三轴压缩下两类砂岩变形破坏的实验研究

本文讨论了围压高达700MPa的条件下,发生实验变形的长石砂岩和石英砂岩的变形模式和变形机制。完整长石砂岩的脆延过渡带在200—400MPa,完整石英砂岩的脆延过渡带在250—350MPa,长石砂岩在600MPa围压以上出现高压脆化现象;两类切口岩石的稳滑粘滑过渡界限分别是200MPa和150MPa。不同的变形模式主要起因于程度不同的碎裂机制。文中还对矿物成分的影响、脆性行为之延伸等有关问题进行了简要讨论     

Simulation of the Influence of Rate- and State-dependent Friction on the Macroscopic Behavior of Complex Fault Zones with the Lattice Solid Model

-- In order to understand the earthquake nucleation process, we need to understand the effective frictional behavior of faults with complex geometry and fault gouge zones. One important aspect of this is the interaction between the friction law governing the behavior of the fault on the microscopic level and the resulting macroscopic behavior of the fault zone. Numerical simulations offer a possibility to investigate the behavior of faults on many different scales and thus provide a means to gain insight into fault zone dynamics on scales which are not accessible to laboratory experiments. Numerical experiments have been performed to investigate the influence of the geometric configuration of faults with a rate- and state-dependent friction at the particle contacts on the effective frictional behavior of these faults. The numerical experiments are designed to be similar to laboratory experiments by Dieterich and Kilgore (1994) in which a slide-hold-slide cycle was performed between two blocks of material and the resulting peak friction was plotted vs. holding time. Simulations with a flat fault without a fault gouge have been performed to verify the implementation. These have shown close agreement with comparable laboratory experiments. The simulations performed with a fault containing fault gouge have demonstrated a strong dependence of the critical slip distance D_c on the roughness of the fault surfaces and are in qualitative agreement with laboratory experiments.     

THE GEOLOGICAL AND ROCK MECHANICAL DISTINCTION EVIDENCE BETWEEN STICK-SLIP AND CREEP IN HOST ROCK SEGMENTS OF FAULT

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.     

Evolution of crustal deformation in the northeast–central Japanese island arc: Insights from fault activity

We evaluated fault activity in northeast–central Japan based on fault orientation, regional stress field, and slip tendency analysis for active and non‐active faults (i.e. faults for which Quaternary activity has not been identified). Slip tendency is generally higher along active faults than non‐active faults, although a high slip tendency was observed along some non‐active faults, indicating their potential to become active. The potential for fault activity along non‐active faults can be modeled using the temporal evolution from non‐active to active during long‐term crustal deformation. The density of potentially active faults varies spatially across the study areas and reflects the temporal evolution of crustal deformation in northeast–central Japan.     

郯庐断裂带白山-卅铺段第四纪以来的活动习性

根据构造地貌遥感解析,发现郯庐断裂带沿庐江白山到桐城卅铺一线显示1组平行断层,现场地震地质调查验证其为1组活动断层。通过断层剖面观测、样品采集及样品测试分析和宏微观构造分析,结果表明,郯庐断裂带在白山—卅铺一带第四纪以来仍具有黏滑、蠕滑交替的变形活动。其中,在柯坦—卅铺一带,最年轻的水系被NE向断层组右旋扭折,其断层物质的微观观测和测龄结果表明该断裂段第四纪时的活动具有脆、塑性过渡变形特征,强烈活动时间处于早、中更新世;而白山剖面断层泥年龄测试结果则反映相应断层段在中、晚更新世曾有过较强烈的活动。断层泥超微(SEM)和显微观测结果亦表明该断裂段曾发生黏滑、蠕滑交替的构造变形事件,且表现为先黏滑后蠕滑;结合水系呈现缓慢扭折表征,近年来沿断裂有不少微震发生,表明郯庐断裂带在白山—卅铺段的最新滑移方式主要表现为蠕滑,也就是说,该段积累的应力以蠕滑或微震等方式缓慢释放,据此推测未来一定时期内不易孕育强烈地震     

