Ground and underground observation of the magnetic field in mine area and its application

我们在日本东北部细仓地下矿井用一对磁通门磁强计观测到地磁场的三个分量。其中一个被放置在地面以下约70米的主廊道中，另一个被放置在1米以下的孔中。利用这种高灵敏度的磁力仪，我们观测到了伴随着断层运动而产生压磁效应的同震磁信号。

We have observed three components of the geomagnetic field using a pair of fluxgate magnetometers in the Hosokura underground mine in northeast Japan. One of them has been placed at the main gallery ~70m below the ground surface and another in a hole 1m below. By virtue of such highly sensitive magnetometers, we observed the co-seismic magnetic signals accompanied with the fault movement which causes the piezomagnetic effect.