Field deployment of coherent seismic wave tomography system (ACROSS)

我们一直在开发一种全新的地下地震层析成像系统。尽管取得了巨大的成功，但基于脉冲震源的传统地震层析成像一直存在分辨率不足的问题；我们开创了一种基于精确谐波的替代方法，并开发了相干技术来监测地下。我们的震源是一个由伺服马达驱动的偏心质量。我们运行这个发射器，测量诱发的地面运动。在不同频率范围内重复测量，我们得到频率传递函数。它的傅里叶变换产生脉冲传递函数，使常规地震波分析成为可能。在2000财政年度，我们制造了一种先进的旋转震源模型，其功率比上述模型大得多，并将仪器部署在深约600米，宽约3000米的巨大隧道网络中。这是一个地震活动频繁的地方，经常发生6级左右的中等地震。地壳性质变化的探测有望成为我们系统的一个很好的应用。在2001财政年度，我们通过一个密集的地震仪和应变仪网络扩展和加强了试验场。

We have been developing a brand-new active seismic underground tomography system. In spite of its great success, conventional seismic tomography, which is based on impulsive sources, has been suffering lack of resolution ; we have initiated an alternative method on the basis of accurate harmonic wave and developed coherent technologies to monitor the underground. Our seismic source is an eccentric mass driven by a servomotor. We run this emitter and measure the induced ground motion. Repeating the measurement for a range of different frequencies, we get frequency transfer function. Its Fourier transform yields impulse transfer function, which enables the conventional seismological wave analysis.In 2000 fiscal year, we manufactured an advanced model of rotary seismic source with much more power than the foregoing model and deployed instruments in a deep enormous tunnel network of around 600m deep and 3000m wide. This was located in a high seismicity place where moderate size earthquakes of around magnitude six often occur. Detection of change of crustal properties is expected to be a good exercise of our system. In 2001 fiscal year, we extended and reinforced the test field through an intensive network of seismometers and strainmeters.