活动断层上盘浅部的高应力异常通常被认为是强震前兆之一,而低应力一般认为不会发生地震是安全的.然而多个震例表明,低应力状态下的地震危险性具有多解性.为进一步探讨强震前的应力异常特征,本研究利用2008年汶川Ms8.0级地震和2013年芦山Ms7.0级地震前的地应力测量结果和地震活动性参数b值,在考虑深部应力对浅部应力影响强度的基础上,建立了浅部应力对深部应力的响应模式,并对强震发生前不同的应力状态与地震危险性的关系进行了讨论.结果表明:活动断层上盘低b值对应浅部高地应力为潜在地震危险区,而对应低地应力则为地震危险性不确定区,需要借助更多的手段进一步确定;2008年汶川Ms8.0级地震前的低应力状态可能反映了区域应力存在较强的调整.本研究对运用断层浅部应力状态评估断层地震危险性具有一定的启示意义.

In the Longmenshan thrust belt, the Dayi seismic gap, an area with few earthquakes, is located between the ruptures of the 2008 Wenchuan Earthquake and the 2013 Lushan Earthquake, with a length of approximately 40–60 km. To date, however, the extent of the seismic hazard of the Dayi seismic gap and whether this gap is under high stress are still hotly debated. To further evaluate the seismic hazard of the Dayi seismic gap with regard to stress, two boreholes (1,000 and 500 m deep) were arranged to carry out hydraulic fracturing in situ stress measurement on either side of the Shuangshi-Dachuan fault zone. This zone has a high seismic hazard and the capacity to undergo surface rupture Through the analogy of this new data with stability analysis using Byerlee’s Law and existing stress measurement data collected before strong earthquakes, the results show that the area surrounding the Shuangshi-Dachuan fault zone in the Dayi seismic gap (Dachuan Town) is in a state of high in situ stress, and has the conditions necessary for friction slip, with the potential hazard of moderate to strong earthquakes. Our results are the first to reveal the in situ stress profile at a depth of 1,000 m in the Dayi seismic gap, and provide new data for comprehensive evaluation of the seismic hazard in this seismic gap, which is of great significance to explore the mechanism of earthquake occurrence and to help mitigate future disaster.

龙门山断裂带大邑地震空区位于2008年汶川地震区和2013年芦山地震区之间,是一个长约40～60km缺少地震发生的区域.关于大邑地震空区的地震危险性以及是否存在高应力仍存在争议.为进一步从应力角度评估大邑地震空区的地震危险性,在具有发生地表破裂型地震能力并且具有高地震危险性的双石-大川断裂带两侧各布置1个钻孔（深度分别为1000和500m）进行水压致裂地应力测量工作.利用这些新数据结合Byerlee定律的稳定性分析和已有强震前的应力测量资料进行类比,结果表明,大邑地震空区双石-大川断裂带（大川镇）附近处于高地应力状态,具备了摩擦滑动的必要条件,具有发生中、强震的潜在危险性.研究结果揭示了大邑地震空区内1000m深度范围内的地应力剖面,为全面评估地震空区地震危险性提供了全新数据,这对于探索地震发生的机理与减灾具有重要意义.

为评估压裂效果及地面监测质量,进行了L606-6井地面微震监测应用研究.监测过程严格执行了安静处布台和有效去噪等应用VS的必要条件,最大限度地提高了信噪比,获得了微震释放能量的平均最小信噪比为3.6％.研究结果表明,微地震时间间歇性和空间随机跳跃性明显,开始破裂需要的积累能量的时间较短,以后逐渐延长;缝网形成过程中每个重要时段的微震群发生的地域和范围仅是整个最后裂缝带中的局部,包括稍远处被诱发的震群,直到形成最后缝网;除几个构成缝网主要形状的特征时段外,多数微震活动的重要时段显示了这些微震在加密缝网,或者"填空";此地域的最大主压应力的方向很可能在水平方向,且在NE30°和NE90°之间.这是一次较典型的水力压裂及其微震监测.借鉴L606-6井地面监测结果,对该块在L606-6井附近的三口井进行了压裂,并进行了井中微地震监测,四口井的裂缝走向和尺度基本一致,某种程度上验证了地面监测结果的可靠性.

