Statistical studies on the focal mechanisms in the Himalaya, Burma and Andaman Sea regions are conducted here by using more than 40 mechanism solutions obtained from the analysis of the distribution of initial motion of P waves. Generally, the pressure directions of the stresses which produced earthquakes in the regions are perpendicular to the trend of the Himalayan mountain belt and the earthquake zones except in northern Burma. Though the pressures in northern Burma are strange in appearance, they harmonize well with the distribution of geological faults in the region. Most of the tension directions are nearly normal to the directions of pressures. Both pressure and tension axes are generally shallow dipping irrespective of focal depths, and this suggests the predominance of strike-slip faulting. In view of the distribution of geological faults in Burma, the faultings of shallow and intermediate earthquakes occurring in northern Burma and its vicinity are characterized by the predominance of the dextral strike-slip faulting. The number of data used in the present study is too small to emphasize the result obtained here, but the hypothesis of the convergence of India and Eurasian continents seems to be not always consistent with the focal mechanisms.
Atmospheric vortices have been classified either according to their horizontal dimensions or to their maximum windspeed. For the purpose of reclassifying them, taking both horizontal dimensions and maximum windspeed simultaneously into consideration, these vortices were located on a maximum windspeed versus diameter diagram (Fig.1). When the s u btropical mesocyclone of 1 September 1960, which formed over tropical waters and hit Japan the next day (Fig.2), was placed on this diagram, it was found that the storm in question was located on the border line between the tropical depressions and the mesocyclones. The mesocyclone was accompanied by arc-shaped echoes around the center and by a curved echo band in the eastern sector far from the center (Fig.3). The area of composite mesohighs was accompanied by an echo band (Fig.9). The pressure field of the storm was characterized by a funnel-shaped profile superimposed by an excess-pressure field of the marked mesohigh with a pressure-jump line along its progressive side (Figs.6 and 7). Due to the fact that most of the squall-line activities took place in eastern sectors of the storm and that the cloud mass encircling the storm center did not grow to the cirrus level, it was characterized by a strictly asymmetric structure (Figs.8 and 11). A three-dimensional analysis of the wind field was made by making use of the existing techniques of time-to-space conversions and interpolation for the construction of vertical space cross-section. and constant level charts. Results showed that the subtropical mesocyclone was characterized by an overall mass inflow which was about five times larger than that of a large thunderstorm, while it was only about one fifth that of a mature hurricane such as Herricane Daisy of 1958 (Fig.14).
Cloud nuclei and giant chloride nuclei observations were made in the fairly clean air-masses on the Pacific Ocean (from the Ogasawara Islands to Tokyo) and near the summit of Mt. Fuji in summer 1970. On the ocean a cloud nuclei spectrum as function of supersaturation had a gentle slope up to 1% in supersaturation degree (S) and gradually approached a mean concentration of Aitken nuclei observed at the same time. The mean values of cloud and Aitken nuclei were respectively 75 per cubic centimeter at 0.3% in S and 450 per cubic centimeter. Referring to the nucleus size distribution estimated from this spectral curve, it was elucidated that cloud nuclei about 0.01 micron in radius (corresponding to little more than 1% in S) were dominant if soluble nuclei were assumed. The local distributions of cloud nuclei in Irozaki, Izu Peninsula and at the mountainside of Mt. Fuji (UCHIDA,1971) were compared with these observations in 1970. The former distributions show a steep slope in a range of more than 0.3% in S when compared with one of smaller percentage range, suggesting that the size distribution of (assumed) soluble cloud nuclei by inland pollution was dominant below 0.03 micron in radius. On the ocean giant chloride nuclei, concentrations were fairly uniform everywhere,10 to 15 per liter in a mass larger than 1×10-9 gr in mild weather. Near the summit of Mt. Fuji, NanagOhasshaku (3,400 m), the pattern of cloud nuclei spectrum was quite similar to that on the ocean. However, the Aitken nuclei concentration observed at the same time had a mean concentration about twice that on the ocean (i.e.,ca.830 per cubic centimeter). If soluble nuclei were assumed, the dominant cloud nuclei radius was estimated at about 0.01 micron as in oceanic observation. Giant chloride nuclei were so scattered in concentration and fairly small in size, except for the rare cases of at most 1 to 3 per liter in masses of 1×10-11 to 3×10-10 gr near the summit (3,400 m). The ratios of concentration of cloud nuclei in 0.3% in S to Aitken nuclei were generally about 0.1 or so.
