Amplitudes of PcP and PcS phases are derived in terms of ray and wave theory. Numerical computations when the core is assumed to be a spherical cavity or a liquid are presented to show that, as far as periods of the waves concerned are shorter than 40 sec, the ray theory solution gives satisfactory approximation if angle of incidence at the mantle-core boundary is smaller than 70°. Amplitudes of diffracted waves with short periods decay from a shadow boundary to wards the shadow zone more rapidly than those with long periods. Frequency dependence of amplitudes of the diffracted waves is obtained in a wide frequency range from the numerical solution, refering to a short wave solution. Amplitudes of direct waves close to the shadow boundary cannot be explained by simple ray theory because of contamination due to diffraction into a lit zone. Ex-pressions for the amplitudes in this area are also derived, together with epicentral distance where waves recognize the existence of the core.

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A method is shown to study the crustal and upper mantle structure from the amplitude and phase spectra obtained from the analysis of long-period P-waves. Taking the amplitude ratio of the vertical component to horizontal one and the phase difference between them, we obtain two observational curves which depend only on the structure beneath a recording station. Comparing these curves with the corresponding theoretical ones derived from an assumption of the horizontal parallel layering of homogeneous media, we can select a most probable model in which the theoretical and observational curves fit well each other.
In order to study the structure under the central mountain area, the records registered at Matsushiro have been analyzed. Among four sets of observational curves corresponding to four regions classified by the incident direction, there appear fairly remarkable differences, implying the possible lateral variations of layer interfaces. Confining, therefore, the validity of the above assumption to each of the four regions respectively, and varying layer parameters of the models so far obtained from gravity, travel time and surface wave studies, we have obtained a few probable models for each region. Taking into account all available information on the structure in this area, we have selected one model for each region. The models obtained reveal that the crustal thickness (the thickness of the intermediate layer is not included) is about 40km over this area, and that there is a thick 7.4km/sec intermediate layer whose thickness is considerably different among the four regions. Although Matsushiro is situated in the tectonic region with a thick underlying intermediate layer, surrounded by highly mountain ranges, travel-time residuals from Jeffreys-Bullen table show a remarkable negative value, suggesting the possibility of rather higher velocity in the upper mantle below the intermediate layer or/and the lack of a low-velocity layer, compared with other tectonic regions.

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Measurement techniques of thermal diffusivity of rocks and minerals at high pressures and temperatures have been developed. The technique utilizes the Angstrom method. Samples as small as several millimeters in linear dimension can be measured. The methods were tested on quartz, fused silica, basalt, and serpentinized peridotite. Linear and cylindrical sample geometries are tested. It is found that, for relatively opaque samples, the cylindrical sample geometry is most suitable for measurements at high pressures. The linear sample geometry is adequate for measurements of small samples at moderately high temperatures.

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The subsurface structure of Oosima Volcano is discussed mainly from the geophysical standpoints on the basis of the available data. First the author summarizes the results of gravimetric surveys and explosion-seismic observations carried out on and around Oosima Island to discuss the deeper structure of the volcano and then proceeds to a discussion of the caldera structure utilyzing the results of the drillings, electric prospecting and gravity measurements. Finally a tentative model of the shallow subsurface structure of Oosima Volcano is presented.

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At Oosima Volcano, Izu, various geomagnetic studies have been continued since its great eruption of 1950-51. And also the results of geophysical and geological investiga-tions of the structure of Oosima Volcano have been accumulated. In 1957, the present author discussed the anomalous change in geomagnetic field observed in the 1953-54 eruption. In the present paper the author would revise this discussion reflecting upon the results of 10 years' observation of magnetic declination and the accumulated re-sults of the subsurface structure of the volcano. The conclusion is that the observed anomalous changes are interpretable by the possible thermal processes beneath the volcano. Its quantitative results on heat supply to the volcano may lend a sugges-tion as to energetics of volcanisms.

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The underground structure in the Matsushiro Earthquake Swarm Area was derived from the data of explosion seismic observations in profiles A and B. First, the number of layers and the velocity in each layer are determined by using the T' curve. Then on the assumption that the dip of each interface is small, the structure of the first approximation was derived. The final models were derived by the method of trials and errors so as to reduce (O-C), the difference between observed and calculated travel times.
The underground structure in profile A consists of the following three layers on the whole:
the first layer : 1.6-2.3 km/s
the second layer : 3.3-4.75 km/s
the third layer : 5.9-6.0 km/s
In profile B the underground structure also consists of three layers, but there is a surface layer in some places:
the surface layer : 0.36-1.2 km/s
the first layer : 1.7-3.2 km/s
the second layer : 4.0-4.4 km/s
the third layer : 6.0 km/s
The underground structures derived by using above velocities are given in Fig. 2 for profile A and in Fig. 3 for profile B.
The underground structure in profile A, which is in the Central Belt of Uplift named geologically and is parallel to its strike, is relatively simple. Generally speaking, the top of the third layer (with the velocity of 6.0km/s) is unusually shallow, about 1.5km from the earth's surface even at the deepest, and has a tendency getting shallower a little toward the southwest. Or it may be said that the depth to the top of the third layer is smaller by 0.3-0.5km in the portion from the middle of E₂ to D₈ than the other portions. The velocity in the third layer is 6.0km/s in the area northeast of Matsushiro and 5.9km/s in the area southwest of Matsushiro. There is a possibility of existence of anomalous structure or a fault between E₄ and E₅ although there are no observation points in this area because of the topography. This anomalous struc-ture may correspond to the low Bouguer anomaly around Mt. Minakami.
The underground structure in profile B, which passes the central part of the epicentral area and crosses the Central Belt of Uplift, is fairly complicated. The velocity in the first layer is 1.7-3.2km/s and this layer becomes thick abruptly near the Chikuma River toward the northwest. The velocity in the second layer is 4.0-4.4km/s and it is noteworthy that the thickness of this layer increases by about 3km almost discon-tinuously around the middle of E1 near Nagano City. From another point of view, the top of the third layer becomes very shallow in the central part of the profile and reaches only about 1km from the earth's surface. This interface becomes deep toward the southeastern end of the profile, so that the deep structure of the Central Belt of Uplift may be defined. At least the layer with the velocity of 6.0km/s might be related to the formation of the Central Belt of Uplift, or it might be said that this layer played an important role for its formation. This profile passes the foot of Mt. Mina-kami at D₇ and the underground structure has anomaly near Mt. Minakami which may correspond to low Bouguer anomaly. There is a large possibility that the anomalous structure in this profile is of the same origin with that in profie A since the locations of anomalous structures are close with each other and their manners are quite similar. It is quite interesting that there exist anomalous underground structures in the area where Matsushiro swarm earthquakes have occurred most frequently. Also it is interest-ing to note that there is no layer with the velocity of about 5.5km/s in the area concerned.
On the other hand by the comparison of the underground structure in this paper with results from other geophysical and geological investigations, several interesting relations are pointed out.

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Viscosity and yielding stress of basalt under high temperature were obtained from the study of hot pressing characteristics of basalt. They were calculated from Mackenzie-Schuttleworth's equation and its integral equation. Viscosity of basalt at 727°C was found to be 10¹² poises and yielding stress was also found to be 10⁹ dynes/cm2.

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