Discrepancy between the azimuth of wave source and the direction of wave approach was discussed based on a tripartite observation of artificial explosions which were detonated at nine different sites in and near the swarm area of the Matsushiro earthquakes in Nagano Prefecture. We obtained arrival time data of those explosions at four tripartite stations with a diameter of about 1km. The epicentral distances were less than 50km.
Calculated directions of wave approach showed a significant deviation from the azimuth of the shot points, and the values of the deviation were found to depend on azimuth. Such a systematic deviation was remarkably reduced by means of station correction, which removes most part of the effect of structure irregularity just beneath the tripartite arrays. The deviations which survived the station correction are considered to result from large scale curvature of the ray paths. Geographycal pattern of the warped paths requires somewhat smaller value of P wave velocity not only in the swarm area of the Matsushiro earthquakes but in its marginal zone.

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The electrical conductivity of synthetic diopside has been determined at atmospheric pressure in the temperature range of 650 to 1500°C. The conductivity does not show any significiant step at about 1385°C (solidus) or 1391.5°C (liquidus). The conduction mechanism of the diopside largely changes near the melting point as inferred from the values of activation energies; 1.38eV for crystalline phase and 11.31eV for liquid phase.

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The focal mechanisms of the earthquake of southeastern part of Akita Prefecture which occurred on October 16, 1970 and its aftershocks are studied by using the initial motions of the P- and S-waves. All available data are obtained from WWSSN, JMA, microearthquake observatories of Tohoku Univ., and temporary stations of Tokyo Univ.
The results are as follows:
1) The mechanism solution of the main shock based on the data of the initial motions of the P and S-waves indicates reverse faulting. The orientation of the tension axis is nearly vertical and that of the pressusre axis is nearly horizontal in the WSW-ENE direction. The fault plane is not distingushed from the auxiliary plane by the distribution of the aftershocks and other data of the field observations.
2) The mechanism solutions for four larger aftershocks are obtained by the use of the data of the initial motions of the P-waves. The mechanism solutions for the other small aftershocks are inferred from the contributions of the regionally superposed initial motions of the P-waves. They indicate that there are two types of the orientation of the earthquake generating stresses in the aftershock area. The orientation of the earthquake generating stress for the north-west region of the aftershock area is different from that of the main shock and the orientation for the rest part of the aftershock area is consistent with that of the main shock.

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The observations on secular changes of the crustal movements by means of extensometers and water-tube tiltmeters have been carried out in Osakayama Tunnel of the former Tokaido Line.
The strain elements have been obtained from these observations of these extensometers for period from 1970 to 1973, and have been compared with the mean variations in the whole period from 1961 to 1973. The azimuths of the main strains in the recent period are equal to those of the mean values. However, the areal strain is negative in the period from 1961 to 1973, but is positive in that from 1970 to 1973.
The observations of the same components (S 38° W) of the linear strain at some departed points in the tunnel have been achieved simultaneously, and the development of the crustal movement area has been detected, recently.
The ground tiltings have been determined by means of water tube tiltmeters at 2 points in the tunnel. It seems that the directions of these tiltings have close correlation with the topography around the observatory. The secular change of the ground tilting is smaller than ±0.1″ for recent ten years.
According to the observations by means of the recording type tiltmeter, it seems that the magnitudes and phases of the annual tiltings depend much on the level of the ground water in the tunnel.

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Source areas of the tsunamis generated in northeast Japan since 1896 are compiled on a bathymetric chart (Newly estimated: 14; Reanalyses: 14). Sources of large tsunamis lie on the steep continental slope off the Sanriku coast. Most of small tsunami sources are located in the sea shallower than the depth of 2000m. Source dimensions are closely related with earthquake magnitude; the Utsu formula for the relation between the earthquake magnitude and aftershock area can be applied well for the tsunami source area. Generally speaking, the magnitudes of tsunami correspond to earthquake magnitude. However, a few tsunamis generated in the vicinities of the west Aomori and Miyagi regions are especially small in comparison with those at other regions.
Judging from the initial motion on tsunami records, most of tsunamis off the Sanriku coast seem to be generated by the reverse fault type earthquake. The sense, up or down, of the initial motion of the 1896 Sanriku tsunami is opposite to that of the 1933 tsunami which is caused by a normal fault earthquake. This suggests that the 1896 tsunami was generated by the reverse fault earthquake. Source dimension of the 1933 tsunami is newly revised and found to be about 300km. This area is smaller than the former estimations, because arrival times at the tide stations of Hokkaido were read too early by misunderstanding a noise as the first motion.

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The observations of long-period (1- to 5- sec) microtremors for elucidating ground characteristics are very scarce until now, though the importance of the short-period microtremors in the earthquake engineering is well recognized. This is perhaps due to the background that almost all the buildings were constructed not so high in the past. It is, however, a fashion that recent buildings are very large both in height and width. In this new situation the technique to know the underground conditions by means of the short-period microtremors has little use. Our present purpose is to try out whether the long-period microtremors are powerful for detecting deeper ground conditions.
In 1973 an observation of the long-period microtremors was carried out in Hachinohe City, Aomori prefecture. The apparatuses employed there are 1cps electromagnetic seismometers having specially designed integration circuits to lengthen the observation capability to longer periods, DC-amplifiers, and 4chs portable magnetic data recorders.
According to the geological survey the Hachinohe area is classified into three major blocks of which bed rocks locate very shallow, moderate, and deep in depths. So, after examining whether the observation reflects differences in the blocks we set up A-line as to intersect the three blocks and observed 10 and more points. In Tokachi-oki earthquake of 1968 a very large acceleration with 2.5sec in period was recorded at Hachinohe Branch Office of the Bureau of Port and Harbor, but no appropriate interpretation to this is achieved yet. Thus the line from Hachinohe Local Meteorological Observatory lying just above the bed rock to the strong motion seismograph site was surveyed as B-line.
First we calculated the Fourier spectra of the records by means of an analog-type spectrum analyzer. Then these were classified into three peculiar types of which peaks in spectrum differ significantly. And it was ascertained that the corresponding subareas show a fairly good agreement to the geologically known blocks.
A very systematic change in the predominant period was observed along the B-line. The shortest period was 0.7sec at the point close to the Meteorological Observatory and the largest period obtained, 2.5sec, was at the same site where the strong motion seismograph had been installed. The well-known law of quarter wave length was applied to the ground structure to estimate the expected predominant periods along the B-line. The coincidence between the calculated and observed periods was very satisfactory. This suggests we might have recorded the strong motions with the periods ranging from 0.7 to 2.5sec in the Tokachi-oki earthquake, if the seismographs had been set along this line.

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A micro-earthquake having a magnitude 2.9 which occurred at the depth of 71km under Tokyo Bay was well observed at four stations around the epicenter. Using the body wave of this earthquake mean effective Q along the path was determined from the slope of the spectra. The value estimated at Kiyosumi on a sandstone foundation is the smallest, 170, and the one at Tsukuba on a granite foundation is the largest, 570, in the frequency range from 5.0 to 15.0cps. The tendency of the regional differences in the attenuation of the seismic wave is almost the same as the previous result for shallow earthquakes. The difference of mean effective Q along the path seems to be caused by the difference of local crustal structure under the stations.

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