The geological structure of Yaimagahara (Narusawa village in Prefecture Yamanashi, northern foot of Mt. Fuji) was investigated by means of VLF-MT method. This area is characterized by volcanic ejecta (basaltic lava flow, tuff breccia, scoria and so on) resulted from the eruption of Mt. Fuji volcano.
VLF-MT measurements were made along 17 lines using 50 m station interval. Apparent resistivity and phase angle between magnetic and electric field were measured at each station. When interpreting the structure by two-layer model, evaluation of the resistivity of the top layer p1 must be done. This evaluation was done in following manner:(1) Value for apparent resistivity at station where value for phase angle is between 41-49 degree is regarded as value for p1, and this value is used as pi near this station.(2) In the area where no station that have a value for phase angle 41-49 degree is present, based on the known geology (boring data, outcrop and so on), the value for pi is estimated from the geological column.
The result of survey indicated that the VLF-MT method is useful for estimation of structure in volcanic area where no outcrops are present.

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Electromagnetic parameters of rocks in short wave band (mainly 15 MHz), such as resistivity and dielectric constant, were examined for various rocks and minerals to derive a proper geological interpretation from radar tomographic data.
In this paper, influences of lithologic characters, for example, mineral or rock type, porosity, grain diameter, were tested in detail.
Obtained results are as follows:
1. Resistivity and dielectric constant decrease as the increase of frequency. The decrease rate of resistivity of dried rock is higher than that of saturated rock, and the decrease rate of dielectric constant is inverse to that of resistivity.
2. Resistivities of minerals are distributed in proportion to the-2--3 power of dielectric constants of those minerals.
3. Minerals can be classified four types on the diagram of resistivity versus dielectric constant, felsic minerals, mafic minerals, clay minerals, and iron ore, in order from high resistivity and low dielectric constant to low resistivity and high dielectric constant.
4. Resistivities of part of sedimentary rocks and volcanic rocks are relatively lower than those of minerals which have the same dielectric constant.
5. Dielectric constant of dried rock is approximated to the Lichtenecker's law.
ε: relative dielectric constant of a dried rock, a-n: volume rate of each minerals or pore, here a+b+…+n=1, ε_a-ε_n: relative dielectric constant of each minerals and pore air.
6. In the case of dried rock, the resistivity increases in proportion to the -2--3 power of the dielectric constant according to the increase of porosity. In the case of saturated rock, dielectric constant continuously increases according to the increase of porosity, but the resistivity mostly decreases at a specific porosity.
7. The resistivity of a rock decreases according to the reduction of its grain diameter.
Some of these results are correspond to the past studies qualitatively except for the result No.2. 4. and 6. which are unknown in the past.

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In order to make clear the occurrence mechanism of earthquake damage to some kinds of objects, to develop earthquake-proof countermeasures for them, to work out rules for identifying the sites liable to be damaged by earthquakes and so on, the structures of grounds have been investigated with many examples of earthquake damages. Objects include embankments, buildings, bridges, tanks, quays, power substations etc. Their damage includes liquefaction and others that have ocurred in sandy ground. In this paper the occurrence mechanism of earthquake damage to objects on sandy ground is studied referring to deformed states of ground and objects, and structures of the ground.
The results are summarized as follows:(1) When the ground under objects is made of sand only, the earthquake damage occurs very rarely;(2) in the ground under earthquake-damaged objects are encountered many upside-down types of ground in which soft clayey soil layers underlie sandy ones. But when they are horizontallystratified, the earthquake damage occurs very rarely;(3) objects are lible to be deformed, when they straddle thick and thin parts of soft clayey soil layers under sandy ground, when they cross buried valleys with upsidedown type grounds, or when comparatively thin soft clayey layers between sandy ground and their underlying hard soil layer tilt;(4) above-mentioned soft clayey layers consist of soils like peat or clay; and (5) the deformation due to earthquakes reflects the structure of the ground.
Also, it is estimated that most of these damages were caused by large differential displacements of nonuniform ground in which the thicknesses of soft clayey layers are non-uniform, or extraordinary vibrations of soft clayey soil layers in buried valley type grounds under earthquakes, just like those in other seismic damages.

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For the purpose of estimating the reliability and utilization of VLF (Very Low Frequency) investigation method, the measured results obtaiued by this method and the seismic method were compared to each other.
The abnormal zone, which is detected by the VLF method, that were thought as the fracture zone in fault and/or low resistant zone in metal deposit, was almost identical to the low velocity zone found by the seismic method.
Furthermore, it was found that the VLF method to detect the water content of fracture zone and cracky dyke.

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