Fundamental Study on the Effective Observation Method and the Propagation Mechansm of Anomalous Radio Wave Noise Occurring Just Prior to Earthquakes

1. 参考文献概述：自1970年以来，对可能与地震有关的异常电磁发射进行了实验观测。观测点几乎接近地面，接收频率小于几MHz。由于观测到的数据很少，这些数据在一般情况下并不完全可以接受。假设震源位于深部，理论研究和数值算例的参考文献都没有找到。近似理论方程的推导和数值计算结果：假设震源位于震源，我们将此问题视为由两层（地面和空气）均匀介质组成的最简单模型。利用几何光学理论，得到了近地表电场强度和源强度的方程。利用其他研究机构的观测数据对方程进行了数值估计。这些结果导致了后面4.3节描述的结论。室内小型地面-空气模型实验：试图验证计算的有效性。测量是在有限的空间内完成的，包括被一些无线电波吸收器包围的干沙。但是由于吸收器的反射和接收天线的不稳定，我们观察到的数据不满意。有效观测考虑：观测点应设在地下深处，以消除地面上方的另一种噪声；观测点应设在低电导率的地面，观测频率较低，以降低传播损耗。

1. Survey of references : The experimental observations of the anomalous electromagnetic emissions possibly related to earthquakes have been carried out from the years of 1970. The observation points are almost near the ground surface, and the receiving frequencies are less than several MHz. As the observed data are few as yet, these data are not entirely acceptable in general. The references of the theoretical investigations or numerical examples assuming the wave source at the deep ground were not found.2. Derivation of the approximately theoretical equations and the results of the numerical calculations : We treated this problem as the simplest model consisted of two-layred (ground and air) homogeneous media, assuming the source was located at the focus of an earthquake. Equations of the electric field intensity near the ground surface and of the strength of the source were obtained, using the geometrical optics theory. Applying the observed data by other research institution to the equations, numerical estimations were carried out. These results lead to the conclusion described later section 4.3. Experiments with the small-sized ground-air model in a room : The experiments were attempted to verify the validity of the calculations. The measurements were done in the limited space including dry sand enclosed by some radio-wave absorbers. But we observed the unsatisfied data because the reflection occured from absorber and the instability of a receiving antenna.4. Consideration for the effective observation : The observation point should be located in the deep ground to remove another noise coming from above the ground, and in the low conductivity ground at lower observation frequency for lower propagation loss.