Coseismic and other short-term strain changes recorded with Sacks-Evertson strainmeters in a deep mine, South Africa
Coseismic and other short-term strain changes recorded with Sacks-Evertson strainmeters in a deep mine, South Africa
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使用 Sacks-Evertson 应变仪在南非的一个深矿井中记录的同震和其他短期应变变化
DOI：
10.1111/j.1365-246x.1982.tb05980.x
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发表时间：
1982
影响因子：
2.8
通讯作者：
R. Green
中科院分区：
文献类型：
--
作者：
A. Mcgarr;I. Sacks;A. Linde;S. Spottiswoode;R. Green
总结。1977年3月和4月，在约翰内斯堡附近的ERPM金矿，在3.1公里深的实验隧道侧壁钻孔的两端安装了三个Sack-Evertson钻孔膨胀仪。在接下来的一年里，在震级为-1至3.7时，震级为50米至约2公里的数百次矿震记录到了从5±10−10到超过5±10−6的同震应变变化。震中以下的坐标和震级是从地下地震检波器阵列记录的地震图中确定的。同震应变阶跃的幅度和极性与基于点源位错理论的理论预期基本一致；具体地说，应变阶跃与地震矩除以震中距离的立方体成正比。在5±10−9或更大的应变水平下，即使产生大于5±10−6的同震台阶并且应变计位于震源半径内的地震，在震前似乎没有任何不稳定的短期迹象。在距离约100m的开挖过程中，观测到的连续应变变化与根据弹性理论计算的变化吻合较好。类似的计算与一些较近的地震之后观察到的震后应变变化是一致的。这些震后应变对地震发生后的时间呈对数依赖关系，似乎是由于地震与邻近矿山开挖的相互作用，而不是由于实际震源区内的变形。
Summary. During 1977 March and April, three Sacks-Evertson borehole dilatometers were installed at the ends of boreholes drilled into the sidewall of an experimental tunnel at a depth of 3.1 km in the ERPM gold mine near Johannesburg. In the following year coseismic strain changes ranging from 5 ± 10−10 to values exceeding 5 ± 10−6 were recorded for hundreds of mine tremors in the magnitude range -1 to 3.7 and at hypocentral distances of 50 m to about 2 km. Hypocentral coordinates and magnitudes were determined from seismograms recorded from an underground array of geophones. Amplitudes and polarities of the coseismic strain steps are generally in excellent agreement with theoretical expectations based on point-source dislocation theory; specifically, the strain steps are proportional to the seismic moment divided by the cube of hypocentral distance. At a strain level of 5 ± 10−9 or greater the tremors do not appear to be preceded by any short-term indications of instability even for tremors producing coseismic steps greater than 5 ± 10−6 and for which the strainmeters were within a source radius of the hypocentre. Continuous strain changes observed at the times when the mine excavation, at a distance of about 100 m, is extended are in good agreement with calculated changes based on the theory of elasticity. A similar calculation is consistent with post-seismic strain changes observed to follow some of the closer tremors. These post-seismic strains show a logarithmic dependence on time following the tremor and appear to be due to the interaction of a tremor with the adjacent mine excavation rather than to deformation within the actual seismic source region.