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公里深处的加速度计阵列的数据，我们证实了相似定律适用于矿震(-2&lt；M&lt；3)。此外，通过对距台阵100m以内的矿震破裂过程的反演，发现它们的滑动分布与天然大地震一样不均匀，破裂速度和地震效率也与之相似。我们广泛分析了安装在Bambanani矿2.4公里深处的石井型应变仪的数据，发现了与M2级地震及其前震和余震有关的应变变化，这些地震发生在应变仪100米范围内。尽管M2级地震的应变步长约为10-4，但在M2级地震前并未发现异常应变变化。通过利用这些应变阶跃记录，我们精确地确定了震中位置。我们从这些数据中推断出…前震前的M2级地震多发生在地质断层上，而无前震的地震发生在断层尖端附近的岩墙上。我们检测到了矿震台网没有检测到的小震的应变步骤，这些步骤之后是显著的震后蠕变状漂移，但没有先兆。对连续的25赫兹资料的分析表明，与震源持续时间为1ms~50ms的正常地震(-1&lt；M&lt；2)相比，地震的阶跃要小得多，持续时间(100ms-100s)要长得多。在一些特别慢的步子之前，会出现应变加速，最大速度可达步幅的三分之一。我们在Mponeng矿2.9公里深的比勒陀利亚断层附近安装了应变计和加速度计。我们观测到了发生在应变计几百米范围内的M2级地震产生的应变变化。两个应变仪记录到了相似的应变变化。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的先兆。较少

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