;双向地震作用下锯末混合土模型场地的动力变化规律与单向地震作用下较为一致。  相似文献   

基于向量式有限元的黏滞阻尼减震结构抗竖向连续倒塌动力反应分析          下载免费PDF全文

曲激婷  宋全宝 《地震工程学报》2019,41(6):1432-1439

向量式有限元是以向量力学为基础的一种新的结构分析方法,在处理结构大变形等复杂行为时具有较大的优势。基于向量式有限元理论建立了黏滞阻尼单元,对附加黏滞阻尼器的平面钢框架结构进行了抗竖向连续倒塌动力分析,结合拆除构件法,采用MATLAB编制可以考虑初始变形的瞬时卸载法程序,实现结构在构件拆除前的静力分析和构件拆除后动力分析的全过程统一。研究了阻尼器布置位置和参数在结构抗竖向连续倒塌中的性能需求,以失效点竖向位移时程曲线、梁端转角、动力放大系数和结构塑性铰分布为参考指标,对比分析布置阻尼器前后钢框架结构的抗连续倒塌能力。结果表明向量式有限元是一种研究结构竖向连续倒塌动力响应的有效方法,合理布置阻尼器能够有效控制剩余结构的变形和振动,降低构件内力,减少塑性铰个数,较大地提高结构的抗竖向连续倒塌能力。  相似文献   

2013年岷县—漳县6.6级地震地磁垂直分量日变化低点时间空间分布特征     

戴勇  高立新  姚丽  朱培育  格根  王磊 《地震》2019,39(3):106-114

2013年6月16日, 中国大陆西部出现地磁低点位移。 异常出现后一个月内, 位于低点位移分界线附近发生7月22日岷县、 漳县交界6.6级地震。 本文通过采用实测低点时间减去理论低点时间的方法剔除低点时间经度效应, 并以剔除经度效应后低点时间为0 h的等值线作为低点位移分界线, 2013年岷县—漳县6.6级地震震中处于6月16日地磁低点位移分界线上。 对异常期间的中国大陆地区地磁垂直分量日变形态进行统计, 发现其存在显著的分区特征, 低点时间为正的区域内日变化形态基本呈现W型, 低点时间为负的区域内日变化形态主要呈现V字型特征。 低点位移异常日期间, 中国大陆存在显著的高梯度带, 本文采用梯度值定量描述低点时间空间变化程度。 在6月13日正常日期间, 中国大陆地区未出现梯度值大于1.5 h/(°)的区域, 在6月16日异常日期间, 出现梯度值大于1.5 h/(°)的区域, 2013年岷县—漳县6.6级地震位于高梯度区边缘。  相似文献   

秦岭—大别东段应力状态研究     

倪红玉  刘泽民  洪德全  赵朋  汪小厉 《地震》2019,39(3):138-148

本文首先通过Snoke发展的利用P波、 SV波和SH波的初动和振幅比方法计算秦岭—大别东段2008年以来83次M_L≥2.5地震的震源机制解, 然后通过FMSI方法反演得到平均应力场的方向特征: 近东西向的水平挤压和近南北向的水平拉张作用, 与参数统计结果一致; 进而通过震源机制的一致性参数分析应力场方向的变化信息。 分析表明震源机制解呈现了由变化紊乱、 偏离平均应力场到变化一致、 趋于平均应力场再到变化紊乱、 偏离平均应力场的变化过程, 在显著地震前, 研究区整体的震源机制一致性参数处于持续低值状态; 计算了2008年以来93次M_L≥2.5地震的视应力, 拟合视应力与震级的关系, 分析扣除震级影响的差视应力随时间变化特征, 近似反映研究区应力大小的变化。 分析表明显著地震前研究区的差视应力值呈现出明显的先上升后下降的变化过程, 在下降过程中发生地震; 最后利用震源机制一致性参数和差视应力综合分析研究区的应力状态, 均表明显著地震前震源区的构造应力场增强。 目前研究区的震源机制一致性参数较高、 差视应力较低, 研究区的应力水平较低。  相似文献   

郯庐断裂带新沂—泗洪段土壤气Rn体积活度和CO2浓度特征研究     

缪阿丽  张扬  方震  李锋  王维  高力 《地震》2019,39(1):48-57

郯庐断裂带江苏段地区4个剖面进行了土壤气Rn体积活度和CO₂浓度测量结果显示, 自北向南土壤气Rn体积活度均值分别为22.9 kBq/m³、 35.5 kBq/m³、 40.2 kBq/m³、 26.6 kBq/m³; 自北向南土壤气CO₂浓度均值分别为0.669%、 0.400%、 0.503%、 1.109%。 土壤气Rn体积活度和CO₂的浓度在空间分布上具有较好的一致性, 这可能与CO₂是Rn的载气有关。 综合分析土壤气Rn和CO₂测量结果以及水准资料可得, 2017年土壤气Rn高值出现在晓店段可能与区域应力应变调整有关。 本研究不仅为研究区以后的土壤气研究提供了参考, 同时也可为研究区的构造活动研究提供地球化学资料参考。  相似文献