Development of shear localization in simulated quartz gouge: Effect of cumulative slip and gouge particle size

Frictional sliding experiments were conducted on two types of simulated quartz gouge (with median particle diameters 5 m and 25 m, respectively) at confining pressures ranging from 50 MPa to 190 MPa in a conventional triaxial configuration. To investigate the operative micromechanical processes, deformation texture developed in the gouge layer was studied in samples which had accumulated different amounts of frictional slip and undergone different stability modes of sliding. The spatial patterning of shear localization was characterized by a quantitative measurement of the shear band density and orientation. Shear localization in the ultrafine quartz gouge initiated very early before the onset of frictional sliding. Various modes of shear localization were evident, but within the gouge zoneR ₁-shears were predominant. The density of shear localization increased with cumulative slip, whereas the angle subtended at the rock-gouge interface decreased. Destabilization of the sliding behavior in the ultrafine quartz gouge corresponded to the extension ofR ₁-shears and formation of boundaryY-shear segments, whereas stabilization with cumulative slip was related to the coalescence ofY-shear segments to form a throughgoing boundary shear. In the coarse quartz gouge, the sliding behavior was relatively stable, probably because shear localization was inhibited by distributed comminution. Two different models were formulated to analyze the stress field within the gouge zone, with fundamentally different predictions on the orientations of the principal stresses. If the rock-gouge interface is assumed to be bonded without any displacement discontinuity, then the maximum principal stress in the gouge zone is predicted to subtend an angle greater than 45° at the interface. If no assumption on displacement or strain continuity is made and if the gouge has yielded as a Coulomb material, then the maximum principal stress in the gouge zone is predicted to subtend an angle less than 45°. If the apparent friction coefficient increases with overall slip (i.e., slip-hardening), then the Riedel shear angle progressively decreases with increasing shear strain within the gouge layer, possibly attaining a zero value which corresponds to a boundaryY-shear. Our quantitative data on shear localization orientation are in reasonable agreement with this second model, which implies the coefficient of internal friction to be about 0.75 for the ultrafine quartz gouge and 0.8 for the coarse gouge. The wide range of orientations for Riedel shear localization observed in natural faults suggests that the orientations of principal stresses vary as much as in an experimental gouge zone.     

鉴定活断层粘滑活动的一种新标志

本文根据实验研究,探讨了活断层泥中石英碎砾表面放射状张裂纹和凹坑的形成机制,提出了放射状张裂纹和凹坑是活断层粘滑活动时石英碎砾中包体发生爆裂的产物的观点。这种放射状爆裂张裂纹和弹坑可以作为鉴定活断层粘滑活动的一种新标志。     

Some properties of unstable slip on rough surfaces

In this paper we report results obtained from various friction experiments under direct and oblique shear loading conditions. We used four rock types of varying brittleness (quartzite, anhydrite, limestone, pyrophyllite) with different surface roughness. The observations concentrate on the time span several milliseconds before dynamic failure occurs. During this period a premonitory, unstable phase of slip (slip 2) occurs. This differs importantly from a premonitory, stable process (slip 1) with durations of hundreds of seconds. On smooth surfaces slip 2 is usually observed with ductile rocks and less reliably with brittle rocks. Slip 2 is mostly accompanied by acoustic emissions, which increase in rate of occurrence and in magnitude until the stick-slip event. Foreshocks are observed during approximately 50% of the slip 2 events on rough surfaces. Foreshocks far exceed the acoustic noise level, which is also prevalent before stick-slip events on rough surfaces. In the direct shear experiment, where two faults are being loaded simultaneously, in about 20% of the cases precursory slip 2 was observed on the opposite side on which the final stick-slip event occurred.     

