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1.
本文介绍了在断层区的岩体中进行的现场大尺度摩擦实验。实验的目的是探索地壳中变形波的存在。实验结果表明,在加载时断层泥屈服时间不一致,加载一端的断层泥先屈服,然后屈服范围逐步扩大,此过程相应于塑性变形波在断层泥中的传播。实验测得试件中塑性变形波波速约为2—3 cm/min,实际相当于10—16km/year。  相似文献   

2.
This paper reports internal structures of a wide fault zone at Shenxigou, Dujiangyan, Sichuan province, China, and high-velocity frictional properties of the fault gouge collected near the coseismic slip zone during the 2008 Wenchuan earthquake. Vertical offset and horizontal displacement at the trench site were 2.8 m (NW side up) and 4.8 m (right-lateral), respectively. The fault zone formed in Triassic sandstone, siltstone, and shale about 500 m away from the Yingxiu-Beichuan fault, a major fault in the Longmenshan fault system. A trench survey across the coseismic fault, and observations of outcrops and drill cores down to a depth of 57 m revealed that the fault zone consists of fault gouge and fault breccia of about 0.5 and 250–300 m in widths, respectively, and that the fault strikes N62°E and dips 68° to NW. Quaternary conglomerates were recovered beneath the fault in the drilling, so that the fault moved at least 55 m along the coseismic slip zone, experiencing about 18 events of similar sizes. The fault core is composed of grayish gouge (GG) and blackish gouge (BG) with very complex slip-zone structures. BG contains low-crystalline graphite of about 30 %. High-velocity friction experiments were conducted at normal stresses of 0.6–2.1 MPa and slip rates of 0.1–2.1 m/s. Both GG and BG exhibit dramatic slip weakening at constant high slip rates that can be described as an exponential decay from peak friction coefficient μ p to steady-state friction coefficient μ ss over a slip-weakening distance D c. Deformation of GG and BG is characterized by overlapped slip-zone structures and development of sharp slickenside surfaces, respectively. Comparison of our data with those reported for other outcrops indicates that the high-velocity frictional properties of the Longmenshan fault zones are quite uniform and the high-velocity weakening must have promoted dynamic rupture propagation during the Wenchuan earthquake.  相似文献   

3.
ZHOU Yong-sheng 《地震地质》2019,41(5):1266-1272
Paleo-seismic and fault activity are hard to distinguish in host rock areas compared with soft sedimentary segments of fault. However, fault frictional experiments could obtain the conditions of stable and unstable slide, as well as the microstructures of fault gouge, which offer some identification marks between stick-slip and creep of fault. We summarized geological and rock mechanical distinction evidence between stick-slip and creep in host rock segments of fault, and analyzed the physical mechanisms which controlled the behavior of stick-slip and creep. The chemical composition of fault gouge is most important to control stick-slip and creep. Gouge composed by weak minerals, such as clay mineral, has velocity weakening behavior, which causes stable slide of fault. Gouge with rock-forming minerals, such as calcite, quartz, feldspar, pyroxene, has stick-slip behavior under condition of focal depth. To the gouge with same chemical composition, the deformation mechanism controls the frictional slip. It is essential condition to stick slip for brittle fracture companied by dilatation, but creep is controlled by compaction and cataclasis as well as ductile shear with foliation and small fold. However, under fluid conditions, pressure solution which healed the fractures and caused strength recovery of fault, is the original reason of unstable slide, and also resulted in locking of fault with high pore pressure in core of fault zone. Contrast with that, rock-forming minerals altered to phyllosilicates in the gouges by fluid flow through degenerative reaction and hydrolysis reaction, which produced low friction fault and transformations to creep. The creep process progressively developed several wide shear zones including of R, Y, T, P shear plane that comprise gouge zones embedded into wide damage zones, which caused small earthquake distributed along wide fault zones with focal mechanism covered by normal fault, strike-slip fault and reverse fault. However, the stick-slip produced mirror-like slide surfaces with very narrow gouges along R shear plane and Y shear plane, which caused small earthquake distributed along narrow fault zones with single kind of focal mechanism.  相似文献   

