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181.
Quantifying Damage, Saturation and Anisotropy in Cracked Rocks by Inverting Elastic Wave Velocities 总被引:1,自引:0,他引:1
Alexandre Schubnel Philip M. Benson Ben D. Thompson Jim F. Hazzard R. Paul Young 《Pure and Applied Geophysics》2006,163(5-6):947-973
Crack damage results in a decrease of elastic wave velocities and in the development of anisotropy. Using non-interactive
crack effective medium theory as a fundamental tool, we calculate dry and wet elastic properties of cracked rocks in terms
of a crack density tensor, average crack aspect ratio and mean crack fabric orientation from the solid grains and fluid elastic
properties. Using this same tool, we show that both the anisotropy and shear-wave splitting of elastic waves can be derived.
Two simple crack distributions are considered for which the predicted anisotropy depends strongly on the saturation, reaching
up to 60% in the dry case. Comparison with experimental data on two granites, a basalt and a marble, shows that the range
of validity of the non-interactive effective medium theory model extends to a total crack density of approximately 0.5, considering
symmetries up to orthorhombic. In the isotropic case, Kachanov's (1994) non-interactive effective medium model was used in
order to invert elastic wave velocities and infer both crack density and aspect ratio evolutions. Inversions are stable and
give coherent results in terms of crack density and aperture evolution. Crack density variations can be interpreted in terms
of crack growth and/or changes of the crack surface contact areas as cracks are being closed or opened respectively. More
importantly, the recovered evolution of aspect ratio shows an exponentially decreasing aspect ratio (and therefore aperture)
with pressure, which has broader geophysical implications, in particular on fluid flow. The recovered evolution of aspect
ratio is also consistent with current mechanical theories of crack closure. In the anisotropic cases—both transverse isotropic
and orthorhombic symmetries were considered—anisotropy and saturation patterns were well reproduced by the modelling, and
mean crack fabric orientations we recovered are consistent with in situ geophysical imaging.
Our results point out that: (1) It is possible to predict damage, anisotropy and saturation in terms of a crack density tensor
and mean crack aspect ratio and orientation; (2) using well constrained wave velocity data, it is possible to extrapolate
the contemporaneous evolution of crack density, anisotropy and saturation using wave velocity inversion as a tool; 3) using
such an inversion tool opens the door in linking elastic properties, variations to permeability. 相似文献
182.
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184.
为了研究地震过程中断层面的相互作用,设计了四类裂纹面状况不同的断裂力学实验。实验结果表明,裂纹面的状况对于含裂纹材料的σc(21/2)值有强烈的影响,并利用断裂力学的原理对结果进行了分析。 实验中解决了如下技术关键: 1.可用三点弯曲、局部受拉、单面启裂、双面贯穿的方法,在脆性材料板状试件(玻璃板、岩石板)以及有机玻璃板中预制中心穿透裂纹。 2.在裂纹端部预计裂纹扩展的区域内粘贴电阻应变片,用以判断并测量裂纹初始扩展及其相应的破坏应力σc的方法。 相似文献
185.
Masaru Nakano Hiroyuki Kumagai Bernard A. Chouet 《Journal of Volcanology and Geothermal Research》2003,122(3-4):149-164
We investigate the source mechanism of long-period (LP) events observed at Kusatsu–Shirane Volcano, Japan, based on waveform inversions of their effective excitation functions. The effective excitation function, which represents the apparent excitation observed at individual receivers, is estimated by applying an autoregressive filter to the LP waveform. Assuming a point source, we apply this method to seven LP events the waveforms of which are characterized by simple decaying and nearly monochromatic oscillations with frequency in the range 1–3 Hz. The results of the waveform inversions show dominant volumetric change components accompanied by single force components, common to all the events analyzed, and suggesting a repeated activation of a sub-horizontal crack located 300 m beneath the summit crater lakes. Based on these results, we propose a model of the source process of LP seismicity, in which a gradual buildup of steam pressure in a hydrothermal crack in response to magmatic heat causes repeated discharges of steam from the crack. The rapid discharge of fluid causes the collapse of the fluid-filled crack and excites acoustic oscillations of the crack, which produce the characteristic waveforms observed in the LP events. The presence of a single force synchronous with the collapse of the crack is interpreted as the release of gravitational energy that occurs as the slug of steam ejected from the crack ascends toward the surface and is replaced by cooler water flowing downward in a fluid-filled conduit linking the crack and the base of the crater lake. 相似文献
186.
