Simple Installation of a Deep Borehole Seismometer Using a Preexisting Well

我们已经开发出一种在已有井中安装深井地震仪的简单方法。开发的要点是（1）双层套管系统下至井底，以保护由于井水运动而产生的影响，（2）在现有井的底部钻孔，以安装钻孔地震仪，（3）阻尼系统，以保护振动噪声传播到内部套管，以及（4）使用光纤电缆传输数字数据。该系统安装和取放方便，并与其它井中地震仪的地震记录进行了比较，证实了该系统的正确性。根据几个钻孔地震仪的数据，研究了札幌市区地下的微地震活动。震中分布呈西北-东南方向的线性趋势，这可能代表了札幌市区下方的盲断层。最后利用地面和井中地震资料研究了沉积层的地震响应。

We have developed a simple method for installing a deep borehole seismometer inside a preexisting well. The developed points are (1)double-casing system down to the well-bottom to protect effects due to well-water movement, (2)boring at the bottom of the preexisting well to install the borehole seismometer, (3)damping system to protect vibration noises propagating the inner casing, and (4)use of an optical fiber cable to transmit the digital data. Our system is easy to install and take up the borehole seismometer.We have confirmed our system comparing the seismograms with those by the other borehole seismometers. Micro-earthquake activity beneath Sapporo urban districts has been studied based on data from several borehole seismometers. The epicentral distribution shows a linear trend with the NW-SE direction ; this might represent a blind fault beneath Sapporo urban districts. Finally we have studied the seismic response of sedimentary layers based on surface and borehole seismic data.