4.
断层岩,尤其是断层泥的磁性异常近年来被研究人员广泛关注,但关于其磁性异常的形成原因尚没有统一的解释．海原断裂是青藏高原东北缘一条重要的走滑断裂,前期研究发现海原断裂带景泰段出露有数十米至上百米的断层岩,是理想的研究材料．本研究选取海原断裂带景泰段老虎山山前一个断层岩剖面作为研究对象,拟通过测量断层岩的磁化率（χ）、非磁滞剩磁（ARM）、饱和等温剩磁（SIRM）、等温剩磁（IRM）以及磁化率随温度变化曲线（χ-T曲线）等磁学参数并结合粒度、碳含量、X射线衍射（XRD）等分析方法来探究海原断裂带老虎山段不同颜色断层岩的磁性特征及其形成机制．磁学研究显示黑色、红色及杂色断层泥相较于围岩和破碎带显示了低磁性,尤其是黑色断层泥,其磁化率值均小于10×10~(-8 )m~3·kg~(-1)．碳含量及矿物相分析结果指示黑色断层泥与断裂带附近石炭系煤层具有相似的矿物相组成,结合相似的χ-T曲线推断石炭系煤层为黑色断层泥的母岩．石炭系煤层经断层活动卷入断层,在断层强烈剪切摩擦作用下不断细化,形成伊利石等黏土矿物,并促使一部分顺磁性含铁硅酸盐矿物或其他含铁矿物发生化学变化形成亚铁磁性矿物,使得黑色断层泥的磁化率较其母岩石炭系煤层有一定升高．通过黑色断层泥的铁磁性磁化率结合χ-T曲线计算获得断层泥所经历的最高温度约为420℃,不超过450℃．老虎山段厚层碳质断层泥的存在为该地区发现的浅层蠕滑现象提供了一种解释．  相似文献   

5.
The viscosity of natural rhyolitic melt from Lipari, Aeolian Islands and melt-bubble emulsions (30–50 vol% porosity) generated from Lipari rhyolite have been measured in a concentric cylinder rheometer at temperatures and shear rates in the range 925–1150°C and 10−3–10−1.2 s−1, respectively, in order to better understand the dependence of emulsion shear viscosity on temperature and shear rate in natural systems. Bubble-free melt exhibits Newtonian–Arrhenian behavior in the temperature range 950–1150°C with an activation energy of 395±30 kJ/mol; the shear viscosity is given by log ηm=−8.320+20624/T. Suspensions were prepared from natural rhyolite glass to which small amounts of Na2SO4 were added as a ‘foaming agent’. Reasonably homogeneous magmatic mixtures with an approximate log-normal distribution of bubbles were generated by this technique. Suspension viscosity varied from 106.1 to 108.37 Pa s and systematically correlates with temperature and porosity in the shear stress range (104.26–105.46 Pa) of the experiments. The viscosity of melt-bubble emulsions is described in terms of the relative viscosity, ηr=ηe/ηm where ηe is the emulsion viscosity and ηm is the viscosity of melt of the same composition and temperature. The dependence of relative viscosity on porosity for magmatic emulsions depends on the magnitude of the capillary number Ca≡G/(σrb−1ηm−1), the ratio of viscous forces acting to deform bubbles to interfacial forces resisting bubble deformation. For inviscid bubbles in magmatic flows three regimes may be identified. For Ca<0.1, bubbles are nearly spherical and relative viscosity is an increasing function of porosity. For dilute systems, ηr=1+φ given by the classical result of Taylor [Proc. R. Soc. London A 138 (1932) 41–48]. For Ca in the range 0.1<Ca<10, emulsions behave as power law fluids and the relative viscosity depends on shear rate (or Ca) as well as porosity. At high Ca (Ca>10) an asymptotic regime is reached in which relative viscosity decreases with increasing porosity and is independent of Ca. Our experiments were carried out for 30<Ca<925 in order to quantify the maximal effect of bubbles in reducing the viscosity of magmatic emulsions relative to single-phase melt at identical conditions of shear rate and temperature. The viscosity of a 50 vol% emulsion is a factor of five smaller than that of melt alone. Rheometric measurements obtained in this study are useful in constraining models of magma transport and volcanic eruption mechanics relevant to transport of volatile-saturated magma in the crust and upper mantle.  相似文献   

