A laboratory experiment to monitor the contact state of a fault by transmission waves   总被引：1，自引：0，他引：1  

Naoto Yoshioka  Koji Iwasa 《Tectonophysics》2006,413(3-4):221-238

We performed a series of laboratory experiments in which elastic waves were transmitted across a simulated fault. Two types of experiments were carried out: (1) Normal Stress Holding Test (NSHT): normal stress was kept constant for about 3 h without shear stress and transmission waves were observed. (2) Shear Stress Increasing Test (SSIT): shear stress was gradually increased until a stick-slip event occurred. Transmission waves were continuously observed throughout the process of stress accumulation. We focused on the change in transmission waves during the application of shear stress and especially during precursory slips.It was found in NSHT that the amplitude of transmission waves linearly increased with the logarithm of stationary contact time. The increase amounted to a few percent after about 3 h. Creep at asperity contacts is responsible for this phenomenon. From a theoretical consideration, it was concluded that the real contact area increased with the logarithm of stationary contact time.We observed in SSIT a significant increase in wave amplitude with shear stress application. This phenomenon cannot be attributed to the time effect observed in NSHT. Instead, it can be explained by the mechanism of “junction growth” proposed by Tabor. Junction growth yields an increase in real contact area. It is required for junction growth to occur that the material in contact is already plastic under a purely normal loading condition. A computer simulation confirmed that this requirement was satisfied in our experiments. We also found that the rate at which the amplitude increased was slightly reduced prior to a stick-slip event. The onset time of the reduction well coincides with the onset of precursory slip. The cause of the reduction is attributed to the reset of stationary contact time due to displacement. This interpretation is supported by the result of NSHT. Taking the time of stationary contact in SSIT into account, we may expect the change in wave amplitude to be, at most, only a few percent. The observed slight reduction in increasing rate is, in this sense, reasonable. The static stiffness of the fault also decreases with precursory slip. It was also found that low frequency waves are a better indicator of precursory slip than high frequency waves. This might suggest that low frequency waves with longer wavelength are a better indicator of average behavior of faults. The problem, however, merits a further investigation. The shifts in phase were also found to be a good indicator of the change in contact state of the fault. The changes in both amplitude and phase of transmission waves are unifyingly understood through the theory of transmission coefficient presented by Pyrak-Nolte et al. Rough surfaces have a tendency to give larger stick-slips than smooth surfaces. The amount of precursory slip is larger for rough surfaces than for smooth surfaces. Although it was confirmed by a computer simulation that rough surfaces have larger contact diameters than smooth surfaces, the rigorous relationship between the surface roughness (contact diameter) and the amount of precursory slips was not established.  相似文献   

Non-volcanic deep low-frequency tremors accompanying slow slips in the southwest Japan subduction zone   总被引：5，自引：1，他引：5  

Kazushige Obara  Hitoshi Hirose 《Tectonophysics》2006,417(1-2):33

Non-volcanic deep low-frequency tremors in southwest Japan exhibit a strong temporal and spatial correlation with slow slip detected by the dense seismic network. The tremor signal is characterized by a low-frequency vibration with a predominant frequency of 0.5–5 Hz without distinct P- or S-wave onset. The tremors are located using the coherent pattern of envelopes over many stations, and are estimated to occur near the transition zone on the plate boundary on the forearc side along the strike of the descending Philippine Sea plate. The belt-like distribution of tremors consists of many clusters. In western Shikoku, the major tremor activity has a recurrence interval of approximately six months, with each episode lasting over a week. The tremor source area migrates during each episode along the strike of the subducting plate with a migration velocity of about 10 km/day. Slow slip events occur contemporaneously with this tremor activity, with a coincident estimated source area that also migrates during each episode. The coupling of tremor and slow slip in western Shikoku is very similar to the episodic tremor and slip phenomenon reported for the Cascadia margin in northwest North America. The duration and recurrence interval of these episodes varies between tremor clusters even on the same subduction zone, attributable to regional difference in the frictional properties of the plate interface.  相似文献   

