Seismicity in deep gold mines of South Africa: Implications for tectonic earthquakes
Seismicity in deep gold mines of South Africa: Implications for tectonic earthquakes
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DOI：
10.1785/0120000226
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发表时间：
2002-06-01
影响因子：
3
通讯作者：
Jordan, TH
中科院分区：
文献类型：
--
作者：
Richardson, E;Jordan, TH
我们研究了与位于南非共和国远西兰德地区的五个深部金矿有关的诱发地震活动，重点是1994年1月至2000年2月由三分量地震检波器的矿内阵列记录的数字数据。每天观测到的地震活动超过1000次，可分为A型和b型两种。A型地震活动在时间和空间上紧密聚集，一般发生在活动采煤工作面或开发巷道100 m范围内；它们的谱在高频处相对丰富，并且在M-max < 1处有较高的矩值截止。我们将这些事件与爆破过程中的动应力和单个采场开挖和关闭引起的准静态应力扰动引起的“裂隙为主”的岩石破裂联系起来。B型事件在时间和空间上分布于整个采矿活动区；它们代表了断层或岩脉等现有剪切带中的“摩擦主导”滑动，并且具有震源缩放特性，与构造地震的推断非常吻合。在远西兰德地区，B型地震的震级可能很大（mb>3），但它们在M-min时表现出明显的较低的震级截止值，类似于0。我们根据剪切破坏成核的临界斑块大小来解释这一截断，并且我们表明数据与速率和状态相关的摩擦模型一致，其中临界滑移距离D-c类似于10(-4)m。该模型的频谱预测和B型事件的加速度图都同意f（max）类似于200 Hz。
We have studied induced seismicity associated with five deep gold mines located in the Far West Rand district, Republic of South Africa, focusing on the digital data recorded from January 1994 until February 2000 by in-mine arrays of three-component geophones. The observed seismicity, which exceeds 1,000 events per day, can be divided into two kinds of events, designated as Types A and B. Type A events are tightly clustered in time and space and generally occur within 100 m of an active mining face or development tunnel; their spectra are comparatively enriched in high frequencies, and they have an upper moment-magnitude cutoff at M-max < 1. We associate these events with the "fracture-dominated" rupture of competent rock induced by dynamic stresses during blasting and quasi-static stress perturbations from the excavation and closure of individual stopes. In contrast, Type B events are temporally and spatially distributed throughout the active mining region; they represent "friction-dominated" slip in existing shear zones such as faults or dikes and have source-scaling properties that agree well with extrapolations from tectonic earthquakes. In the Far West Rand region, Type B events can have large magnitudes (M > 3), but they show a distinct lower magnitude cutoff at M-min similar to 0. We interpret this cutoff in terms of a critical-patch size for nucleation of shear failure, and we show that the data are consistent with a rate- and state-dependent friction model in which the critical slip distance D-c similar to 10(-4) m. Both the spectral predictions of this model and accelerograms of Type B events agree that f(max) similar to 200 Hz.