6.
The viscosity of lower crust of Qinghai-Tibet Plateau on earth should be determined. It has become a predominant problem in quantitative research on geodynamics. Its order of magnitude will have a great influence on the results of quantitative modeling. To obtain the viscosity of lower crust of Qinghai-Tibet Plateau, this parameter was calculated by three methods. The first is based on the estimation on the temperature state of Qinghai-Tibet Plateau in the deep part, and the viscosity of lower crust of northern Plateau was recomputed with strain rate derived from rheology law and GPS observation. Effective viscosity of middle crust in Kunlun region is between 1020 and 1022 Pa·s, and that of lower crust is between 1019 and 1021 Pa·s; the second is based on three kinds of rheological models used to fit the post-seismic deformation recorded by cross-over fault GPS sites set after M s8.1 Kunlun earthquake in 2001. The viscosity of lower crust obtained by this method is of 1017 Pa·s order of magnitude. However, higher viscosity is required to fit the data of south fault better, and the lower one is required to fit the data of north fault better. The viscosity of lower crust, which was obtained by fitting the cross-over fault post-seismic deformation after M s7.6 Luhuo earthquake in 1973, is of 1019 Pa·s order of magnitude. Non-linear relationship between effective viscosity and strain rate is ignored in the former research of effective viscosity. This research shows the difference of effective viscosity obtained from laboratory experiment, and shorter and longer time post-seismic deformation after large earthquakes can be explained in phase. Supported by National Basic Research Program of China (Grant No. 2004CB418405), National Natural Science Foundation of China (Grant No. 40774048), Important Direction Item of Knowledge Innovation Project of Chinese Academy of Sciences (Grant No. KZCX2-YW-123) and Basic Scientific Research Project of Earthquake (Grant No. 02076902-05)  相似文献   

7.
—A microphysical model of seismic wave attenuation is developed to provide a physical basis to interpret temperature and frequency dependence of seismic wave attenuation. The model is based on the dynamics of dislocation motion in minerals with a high Peierls stress. It is proposed that most of seismic wave attenuation occurs through the migration of geometrical kinks (micro-glide) and/or nucleation/migration of an isolated pair of kinks (Bordoni peak), whereas the long-term plastic deformation involves the continuing nucleation and migration of kinks (macro-glide). Kink migration is much easier than kink nucleation, and this provides a natural explanation for the vast difference in dislocation mobility between seismic and geological time scales. The frequency and temperature dependences of attenuation depend on the geometry and dynamics of dislocation motion both of which affect the distribution of relaxation times. The distribution of relaxation times is largely controlled by the distribution in distance between pinning points of dislocations, L, and the observed frequency dependence of Q, Q, Q∝ωα is shown to require a distribution function of P(L)∝L -m with m=4-2α The activation energy of Q ?1 in minerals with a high Peierls stress corresponds to that for kink nucleation and is similar to that of long-term creep. The observed large lateral variation in Q ?1 strongly suggests that the Q ?1 in the mantle is frequency dependent. Micro-deformation with high dislocation mobility will (temporarily) cease when all the geometrical kinks are exhausted. For a typical dislocation density of ～ 108 m?2, transient creep with small viscosity related to seismic wave attenuation will persist up to the strain of ～ 10?6, thus even a small strain (～ 10?6?10?4) process such as post-glacial rebound is only marginally affected by this type of anelastic relaxation. At longer time scales continuing nucleation of kinks becomes important and enables indefinitely large strain, steady-state creep, causing viscous behavior.  相似文献   

8.
This study aims to assess whether luminescence emission from fault gouge samples from the San Andreas Fault Observatory at Depth (SAFOD) can be used to determine the age distribution of distinct deformation microstructures. Such age determination could help constrain some of the proposed micromechanical models for shear localization in fault gouge, in addition to providing more accurate time constraint on the seismic cycle itself. The mechanism by which previously trapped charge is reset in minerals in fault gouge is thought to be a combination of frictional heating and mechanical deformation, and these processes may be localized to grain surfaces. An added dating complexity specific to deep samples is the high ambient temperature conditions, which act as a barrier to charge storage in lower energy trapping sites. In this work luminescence experiments are being conducted on minerals from whole-rock samples of intact fault gouge from the SAFOD Phase III core. Initial studies indicate (i) the thermal and radiation history of the mineral lattice can be assessed with TL, (ii) trap resetting is evident in both TL and IRSL data, (iii) a small charge-trapping window between drill hole ambient temperature of ∼112 °C and higher energy lattice excitation via rupture events is evident in TL data from ∼300 to 400 °C, and we tentatively link the source of IRSL to TL within this 300–400 °C region, (iv) IRSL data have low natural intensity but good luminescence characteristics, and (v) SAR IRSL De data have high over-dispersion but demonstrate ages ranging from decades to centuries may be measured.  相似文献   

