Based on the maps of distribution of foci of earthquakes in and near the Japanese Islands which were shown in Part I of this paper, the vertical distribution of earthquakes is investigated.
1) Two kinds of cross sections are shown. The first ones are cross sections almost parallel to the islands arcs, volcanic belts, deep oceanic trenches and gravity anomaly axes. The second ones are cross sections intersecting those geophysical features.
2) The foci of earthquakes within the distance of 125km from these cross sections have been projected from both sides. The projections show the vertical distribution of foci of earthquakes in detail. Other geophysical features are also shown in these projections.
3) The equal focal depth axes which show the average depth of foci of earthquakes have been drawn.
The main results are as follows:
1) Most foci of earthquakes are distributed with the gradient of about 40° from the ocean to the continent side. The gradient is steeper (about 55°) in the Shichito-Bonin and Kyushu region, and in these regions, volcanic belts, trenches and gravity anomaly axes are closer to each other than in other regions.
2) Shallow earthquakes are concentrated in the regions between positive and negative gravity anomally axes. The nests of earthquakes are very clearly recognized.
3) The volcanic belts are situated between the 100km and 200km equal focal depth axes.
4) In the south-western part of Honshu, the distribution of foci of earthquakes are quite different from that of other parts of the Japanese Islands.

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Study of seismicity by means of mobile observations of ultramicro-earthquakes occupies an important position in the project of earthquake prediction in Japan. We searched the Matsushiro earthquake swarms for the problems and troubles involved in the study of seismicity by means of our mobile observation system.
In spite of the doubtful accuracy in determining the distribution of hypocenters from the frequency distribution of S-P times, the results of our observations proved the reliability and the usefulness of the mobile observation system for the purpose of surveying the seismicity in a certain area and its variation with time. It proved to be especially useful in places where the seismicities could not be determined on a routine basis.
In order to get more precise information about the seismicity of ultramicro-earthquakes, the followings should be taken into consideration:
1) It is preferable that three component seismographs should be used in order to distinguish P and S as many earthquakes as possible, though it necessitates a heavy cargo.
2) It is necessary to devise some methods in order to account for the earthquakes which have indistinct S-P times and are not accounted for consideration of the frequency distribution of S-P times.
3) A cautious attitude should be taken in selecting places where the transducers are set up, in order to get seismic wave forms of good quality, though it reduces the area of observation.
4) Extensive studies on the physical processes which lie behind the time variations of seismic activities should be undertaken.
5) Long period observations which are much greater than the short period perturbations of seismicity should be carried out frequently. The intervals between each observation should be shorter than the periods of the variations of seismicity which being studied.

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The internal structure of the moon is examined in the light of the thermal state in which the present surface heat flow is used as a limiting condition. The thermal history is calculated for several models of the initially cold and hot moon. Main interests are: 1) to clarify the change of the thermal character of the moon when a gravitational separation of the iron core from the mantle is occurred; 2) to study the thermal history of the outer parts of the moon assuming a longenduring or an instantaneous formation of the crust resulting from the differentiation of the mantle.
The cold moon models give the observed heat flow provided that the average U concentration of the moon lies less than 1.5×10^-8gr/gr. In this case, the core and the crust would not form.
In the hot moon, the core and crust are formed during the early stage and therefore the present surface heat flow is not excessive, even if the crust is present. The instantaneous formation of the crust together with the concentrations of U less than 1×10^-8gr/gr are required to explain the present surface heat flow.

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Empirical formulas for the determination of the earthquake magnitude M from the duration of oscillation F-P have been derived from the observational data obtained by the Wakayama Micro-earthquake Observatory, Earthquake Research Institute.
The instruments used by the Observatory and its substations are the short period vertical seismographs of the same characteristics (T₁=1.0sec, T₂=0.025sec, velocity sensibility=40-120uμ kine/mm at 1 to 10c/s).
The formula obtained from the comparison of the F-P (sec) observed by the network with the M determined by the Japan Meteorological Agency is:
M=-2.53+2.85log(F-P)+0.0014Δ
where Δ is the epicentral distance in km. This formula is applicable to the earthquakes with Δ<1000km and focal depth ≤60km.
Since the coethclent for Δ is very small, the correction term of Δ can be neglected for the earthquakes with Δ<200km, and in this case the following simpler formula is more conveniently applied:
M=-2.36+2.85log(F-P).
The magnitudes obtained by the former and the latter formulas are designated, in the figures and table, M_F-P and M′_F-P respectively.
The largest merits of this method are:
1) Wide range of magnitude can be covered with a single seismograph, since there is no difficulty in reading F-P such as ‘saturation’ or ‘under exposure’ in the case of maximum amplitude.
2) The treatment is very simple, especially for the earthquakes of short epicentral distances.

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The third observation of ultra microearthquakes were carried out by the Research Group of Ultra Microearthquakes from August 10th to August 25th 1965, in the vicinity of Wakayama.
The purposes of the observation are 1) to learn the precious seismicity of ultra microearthquakes in the seismic region, 2) to find the reliability of the observation method and estimate the approximate structure of the crust in this region.
Seven of the observations were small aperture seismometer array stations and the others were single seismometer site observation stations. Authors had charge the arrangement of the result obtained by these array stations, and found the accuracy of the apparent velocity of P waves and the azimuth determined by each temporary seven stations. Accuracy of hypocenter location also has been verified by the comparison of the result obtained by three methods (i. e., S-P times, arrival time, and tripartite method) independently, but we could not estimate the certain structure of the crust in this region.

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