2015年金口河发生了MS 5.0级地震,为揭示地震与地应力的内在关系和动力学背景,对距震中约12km的2个钻孔的水压致裂地应力测量资料进行了分析研究,利用拜尔利准则和应力莫尔圆分析了峨边-金阳断裂带北部断层的稳定性,并结合地震活动性参数b值探讨了金口河地震发生的动力学背景.研究结果表明:在钻孔94.90～722.10 m的深度内,最大水平主应力为5.89～14.50 MPa,最小水平主应力在3.79～10.30 MPa,应力水平较低;最大水平主应力方向在N50°W～N68°W,趋于北西至北西西向,与区域构造应力场一致;YJP-1孔三向主应力的相对大小表现为有利于逆断层和走滑断层的活动,DPS-1孔三向主应力的相对大小表现为有利于正断层的活动;DPS-1孔有效应力条件下的 μm(最大剪应力与平均应力之比)平均值为0.46,已接近断层摩擦滑动临界值下限0.51,有利于正断层的滑动;峨眉-烟峰断层弯曲构造部位应力闭锁集中区,是导致钻孔附近水平构作用较弱的主要原因.研究结果对于揭示金口河MS 5.0级地震前的动力背景具有重要意义.

贵州东南部位于盖层极不发育的榕江加里东褶皱带内,为查明该区域内的地应力状态,在贵州省黔南州境内进行了7个钻孔的水压致裂地应力测量工作,同时结合贵州西部已有研究结果和贵州西北部1个钻孔的地应力测量资料,对贵州东南部与西部和西北部的地应力分布差异进行了对比研究,最后结合断层的活动性质以及Byerlee准则探讨了测孔区域断层的稳定性,结果表明:水平主应力在研究区占主导地位,最大水平主应力方向表现为北西向;根据安德森断层理论,三向主应力的相对大小有利于逆断层和走滑断层的活动,这与研究区发育的活动断层性质相对应;最大和最小水平主应力的线性拟合结果表明,研究区水平主应力的梯度大于黔西煤层地区、广西盆地东北部和全国的地应力梯度值,最大水平主应力的值在相近深度上大于黔西、黔西北地区和广西盆地东北部;三都断裂带附近存在较高的构造应力,μm值(最大剪应力与平均主应力的比值)较高,表明断层处于摩擦极限平衡状态;而三江-融安断裂两侧的构造作用存在较为明显的差异,西侧的构造作用强于东侧;虽然部分钻孔内的μm值都处于高值,但区域应力方向与断层多以较大角度相交,因此断层是稳定的,这与研究区的地震活动性相吻合.

尼泊尔那苏瓦卡里水电站隧洞工程大部分埋深较大,在高地应力状态下很可能会面临软岩变形和硬岩岩爆等复杂地质灾害.文章采用水压致裂法对尼泊尔那苏瓦卡里水电站进行了三维地应力测量,测点处的最大主应力为10.47 MPa,方位角为18°和15°,近水平;中间主应力为9.01 MPa,方位角和倾角分别为158°和71°,倾角较大;最小主应力为6.34 MPa,方位角和倾角分别为285°和12°.工程区现今地壳应力场表现为构造应力起主导作用的基本特征,工程区地应力状态为中等应力水平.根据测量结果对隧洞围岩破坏机理进行了研究,结果表明,隧洞围岩破坏形式为劈裂剥落,隧洞轴线与主应力方向大角度相交以及中等偏高的应力水平是导致围岩发生破坏的主要原因.

建立了三维有限元模型,采用约束回归分析方法,对实际地应力场进行评估,使模拟结果更接近实际地应力场,为岩土工程地应力评估研究提供了一种有效方法.