9.
本文利用德国Wissel公司生产的新型穆斯堡尔谱仪(Bench-MB500)对山东龙口常庄子村北黄县弧形断裂断层剖面上的多种断层泥样品进行了穆斯堡尔谱测试分析,讨论了该断层剖面上铁元素地球化学分布特征及其地震地质意义。结果显示,该断裂中央部分比较年轻的断层泥相对富集para-Fe~(2+),而两侧较老的断层泥基本由para-Fe~(3+)组成;剖面断层泥样品中铁元素的地球化学特征与断层的活动演化历史密切相关,显示了断裂带内存在复杂的水岩相互作用。  相似文献   

10.
以走滑型地震为例提出了震源孕育的三维组合模式．在以往的组合模式基础上增加了震源下部的应力调整单元．这一应力调整单元由流变介质组成,孕震时不积累应力,而是将应力转移至上部的应力积累单元;在发震时该单元以其特有的粘滞性可以止裂;震后以其变形的时间依赖性可以控制余震发生．该调整单元的作用可以由地震后断层的蠕动曲线得到部分验证．  相似文献   

11.
Measurements were made of the amounts of D,18O, and H2O+ in fault gouge collected over a depth of 400 m in the San Andreas fault of California. The amounts and isotopic compositions of the pore fluids, also analyzed, suggest that formation waters from adjacent Franciscan rocks have migrated into the gouge and mixed with local meteoric water. Thus the gouge is an open system permeable to fluid flow. This permeability has important implications concerning heat flow along the fault zone.Analyses of the fault gouge itself give information on the amounts, timing, and conditions of formation of the clay minerals.Stable-isotope analyses of materials from fault zones are good indicators of water-rock interactions that bear importantly on processes taking place in seismically active regions.  相似文献   

12.
高温高压下红河断裂带断层泥力学性质的研究   总被引：2，自引：0，他引：2       下载免费PDF全文
断层泥在室温高压下的应力-应变曲线呈非线性、线性等阶段性变形,在高温高压下则呈非线性变形,两者均表现出渐进破坏。含水量、矿物成分和温压条件对变形特征和破坏强度有重要影响。曲线的初始弹性模量小于有效弹性模量。断层泥在温度T≥400℃和σ_3≥300MPa时发生岩化,据此岩化温压条件可估计出未岩化断层泥存在深度将不超过10—15km。由于断层泥具渐进破坏特征,故在高温高压条件下断层泥有利于断层活动呈现稳滑  相似文献   

13.
An improved understanding of postseismic crustal deformation following large subduction earthquakes may help to better understand the rheological properties of upper mantle and the slip behavior of subduction interface. Here we construct a three-dimensional viscoelastic finite element model to study the postseismic deformation of the 2014 MW8.1 Iquique, Chile earthquake. Elastic units in the model include the subducting slab, continental and oceanic lithospheres. Rheological units include the mantle wedge, the oceanic asthenosphere and upper mantle. We use a 2 ​km thick weak shear zone attached to the subduction fault to simulate the time-dependent stress-driven afterslip. The viscoelastic relaxation in the rheological units is represented by the Burgers rheology. We carry out grid-searches on the shear zone viscosity, thickness and viscosity of the asthenosphere, and they are determined to be 1017 ​Pa ​s, 110 ​km and 2 ​× ​1018 ​Pa ​s, respectively. The stress-driven afterlsip within the first two years is up to ~47 ​cm and becomes negligible after two years (no more than 5 ​cm/yr). Our results suggest that a thin, low-viscosity oceanic asthenosphere together with a weak shear zone attached to the fault are required to better reproduce the observed postseismic deformation.  相似文献   