某水电站左岸深裂缝对工程荷载下边坡稳定性影响的FLAC3D分析 总被引:7,自引:1,他引:7
简要介绍了某水电站下坝址区左岸深部裂缝的发育分布特征,在此基础上,采用FLAC^3D就深裂缝的存在对工程荷载作用下坝基岩体的变形和稳定性状况进行了初步分析和评价,结果表明,尽管左岸边坡中存在深裂缝,但岸坡在工程荷载作用下变形较小,整体稳定性仍较好。 相似文献
187.
Yoshihiro Hiramatsu Muneyoshi Furumoto Kin’ya Nishigami Shiro Ohmi 《Physics of the Earth and Planetary Interiors》2002,132(4):269-279
We analyze high sampling waveforms of the initial part of P-wave recorded at the 1800-m-deep borehole seismographs at the Nojima fault from December 1999 to May 2000 to clarify the initial rupture process of microearthquakes. We select 12 events with high S/N, whose magnitudes range from −0.3 to 2.2 and hypocentral distances from 1 to 11 km. We adopt the two different source models by Sato and Hirasawa (1973) and by Sato and Kanamori (1999). The former (model by Sato and Hirasawa (SH model)) generates only a ramp-like onset of velocity pulse. The later (model by Sato and Kanamori (SK model)) is able to generate a weak initial phase that is controlled by a trigger factor and the length of pre-existing crack. We perform the waveform inversion to estimate the optimum source parameters of each model. Waveforms of 5 of the 12 events are clearly reproduced by both SH model and SK model with a large trigger factor and a small length of pre-existing crack. The others are explained by not SH model but only SK model with a small trigger factor and a large length of the pre-existing crack, indicating that the weak initial phase is a nucleation phase and reflects the source process. These seven events satisfy roughly a relation that a large event has a large length of the pre-existing crack; the final crack length is proportional to the length of the pre-existing crack. 相似文献
188.
花岗岩动三轴抗压强度的裂纹模型研究(I):理论基础 总被引:3,自引:0,他引:3
简要地介绍了岩石材料在压应力作用下的裂纹模型。应用虚拟力方法(Pseudo-tractionmethod)考虑2阶虚拟力情形,求解裂纹组应力强度因子表达式,为岩石动三轴抗压强度的裂纹模型研究提供理论基础。 相似文献
189.
190.
浅析某油田地下水石油类污染途径 总被引:1,自引:0,他引:1
研究区处于东北某油田区,该油田已有近50年的开发历史。随着对石油需求的不断增加,大量的石油被开采了出来。但是在开采过程中由于对落地原油及开采过程中油田废水的处置不当,致使地下水遭受了污染。因此保护地下水免受进一步污染对当地居民的身体健康和人身安全都是非常必要的。笔者基于研究区水样测试的结果石油类污染物浓度等值线图,发现地下水中石油类污染小范围内呈面状分布外,主要呈点状分布于研究区。通过结合对研究区地质环境、构造背景、地表水流和污染源的大量调查研究,分析得出石油类污染物主要是通过由过量开采地下水引起的地裂缝和新构造断裂引发的地裂缝以及事故性污染到达地下水的。研究区的ZK6号井附近由于长期的超量开采地下水从而改变了地下水流向,在地表则形成了地面沉降并引发了此处的地裂缝,致使此地下水油类的污染非常严重。另外,新构造断裂在北西向、北北东向及东西向3组壳断裂带的基础上继承性运动,致使下伏含油层油气沿裂缝上窜污染上覆含水层,同时在油田地表发育大量的地沟、地裂缝,地表洒落的原油及其他污染物通过这些地裂缝污染含水层。 相似文献