Research on earthquake preparation process - Accomplishment of observation networks installed very close to earthquake sources in South Africa gold mines -

通过分析安装在南非Mponeng矿2.6 km深度的加速度计阵列的数据，我们证实了矿震（-2<M<3）的相似性规律。此外，通过对距阵列100米范围内的矿震破裂过程的反演，我们发现它们的滑动分布与自然大地震一样不均匀，并且它们的破裂速度和地震效率也与自然大地震相似。我们广泛分析了Bambanani矿安装在2.4 km深度的ishii型应变仪的数据，并检测了发生在应变仪100m范围内的M2级地震及其前震和余震的应变变化。然而，在M2级地震发生之前，没有观察到异常应变变化，尽管它们的应变步长约为10-4。利用这些应变阶跃记录，我们精确地确定了震源位置。从这些数据推断，有前震的M2级地震更多地发生在地质断层上，而没有前震的地震则发生在断层尖端周围的堤防上。我们检测到矿井地震台网未检测到的小震动的应变步骤，这些步骤之后是明显的震后蠕变样漂移，但之前没有先兆。对连续25Hz数据的分析显示，与震源持续时间为1ms ~ 50ms的正常地震（-1<M<2）相比，震源持续时间为100ms ~ 1000s的地震有许多更小的持续时间（100ms ~ 1000s）。在一些特别慢的步骤之前，有应变加速，最大可达步骤的三分之一。我们在Mponeng矿2.9公里深处的Pretorius断层附近安装了流量表和加速度计。我们观察到M2级地震产生的应变变化，这些地震发生在距离应变仪几百米的范围内。两种应变仪记录了相似的应变变化。我们观察到最大应变步长为10-5，但没有记录到如此大的应变步长。少

By analyzing data from the accelerometer array installed at a depth of 2.6 km at the Mponeng mine in South Africa, we confirmed that the similarity law holds for mine tremors (-2<M<3). Further, by an inversion of rupture process of mine tremors that occurred within 100m from the array, we found that their slip distributions are as heterogeneous as those of natural large earthquakes, and that their rupture velocities and seismic efficiencies are also similar to those. We extensively analyzed data from the Ishii-type strainmeter installed at a depth of 2.4 km at the Bambanani mine and detected strain changes related to M2 class tremors and their foreshock and aftershocks that occurred within 100m from the strainmeter. No anomalous strain changes just before the M2 class tremors, however, were seen before the tremors, in spite of their large strain step of about 10-4. By utilizing these strain step records, we precisely determined hypocentral locations. We inferred from these data that th … More e M2 class tremors preceded by foreshocks occurred on a geological fault but that events without foreshocks occurred in the dyke around the fault tip. We detected strain steps for small tremors that were not detected by the mine seismic network These steps were followed by significant post-seismic creep-like drift, but not preceded by forerunners. Analysis of the continuous 25Hz data reveals many smaller steps with much longer durations (100ms-100s) than seen in normal earthquakes (-1<M<2) with source durations of 1ms〜50ms. Some of the especially slow steps were preceded by accelerations in strain, the maximum being as large as one-third of the step. We installed straimneters and accelerometers near the Pretorius fault at a depth of 2.9 km in the Mponeng mine. We observed strain changes generated by M2 class tremors that occurred within a few hundreds meter from the strainmeters. Similar strain changes were recorded by the two strainmeters. We observed a strain step of 10-5 at maximum but no forerunner was recorded for such a large strain step. Less