Research into the Regional Characteristics of the Tectonic Stress Field in Jiashi, Xinjiang and Its Surrounding Areas

Jiashi and its surrounding areas are composed of many structural zones. Using the focal mechanism solutions of 59 moderately strong earthquakes in Jiashi and its surrounding areas, and combining these with the calculation results of system cluster and stress field inversion, we analyzed the evolvement characteristics of the stress field for different times and different regions. The results were as follows: The earthquakes in Jiashi are mainly strike-slip. However, those of the Kalpin block are mainly reverse events, showing an obvious thrusting. The regional characteristics are different from other areas. The direction of the regional principal stress field is near NS. However, under different tectonic backgrounds, the directions of the stress fields are different. The direction of the principal compress stress is near NS in the Kashi-Wuqia area. But before and after the 3 earthquakes with M7.0, dynamic evolution from NW to NS and then to NE with time process was observed. The Kalpin block has been dominated by a consistent stress field in the NW direction for a long time. However, the direction of the stress field of the Jiashi region is NE. Since 1996, the direction of the regional stress field has changed obviously. The direction of the P axis was deflected towards the NE, and the plunge angle increased. The result shows clearly the regional characteristics and variation of the distribution pattern of the stress field in different tectonic environments.

Present Tectonic Stress Field in the Capital Region of China Inverted from Focal Mechanisms of Small and Strong Earthquakes

A dense seismic network was installed in the capital region of China in recent years,which makes it possible to resolve the focal mechanisms of small earthquakes. We gathered large earthquake focal mechanisms from the last fifty years and moderate or small earthquake focal mechanisms from between 2002 and 2004,and calculated the present tectonic stress field of the capital region by the grid search method, which weighs different sized earthquakes and can improve the accuracy of the stress field inversion. The analysis of inversion results of different sub-regions shows that the azinuth of the maximum principal compressive stress axis is NE43°- 86° in the Beijing-Zhangjiakou-Datong area,NE38°-86° in the Tangshan area,and NE79°- 81° in the Xingtai area. Inversion results of this paper are similar to previous results,which proves the correctness of the approach. As revealed by the results,the stress field of the capital region is characterized by overall consistency and sub-regional differences. This study provides reference for earthquake mechanism explanation and geodynamics research.

Characteristics of the Mesozoic and Cenozoic Tectonic Stress Fields of the Urumqi-Usu Region, Xinjiang

Based on the study of folds and related conjugate shear joints, the tectonic stress fields of the Urumqi-Usu region to the north of the North Tianshan Mountains have been reconstructed. Furthermore the author discussed the tectonic movements and their dynamic features. The early tectonic movement in the investigated region occurred from the end of the Late Jurassic to the initial stage of the Early Cretaceous, with the maximum (tensile) and minimum (compressional) principal stress trajectories in the tectonic stress field being in E-W and S-N directions respectively; the late tectogenesis took place from the end of the Early Pleistocene to the initial Middle Pleistocene, with the maximum and minimum principal stress trajectories in the late stress field striking in WNW and NE-NNE directions respectively. Through computer-aided simulated calculation by the finite element method and analysis of geological structure, it has been ascertained that the early tectogenesis is a nearly N-S compressive movement and the late one a NE to nearly N-S compressive movement with reverse shear. The dynamic force which caused the tectogeneses came from the movement of the southern major fault, i.e. the North Tianshan Mountains.

Ambient tectonic shear stress field in Southern California and seismic hazard regions

ccording to the fracture mechanics rupture model of earthquakes put forward by us, several equations to compute tectonic ambient shear stress value τ0 have been derived [equations (1), (2), (3), (5)].τ0 values for intermediate and small earthquakes occurred in Chinese mainland and Southern California have been calculated by use of these equations. The results demonstrate that the level and distribution of τ0 are closely related to the location where large earthquakes will occur, i.e. the region with higher level of τ0 will be prone to occur large earthquakes and the region with lower level will usually occur small earthquakes. According to the spatial distribution of τ0 , the seismic hazard regions or the potential earthquake source regions can in some degree be determined. According to the variation of τ0 with time, the large earthquake occurrence time can be roughly estimated. According to the distribution of τ0 in Southern California and variation with time, three high stress level regions are determined, one (Goldfield area) of them is the present seismic hazard region.