Evolution of the ductile shear zone of the Paishanlou gold deposits,western Liaoning,China

The combination of field surveys with analysis of microstructure of tectonite and Electron Backscatter Diffraction (EBSD) on quartz fabric indicated that three periods of ductile shear events developed in the Paishanlou gold deposits and the E-W and NE-striking ductile shear zones were formed during each event. The E-W-striking ductile shear zone, accompanied by compressional and dextral shear slip, was shear-cut by the NE-striking shear zones, accompanied by compressional-sinistral shear slip and sinistral-normal shear slip, successively. An E-W-striking ductile shear zone developed at a deeper tectonic level and at middle- to high-temperatures, accompanied by abundant microstructures, including microlayering between a polycrystal quartz belt and mica, and quartz deformation was depended on cylinder (10-10) 〈a〉 or 〈c〉 glide. The development of an E-W-striking shear zone can be seen as a tectonic pattern in the region of the Paishanlou gold deposits of the collision between the Mongolian tectonic belt and the North Archean Craton from Suolun to the Linxi suture zone during the Indosinian. The NE-striking ductile shear zone developed approximately 160 Ma during the early Yianshanian at middle to shallow tectonic levels and at middle- to low-temperatures, accompanied by typical microstructures, including polycrystal quartz aggregation and quartz subgrain rotation recrystallization, etc., and quartz deformation was depended on prismatic (1011) 〈a〉 glide. The last ductile shear event around the NE-striking shear zone developed at low temperatures and shallow tectonic levels, yielding to a pre-existing NE-striking shear zone, accompanied by abundant microstructures, including low-temperature quartz grain boundary migration and bulging recrystallization. The last ductile shear movement may be related to lithosphere thinning and the destruction of the North China Craton from approximately 130-120 Ma, and this shear event resulted directly in the mineralization in the Paishanlou region.     

Fault dimensions,displacements and growth

Maximum total displacement (D) is plotted against fault or thrust width(W) for 65 faults, thrusts, and groups of faults from a variety of geological environments. Displacements range from 0.4 m to 40 km and widths from 150 m to 630 km, and there is a near linear relationship betweenD andW ². The required compatibility strains (e _s) in rocks adjacent to these faults increases linearly withW and with and ranges frome _s=2×10^–4 toe _s=3×10^–1. These are permanent ductile strains, which compare with values ofe _s=2×10^–5 for the elastic strains imposed during single slip earthquake events, which are characterised by a linear relationship between slip (u) andW.The data are consisten with a simple growth model for faults and thrusts, in which the slip in successive events increases by increments of constant size, and which predicts a relationship between displacement and width of the formD=cW ². Incorporation of constant ductile strain rate into the model shows that the repreat time for slip events remains constant throughout the life of a fault, while the displacement rate increases with time. An internally consistent model withe _s=2×10^–5, giving repeat times of 160 years and instantaneous displacement rates of 0.02 cm/yr, 0.2 cm/yr, and 2.0 cm/yr when total displacement is 1 m, 100 m, and 10 km, and slip increasing by 0.5 mm with each event, gives a good approximation of the data. The model is also applicable to stable sliding, the slip rate varying with ductile strain rate and withW ².     

基岩区断层活动特征和时间的研究——以康定-磨西断裂段为例

为了探讨基岩裸露区断层的活动特征、期次和时间,在鲜水河断裂带东南段的康定-磨西断裂段采集了一系列断层岩和断层泥样品,运用TL、ESR、K-Ar、石英形貌分析和变形显微构造分析法进行了综合测试。结果表明,断裂段经历了多种机制(韧性剪切和脆性断裂)、多期次、多种运动方式(左旋和右旋)的活动,最新一次较强烈活动的下限时间是晚更新世末或全新世初     

