An efficient force system for an appropriate design of a shear wave generator is found to be a horizontal single force or a horizontal single couple in the vertical plane. The transverse displacement of waves due to this type of force system is of SH wave, involving small amplitudes of P and SV waves.

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In this paper the propagation of Love-type SH waves in a monoclinic crystalline internal stratum of finite thickness lying between two semi-infinite non-isotropic elastic layers has been investigated. The intermediate layer is supposed to be composed of dipotassium tartrate. The dispersion relation is derived and discussed. Some of the limiting cases are considered. The interesting results obtained in the case of crystalline media are clarified in contrast with an isotropic case or with a transversely isotropic case.

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The focal mechanism of the Kita-Mino earthquake of August 19, 1961, is investigated in relation to an active (Quaternary) fault, the Hatogayu-Koike fault, running in N35°E direction along the Uchinami River near the border region of Fukui and Gifu prefectures in central Japan.
The re-located hypocenter is situated at the northeast end of the Hatogayu-Koike fault and is shallow in depth. The re-analysis of the first motion data of Japanese stations yields a fault plane solution of the "quadrant type, " while in a previous work, the P-wave first motion data of this earthquake was explained only as the "cone-type." The spatial distribution. of aftershocks is concentrated on the area along the Hatogayu-Koike fault. The observed trend of the static vertical displacements changes near tbe fault. These facts lead to a conclusion that the Kita-Mino earthquake of 1961 was a result of right-lateral and reverse faulting of the Hatogayu-Koike fault. A comparison of the synthesized seismograms calculated for a semi-infinite medium with the long-period seismograms recorded at Abuyama, about 170 km distant to the southwest from the epicenter, yields rupture velocity and rise time estimates.
Focal parameters thus obtained are as follows; origin time 1961, August 19, 5h, 33m, 32.8sec (GMT); epicenter 36°05′N, 136°44′E; focal depth 2 km; fault plane, dip direction N55°W, dip angle 60°; slip direction of the hanging wall 130°(right lateral and reverse); fault length 12km; fault width 10km; average dislocation 2.5m; rise time 2sec; rupture velocity 3km/sec; seismic moment 0.9×10²⁶ dyne·cm; stress drop 160 bars; strain energy released 1.7×10²² ergs.

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It is verified that an oblique rigid opening results in good fit of the rifted portions of arc on each side of the Mariana trough. The good fit suggests that there has been rigid plate accretion and that a plate 200km wide and 1500km long can stay undeformed between active consuming and accreting Plate boundaries.

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Tectonic implications of subcrustal, normal faulting earthquakes in the western Shikoku region have been investigated in sorme detail, mainly based on the faulting mechanism of the Bungo channel earthquake of August 6, 1968 (M=6.6, h=45km) and its aftershocks. A synthetic study of the focal mechanism solution, spatial distribution of aftershocks, seismic waves observed in the near and far fields, and vertical tectonic movements, indicates that the main shock was caused by normal faulting with some left-lateral motion of a western block downwards relative to the eastern side, along a steep westerly-dipping fault plane with dimension of 18-20km, which was formed by the rupture initiating at a depth of 45km and spreading upwards and northeastwards. The fault parameters estimated by a comparison between the observed and synthetic seismograms are: seismic moment 2.0-2.2×10²⁶dyne·cm, average fault displacement 0.8-1.0m and stress drop 33-40bars. These parameters explain the measured elevation changes.
The focal mechanism of a series of the 1968 earthquakes, a foreshock, main shock and aftershocks, as well as many other earthquakes around the region, is consistently of the normal faulting type, in contrast to low-angled reverse faulting in Hyuganada earthquakes. This result suggests that all must have been generated under the same tensional stresses working horizontally in an E-W direction. Possible causes of the tensional stresses are discussed in relation to the descending Philippine Sea plate. Some tectonic models such as tearing, simple bending of the plate along the hinge line, gravitational drag, and thermal stress due to cooling, are tentatively examined.

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An ocean-bottom seismographic observation was performed at the central part of the Fiji Plateau in Aug. 20-29, 1973. It was found that intense micro-earthquake activity, including two swarm activities, were taking place in the neighbourhood of an ocean-bottom seismographic station located very close to the spreading center inferred by CHASE (1971). The average daily frequency of occurrence was about ll earthquakes per day at the station. The sea floor of the Fiji Plateau was unusually restless with numerous small tremors, which seem to be generated by natural earthquakes. The central part of the Fiji Plateau seems to be tectonically very active at present.

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