Field deployment of coherent seismic wave tomography system (ACROSS)

我们一直在开发一种全新的有源地震地下层析成像系统。传统的基于脉冲震源的地震层析成像虽然取得了很大的成功，但分辨率一直不高；我们已经提出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块。我们运行这个发射器，并测量诱发的地面运动。对一系列不同的频率重复测量，得到频率传递函数。它的傅里叶变换产生脉冲传递函数，这使得常规的地震波分析成为可能。在2000财年，我们制造了比上述模型更大功率的先进旋转震源模型，并在深约600米、宽约3000米的巨大隧道网络中部署了仪器。该地区地处地震高发区，经常发生6级左右的中等规模地震。探测地壳性质的变化预计将是我们系统的一项很好的工作。在2001财年，我们通过密集的地震仪和应变仪网络扩大和加强了试验场。

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.