FRICTIONAL PROPERTIES OF A NATURAL FAULT GOUGE FROM DRILLED CORES IN THE LONGMENSHAN FAULT ZONE CUTTING GRANITIC ROCK

In this paper, we report friction experiments performed on natural fault gouge samples embedded in granitic rock from drilled core by a project entitled "the Longmenshan Fault Shallow Drilling(LMFD)". Compared with other natural fault gouge, this yellow-greenish gouge(YGG)is dominantly chlorite-rich. The maximum content of chlorite reaches 47%in the YGG. To understand the frictional properties of the YGG sample, experiments were performed at constant confining pressure of 130MPa, with constant pore pressure of 50MPa and at different temperatures from 25℃ to 150℃. The experiments aim to address the frictional behavior of the YGG under shallow, upper crustal pressure, and temperature conditions. Compared with previous studies of natural gouge, our results show that the YGG is stronger and shows a steady state friction coefficient of 0.47~0.51. Comparison with previous studies of natural gouge with similar content of clay minerals indicates a sequence of strengths of different clay minerals:chlorite > illite > smectite. At temperatures up to 150℃ hence depths up to~8km in the Longmenshan region, the YGG shows stable velocity-strengthening behavior at shallow crustal conditions. Combined with the fact of strong direct velocity effect, i.e., (a-b)/a>0.5, faults cutting the present clastic lithology up to~8km depth in the Longmenshan fault zone(LFZ)are likely to offer stable sliding resistance, damping co-seismic rupture propagating from below at not-too-high slip rates. However, as the fault gouge generally has low permeability, co-seismic weakening through thermal pressurization may occur at high slip rates(>0.05m/s), leading to additional hazards.     

民乐盆地某些活断层断层泥中石英颗粒的表面特征及其地震地质意义

本文对民乐盆地三条活动断层断层泥内石英颗粒表面的显微构造作了较系统的研究。根据这些石英颗粒表面特征对该区莺落峡等断层的滑动性质和断层活动的相对年代进行了讨论。提出了以下的新看法:莺落峡断层的中段为粘滑段,东西两段为蠕滑段,古震源在该断层的黑河口一带,发生的时代大致在晚更新世晚期或全新世早期;茨湖断层具有最新活动特征,粘滑标志明显。另外清水沟老断层在全新世时也有新活动。     

The frictional behavior of lizardite and antigorite serpentinites: Experiments,constitutive models,and implications for natural faults

Laboratory studies of the frictional behavior of rocks can provide important information about the strength and sliding stability of natural faults. We have conducted friction experiments on antigorite and lizardite serpentinites, rocks common to both continental and oceanic crustal faults. We conducted both velocity-step tests and timed-hold tests on bare surfaces and gouge layers of serpentinite at room temperature. We find that the coefficient of friction of lizardite serpentinite is quite low (0.15–0.35) and could explain the apparent low stresses observed on crustal transform faults, while that of antigorite serpentinite is comparable to other crustal rocks (0.50–0.85). The frictional behavior of both types of serpentinite is well described by a two-mechanism model combining state-variable-dominated behavior at high slip velocities and flow-dominated behavior at low velocities. The two-mechanism model is supported by data from velocity-step tests and timed-hold tests. The low velocity behavior of serpentinite is strongly rate strengthening and should result in stable fault creep on natural faults containing either antigorite or lizardite serpentinite.     

The influence of edifice slope and substrata on volcano spreading

Gravitational volcano spreading is caused by flow of weak substrata due to volcanic loading, and is now a process known to affect many edifices. The process produces extension in the upper edifice, evidenced by gräben and normal faults, and compression at the base, seen in strike–slip faults and thrusts. Where spreading is identified, host volcanoes have a range of fault densities, variable rift and gräben shapes, and different degrees of structural asymmetry. Previous studies have suggested a link between edifice shape and structure and the proportion of brittle to ductile material in the substrata or lower edifice. We study this link using refined sand cone analogue models standing on a brittle–ductile/sand–silicone substrata. Two scenarios have been investigated, the first mainly represents oceanic volcanoes with a ductile layer within the edifice (type I), where there is an outer ductile free surface. The second represents most continental volcanoes that have ductile substrata (type II). We apply the model results to natural examples and develop quantitative relationships between slope, brittle–ductile ratio fault density, spreading rate and structural style. Displacement fields calculated from stereophotogrammetry show significant differences between different slope models. We find that more faults are produced when the cone is initially steeper, or when the brittle substratum is thinner. However, the effect of the brittle layer dominates over that of slope. The strike–slip movements are found to be an essential feature in the spreading mechanism and the gräben are in fact transtensional features. Strike–slip and graben faults make a conjugate flower pattern. The structures produced are well-organised for type II edifices, but they are poorly organised for type I models. Type I models represent good analogues for oceanic volcanoes that are commonly affected by large slumps bounded by an extensional zone and lack of well-formed sector gräben. The well-observed connection between oceanic volcano rifts and large landslide-slumps is confirmed to be a consequence of spreading.     

