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1.
采用煤矿井下专用的小孔径水压致裂地应力测量装置,在山西省的晋城、潞安、汾西、华晋、阳泉、平朔、大同等矿区,完成了160个测点的地应力测量,测点地质条件涵盖了山西省煤矿大部分条件.基于实测数据,分析了地应力与测点埋深的关系,不同深度条件下煤矿矿区井下地应力状态;绘制出山西省煤矿矿区井下地应力分布图,并与震源机制解的分析结果进行了比较,得出山西省煤矿矿区井下地应力场分布特征与变化规律.煤矿井下水平应力总体上随着埋深增加而增大,但由于各矿区地质条件差异较大,导致地应力测试数据离散性也较大;埋深小于250 m的岩层应力状态主要为σH>σh>σV型,埋深处于250~500 m的岩层应力状态以σH>σV>σh型为主,埋深较大的矿区主要为σV>σH>σh型;最大水平主应力与垂直主应力的比值绝大部分集中在0.5~2.0之间,而且随着埋深增加,侧压比呈现减小的趋势,并向1附近集中;最大水平主应力与最小水平主应力的比值主要集中在1.5～2.0之间;平均水平主应力与垂直主应力的比值大多处于0.5～1.5,尤以0.5～1.0之间最多;山西省煤矿矿区从北到南,最大水平主应力方向发生了较大变化.北部最大水平主应力方向为NE,往南发生偏转到NNW;靠东部与西部偏向NW;靠东南部出现了多变的方向.井下实测数据与震源机制解相比在部分区域一致性较好,而在另一些区域存在明显的差异.特别是在受较大地质构造影响的区域,水平主应力方向往往发生明显的扭转和变化. 相似文献
2.
A new method for obtaining from volcanic surface features the orientations of the principal tectonic stresses is applied to Aleutian and Alaskan volcanoes. The underlying concept for this method is that flank eruptions for polygenetic volcanoes can be regarded as the result of a large-scale natural magmafracturing experiment. The method essentially relies on the recognition of the preferred orientation of radial and parallel dike swarms, primarily using the distribution of monogenetic craters including flank volcanoes. Since dikes tend to propagate in a direction normal to the minimum principal stress (T-axis), the method primarily yields the direction of the maximum horizontal compression (MHC) of regional origin. The direction of the MHC may correspond to either the maximum (P-axis) or intermediate (B-axis) principal stress.The direction of MHC obtained at 20 volcanoes in the Aleutian arc coincides well with the direction of convergence between the Pacific and North American plates. This result provides evidence that in the island arc the inferred direction of MHC is parallel to the maximum principal tectonic stress. In the back-arc region, general E-W trends of MHC are obtained from seven volcanic fields on islands on the Bering Sea shelf and the mainland coast of Alaska. These volcanic fields consist mostly of clusters of monogenetic volcanoes of alkali basalt. In the back-arc region, the trends of MHC may correspond to an E-W intermediate, a vertical maximum, and a N-S minimum principal stress.Implications for the tectonics of island arcs and back-arc regions are: (1) volcanic belts of some island arcs, including the Aleutian arc, are under compressional deviatoric stress in the direction of plate convergence. It is improbable that such arcs would split along the volcanic axis to form actively spreading marginal basins. (2) This compressional stress at the arc, probably generated by underthrusting, appears to be transmitted across the entire arc structure, but is apparently replaced within several hundred kilometers by a stress system characterized by horizontal extension (tensional deviatoric stress) in the back-arc region. (3) The volcanoes associated with these two stress systems differ in type (polygenetic vs. monogenetic) and in the chemistry of their magmas (andesitic vs. basaltic). These differences and the regional differences in orientation of the principal tectonic stresses suggest that the back-arc stress system has its own source at considerable depth beneath the crust.Lamont-Doherty Geological Observatory Contribution No. 2503. 相似文献
3.
本文根据1975-1984年期间发生的多个小地震的P波初动方向数据,推断了青、甘、川、滇地区平均主应力轴的方向。结果表明,该地区压应力轴（P轴）和张应力轴（T轴）方向皆水平,但其方位由北到南呈现规则转动的趋势,即主压应力轴在北部青甘地区大致取NE-SW方向,到中部川西北地区转为近E-W方向,再到南部云南地区转为NNW-SSE或近N-S方向。形成应力轴方向这样特定分布图象的原因,可用印度板块向北对青藏高原的推挤和缅甸中源地震带地区下沉物质对云南地区的拖曳作用来解释。 相似文献
4.
