The displacements due to a periodic and impulsive line source of SH waves in a dipping layer overlying an elastic solid are theoretically investigated using a reflected wave formulation. A formal solution is found by which the contributions due to head and reflected waves are determined by evaluation of the integrals by the method of steepest descent. Although the individual waveforms are similar for the wedge and the horizontally layered case, the synthetic seismograms are markedly different due to the difference in travel times.
Using ray paths, the contributions of the integrals have been interpreted. The range of existence of head waves has been examined and the discontinuities in the wedge associated with diffracted waves studied. In the case of a free or rigid lower boundary of the wedge, the dispersion relation has been determined.

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Gravity was measured at sea by use of the T.S.S.G. surface ship gravity meter. The mechanism of the T.S.S.G. and the method of data processings have already been dealt with in papers by Tomoda et al., (1962, 1968), but since then improvement has been made in both respects. In this paper methods of data processings are described with special emphasis on the 2nd order correction for finite sampling intervals and also on the effect of elasticity on the dynamic gravity meters. Effects of horizontal accelerations are also discussed in relation to the T.S.S.G., which have mattered with Vening-Meinesz submarine gravity meters, La Coste-Romberg gyrostabilized shipboard gravity meters or Graf-Askania surface ship gravity meters.

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Analysis of microseisms observed at the German stations Moxa and Berggiesshübel was performed and the result was utilized to improve the signal-to-noise ratio for the observation of the real seismic events.

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Crustal and upper mantle structure in the Chugoku region has been studied by the same method as described in Part 1 of this paper, by analyzing the seismograms of long-period P-waves recorded at Shiraki. Further theoretical evaluation of the method for the dissipative and anisotropic media is made, in addition to Part 1. The observational curves of the amplitude ratio and phase difference for 25 shocks are classified into six sets by the direction of wave approach to Shiraki. The first high peaks of the curves for waves approaching from the near south to southeast direction appear at frequencies higher than those from the other directions. This suggests that the crust becomes thinner towards this direction. Comparing these observational curves with the theoretical curves, which are calculated by varying layer parameters of the models so far proposed for the structure near this region, four combinations of probable models are finally obtained and the average layer thicknesses are estimated. Among these models, model SHK70-4 is considered as most probable, whose thicknesses of the crust and 7.4km/sec intermediate layer are about 41km and 26km, respectively. However, models SHK70-2 and 3 cannot be excluded. The former, which has a crustal thickness of about 26km and the thickness of the intermediate layer of about 17km, is more probable than the latter. From travel-time studies late arrivals of P-waves at Shiraki as much as about 0.6 seconds are observed, compared with those at Matsushiro and Tsukuba. This implies that the upper mantle with a lower velocity is fairly thicker around this area than in the central mountain area and the Kanto plain.

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In order to discuss the stability of crustal structure deduced from seismic refraction measurements, the relationship between the depth to the Moho and the pressure acting on it is investigated by analysis of approximately 360 refraction data obtained in both continental and oceanic regions. It is found that there is a linear relationship between the depth to the Moho and pressure in vast areas extending from continents to ocean basins. The isostatic pressure versus depth relationship of the Moho is determined from about 200 refraction data obtained in stable areas. The division of data into two groups, one in stable areas and the other in active tectonic areas, is based mainly on the occurence of shallow and intermediate depth earthquakes. If the pressure deviation from the isostatic relationship exceed 95% confidence levels, these values are denoted pressure anomalies of the Moho, and the crust-mantle structures of such pressure anomalies are judged to be out of isostatic equilibrium. Because the pressure anomalies may correspond to the vertical component of forces acting on the rocks of unstable crust-mantle structures, inferences about the force mechanisms of tectonic processes acting on the island arc and trench systems are discussed through investigations of the pressure section on the Moho. The pressure sections on the Moho are presented for the Kuril-Kamchatka, Japan, Izu-Ogasawara, Honshu-Mariana, Tonga and Puerto Rico island arcs and associated trench systems. From those investigations, it is revealed that tectonism in the island arc and trench systems is controlled by forces acting in opposite directions; i.e., there is an upward force of about 500kg/cm ² acting on the upper mantle rock under the island arc and a downward force of about 1000kg/cm ² acting on the upper mantle rock in trench.

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Seismic measurements at over seventy points on the Aso caldera have revealed the nature of stationary ground tremor on the atrio area, which cannot be attributed to traffic passage nor to the volcanic activity.
The tremor is sinusoidal and stationary, the wave characteristics suffering little temporal change at any fixed point. On the contrary, it changes remarkably with change of observation location.
The spatial trend of observed waveform has a definite correlation with the topography, which suggests the possibility of its usefulness to structural interpretations of the Aso caldera.
The particle motion at the ground surface is observed to be confined in a horizontal plane. The spatial phase relation of the tremor shows that it is not a simple standing wave phenomenon but has a complicated propagating nature and that the particle motion is transversal to the direction of wave propagation.

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