Abstract

Fault-slip induced by underground longwall mining could trigger dynamic failure to nearby mine openings. A better understanding of fault-slip behavior and the associated seismicity is significant for estimating the triggered damage and finding a feasible way to predict potential larger events. In this study, a displacement-dependent moment tensor method is introduced and embedded in the FLAC3D code to simulate both small-scale direct shear test and field-scale mining-induced fault slip. For the direct shear test model, the numerical results agree well with reported experiments in respect to mechanical behavior and seismicity characteristics, such as moment magnitude, frequency-magnitude distribution (FMD), and variation of b-value. Numerical results show that a clustering process is essential to produce realistic FMD, and associated parameters are given. Material heterogeneity of the fault influences the event magnitude. Based on a case study, a field-scale model is built to investigate the fault-slip behavior as a longwall face approaches a fault. For individual contacts, ΔCFF (Coulomb Failure Function) is a useful indicator to evaluate the likelihood of slip. It gradually increases, followed by a quick rise before slip occurs, but sharply drops after slipping. Numerical simulation shows that shear slip initializes on the roof segment of the fault and gradually migrates to the seam and floor segments. Seismicity starts on the roof segment when the longwall face is 100 m away from the fault, but it increases strongly when the distance is less than 50 m and gradually moves toward the seam and floor segments, which is consistent with field observations. Simulated magnitude of the events and the b-value (0.8) also show reasonable agreement with field measurements. The numerical simulation also indicates that a significant drop in b-value usually precedes larger events triggered in the following advancement of the longwall face, which can be regarded as a precursor for larger events.

Article Highlights

• A displacement-dependent moment tensor method is proposed to reproduce the slip process and the associated seismicity as a longwall face approaches a fault.

• Shear slip initializes on the roof segment of the fault and gradually transfers to the seam and floor segments.

• A significant drop in b-value can be a precursor for large events induced by subsequent fault-slip and provide opportunities to mitigate damages.

中文翻译：

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一种模拟断层滑动诱发地震活动的位移相关矩张量方法

摘要

地下长壁开采引起的断层滑移可能引发附近矿井的动态故障。更好地了解断层滑动行为和相关的地震活动对于估计触发的损害和找到预测潜在更大事件的可行方法具有重要意义。在这项研究中，引入了位移相关矩张量方法并将其嵌入到 FLAC3D 代码中，以模拟小规模直剪试验和现场规模采矿引起的断层滑动。对于直剪试验模型，数值结果与报告的力学行为和地震活动特性的实验结果非常吻合，例如矩震级、频率-震级分布 (FMD) 和b 的变化-价值。数值结果表明聚类过程对于产生真实的 FMD 是必不可少的，并且给出了相关的参数。断层的物质异质性影响事件的大小。在案例研究的基础上，建立了一个现场比例模型来研究长壁工作面接近断层时的断层滑动行为。对于单个接触，ΔCFF（库仑失效函数）是评估滑动可能性的有用指标。它逐渐增加，然后在滑移发生前迅速上升，但在滑移后急剧下降。数值模拟表明，剪切滑移从断层顶板段开始，并逐渐向煤层和底板段迁移。长壁面距断层 100 m 时，地震活动从顶板段开始，但距离小于 50 m 时强烈增加，并逐渐向煤层和底板段移动，与现场观测结果一致。事件的模拟幅度和b值 (0.8) 也显示出与现场测量的合理一致性。数值模拟还表明b的显着下降- 值通常先于长壁工作面推进中触发的较大事件，这可以看作是较大事件的先兆。

文章亮点

• 当长壁工作面接近断层时，提出了一种依赖位移的矩张量方法来重现滑动过程和相关的地震活动。

• 剪切滑移在断层顶板段开始，并逐渐转移到接缝和底板段。

• b值的显着下降可能是由随后的断层滑动引起的大事件的先兆，并提供了减轻损害的机会。