Deveropment of high resolution tomography method based on coherent seismic wave

我们基于一种全新的理念开发了一种主动式井下层析成像系统。1997财年，我们建立了测试系统，并准备制造一个震源，这是本研究的中心。1998财年，我们制作了信号源，并将其安装到测试系统中。并进行了改进。(1)建立了精确控制人工震源的原型模型。在这个源中，一个电动伺服马达驱动一个偏心质量。旋转的频率保持非常恒定。建立了由高灵敏度反馈地震仪、放大器、AD转换器和PC机组成的传感器单元的原型模型，PC机管理AD转换的时序，并通过叠加的方式对数据进行压缩。(3)建立了为数据分析提供基础的数学理论。建立并验证了弹性波场的几种数值分析方法，包括多层介质半解析法、有限差分格式等。我们计算了许多正演问题。(4)尝试建立了一种新的估计地下结构的反演算法。然而，有必要建立弹性波在非弹性区域的散射的简明模型。我们制定了对这一现象进行新的实验研究的计划。

We have developed an active underground tomography system based on a new-brand idea. In 1997 fiscal year, we set up testing system and prepared the manufacturing of a seismic source which was the center of the present research. In 1998 fiscal year, we manufactured the source and installed it in the testing system. We have been running it and made improvements.(1) We established a prototype model of the accurately controlled artificial seismic source. In this source, an electric servomotor drives an eccentric mass. The frequency of the rotation is maintained extremely constant. As a result, the source could emit very pure sinusoidal wave.(2) We established a prototype model of a sensor unit, as a combination of high sensitivity feedback seismographs, amplifiers, AD converters and a PC.This PC manages the timing of AD conversion and condenses the data by stacking.(3) We also developed mathematical theory which affords the basis for the analysis of data. We made and tested several numerical analysis methods of elastic wave field including a semi analytic method of multi-layer medium a finite difference scheme. We have calculated many forward problems.(4) We attempted to build a new inversion algorithm that estimated the under ground structure. It was revealed, however, necessary to prepare a concise model of scattering of the elastic wave by inelastic region. We established a plan of new experimental study of this phenomenon.