Seismic potential of Southern Italy   总被引：1，自引：2，他引：1  

S. Jenny  S. Goes  D. Giardini  H.-G. Kahle 《Tectonophysics》2006,415(1-4):81-101

To improve estimates of the long-term average seismic potential of the slowly straining South Central Mediterranean plate boundary zone, we integrate constraints on tectonic style and deformation rates from geodetic and geologic data with the traditional constraints from seismicity catalogs. We express seismic potential (long-term average earthquake recurrence rates as a function of magnitude) in the form of truncated Gutenberg–Richter distributions for seven seismotectonic source zones. Seismic coupling seems to be large or even complete in most zones. An exception is the southern Tyrrhenian thrust zone, where most of the African–European convergence is accommodated. Here aseismic deformation is estimated to range from at least 25% along the western part to almost 100% aseismic slip around the Aeolian Islands. Even so, seismic potential of this zone has previously been significantly underestimated, due to the low levels of recorded past seismicity. By contrast, the series of 19 M6–7 earthquakes that hit Calabria in the 18th and 19th century released tectonic strain rates accumulated over time spans up to several times the catalog duration, and seismic potential is revised downward. The southern Tyrrhenian thrust zone and the extensional Calabrian faults, as well as the northeastern Sicilian transtensional zone between them (which includes the Messina Straits, where a destructive M7 event occurred in 1908), all have a similar seismic potential with minimum recurrence times of M ≥ 6.5 of 150–220 years. This potential is lower than that of the Southern Apennines (M ≥ 6.5 recurring every 60 to 140 years), but higher than that of southeastern Sicily (minimum M ≥ 6.5 recurrence times of 400 years). The high seismicity levels recorded in southeastern Sicily indicate some clustering and are most compatible with a tectonic scenario where the Ionian deforms internally, and motions at the Calabrian Trench are small. The estimated seismic potential for the Calabrian Trench and Central and Western Sicily are the lowest (minimum M ≥ 6.5 recurrence times of 550–800 years). Most zones are probably capable of generating earthquakes up to magnitudes 7–7.5, with the exception of Central and Western Sicily where maximum events sizes most likely do not exceed 7.  相似文献   

Les failles récentes des Grands-Moulins (Savoie) : un Sackung (tassement gravitaire) majeur dans les Alpes françaises     

Jean-Claude Hippolyte  Marc Tardy  Gérard Nicoud 《Comptes Rendus Geoscience》2006,338(10):734-741

In Savoy, the Grands-Moulins recent fault scarps, previously interpreted as seismic fault ruptures, are in fact part of a major Sackung (deep seated gravitational spreading) of the French Alps (9 km long). We mapped more than 60 sackung scarps, some of them reaching 1330 m long and 30 m high. These antislope scarps stop the active screes and offset relict Dryassic rock glaciers by 16 m. We present geomorphologic observations attesting for their gravitational origin. This Sackung is primarily due to glacial debuttressing, while seismic shaking could be a triggering mechanism. To cite this article: J.-C. Hippolyte et al., C. R. Geoscience 338 (2006).  相似文献   

大变形有限元法分析边坡稳定性     

杨涛  周德培  苏金蓉 《山地学报》2006,24(1):101-104

边坡稳定性分析的重要任务是确定边坡潜在滑面的位置及相应的安全系数,鉴于坡体位移可在现场监测中直接得到,提出边坡潜在滑面确定的位移判据,采用大变形有限元首先计算出边坡的位移场,然后在开挖面的不同高度作塑性区内的水平位移参考线,依次连接参考线上的位移突变点即得到边坡失稳的潜在滑面位置,分析滑面上的应力以及岩体抗剪强度即得到边坡的整体安全系数。  相似文献   

Weathering characteristics of arctic islands in northern Norway     

yvind Paasche  Jrund Raukleiv Strmse  Svein Olaf Dahl  Henriette Linge 《Geomorphology》2006,82(3-4):430-452

The arctic islands of the Lofoten-Vesterålen archipelago in northern Norway have a wide distribution of weathered land surfaces commonly located above 250 m with several apparent similarities. In order to investigate the characteristics of (deep) weathering in this region, northern Langøya and Hadseløya were chosen for in-depth analyses. Eight weathering profiles were excavated from various surfaces, and the stratigraphies were logged in detail. Material was collected throughout the weathering horizons, and all samples were subsequently analysed for clay mineralogy (< 63 μm fraction) and grain size distribution. The sampling strategy was complemented by samples from additional saprolites and other landforms such as moraines and rock glaciers. The XRD results indicate that the presence of secondary minerals, such as gibbsite (Al(OH)₃) and kaolinite (Al₂Si₂O₅(OH)₄), are very common throughout the profiles. Gibbsite is an extreme end product of silicate weathering and usually associated with a warmer and more humid climate, as found in Scandinavia during the Tertiary. The grain size analyses (< 63 μm) show that the finer silt fractions (< 8 μm) tend to be high in the profiles (20–40%), with significant amounts of clay (5–15%) demonstrating that the regolith itself is susceptible to frost sorting mechanisms.¹⁰Be exposure dates from in situ quartz knobs on tors and boulders of local origin suggest > 40,000 years of subaerial conditions. Considering the steady surface erosion, this figure should be viewed as an absolute minimum age estimate. Mapping of the superficial sediments and geomorphological features of the study areas has revealed several common morphological features, which indicate dominance of glacial and periglacial processes in the areas lying below the lower boundary of blockfields (c. 250 m). The weathering mantles are not a periglacial end product, but rather a relict tertiary landform that were modulated by permafrost processes as well as biological processes at later stages. The regolith cover constrain the vertical extension of warm-based Quaternary ice sheets challenging the notion of a parabolic ice mass consuming every mountain top of Lofoten and Vesterålen.  相似文献   