Study on the Recent Tectonic Stress Field in the Yunnan Region

In this paper, using focal mechanism solutions of moderate-strong earthquakes in Yunnan and its adjacent areas, and based on the statistical analysis of the parameters of focal mechanism solutions, we discussed in detail the earthquake fault types and the characteristics of the modern tectonic stress field in the Yunnan region. The results show that most moderate-strong earthquakes occurring in the Yunnan region are of the strike-slip type, amounting to 80% of the total. Normal faulting and normal with strike-slip and reverse and reverse with strike-slip earthquakes is almost equivalent in proportion, about 8% each. The tectonic stress field of the Yunnan region is near-horizontal, and the dips of earthquake fault planes are large. There are three main dynamic sources acting on the Yunnan region: one is the NE, NNE and NNW-directed acting force from Myanmar, Laos and Vietnam; the second is the SE-SSE directed force from the Sichuan and Sichuan-Yunnan rhombus block and the third is the NW-NNW directed force from the South China block. These three acting forces have controlled the faulting behavior of the main faults and the characteristics of strong earthquake activity of Yunnan and its adjacent regions.

Study on the Recent Tectonic Stress Field in the “Huoshan Seismic Window” Region

The focal mechanisms of 62 moderate-small earthquakes since 1980 in the"Huoshan seismic window"region are calculated with the method developed recently by Snoke,combining the use of the first motion of P,SV and SH waves with their amplitude ratios.Based on these abundant focal mechanisms,the mean tectonic stress field in the"Huoshan seismic window"region is inverted with the average stress tensor method,and the result shows that the"Huoshan seismic window"region is horizontally compressed in the near EW direction and horizontally dilated in the near NS direction,which is in accord with statistical results of focal mechanism parameters.We estimate the difference(also referred to as consistency parameterθ)between the force axis direction of the focal mechanism solution and the mean stress tensor,then further analyze the variation characteristics ofθversus time,and the relationship with moderately strong earthquakes in the east China region.The result indicates thatθin the"Huoshan seismic window"region is in good correspondence with moderately strong earthquakes in the East China region.Whenθis lower than the mean value,corresponding moderately strong earthquakes may occur in the East China region.

A workfow to Predict the Present-day in-situ Stress Field in Tectonically Stable Regions

Knowledge of the present-day in-situ stress distribution is greatly import-ant for better understanding of conventional and unconventional hydro-carbon reservoirs in many aspects,e.g,reservoir management,wellbore stability asssment,etc.In tectonically stable regions,the present-day in-situ stress field in terms of stress distribution is 1argely controlled by lithological changes,which can be predicted through|a numerical simulation method incorporating specific mechanical properties of the subsurface reservoir.In this study,a workflow was presented to predict the present-day in-situ stress field based on the finite element method(FEM).Sequentially,it consists of:i)building a three-dimensional(3D)geometric framework,i)creating a 3D petrophysical parameter field,11)integrating the geometric framework with petrophysical parameters,iv)setting up a 3D heterogeneous geomechanical model,and finally,v)calculating the present-day in-situ stress distribution and calibrating the prediction with measured stress data,e.g.,results from the extended leak-off tests(XLOTs).The approach was sucessfully applied to the Block W in Ordos Basin of central China.The results indicated that the workflow and models presented in this study could be used as an effective tool to provide insights into stress perturbations in subsurface reservoirs and geological references for subsequent analysis.

Quantitative Assessment and Zonation of Regional Crustal Stability in China

On the basis of the synthetic analysis of present regional tectonic stress field in China, this paper follows three steps to do crustal stability assessment: (1) zonation of preevaluation area for regional crustal stability assessment and zonation; (2) choice, taking value and weight distribution of quantitative evaluation indices and determination of evaluation standards; (3) assessment and zonation of regional crustal stability using fuzzy mathematics in China.

Analysis of faults stability with dynamic phenomena in the mice based on slide criterion and in-situ stress measurement

For the study on the relationship between the dynamic phenomena in the min- ing such as mine earthquakes,outburst and faults slide,firstly,double shear friction ex- periments of sandstone were made,and its slide criterion was suggested considering the viewing of engineering.Secondly,in order to study the stability of underground rock and zone of tectonic stress field,based on the analysis on distribution characteristic of initial rock stress measurements,the geology structural model was built and tectonic stress field was made a back-analysis by applying finite element method.The calculating results fit with the analysis result of earthquakes mechanism and the distribution characteristic of the measurements.The high stress regional centers station locates discontinuous zone of I level faults and is corresponding to underground earthquakes scene.From then it is cer- tain that tectonic stress is the major origin and necessary condition of mine earthquakes. The instability slide of the faults is the main manifest and the mining activity is the leading factor.Beipiao fault has a dominate effect on other sub faults and tectonic stress area and is dynamical fountain of dynamic phenomena in the Beipiao Mines.

