Using the transmission (reflexion) coefficients in an L-shaped open channel, which were given in a previous paper (MOMOI, 1974), resonance oscillations in an L-shaped channel with a closed arm at one end are dis-cussed in this paper. In the arm, two types of high resonance are found. One is of a conventional type (kd₂<<1 where k: wave number and d_j: widths of the windward channel (j=1) and arm (j=2)) which is well known in real harbours open to the sea, and the other is of a specific type (kd_j=mπ-ε where m: positive integers and ε: a small number). For the former, we introduce a mouth hypothesis which is useful to explain the behaviors of the resonance (i.e., linearity and odd number fractionality) in rectangular har-bours. In the latter case, the one-degree-lower (m-1)th mode is consider-ably excited at kd_j=mπ-ε by degrading the energy of the resonant mth mode.

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An ocean-bottom seismographic network observation was performed around the northern part of the Japan trench, including the aftershock area of the 1968 Tokachi-oki earthquake (M=7.9). The method of observation is an anchored buoy system.
It is found that a high seismic activity of micro-earthquakes exists in the oceanic lithosphere of the east side of the axis of the Japan trench. This suggests that the oceanic lithosphere is capable of generating earthquakes. The seismicity in the oceanic lithosphere was about five times greater than in the island arc side in the summer of 1970. This will be interpreted that the post-seismic activity of the 1968 Tokachi-oki earthquake has migrated into the oceanic lithosphere crossing the Japan trench.
It is also found that a high micro-earthquake activity exists along the inner wall region of the Japan trench, implying the presence of a tectonic activity there. The depth distribution of these earthquake foci shows that the deep seismic zone extends within the upper part of the lithosphere.

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The ray path and its travel time in a weathered layer in which the velocity gradient is constant in the direction of depth are well known, if a source and observation points lie on the same horizontal plane surface. Several other problems concerning the weathered layer are considered in the present paper. The elimination of the incident angle from the equations of the ray path and travel time will result in the equation of wave front. But this elimination is not easy. Some techniques are employed in the elimination of the incident angle. It is pointed out that the wave front becomes a circle again which intersects rays perpendicularly.
The elimination of a common parameter from the equations of the dis-tance and travel time will give the equation of the distance-time relation, even if a source and observation points do not lie on the same plane surface. Some techniques are employed in the successful elimination of the common para-meter (TAZIME, 1957). Distance-time curves are illustrated in a figure where the depth of the source is fixed and horizontal distances of observation points are variable.
If the horizontal distance of the source is fixed and the depths of obser-vation points are variable, the depth-time curves along a bore hole are ob-tained and are shown also in another figure (TAZIME et al., 1975).

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Leaking energies of long waves from a rectangular bay bordering on a straight band of shallow water which in turn borders on deep water are evaluated under some specifications of the ratio of the shelf to bay widths B/2 and the depth ratio R. The effects of the shelf width and depth ratio upon the leaking energy are then examined.
Using the same model as that used in the evaluation of the leaking energy, the transmissity of edge waves through a rectangular concave irreg-ularity is elucidated under the specifications of B=1 and R=5 allowing for the application of the results to the geometry of the coast and continental shelf on the southeast side of Hokkaido in Japan. The important features exposed are the significant effects of the bay, shelf and bay-shelf resonances upon the transmission of edge waves. On the occurrence of a longitudinal bay resonance the energy scattered is directed primarily towards the deep water with a small contribution to the generated edge waves, while in the case of the occurrence of a higher mode bay resonance the energy scattered around the bay entrance contributes primarily to the generated edge waves. In addition to the outstanding effect of the bay resonance, the bay-shelf reso-nance which occurs through the bay and continental shelf has a considerable influence upon the scattering of energy in such a way that the scattered energy into the deep water is highly excited at the points corresponding to the resonance of the normal plane leaky mode on the "supposed continental shelf" with the width of the sum of the bay length and the width of the shelf stretching along the deep water.

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The focal mechanism of the Iwate-Oki earthquake (M_s=7.2) of June 12, 1968, is studied on the basis of P-wave first motion and Love and Rayleigh wave radiation patterns. This earthquake represents a low-angle thrust fault with a left-lateral strike-slip component. The direction of slip vector is N55°W, which is parallel to that of the neighboring Tokachi-Oki earthquake (M_s=7.9). The source parameters determined are: dip angle=30° and dip direction=N119°W for the fault plane; dip angle=76° and dip direction= N125°E for the auxiliary plane; seismic moment=5.1×10²⁶ dyne·cm; fault dimension=80×30km2; slip dislocation=48cm; stress drop=12bar; strain drop=0.27×10^-4; released strain energy=0.70×10²²erg. This earthquake was accompanied with small tsunamis. The sea bottom crustal deformation calculated from the seismic fault parameters fits the tsunami data very well. The generation mechanism of tsunami of the Iwate-Oki earthquake resembles that of the Tokachi-Oki earthquake of 1968.

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A measurement of complex elastic constants is made on two single crystal MgO specimens using a resonance method. The results on the real part of the elastic constants are consistent with those reported by CHANG and BARSCH (1969) and SPETZLER (1970) except for a small difference in C₁₂. The elastic constants at a theoretical density of 3.584g/cm3 are C₁₁= 2.978±0.004, C₁₂=0.970±0.005, C₄₄=1.563±0.002, C_s=(C₁₁-C₁₂)/2= 1.004±0.001, and K=(C₁₁+2·C₁₂)/3=1.639±0.006 in Mbar at 293K. The small deviations of the elastic constants in different specimens from the above valucs are well related to the deviation of the actual density from the theoretical one. The internal frictions relating to respective elastic constants are Q^-1₁₁=0.23±0.61, Q^-1₁₂=-0.35±1.79, Q^-1₄₄=1.87±0.16, and Q^-1_s=0.51±0.14 in units of 10^-4 at room temperature and 1MHz. The dominant dis-sipation is not caused by the shear on a plane of easy glide {110}<110>, but the shear on {100}.

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Gravity values from the central Honshu to the northern part of the Izu-Bonin (Izu-Ogasawara) Arc have been compiled, and the free air and Bouguer gravity anomaly maps as well as gravity tables have been given. The broad gravity low over the triple junction between the Pacific plate, the Eurasia plate and the Philippine-Sea plate has been explained by considering the possible behavior of the Pacific plate descending from the junction between the Japan and the Izu-Bonin Trenches: It may be that the slab descending at the Japan Trench and the slab descending at the Izu-Bonin Trench geometrically have converging velocity components under the junction area to cause subduction of the Philippine-Sea plate beneath the Eurasia plate, and this subduction gives rise to the negative gravity anomaly. Explanation of some other gravity lows observed over the Japanese Islands has also been made tentatively.

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