Chengdu-Lanzhou Railway is located in the alpine valley area at the eastern edge of Qinghai-Tibet Plateau. Due to the collisions of the India plate and Eurasian plate, regional tectonic deformation is severe. The railway line stretch across the Sichuan-Qinghai and the southern Gansu block, across the Longmenshan fault, Minjiang fault, East Kunlun fault, Diebu-Zhouqu-Bailongjiang fault and other active faults, and the regional tectonic stress field is very complicated. In order to study the in-situ stress distribution law and fault stability of Chengdu-Lanzhou Railway, hydraulic fracturing in-situ stress measurements were carried out in four boreholes along the railway area, the magnitude and direction of the in-situ stress in different positions are obtained, and the distribution law of stress parameters with depth-variant is established. The results show that in-situ stress presents a good linear relationship with depth-variant, and the horizontal stress is generally higher than the vertical stress within the measurement depth ranges, indicating that the regional stress field is dominated by tectonic horizontal stress. Within 750 m depth, the maximum horizontal principal stress is 25 MPa, belonging to middle-high stress level, and the lateral pressure coefficient decreases slowly with depth. The directions of maximum horizontal principal stresses are different in different tectonic units. The direction of maximum horizontal principal stress is NNE in the southern Gansu block while NW in the Sichuan-Qinghai block. According to Coulomb frictional failure criteria, the stability of the fault in the engineering area is analyzed. The results provide meaningful information for further research on tectonic stress field, fault activity and tunnel construction.

对二瓦槽水电站气垫式调压室进行了两组水压致裂法三维地应力测量.测量结果表明:测区应力场方向分布较均衡,最大主应力9.36～ 10.89 MPa,最小主应力6.66～7.56 MPa,最大主应力方位336°～340°,倾角10°～17°,主要受到水平方向压性构造应力的作用.抗劈裂稳定性评价表明:测区最小主应力是气垫式调压室室内最大气压力的1.8 ～2.0倍,满足岩体抗劈裂稳定最小主应力要求.测试结果可为气垫式调压室设计和建设提供依据.

如何利用有限的地应力资料对整个工程区地应力状态进行评估及预测一直是工程设计中的难点之一.文章利用水压致裂法对巴基斯坦某水电站的3个钻孔进行了地应力测量,通过测量获得了工程区地壳浅部现今地应力特征,并利用侧压系数变化规律对深部地应力值进行了预测.测试结果表明:在123～346 m测量深度范围内,地应力值一般随着深度的增大而升高,最大水平主应力量值为4.28～13.86 MPa,最小水平主应力量值为3.02～8.19MPa;在隧道埋深最大处,水平主应力则达到了40 MPa,表明工程区应力场以水平应力为主.利用强度应力比法和Hoek-Brown岩体强度估算方法对工程区应力状态进行了评价,研究表明工程区处于高地应力状态.测试结果说明最大水平主应力优势方向为NEE向,该方向与前人研究成果较为一致,工程区现今构造应力场与印度板块和欧亚板块相互碰撞有着密切关系.根据实测地应力测量结果及地应力预测结果,对水电站输水隧洞围岩大变形进行了探讨,结果表明:当埋深超过300 m时,围岩将发生大变形;当埋深超过800 m时,围岩将发生严重的挤压变形.

对二瓦槽水电站气垫式调压室进行了高压压水试验.试验成果显示:测段岩体在5 MPa高水压压力作用下透水率绝大部分在0.26～0.98 Lu之间,小于1.0 Lu;裂隙岩体水力劈裂压力值在10.5～ 12.0 MPa之间,对高水头压力具有较好的承载性.试验结果表明:围岩整体抗渗性能较好,但对于局部出现的软弱结构面需进行灌浆处理.试验结果可为气垫式调压室设计和建设提供依据.

This paper summarizes in situ stress data by hydraulic fracturing method over the past 10years along the Longmenshan fault belt, and these data can be divided into three segments: northern, middle, and southern. The orientations of the maximum horizontal stress rotate from north-northwest in the northern to northwest in the middle, and to west-northwest in the southern. The stress magnitudes are characterized by higher values in the two ends and lower values in the middle segment. Furthermore, three stress measurement campaigns in two boreholes on the northern segment of the Longmenshan fault belt, before and after the great earthquake, show clear stress decrease of 23%–29% in the shallow crust after the earthquake. Analysis using the mathematical fitting method also indicates a decrease in regional stress state after the earthquake. Meanwhile, the frictional characteristic indexes based on the stress measurements further imply that the frictional strength of the Longmenshan fault belt is characterized by a strong southern segment, a weak middle segment, and a moderately strong northern segment. The analysis based on the stress data implies that the northern and southern segments of the fault belt are extremely important stress concentration and transformation nodes of the regional stress regime.

