If one axial symmetry is assumed, three components of the displacement can be generally devided into two groups. One corresponds to the displacement of SH wave and the other does to the displacement made of P and SV waves in rectangular coordinates. The general rule has been obtained which finds displacement potentials φ and φ, including the following conditions: displacement pontentials must be the solution of the wave equation of P and S waves and the displacements made of φ and φ should satisfy the equation of motion.
The well known displacement potentials in rectangular and cylindrical coordinates are reduced to the special cases of the general rule. In the present paper the displacement potentials in spherical coordinates have been given by the general rule. Displacement potentials in different coordinates can be related to each other.
The density of energy flow has been expressed with the displacement potential in the general coordinates. Energy flows of spherical waves will be easily calculated by the use of the displacement potentials in spherical coordinates. Energy flows exist not only in radial direction but also in direction of the latitude. The flows in lateral direction mean diffracted waves.
The origin of φ does not always coincide with that of φ, as in case of reflected S and P waves. The expression becomes very complicated as to energy flows due to the interferences of P and S waves.

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Based on records of tide gauges, two small tsunamis accompanying the earthquakes on April 21, 1969 (M=6.5) and July 26, 1970 (M=6.7) are investigated. Both earthquakes occurred in the Hiuganada region, southwestern Japan. A part of the estimated tsunami sources seems to overlap on the continental slope. The dimensions of these tsunami domains are inferred to be 3O-40km, taking account of the aftershock areas. Judging from the features of the initial part of records, the subsidence of the bottom seems to have occurred in the eastern part of the tsunami sources.
Beside these tsunamis, eight others were generated in Hiuganada during the period from 1926 to 1970. The percentage of tsunamigenic earthquakes is 100% in earthquake magnitude M>7.0 and about 70% in 6.5<M<6.9. These percentage are large in comparison with those obtained for the whole region of Japan. The magnitudes of various tsunamis are compared on the basis of the mean values of the maximum wave-heights observed at the same tide stations on the coast of Kyushu and Shikoku. Tsunami energy is closely related to earthquake magnitude, and the lower limit of tsunami energy observed in this region seems to be of the order of 10¹⁸ ergs. The geographic distributions of the seismic intensity I=4 (JMA scale) for tsunamigenic earthquakes are shown to indicate the relation of this area to the location and the dimension of this tsunami source.

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P_n velocities in the north-eastern and the south-western Japan were determined by utilizing the time-term method. Analyzed travel times observed by the Japan Meteorological Agency were of the epicentral distances between 175km and 600km. The P_n velocroties in these regions were determined as 7.71±0.12km/s and 7.80±0.16km/s, respectively.
AKI (1968) proposed an anisotropic laminated model for the upper mantle in Japan in order to explain the phase velocities of Love and Rayleigh waves. However, the P_n velocity for this model is too large; namely about 8.07km/s. A new model, AN-1 is presented. This model well explains the observed P_n and S_n velocities as well as the surface wave velocities.

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An aftershock sequence accompanied by the earthquake occurred at the central part of Gifu Prefecture on Sept. 9, 1969 was studied. Because of short epicentral distances, a number of shocks were recorded at the Inuyama seismological network from the beginning of the main shock to the end of the November of 1970. These data were useful for the long-term investigation of the aftershock sequence. Those data recorded at Takayama seismological station and temporary stations at Hirayu and Okuzumi were also used in this study. The following results were obtained:
1) Epicenters of aftershocks were distributed along NW-SE direction. It was likely that they were represented by a two dimensional normal distribution with standard deviations of 2.2-3.5km and 3.5-5.0km across and along an assumed fault, respectively. The epicentral region was found to spread gradually towards both sides of the fault.
2) With the use of both data recorded at Inuyama and J. M. A. networks, the epicenter of the main shock was recalculated to the point where aftershocks were clustered.
3) The daily frequency of aftershocks for 450 days from two hours later from the main shock was well represented by single formula, n(t)=k·t^-p, with p=0.95.

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The co-operative observations of micro-earthquakes were carried out during summers in 1963, 1964 and 1965. Periods of the observations were about two weeks. The ultrasensitive seismometers worked on during the period from 9p.m. to 4a.m. on the next day, because of high ground noise in the day time. The instruments at that time were not so developed as the ones nowadays, then the opereators suffered from the various troubles of instruments and every day livings. As each party had been formed by the most excellent seismologists at that time, however, the results of the observations are worthy of analysing even the pressent time in order to get percepts for the future studies.
The discussions at the meetings held before the co-operative observations took up various significant topics. For instance, the fowllowings were discussed; what are the field conditions for the study of ultramicro-earthquakes; where is the model district to satisfy these conditions; what is the most effective arrangement of the stations; what subject should be investigated now, and so on. After the observations, the results of reconsiderations had been discussed, i. e, . the needs of man powers, the improvements of recording systems, the automatic data processings and the more basic studies were pointed out.
The detectability is defined as the ratio of the number of observed earthquakes to the number of earthquakes which should be observed. The first assumption is the ground motions which are judged as the ones due to earthquakes must be observed, at least, at two stations almost simultaneously. The second assumption is the detectable distance must be greater than the greatest epicentral distance among the ones associated with the stations which observed the earthquake. Therefore, it may be said that the station failed to observe the earthquake if that station whose epicentral distance is less than the detectable distance did not record this earthquake motion.
It is concluded;
(1) The detectability is depend on the institute in charge of the observation.
(2) The detectabilities of routine stations for micro-earthquakes are lower than the ones of the temporary stations for ultramicro-earthquakes.
(3) Generally, the detectability of the station situated on the ground of lower noise level is higher than the one of the station of opposite ground condition.
(4) The all-inclusive conclusion is that all the station whose detectabilities greater than 90% had been set up on the less noisy ground and the staffs at that stations read up carefully even the small earthquake motions as the ground noise.

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Equations for unsteady Pekeris-type mantle convection are solved numerically. Medium with variable viscosity is considered and the viscosity is assumed to be expressed by μ=μo·exp (λP+γT). Horizontal and vertical scales of convective layer are taken as 1190 and 700km, respectively.
The following four models are examined:
A1: constant viscosity.
A2: pressure dependent viscosity (exponentially increasing with depth).
A3: temperature dependent viscosity (exponentially decreasing with temperature).
A4: pressure and temperature dependent viscosity.
It is concluded that a horizontally elongated pattern is unstable and is disrupted into three or more sub-cells, when the viscosity varies exponentially (either decreasing or increasing) with depth. For Model A3, the stream lines are concentrated into uprising region, and therefore, the effective cooling of the mantle is realized. For Model A2 and A4, the effective convective cell is confined into the upper part.

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Thermal coupling of the crust and the mantle is examined for a mantle convection of Pekeris-type. Thermally stable stage (no horizontal temperature gradient) is given as an initial condition for the mantle laid under the continental crust. In the meantime, this state is disturbed by the high radioactivity and the low thermal conductivity of the crust. Convection current is generated under the central part of the continental crust at about 10⁸ years after start. Even if an initial pattern directed from ocean toward continent is existed within the mantle, a counter current from continent toward ocean develops under the continent within a time range of 10⁸ years.
It is concluded that the mantle convection is strongly affected by the thermal properties of the crust within a geologic time scale.

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