Zoltán Wéber 《Journal of Seismology》2016,20(3):987-999
Between 2013 June and 2015 January, 35 earthquakes with local magnitude M L ranging from 1.1 to 4.2 occurred in Nógrád county, Hungary. This earthquake sequence represents above average seismic activity in the region and is the first one that was recorded by a significant number of three-component digital seismographs in the county. Using a Bayesian multiple-event location algorithm, we have estimated the hypocenters of 30 earthquakes with M L ≥1.5. The events occurred in two small regions of a few squared kilometers: one to the east of Érsekvadkert and the other at Iliny. The uncertainty of the epicenters is about 1.5–1.7 km in the E-W direction and 1.8–2.1 km in the N-S direction at the 95 % confidence level. The estimated event depths are confined to the upper 3 km of the crust. We have successfully estimated the full moment tensors of 4 M w ≥3.6 earthquakes using a probabilistic waveform inversion procedure. The non-double-couple components of the retrieved moment tensor solutions are statistically insignificant. The negligible amount of the isotropic component implies the tectonic nature of the investigated events. All of the analyzed earthquakes have strike-slip mechanism with either right-lateral slip on an approximately N-S striking or left-lateral movement on a roughly E-W striking nodal plane. The orientations of the obtained focal mechanisms are in good agreement with the main stress pattern published for the epicentral region. Both the P and T principal axes are horizontal, and the P axis is oriented along a NE-SW direction. 相似文献
5.
The source mechanism of 19 earthquakes that occurred in Peru (1990–1996) is studied using broad band data. Focal mechanisms are obtained using polarities of P wave and body wave form inversion. Shallow earthquakes show complex source time functions, intermediate and deep depth shocks have simpler ones. Stress distributions have been obtained from focal mechanisms estimated in this study and previous studies. Shallow earthquakes show reverse faulting with an ENE-WSW to E-W oriented pressure axes. Intermediate depth shocks indicate horizontal extension on E-W direction, normal to the Peru-Chilean trench. Earthquakes with foci at very deep depth show horizontal extension in the E-W direction in Peru-Brazil and N-S in Peru-Bolivia borders. This difference in stress orientation may indicate a different origin for deep activity at each region. 相似文献
6.
Pavel Peška 《Studia Geophysica et Geodaetica》1993,37(2):141-150
Summary A set of overcoring measurements in deep mines near Píbram is re-interpreted in order to obtain information on the regional component of in situ stress. This is achieved by averaging 17 complete stress tensors measured at the deepest level of the mine, at a depth of 1240 m. The computations indicate that (1) the mean principal stresses act roughly in the horizontal and vertical directions, and (2) the maximum principal stress is horizontal, acting NW - SE, which was also confirmed by the data from all 42 sites of the mine area. The NW - SE orientation of SH is consistent with the stress pattern in Western Europe and also with borehole breakouts observed within the Bohemian Massif, but the quality of the stress indicator obtained is poor — the standard deviation of the SH direction is 26°. High variance of the directional data is discussed with respect to stress redistribution due to the mine workings and the contact separating Proterozoic sediments from the Variscan pluton. 相似文献
7.
在距唐山地震震源约百公里的大港油田,以水压致裂法,在深度1000——4000米之间,测定了69次地应力值,对比了1973——1980年大地震前后八年内的应力值变化.在主震前,构造应力场出现明显变化:(1)水平应力梯度降低,即在最大与最小水平主应力方向呈现应力松弛;(2)水平应力与深度的相关系数降低,即构造应力场受到扰动;(3)断层滑动系数增高,断层出现无震蠕动.此外,结合地质构造与应力测量结果,对唐山地震发生过程中的一些异常现象,如无震蠕动、地下水位变化、浅层和外围地区的应力松弛,以及应力沿断层面向深层和闭锁区的转移等,进行了分析和讨论. 相似文献
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SUN DongSheng LIN WeiRen CUI JunWen WANG HongCai CHEN QunCe MA YinSheng WANG LianJie 《中国科学:地球科学(英文版)》2014,57(6):1212-1220
In situ stress state becomes more and more significant with in-depth research on geodynamics and energy development.However,there has not been an economic and effective method developed to determine deep three-dimensional in situ stress.The Anelastic Strain Recovery(ASR)method is a newly developed technique that can determine three-dimensional in situ stresses.After the 12 May 2008 Ms8.0 Wenchuan earthquake,the ASR method was used for the first time in mainland China to measure the in situ stresses in the WFSD scientific boreholes in Sichuan Province,China.In this paper,the basic procedure of the ASR method is introduced in detail and the compliances of ASR for boring cores are investigated.The results show that the maximum principal stress direction was NW64°at a measured depth(MD)of 1173 m(vertical depth 1151 m)in WFSD-1.The ratio of shear mode to the volume mode compliance of ASR was 2.9.And the three principal stresses at 1173 m MD in WFSD-1are 43,28 and 25 MPa.Combined with stress measurement results determined using other in situ measurement methods along the Longmenshan fault zone,the directions of the maximum horizontal principal stress changes from E-W to NEE-SWW to NWW-SEE when moving from NE to SW along the Longmenshan fault zone.This change is in agreement with the stress regime of the Longmenshan fault zone of the Wenchuan Earthquake,which supports a stress regime consisting predominantly of thrusts in the southwest and strike-slip in the northeast. 相似文献
10.