印度与欧亚大陆碰撞构造变形数值分析

在全面考虑了大陆构造变形三重非线性特征的基础上，用动态有限元法研究了藏东对印度与欧亚大陆碰撞作用的大变形响应。数值模拟结果显示了明显的纵向收缩变形，变形主轴多具有顺时针转动的趋势，但横向位移在总体上并不显著。其最大值正位于红河和鲜水河断裂之间，这一结果论证了印度板块对欧亚大陆的碰撞可能是川滇菱形块体向南东运动的动力来源。红河、鲜水河、昆仑及阿尔金活断层在碰撞作用下发生了顺时针的旋转变形；而且，计算结果模拟出了红河断裂由左旋变为右旋，另３条断裂始终左旋的运动特征     

潮汐应力对地震的触发作用

文中计算了由日、月引潮力在地球内产生的潮汐应力场,研究了潮汐应力对地震的触发作用.采用的地球模型是分为十五层的球对称模型.对于近30年来我国或我国邻近发生的七十次较大的地震,计算了震源处在发震时刻的球坐标系中的潮汐应力.通过坐标变换,得到了发震断层面中的正应力及沿错动矢量方向的剪应力.根据岩石的库仑剪破裂准则来判断潮汐应力对所研究的震例是否具有触发作用.结果表明,在七十个震例中,潮汐应力对其中四十三个有触发作用.对于华北地区的十八个震例,潮汐应力对其中十四个有触发作用.还可看出,对于浅源走滑型地震有较明显的触发作用,而对浅源斜滑及倾滑型地震则没有明显的触发作用.对国外七十二个震例的计算结果得到了类似的结论.最后,对华北地区中任一可能的发震地点,提出一种根据潮汐应力来预测发震的危险时间范围的方法.      

Creep,stable sliding,and premonitory slip

Summary The current status of laboratory investigations into creep, stable sliding and premonitory slip is reviewed and some new material is presented. It is postulated that pre-cut rocks and those with simulated gouge layers undergo a transition with increasing confining pressure from (1) stable sliding to stick-slip, to (2) sliding along the pre-cut with deformation of the country rock, to (3) homogeneous flow of the specimen without slip along the pre-cut. Stick-slip behavior is not always present. Decreasing displacement rates are found to enhance stick-slip. Mixtures of gouge are found to be significant in controlling the behavior of sliding with 10–20 percent of anhydrite mixed with quartz or clays mixed with anhydrite shifting the sliding mode from stable stick-slip or stick-slip to stable sliding, respectively. Premonitory slip may be one of the most significant short term precursors of earthquakes. Although widely recognized in the laboratory, little systematic work has been completed. Variations in pore pressure, resistivity and seismic velocities have been investigated. Clearly much work needs to be done into these topics before a clear understanding is achieved.     

雅鲁藏布大峡谷地区构造和地震活动特征

雅鲁藏布大峡谷地区位于喜马拉雅东构造结前锋地带,新构造运动和地震活动都十分强烈,两者关系密切。区内发育有北北东-北东向和北西西-北西向两组断裂构造,调查研究表明,它们的规模、性质、活动时代、活动强度等特征具有明显的差异：北西西-北西向断裂规模较大,多为逆冲、逆走滑断层,形成较早;北北东-北东向断裂单条规模相对不大,常集中分布,构成北北东向的剪切拉张断裂构造带,形成较晚,第四纪晚期活动明显。强震主要发生在喜马拉雅山差异运动强烈地带或地段,如块体周边的深大断裂带及其附近。7级以L地震主要与断裂构造带中规模较大、全新世强烈活动段、断裂几何构造复杂部位或多组方向断裂交汇密切相关。其中,7．5级以上地震发生在断裂构造带中走滑分量较大的北西向和北东向断裂带上。