The earthquake detection capability of the Matsushiro Seismological Observatory was investigated based on seismograms of shortand long-period components of the World-wide Standard Seismograph in the period from January 1968 to December 1969. The operational constants are shown in Table 2. The results are summarized in the following. (1) The total number of earthquakes used in this investigation is 8,423, which were registered in the Preliminary Determination of Epicenters, NOAA with assigned magnitude (MB). The frequency of occurrence of the earthquakes according to magnitude and epicentral distance from MAT is listed in Table 1. Of these earthquakes,4,946 shocks were detected by SP component, and 3,902 shocks, by LP component. The detection capability according to magnitude and epicentral distance is listed in Table 4. The corresponding capability at Tsukuba, but for a different period of time, is also listed in the same tabel for reference. (2) The detection capability by SP is higher than that by LP except in the range of 90° ≤ Δ ≤ 109°, and the detected phase is mostly P or P'. Whereas the detection capability by LP depends mainly on S and L phases, except for local or distant but large earthquakes. Therefore, in the shadow zone of P phase, that is,90° ≤ Δ ≤ 109°, the capability by LP exceeds that by SP. (3)I Compared with the Tsukuba Seismic Station, where the same investigation was carried out, Matsushiro shows a higher detectability for all magnitudes and distances. This is mainly because of a quieter background noise at MAT, which allows of higher operational sensitivity of seismographs, rather than because of any inherent characteristics of the site. No lower detectability in the winter is seen at Matsushiro as is the case at Tsukuba. (4) When many aftershocks of a large earthquake occur at a near or intermediate distance (<40°), the detectability rises higher both in SP and LP. (5) The world-wide detectability maps by SP and LP at MAT are given in Figs.4,5 and 6. Generally speaking, with an incremental detection probability of 90% the Matsushiro Seismological Observatory can detect body waves of earthquakes of 4¾ in MB magnitude over an epicentral distance of 90°. Such a probability of detect surface waves, however, deteriorates by about 10%. (6) The Matsushiro Seismological Observatory is equipped with many other instruments and its observation window is very large both in dynamic range and frequency band.
In the latter half of the 19th Century, J. MILNE thought that seismic intensity might be dependent on acceleration of earthquake motion. Later, in 1902, F. OMORI added the value of acceleration to his list of seismic intensity, in 1932 M. ISHIMOTO added acceleration values to the C. M. O. list of seismic intensity, and in 1943, H. KAWAsum'revised their values. The, C. M. O. (Central Meteorological Observatory) list was made in 1908. This list has been used up to date. But, in the cases of natural earthquakes, seismic intensities are often not in accord with accelerations of ground motion. So the author was doubtful of the acceleration values of the C. M. O. list of seismic intensity. As the shaking table was made in the year 1970, the author made an experiment on the seismic intensity. We vibrated this table, on which a man sat, and measured the intensity of the vibration. The periods of the table were from 0.26 sec to 9.82 sec, and their amplitudes from 2.5 cm to 8.1 cm. The results of this experiment we r e tabulated and are now shown in Fig.1. The vertical axis shows the amplitude of the shaking table, and the horizontal axis its period. Intensities of these vibrations are shown by marks. If we classify them by straight parallel lines, we can draw solid lines as shown in Fig.1. Intervals of these lines are equal to each other. The broken lines are the long established intensity level depending on acceleration of ground motion. The result of this experiment does not agree with these broken lines. Fig.2 shows this disagreement. So the author thinks that seismic intensity does not depend on acceleration of ground motion. Fig.1 shows that the intensity of the vibration depends on velocity or the square of velocity and so on. Fig.3 shows the relation between intensity and velocity. Fig.4 shows the relation between intensity and the square of velocity. These relations show good agreement. R. MALLET has -reported that intensity depends on the velocity of ground motion. But the author thinks that intensity depends on the energy of the ground motion. Because, in other physical phenomena (light and sound etc. ), intensity depends on energy. So we emphasize that seismic intensity depends on the energy which passes through a unit area per unit time.