14.
The viscosity of earth medium can explain many geophysical phenomena. The uplifting velocity of Ti- betan Plateau may be caused by extrusion of the low viscosity channel in middle and lower crust[1]. The post-deformation after earthquake also relates to the rheology of earth medium[2]. The aftershock sequence is considered a process of strain release after stress dropped[3]. There are two kinds of models in the study of rheological character of crustal medium, elastoplas- only when the forced…  相似文献   

15.
In coseismic surface rupture zones caused by the 2008 Mw 7.9 Wenchuan earthquake, some thin-layered fault gouges with strong deformation were observed in different locations. In this paper, fault gouge samples were taken as research objects from the Bajiaomiao village in the south-west segment of the principal rupture and the Heshangping village and the Shaba village in the north-east segment of the principal rupture where larger displacements were measured. Fabric characteristics of the fault gouge samples and the morphologies and structures of micro-nanometer grains on Y-shear surfaces were then analyzed by using a stereoscope and SEM. Observation results showed that obvious Y- and R-shears and obvious scratches were well developed in coseismic gouges caused by the 2008 Wenchuan earthquake. Micro-nanometer grains in the fault gouge of the Wenhcuan earthquake were formed mainly due to breaking, grinding, and powdering of fault slipping friction surface. Heat caused by fault slipping (maybe also including heat caused by thermal decomposition) played an important role in producing micro-nanometer sized grains. Existence occurrence state of micro-nanometer sized grains on fault slip surface includes singled grains and their complexes with shapes of ball, silkworm, pancake and mass. The structures mainly include dispersed and close-packed structures besides a few of striped and layered structures. All these structures were formed at the extreme unbalance conditions caused by rapid deforming during an earthquake. There always exist some voids between structures due to loosely contact. Only alienated grains are included in the stripped structure. But there are some singled grains with no deformation in dispersed and close-packed structures besides complexes of grains with morphologies of ball, silkworm, pancake and mass. The striped and close-packed structures are the results of plastic deformation, and the dispersed and layered structures are the results of brittle deformation whereas loose contact of different structures was caused mainly by discontinuous dynamic friction (fault stick-slipping). The structures of the micro-nanometer sized grains in coseismic fault gouge caused by the Wenchuan earthquake are the geological records of seismic fault slipping (it is not pseudotachylite), which could be used as an index of paleo-seismic events.  相似文献   

16.
A number of finite-element calculations of convection in a variable-viscosity fluid have been carried out to investigate the effects of non-Newtonian flow when rheology is also subject to a strong temperature and pressure influence. A variety of cases has been studied in the range of effective Rayleigh numbers between 104 and 106, including different modes of heating and a range of values for activation energy and activation volume. Power-law creep with a stress exponent of 3 turns out to lead to considerably different flow pattern and heat transfer properties than Newtonian rheology. In general, the effect is to reduce viscosity contrasts imposed by p,T dependence, which can lead in some circumstances to the mobilisation of otherwise stagnant regions within the cell. The properties of non-Newtonian flow can be closely imitated by a Newtonian fluid with a reduced value of the activation enthalpy bH* with b?0.3–0.5. It appears possible that non-Newtonian rheology plays a key role in determining the convective style in a planetary mantle.  相似文献   

17.
为更好地理解层状硅酸盐对断层强度、滑动速度依赖性及地震活动特征的影响,利用双轴摩擦实验对含白云母岩盐断层带在干燥及含水条件下摩擦的速度依赖性进行了实验研究,并观测了摩擦滑动过程中的声发射,分析了断层带的微观结构.实验结果表明,干燥条件下含白云母岩盐断层带在0.1 ～ 100μm/s的速度范围内表现为黏滑和速度弱化,增大σ2会使断层带从速度弱化向速度强化转化,速度依赖性转换出现在0.1 μm/s,其中断层滑动表现为稳滑或应力释放时间较长的黏滑事件;含水条件下含白云母岩盐断层带在0.05 ～0.01μm/s的速度范围内表现为速度强化,0.1 ～10μm/s的速度范围内表现为速度弱化,50～100μm/s的速度范围内又转换为速度强化行为.含白云母岩盐断层带在干燥条件下一次黏滑伴随一个或一丛声发射事件,而在含水条件下与稳滑相对应,滑动过程中并未记录到声发射事件.显微结构观察表明,速度弱化域的主要变形机制是岩盐颗粒的脆性破裂和局部化的滑动;干燥条件下,速度强化域的主要变形机制是岩盐颗粒的均匀破裂;含水条件下2个速度强化域对应不同的微观机制,高速域的速度强化受控于岩盐颗粒在白云母相互连结形成的网状结构上的滑动及其均匀碎裂作用,而低速域的速度强化还受岩盐的压溶作用控制.通过与岩盐断层带摩擦实验结果对比可知,白云母的存在对于燥岩盐断层带摩擦滑动方式和速度依赖性没有显著影响,而在含水条件下白云母的存在使得岩盐断层带滑动趋于稳定.实验结果为分析含层状硅酸盐断层的强度和稳定性提供了依据.此外,在速度依赖性转换域上观察到的应力缓慢释放的现象进一步证实了在岩盐断层带摩擦滑动过程中观察到的现象,这对慢地震机制研究具有参考意义.  相似文献   

