The mechanism of occurrence of local earthquakes frequently taking place in Wakayama area was studied from the push-pull pattern of initial motions and the amplitude distribution of P- and S-waves. The mechanism can safely be (concluded) to be of a cone-type rather than a quadrant one as far as the present data are concerned.
A consideration based on the former type of mechanism suggests that the focal volume corresponding to each of the earthquakes is asymmetrical in shape with its radius differing according to directions.

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The crustal structure as shown in Fig. 6 was derived from observations of the second Hokoda explosion. That is, in the Kwantô area the first layer has a velocity of 1.74km/sec with a thickness of 0.92km and ceases to exist in the farther north of Hitati. The second layer has a velocity of 5.5km/sec with a thickness of 4.3km, however, its bottom surface begins to taper northward at a distance of Δ=40km from Hokoda, and near Tamura the third layer with velocity of 6.2km/sec comes near the earth surface.
In North-east Japan, except Siroiwa and Kaneyama, the surface is covered by a certain thin layer and the second layer, corresponding to that of Kwantô area with a velocity of 5.5km/sec, has a velocity of 5.8km/sec with thickness 4-8km.
The velocity of P_n waves is 7.7km/sec and the depth of the Mohorovicic discontinuity is 27.5km under Hokoda and tapers northward with inclination of about 2°. The depth of the Mohorovicic discontinuity is verified by reflected waves observed at Sano.
Hitati is a singular point and the third layer is supposed to be upheaved near to the earth surface. The correspondence of this feature to the surface geology and gravity data is very good.

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At the midnight of August 26, 1957, the Research Group blasted about one ton of explosives at a site of an abandoned aerodrome near Hokoda town, Ibaragi Prefecture, and seismic waves from it were observed at 18 temporary stations as shown in Fig. 1 and Table 1. The shot point was shifted by 188m in the S 57° W direction from the first shot point.
Essential objects of these observations are summarized to the following two points. First, this observation forms a profile reverse to Kamaisi Explosions in order to verify the crustal structure of the North-east Japan previously obtained by us. Secondly we aim at finding the connection between the crustal structure of the northern part of Kwantô District and that of North-east Japan.
Observed travel times are given in Table 2 and Table 3. Travel time diagrams are shown in Fig. 2 and Fig. 3.

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The equation of equilibrium of a homogeneous and isotropic elastic body was solved in the prolate and oblate spheroidal coordinates for the cases of m=0, 1 and 2. The solutions consist of three parts: the first part (Eq. (17)) satisfy Δ=0 and ω=0, the second part (Eq. (18)) Δ=0 and ω≠0 and the third part (Eqs. (80), (82), (83)) Δ≠0 and ω≠0.

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