北山及邻区晚古生代基性岩墙群几何特征及构造意义--基于遥感影像研究

北山及邻区广泛发育晚古生代基性岩墙群,反映了该地先存裂隙(节理)的区域构造应力场和岩墙群形成后经历的构造活动,对探究岩浆活动、反演构造演化过程及分析岩墙几何特征与构造应力之间的耦合关系具有重要意义。综合遥感和地质方法,在遥感影像中解译提取1777条基性岩墙,通过几何工具计算得到岩墙走向数据,总结岩墙群空间分布规律,同时与其形成时的大陆动力学演化背景相对应。结果表明,北山及邻区岩墙优势走向方位集中于0°~65°与320°~360°,绝大部分岩墙是在伸展作用中张性区域应力场控制下形成的,具张性性质或剪张性性质,部分岩墙受后期碰撞挤压环境影响,具张剪性性质。岩墙群主导成因机制是区域伸展构造作用,兼以地幔柱远程效应及热点作用。

云南地区中小地震震源机制解及分区特征分析

利用云南地区2008年至2022年4月M_(W)≥3.0共1096个地震震源机制解,进行统计和区域构造应力场特征分析.结果表明:①云南地区震源机制解以走滑断层型为主,走滑断层型地震为702个,占比为64%;其次是正断层型地震为125个,占比为11.4%,说明云南地区断裂以走滑断层型和正断层型为主;②云南地区以走滑断层型地震占比最多,滇西北地区的正断层型地震占比显著高于其他区域,小滇西地区几乎没有逆冲型大断层;③云南地区断层受到的应力以水平向剪切应力为主,主压应力轴P轴的方位角的优势分布方向以NNE和SSW向为主,断层面多为高倾角,滇西北地区正断层型地震显著多于其他地区,说明滇西北地区是云南地区应力转换带.

中国大陆及邻区现代构造应力场分区

以“中国大陆地壳应力环境基础数据库”资料为基础 ,总结了中国大陆及邻区现代构造应力场的基本特征 ,提出了划分构造应力分区的原则 ,将中国大陆及邻区现代构造应力场划为四级应力区 .指出一级构造应力区主要受板块边界的几何特征和作用在边界上的力所控制 ,应力作用在大范围和长时间内保持均匀和稳定 ;二级构造应力区受控于区域块体间的相互作用 ,在较大区域范围内应力作用具有较强的相关性 ;三级构造应力区受控于区域内部块体间的相互作用 ,在一定区域范围内应力结构具有相似性 ;四级构造应力区受控于块体和断裂相互作用的影响 ,其应力性状 (方向、强度、结构等 )一致性较好 .

四川盆地荣县—威远—资中地区发震构造几何结构与构造变形特征:基于震源机制解的认识和启示

四川盆地荣县—威远—资中地区属于历史弱震区,然而2019年相继发生多次破坏性地震事件.本文基于四川区域地震台网宽频带地震仪记录波形资料,利用CAP(Cut and Paste)波形反演方法,获得了2016年以来发生在荣县—威远—资中地区的26个M S≥3.0地震的震源机制解、震源矩心深度和矩震级,对该区域发震构造几何结构与变形特征及构造应力场特征进行了初步分析.主要获得如下认识:(1)26个M S≥3.0地震的震源矩心深度在1.5~5 km之间,平均深度3.4 km,表明事件发生在上地壳浅部沉积层内;震源深度分布揭示发震断层面倾向SE、缓倾角.(2)26个地震的震源机制全部为逆冲型,表明发震构造整体为逆断层性质.节面优势方位NNE-NE,结合走向与倾角统计结果,本文推测发震构造可能为威远背斜南翼一系列倾向SE、走向NNE-NE的缓倾角盲冲断层.(3)P、T、B轴优势方位单一,表明研究区域处于相对简单的构造应力环境.区域应力场反演获得的最大主压应力轴σ1方位NW-SE,近水平,与目前已知的该区域构造应力场水平主压应力方向一致,反映区内构造活动主要受区域构造应力场控制;其明显有别于四川盆地南缘2019年6月17日长宁M S6.0地震余震区NE-SW向的最大主压应力轴方位也揭示出四川盆地构造应力场具有明显的分区特征.(4)26个地震整体的应变花表现为NW-SE向挤压白瓣形态,表明区内发震构造整体呈NW-SE向纯挤压变形模式,明显有别于2019年长宁M S6.0地震序列NE-SW向挤压兼具小量NW-SE向拉张分量的构造变形模式,进一步表明四川盆地构造变形模式也具有明显的分区特征.

