A simple source model, in which only far-field term is considered, is used to determine the fault size and the moment of small earthquakes (4.2<M<5.0). This model gives a relation between the fault dimension and the spectrum of observed seismograms. The model is tested for Gifu-ken Chubu earthquake on September 9, 1969(M=6.6), for which detailed fault parameters had been obtained from geodetic and near-field seismic observations. This test demonstrates that the moment and the fault dimension estimated by the present method agree with those determined by the nearfield data within a factor of two.
This simple method is applied to small earthquakes with magnitude 4.2 to 5.0 which occurred in 1966-1972 in the Kii peninsula region, using the long-period seismograms observed at SHK. The fault length and seismic moment for the earthquakes are estimated to be about 2km to 9km and about 1×10²² dyne·cm to 2×10²³ dyne·cm, respectively. The estimated fault lengths coincide with the linear dimension of the aftershock areas, within a factor of two or so. By using AKI (1966) and KEYLIS-BOROK (1959) formulas, the stress drop and dislocation are estimated to be about 0.4 bar to 13 bars and about 0.3cm to 3.4cm, respectively. It is concluded that the simple fault model is useful for estimating the fault length of the small earthquakes when no other information as to the dimension is available.

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Analytical expressions for the strain and tilt fields due to an inclined rectangular fault in a semi-infinite medium with an arbitrary Poisson's ratio are derived. Since only simple algebraic functions are involved, numerical computation can be quickly carried out.

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The seismograms obtained by long-period seismographs in Tokyo at the time of the Sanriku earthquake of March 3, 1933 are analysed. As a first step, we examine the differences of the near-field properties of theoretical seismograms for a semi-infinite medium from those for an infinite medium. The wave forms of the horizontal components of displacements in the two media do not show much difference, while those of the vertical components are considerably different.
In the next step, an attempt is made to estimate the focal parameters, such as the rise time and the rupture velocity, by comparing wave forms of direct P and SP waves. A good agreement of wave forms of the first half cycle on EW components of the synthesized and observed seismograms yields the following conclusions: (1) the rise time of the source time function is about 5 sec, (2) the average dislocation over the fault is 2-5m, (3) the particle velocity of the fault motion is 20-50cm/sec, (4) the rupture velocity is about 3.0km/sec, (5) the effective stress is 40-140 bar, and (6) the rupture began at the northern part of the fault area and propagated to the south.

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The thermal and elastic plane wave motion of small amplitude in a homogeneous, isotropic and thermally conducting solid which occupies a half-space is considered. The presence of the thermal waves effect change in the angle of emergence.

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Using the data obtained at the Urakawa Seismological Observatory (KMU), the seismicity in and near Hokkaido was investigated for the period from May 1964 through December 1972. An aftereffect of the 1968 Tokachioki earthquake of magnitude 7.9 has been recognized up to date, the end of 1972. Some features of aftershock and foreshock sequences detected at KMU are described. Aftershock activity differs considerably from place to place in the region concerned, but it shows no systematic trends. The phenomenon of secondary aftershocks is not rare. Considering the relation of the number of aftershocks to the magnitude of a triggering earthquake, the secondary aftershock activity is comparable to the primary aftershock activity in most cases.

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Kanto earthquake of 1923 was associated with various sorts of seismic and tectonic effects such as surface displacements, seismic damages, tsunamis and volcanism. The writer previously proposed a fault-origin model of the earthquake from a geodetic viewpoint. The present paper is to develop the geodetic model on the idea that the various sorts of the associated effects in 1923 can be interpreted with a simple fault-origin model, equally well. The geodetic model is slightly revised to fit the effects. Thus it is found out that the fault model can be much simplified except for the area immediately adjacent to the fault. The fault is tectonically interpreted as one of the transform faults along the northeastern boundary of the Philippine-Sea plate with the Asian plate.

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The source process of a deep-focus earthquake (h=544km) of January 29, 1971 in the Sea of Okhatsk is investigated on the basis of the primary P and SH pulses, which are deduced from the WWSSN long-period seismic signals after eliminating the influence of the seismograph, crust and mantle by the deconvolution technique. The shape of the primary P and SH pulses is characterized by a uni-directional, single pulse. The pulse widths of these primary pulses vary depending on the location of stations. The pulse width of the primary SH pulses is comparable to that of the primary P pulses at stations placed in nearly the same azimuth and having nearly the same epicentral distance. These results strongly suggest that the earthquake occurred in the form of shear faulting, the model of which was inferred to be a uni-lateral propagating fault. In the deduction of this inference, the primary SH pulses especially played an important role. Source parameters for the present earthquake are determined by comparing the theoretical P and SH wave displacements directly with the primary P and SH pulses. Seismic moment Mo, rupture velocity υ, fault length L, fault width W, displacement discontinuity D and stress drop Δσ determined are as follows: Mo=2.8×10²⁶dyne·cm, υ=4.5km/sec, L=20km, W=10km, D=1.2m and Δσ=240 bars.

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The thermal diffusivity of single crystal quartz, fused quartz and polycrystalline quartz have been measured at temperatures up to 700°C and pressures up to 33kb. The Ångström method has been proved to be applicable to the high pressure experiment, in which the sample was surrounded with solid pressure medium, by comparing the present results on fused quartz with those previously determined by various workers. The pressure derivative of thermal diffusivity for single crystal quartz at room temperature was 5.6×10^-4 cm² sec^-1 kb^-1 in the direction parallel to the C axis and 3.1×10^-4 cm² sec^-1 kb^-1 in the direction perpendicular to the C axis, while the value for polycrystalline quartz was 4.5×10^-4 cm² sec^-1 kb^-1. The pressure dependence of thermal diffusivity for single crystal quartz was also calculated based on the lattice model and the result was found to agree fairly well with the experimental results.

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