Use of the hydraulic fracturing technique for determiningin situ stress is reviewed, and stress measurements in wells near the towns of Livermore, San Ardo, and Menlo Park, California are described in detail. In the Livermore well, four measurements at depths between 110 and 155 m indicate that the least principal compressive stress is horizontal and increases from 1.62 to 2.66 MPa. The apparent direction of maximum compression is N 70° E (±40°). At the San Ardo site the least principal stress is that due to the overburden weight. At depths of 240.2 and 270.7 m the minimum and maximum horizontal stresses are estimated to be 11.4 and 22.5 MPa, and 12.0 (±1.1) and 15.8 (±3.3) MPa, respectively. From an impression of the fracture at 240.2 m, the direction of maximum compression appears to be about N 15° E. The rock in the Menlo Park well is too highly fractured to yield a reliable measurement of the horizontal stresses. The data indicate, however, that the least principal stress is vertical (due to the overburden weight) to a depth of 250 m. 相似文献
11.
The values of maximum tangential stresses, as well as their spatial orientations, are calculated at each point of the mantle. These calculations are performed for successive stages of the supercontinental cycle in terms of a numerical 2-D model of assembling and diverging continents driven by mantle flows; in turn, the flows themselves are formed under the thermal and mechanical action of continents. Zones of maximum tangential stresses, within which their values are equal to or exceed 30 MPa (300 bar), are shown to be located in places where ascending or descending mantle flows approach the horizontal mantle boundaries. These zones have the shape of a bowl with the broad side toward the boundary, and their maximum tangential stresses are oriented at an angle of about 45° to the horizontal. The dimensions of these zones amount approximately to 300 km laterally and 300 km in depth. Their subhorizontal and subvertical tangential stresses are close to zero. It is also shown that the stress values vary significantly during the evolution of the suboceanic mantle under a new opening ocean (after the breakup of a supercontinent). Thus, the maximum tangential stresses in this vast mantle region at the stage of fast ocean opening are, on average, more than two times higher than at the subsequent slow stage. Note that, at all stages, the axes of the maximum tangential stresses are oriented nearly horizontally or vertically almost throughout the aforementioned area. 相似文献
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Abstract The Nojima Fault in Awaji, Hyogo prefecture, Japan, was ruptured during the 1995 Hyogo-ken Nanbu earthquake ( M JMA = 7.2). Toshima is located close to the fault segment, in which a large dislocation has been observed on the Earth's surface. Ikuha is near the southern end of the buried fault that extends from the surface rupture. Stresses are measured on core samples taken at depths of 310 m, 312 m and 415 m at Toshima and a depth of 351 m at Ikuha. The measured stresses show that both sites are in the field of a strike–slip regime, but compression dominates at Toshima. Defining the relative shear stress as the maximum shear stress divided by the normal stress on the maximum shear plane, the relative shear stress ranges from 0.42 to 0.54 at Toshima and is approximately 0.32 at Ikuha. While the value at Ikuha is moderate, those at Toshima are comparably large to those in areas close to the inferred fault of the 1984 Nagano-ken Seibu earthquake. Value amounts greater than 0.4 suggest that there are areas of large relative shear stress along faults, thus having the potential to generate earthquakes. Provided that the cores are correctly oriented, the largest horizontal stresses at shallow depths are in the direction from N113°E to N139°E at Toshima and N74°E at Ikuha, indicating that the fault does not orient optimally for the stress field at both sites. The slip is known to be predominant in the right-lateral strike–slip component. Although this slip may appear contradictory to the stress field at Toshima, the slip direction is found to be parallel to the measured stresses resolved on the fault plane for the first approximation. The ratio of shear stress to normal stress on the fault plane is roughly estimated to be greater than zero and smaller than 0.3 near Toshima. 相似文献
14.