As a north-westward fault zone located at the Western side of Yishu fault ( in Shandong section of Tan-Lu fault zone) controlling Changqing-Linyi moderately strong seismic belt, the in-situ stress state presented in Mengshan fault zone plays an important role in the hazard research on the seismic activities in central Shandong. The hydraulic fracturing stress measurements of two deep boreholes located in the vicinity of Mengshan fault zone have been carried out; resulting in the maximum horizontal principal stress SH as 7.0-17.0 MPa and the minimum horizontal principal stress S-h as 5.0-11.0 MPa. The measurement results show that the relative size of triaxial principal stress at the depth over 300 m tends to S-H>S-v >= S-h, and that tends to S-H>S-v>S-h in the range of the depth between 400 to 450 m. The direction of the maximum horizontal principal stress presents NE-NEE, which is consistent with results acquired from other data. The average values of the lateral pressure coefficient obtained by measured data are maximum lateral pressure coefficient K-Hmax=1.54 at Borehole ZK134 and K-Hmax=1.38 at Borehole ZK8. According to Byerlee's law, Mengshan fault zone lies in a relatively stable in-situ stress state, mu m (the ratio of the maximum shear stress to the average principal stress) presented in two boreholes shows little change between the years of 2010 and 2011 indicating that the fault zone is in a steady state at the moment.

The M(s)7. 0 Lushan Earthquake in the southern segment of Longmenshan Fault has brought great loss to the local natives and societies. To analyze the earthquake from the viewpoint of stress buildup in the upper crust is helpful and meaningful to understand more about the seismogenic mechanism. In the past 21 years, the research group accumulated and collected lots of in-situ stress data from 22 boreholes. These in-situ stress data show that the stress regime is of reverse faulting, and that the orientation of the maximum horizontal principal stress is N44 degrees-64 degrees W. At the same time, the stress measurements indicate that the stress state in the research area is relatively stable. In this paper, the authors suggest adopting the ratio of half maximum differential stress to the mean effective stress, mu(m), to reflect the capability and stress level of the upper crust. According to the theoretical analysis, mu(m) has similar physical meaning with mu, so we can replace mu with mu(m) to do rock friction analysis. The mu(m) based on all the stress measurements ranges from 0. 39 to 0. 56, approximately approaching the lower limit defined by the Byerlee law, mu = 0. 6, which also agrees well with the static friction coefficients of gouge specimen from the Longmenshan fault after Wenchuan Earthquake tested in the laboratory. Therefore, the occurrence of the Lushan Earthquake proves that the upper crust of the research area is in the critical frictional equilibrium state or sub-equilibrium state. The focal mechanism solution of Lushan Earthquake is reverse faulting, with the main P axis of 122 degrees, which is consistent with the stress state defined by the in-situ stress measurements. Compared with the research findings made by other geoscientists, the Lushan Earthquake can be regarded as one induced earthquake due to the stress increase caused by the Wenchuan Earthquake on the southern segment of Longmenshan fault.

Earthquake and subsequent rainfall infiltration always easily induced slope failure. The paper takes one slope as the studying example to assess the preliminary joint effect of earthquake disturbing and subsequent rainfall on slope failure. Based on the unsaturated infiltration theory, subsequent rainfall unsaturated seepage fields of un-disturbing and seismic slope were simulated separately. The results of earthquake disturbing slope compared with the initial one were discussed in detailed. The conclusion showed seismic slope is inclined to rainfall infiltration, which obviously increased the pore water pressure and induced rise of ground water.

The hydraulic bearing capacity of rock mass is the ability to bear high water pressure in hydraulic engineering filed.The hydraulic jacking test including nine measured sections has been performed in Upper Tamakoshi Hydropower project in Nepal.The results show that the splitting capacity of rock mass at the left plant is higher which could be up to 10.5MPa and the minimum value is 9.2MPa;the splitting capacity of the rock mass at right side varies from 6.7MPa to 7MPa;and that at the bottom of the plant varies from 8.6MPa to 9.5MPa.The results could explain the good water penetration resistance of site rock mass.The test data not only is greatly benefit to the project design and construction,but also provides an important reference to understand the parameters of the rock mass in the south Himalayas.