赵楼井田地应力特征及地质构造形成机制

采用钻孔套芯应力解除法在赵楼煤矿井底车场位置选点进行了地应力测量。测量结果表明,最大主应力方向为NEE,反映出测点附近应力场为以NEE向挤压为主的水平构造应力场,与邻近的万福煤矿实测地应力结果基本一致。由区域布格重力场和震源机制解资料得出,鲁西南地区现代地应力场为NEE向水平挤压的构造应力场,赵楼井田地应力场受区域构造应力所控制。通过地质构造成因分析,认为井田构造早期以EW、NE向褶曲为主,晚期以近NE、NW向断层为主,并使早期断层性质发生转换,不同期次构造组合形成了矿井现今复杂的构造格局。

兰州至玛曲地区地应力测量与现今构造应力场特征研究

兰州—玛曲地区是印度板块北东向推挤引起青藏块体强烈变形的前缘区,该区的现今构造应力场研究对研究大陆动力学问题具有重要意义.本文给出了兰州—玛曲地区不同地点的现今地应力实测值的大小和方向.测量方法采用压磁应力解除法,测点分别布置在阿姨山、大水、尕海、玛艾以及清水.为系统研究本区及邻近地区现今构造应力场特征,对已有应力实测数据进行了整理分析.研究结果表明,本区及邻区几十米浅表部应力与其他地区相比,属于中等大小量值;应力随深度增加而加大,但在不同构造单元,应力增加梯度有所不同;最大水平主应力方向总体上为北东向,不同构造单元上方向有所不同,鄂尔多斯地块最大水平主应力方向为近东西向,河西走廊带最大水平主应力方向在北北西—北东方向内变化,祁连山东南端最大水平主应力方向变化较大,西秦岭地块是现今地应力的一个过渡带,最大水平主应力方向由北侧的NE向逐渐转变为中部的EW向和南侧的SEE向.本文给出的结果与由GPS观测给出的该区域应变场分布具有一致性.

云南地区现代构造应力场研究

利用云南及周边地区中强地震震源机制解资料,采用对震源机制参数进行统计的方法,详细分析了地震断层类型和云南地区的现代构造应力场特征。结果表明,云南地区发生的中强地震走滑型地震占绝大多数,比例为80%,正断型和正走滑型与逆断型和逆走滑型地震所占的比例相当,分别约为8%。云南地区应力场接近水平,地震错动面的倾角较陡。云南地区有3个方面的主要力源:一是来自缅甸、老挝和越南的NE、NNE和NNW向作用力;二是来自四川及川滇菱块的SE、SSE向作用力;三是来自华南地块的NW、NNW向作用力。这3方面的作用力控制了云南及其邻区的主要断层活动及强震活动。

川滇地区活动块体划分与现代构造应力场分区研究综述

总结了30多年来川滇地区活动块体划分与现代构造应力场分区的主要研究认识,对二者之间的联系进行了初步讨论。对于川滇地区活动块体的划分,不同学者给出的宏观格局基本一致,但对其中一些次级块体的划分和边界断裂存在不同的认识。学者们对川滇地区现代构造应力场整体特征的认识较为一致,但对应力场的具体划分存在不同看法。川滇地区活动块体的划分格局基本确定了现代构造应力场的分区,但二者并不完全一致。开展这两方面的深入研究,对进一步认识川滇地区构造变形特征具有重要意义。

川东北宣汉—达县地区晚中生代—新生代构造应力场转化及其油气意义

构造应力是地壳中较为活跃的能量之一,构造应力作用方式和转变形式的研究对油气藏勘探开发有重要的指导意义。通过研究直立褶皱、共轭节理、断裂面擦痕等各种构造形迹,重建宣汉—达县地区晚中生代—新生代构造应力场,分析其构造活动规律。燕山晚期,川东构造带自SE方向的扩展影响到宣汉—达县地区,形成一系列NE向断裂和褶皱;喜马拉雅期,川东构造带逐渐趋于平静,大巴山构造自NE方向挤压,造就NW向断裂和褶皱的形成。不同方向、时期、强度的构造应力场叠加控制了研究区油气藏的形成和演化,阶段性的构造活动对研究区的叠加作用改善了储集层物性,较好地控制了圈闭的发育,将岩性油气藏调整为构造-岩性复合控制的油气藏,同时产生的构造应力和岩石中形成的裂缝分别为油气运移提供动力和通道。

区域构造应力场的数值模拟与应用

以淮南潘一矿为工程背景,依据地质动力区划方法,进行I～V级活动断裂的划分,确定区域构造形式,研究了C13-1煤层构造格架、主要断裂特点,在此基础上,建立了构造应力场的地质模型,结合地应力测量和岩体应力分析,确定区域岩体应力分布规律。其结果表明,煤矿区域原岩应力分布状态主要受断裂构造的支配,断裂构造的叠加扰动使原岩应力场重新分布,从而在时间和空间上制约着潘一矿煤与瓦斯突出的区域性分布,为安全生产提供保障。