日本本州及其邻近区域的应力状态以及弧后盆地的演化机制一直是人们所关注的问题.本文对2011年3月11日东日本大地震地震序列(2011年3月11日至2012年3月15日)的哈佛双力偶解进行了聚类分析,得到五种类型的震源机制解:与主震类型一致的低倾角逆断层型地震;主张应力方向垂直于日本海沟走向的正断层型地震;主张应力方向平行于日本海沟走向的正断层型地震;主压应力方向平行于日本海沟走向的逆断层型地震;包括走滑型地震在内的其他类型地震.东日本大地震地震序列中发生在弧前增生楔地震的震源机制解与大地震发生之前地震的震源机制解特征有显著区别,反映出该地区的应力状态与震前相比有较大改变.东日本大地震及其前震释放了附近区域的累积弹性应力,主震破裂区附近太平洋板块和其上覆板块接近完全解耦,降低了日本海盆地、中国东北地区的近东西向挤压应力水平.不过,整个本州岛东部区域太平洋板块和其上覆板块并没有完全解耦,但应力水平并不高.我们认为,日本海及中国东北应力水平的降低会使该区域的近东西向挤压型地震的危险性降低,而使NNE-SSW走向的走滑型地震活动性增强.同时,火山活动性也会增强.尤其是本州岛地区,存在近期火山爆发的可能性.东日本大地震地震序列的震源机制解特征还提示我们,日本海的应力状态及日本海的演化可能在一定程度上取决于太平洋板块和上覆板块的耦合状态.持续的弱耦合将不仅使得弧后大范围的地区保持岩浆上涌所必须的拉伸应力环境,而且还会因弧前隆起区发育大量正断层型地震而向深部提供促使岩浆生成所必须的水,因而造成日本海的再次扩张. 相似文献
15.
Shahrokh Pourbeyranvand 《Acta Geophysica》2018,66(6):1273-1290
The Alborz is one of the most important seismotectonic provinces in Iran. Furthermore, emplacement of Tehran as a mega city in southern part of the Alborz intensifies the seismic vulnerability in this area. In this study, the focal mechanism data from teleseismic and local seismic networks are used for stress tensor inversion. The earthquake focal mechanisms in the Central Alborz are divided into several groups with respect to their location. Two different stress tensor inversions, linear and nonlinear, are used for obtaining the principal stress orientations. The results show spatial variations in tectonic stress field, consistent with fault orientations and faulting mechanisms. The maximum compressional stress directions obtained in this study are confirmed by fast S-wave polarization axes reported by a previous shear wave splitting study. The maximum horizontal stress directions are also compared with GPS strain rates. The results indicate a partitioning of deformation in the area due to regional stresses along preexisting faults. 相似文献
16.
The andesitic stratovolcano Volcán de Colima is one of the most active volcanoes in Mexico. The recent eruption of Volcán de Colima began in November 1998 and was preceded by a 12-month period of seismic activity that included five earthquake swarms. About 600 events with magnitudes from -0.5 to 2.7 were located within a 50-km2 area extending northward from the crater of Volcán de Colima to the Pleistocene volcano Nevado de Colima. The majority of hypocenters within this area did not exceed 5 km depth below sea level. We investigated earthquake focal mechanisms and seismotectonic deformations of the volcanic edifice. Focal mechanisms during four earthquake swarms indicated normal faulting associated with extensional processes, which is in agreement with the general stress regime near the volcano revealed by field measurements of fault slips. Earthquakes in the fifth swarm had focal mechanisms associated with inverse faulting, showing a significant change in the stress situation just before the beginning of the eruption. The calculated deformations varied from 1.3᎒-11 to 2.7᎒-9. The first swarm of November-December 1997 resulted in a N-S horizontal elongation that was two times greater than the E-W horizontal shortening. The volume was also subject to vertical shortening. The second and third swarms, observed in March and May 1998, showed uniform horizontal N-S and E-W elongations accompanied by a vertical elongation of the volume. In June-July 1998, the situation of November-December 1997 was repeated, with N-S horizontal elongation greater than the E-W horizontal shortening of the volume accompanied by intensive vertical shortening. During the last swarm of October-November 1998, slight E-W elongation of the seismic volume was accompanied by strong N-S shortening and very slight vertical shortening. We assume that the seismic activity prior to the 1998 eruption of Volcán de Colima developed along two intersecting tectonic structures, the N-S-trending Colima rift, and the E-W-trending system of faults associated with Tamazula fault. During the first stage (November 1997-July 1998) the passageway for magma was developed along the Tamazula fault system under horizontal extension without any surface manifestation. In October-November 1998, the seismic events began to cluster along the Colima rift structures under predominantly compressional stresses; this condition culminated with the extrusion of andesitic block lava from the summit crater. 相似文献
17.