18.
周云好  庄昆元 《地震学报》1990,12(3):248-256
本文用粘弹性理论,探讨了老断层失稳扩展型地震的孕育过程中,断层泥的作用问题.得到了如下结果:即使区域背景场和扰动场保持不变,断层局部应力场仍会因断层泥的蠕变而变化.其中切向应力分量σ0ηη(t),在其它所有分量都缓慢衰减的同时缓慢增大.一旦这个应力分量在断层尖端附近的极大值点,积累至大于岩石的断裂强度,断层的失稳扩展便会从这点发生.与空腔断层相比,断层泥使σ0ηη(t)的突变过程变成了缓慢渐近过程,并使σ0ηη(t)的渐近值有所降低,因而会推迟和减少地震的发生.文中还讨论了断层失稳扩展方向等问题.   相似文献   

19.
张超 《地震学报》1984,6(1):29-40
根据形变测量资料和有关实验结果以及某些地震前兆特征,本文提出了一种在粘弹性介质半空间中断层滑动面沿断裂带走向扩展,即断层蠕动传播的力学模型.为了研究其附近的形变特征,导出了蠕动传播所产生位移场的解析表达式,并通过数值积分计算了在广义开尔文介质中,滑动时间函数为△U=B(1-e-t/T),而蠕动事件沿断裂带单侧和双侧传播导致的附近介质位移的时空分布.根据1976年唐山地震前沧东断裂带上的短周期测量资料并参考模型所得出的结果,对震前的断层运动作了反推.结果表明,地震前沿沧东断裂带发生过明显的蠕动传播,其初始蠕动发生在小站和沧州之间,随后蠕动沿着断裂带向东北和西南传播,向西南扩展的滑动面是顺扭走滑运动,向东北扩展的滑动面以顺扭走滑运动为主并略有压性倾滑运动分量.   相似文献   

20.
An earthquake of Mw6.4 occurred in Pishan County in Xinjiang Province, northwestern Tibetan Plateau, on July 3,2015. The epicenter was located on an active blind thrust system located at the northern margin of the Western Kunlun Mountain Orogenic Belt southwest of the Tarim Basin. We constructed a shovel-shaped fault model based on the layered-crust model with reference to the seismic reflection profile, and obtained the rupture process of the earthquake from the joint inversion of Interferometric Synthetic Aperture Radar(InSAR) measurements, far-field waveform data, and Global Positioning System(GPS) data. The results show that the seismic fault dips southward with a strike of 109°, and the rupture direction was essentially northward. The fault plane rupture distribution is concentrated, with a maximum recorded slip of 73 cm. The main features of the fault are as follows: low inclination angle(25°–10°), thrust slip at a depth of 9–13 km, rupture propagation time of about 12 s, no significant slip in soft or hard sedimentary layers at 0–4 km depth and propagation from the initial rupture point to the surrounding area with no obvious directionality. The InSAR time-series analysis method is used to determine the deformation rate in the source region within 2 years after the earthquake, and the maximum value is ~17 mm yr-1 in the radar line-of-sight direction. Obvious post-earthquake deformation is evident in the hanging wall, with a similar trend to the coseismic displacement field. These results suggest that the Pishan earthquake has not completely released the accumulated energy of the region, given that the multilayer fold structure above the blind fault is still in a process of slow uplift since the earthquake. Post-earthquake adjustment models and aftershock risk analysis require further study using more independent data.  相似文献   

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