Fault slip and rupture velocity inversion by isochrone backprojection     

Gaetano Festa  Aldo Zollo 《Geophysical Journal International》2006,166(2):745-756

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考虑滑脱效应和温度场的煤层气渗流数值模拟     

肖晓春  潘一山 《中国地质灾害与防治学报》2006,17(3):91-95

由于煤层气的解吸热效应,煤层气的运移过程是一个非等温过程。因此,温度场对煤层气渗流有着重要的影响。前人在研究煤层气渗流规律的研究中并没有同时考虑滑脱效应和温度场因素的影响,而在实际的深部开采中综合考虑滑脱效应和温度场的影响对研究深部煤层气运移规律有着重要的意义。因此本文建立了考虑滑脱效应及温度场的煤层气渗流数学模型,利用有限元数值方法研究了考虑滑脱效应和温度场耦合的煤层气运移规律;研究了考虑滑脱效应和温度场对压力场分布的影响;对考虑滑脱效应及温度场因素的煤层气产量进行了预测。得出了随着温度的升高煤储层的压力在降低,温度的升高对煤层气的产量有着负面的影响这一重要结论。  相似文献   

青藏高原东缘缅萨洼金矿成矿流体地质地球化学特征   总被引：3，自引：0，他引：3  

李晓峰毛景文  刘娅铭徐庆鸿　朱和平 《岩石学报》2005,21(1):189-200

缅萨洼金矿位于中国中轴构造带的中南段,青藏高原的东缘,赋存于金河-箐河断裂带次级断裂羊坪子韧性剪切带中本文根据对该矿床硫化物流体包裹体的氦氩同位素、硫化物的硫同位素以及与硫化物共生的石英的流体包裹体特征、成分以及氢氧同位素组成的测定,讨论了缅萨洼金矿的成矿流体来源及其矿床成因。结果显示,该矿床硫化物流体包裹体中的3He/4He变化较小,为0.69-0.82,显示了地幔流体参与成矿作用的可能性。而4He的含量变化范围较大,一般在2.19-10.62×10-6cm3STP/g(方铅矿除外)与3He/4He相比,40Ar/36Ar的比值则变化较小,一般为251-509。而硫化物的δ34S同位素变化范围在-1.8-2.2‰,平均值为0.5‰,说明硫的地幔来源。与硫化物共生的石英的流体包裹体的类型主要有富液相的盐水溶液包裹体、富气相的盐水溶液包裹体、三相CO2包裹体、纯液相CO2包裹体以及有机流体包裹体。成矿流体的氢氧同位素则显示成矿流体来源于岩浆水(或地幔流体)与大气降水的混合流体,本文认为,缅萨洼金矿的成矿流体为地幔流体与大气降水的混合流体,是渐新世印度大陆与亚洲大陆碰撞之后,该地区大规模走滑与剪切作用过程中,局部伸展作用的产物。  相似文献   

苏鲁造山带超高压变质作用及其P-T-t轨迹   总被引：23，自引：25，他引：23  

张泽明张金凤  游振东沈昆 《岩石学报》2005,21(2):257-270

基于超高压变质岩的岩石学,特别是超高压矿物生长成分环带、扩散环带和蚀变作用研究,综合前人的岩石学和年代学研究成果,提出苏鲁造山带超高压变质作用峰期发生在1000-1100℃和6-7GPa条件下,俯冲深度相当于200km,形成年代为240-250Ma。在此基础上,重塑了一个包括八期变质作用的P-T-t轨迹,揭示出超高压变质岩经历了三个不同的折返阶段,即从200km到100km深度的快速折返阶段,抬升速率为5km/Ma,冷却速率为10℃/Ma;从100km到30km的快速折返,抬升速率为4km/Ma,或为近等温降压,或为缓慢降温的快速降压过程;从下地壳到近地表的缓慢折返阶段,抬升速率为1km/Ma,但为快速降温过程,冷却速率可达20℃/Ma。  相似文献