Zhigang Xu Zhouchuan Huang Liangshu Wang Mingjie Xu Zhifeng Ding Pan Wang Ning Mi Dayong Yu Hua Li 《地震科学（英文版）》2016,29(2):105-115
We applied the g CAP algorithm to determine239 focal mechanism solutions 3:0 M We 6:0T with records of dense Chin Array stations deployed in Yunnan,and then inverted 686 focal mechanisms(including 447 previous results) for the regional crustal stress field with a damped linear inversion. The results indicate dominantly strike-slip environment in Yunnan as both the maximum(r1) and minimum(r3) principal stress axes are sub-horizontal. We further calculated the horizontal stress orientations(i.e., maximum and minimum horizontal compressive stress axes: S H and S h, respectively) accordingly and found an abrupt change near *26°N. To the north, S H aligns NW-SE to nearly E-W while S h aligns nearly N-S. In contrast, to the south, both S H and S h rotate laterally and show dominantly fan-shaped patterns. The minimum horizontal stress(i.e., maximum strain axis) S h rotates from NW-SE to the west of Tengchong volcano gradually to nearly E-W in west Yunnan, and further toNE-SW in the South China block in the east. The crustal strain field is consistent with the upper mantle strain field indicated by shear-wave splitting observations in Yunnan but not in other regions. Therefore, the crust and upper mantle in Yunnan are coupled and suffering vertically coherent pure-shear deformation in the lithosphere. 相似文献
18.
西沙群岛独特的构造位置决定了其构造运动背景和地壳应力场动力源的复杂性.位于西沙群岛石岛、深达1268.07m的西科1A井在1257.52m钻遇花岗岩基底.在1125.8~1262.0m开展5次水压致裂地应力测量,获得最大水平主应力为17.09~20.85MPa,最小水平主应力为15.97~18.29MPa,估算垂直主应力为22.86~26.68 MPa,地壳应力结构为SVSHSh,以垂直主应力为主导,该应力结构特征有利于正断层活动,表明西沙群岛地壳基底处于拉张的应力环境.受西沙海槽断层影响,水平应力值较低.印模测试显示基底地壳应力方向以近东西-北西向为主,与已有的GPS测量、横波分裂和面波反演结果较为吻合,显示西沙群岛岩石圈尺度上变形一致性较好.西沙群岛地壳应力场的力源受板块运动和地幔物质上涌作用联合制约.综合南海西北部实测地应力数据分析,显示该区域主应力方向较为一致,应处于统一、稳定的构造运动背景之中.西科1A井水压致裂试验是我国首次涉海深孔地壳应力测量,具有重要的地球动力学意义,提供了研究南海地球物理场的宝贵基础资料. 相似文献
19.
A geochronological and structural study of dykes is used in order to define the stress field in Sardinia. The Plio-quaternary volcanism of Sardinia (between 5 and <0.2 My old) is mostly fissural and contemporaneous with an intraplate regime which reactivated normal faults of various orientations. Dykes in the Logudoro, Montiferro and Monte Arci areas (west-central and northern Sardinia) are 3.4 to 1.8 My old. Their orientations vary around a north-south mean direction which is the most frequent in the Tyrrhenian Basin. The reactivation of normal faults of various orientations may be linked to a stress regime characterised by a maximum vertical principal stressσ 1 and horizontal principal stressesσ 2 andσ 3 having close values and which can easily interchange. In these conditions, the magmatie liquid can intrude into preexisting fractures of different orientations, especially into the fractures that have an orientation close to the planeσ 1 σ 2 (with N-S orientation in Sardinia). This plane is concordant with the convergent motion of Europe and Africa plates. The influence of the pre-existing fractures on dyke orientations seems more important in this area than in southern France where there is a different tectonic regime (Féralt) andCampredon, 1983). 相似文献
20.
利用法国斯仑贝谢公司在我国四川油气井服务时所作的四臂井径测井曲线,分析了四川盆地中井位附近的地壳水平主应力方向.共分析了12口井的井径测量曲线,测量深度从地表下约2,000m至4,700m,各井的测量段从50m左右至1,360m不等.编制了对测量曲线采样、插值并作简单统计处理,从而获得崩落孔孔径平面投影图的计算机程序.处理结果表明,大多数孔显示了NNW-SSE或近N-S向的优势崩落方向,说明四川盆地最小水平主应力即为此方向.此结果与由平均震源机制结果得出的四川附近地壳区域应力场图象大体协调一致. 相似文献