Simple Installation of a Deep Borehole Seismometer Using a Preexisting Well

我们开发了一种简单的方法，可以在已有的井中安装深井地震检波器。开发的要点是：(1)下至井底的双套管系统，以保护井水运动的影响；(2)在已有井的底部钻孔，安装井内地震仪；(3)阻尼系统，以保护振动噪声在套管内传播；(4)使用光纤电缆传输数字数据。该系统安装方便，无需占用钻孔地震仪。通过与其他钻孔地震仪的地震图比较，我们证实了我们的系统。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NW-SE方向的线性趋势；这可能是札幌市区地下的一个盲区。最后结合地面和钻孔地震资料，对沉积层的地震响应进行了研究。

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.