General features of storm surge caused on the coasts of the Kanto and Tokai districts are investigated by use of hourly reading s of tidal records for the ten years from 1953 to 1962. Storm surges on these coasts are mainly caused by two mechanisms: one is the sea level rise in response to atmospheric pressure fall, and the other is the so-called ‘wind set-up’. In the previous paper (Isozmu,1969), it was shown statistically that there exist sea level variations travelling from east to west along the Pacific coast of West Japan in the variation of daily mean sea level. But they are not seen to accompany the storm surges analyzed here. In the heads of Ise Bay and Tokyo Bay which are shallow in depth, the effect of ‘wind set-up’ superposed on sea level rise caused by atmospheric pressure fall is remarkable, and sometimes extraordinary destructive surges develop there. On the coasts facing Surug a Bay, Sagami Bay or the open ocean the rise of sea level caused by wind set-up is relatively small comp ared with that due to atmospheric pressure fall because there are only narrow strip of shallow waters between these coasts and the deep ocean. In addition, the surge height is affected also by wind waves and swell, i.e. the so-called ‘wave set-up’. This effect is most predominant in the storm surge at Maisaka. For example, in the storm surge that accompanied the Typhoon ‘Wilda’, Sept.25,1964, the sea levelrise contributed by the effect of wave set-up was about twice as large as the rise due to atmospheric pressure fall. Storm surges at Okada Harbor, Oshima Island are mainly caused by deep atmospheric pressure fail accompanying the pas sage of a typhoon and the effect of wind set-up is of course rather weak. These surges also contain interesting sea level changes which are represented qualitatively by KAJIURA (1956), who maintained that there exist sea level changes related to the distribution of wind stress curl in the area of a typhoon moving with a circular wind system.
The regional seismicity before the Matsushiro Earthquake Swarm was studied for large, small and micro-earthquakes. Findings are as follows. 1) Past major earthquakes and swarms near Matsushiro occurred outside the swarm region, and the swarm region had been left unaffected for many years. 2) For a period of 8 years prior to the swarm, the region where the swarm initially started was comparatively quiet, and a higher activity was found in the surrounding region where the swarm was to extend in its later stages. 3) A small swarm activity o ccurred from April 1963 to June 1964 with several rises and falls. These earthquakes, however, did not occur in the initial swarm region. The Matsushiro swarm started after this activity had once diminished. 4) The “m” value was smaller (m=1.65) before the swarm and increased up to m=2.02 after the start of the swarm. 5) The regional seismicity before the swarm showed a pattern that is usually found for large earthquakes, i.e. the regional seismicity is abnormally low for a certain period of time before the occurrence of a large earthquake.
For the purpose of studyin g airflows over mountain regions, we have developed a superpressure balloon and a precise pressure radiosonde system. First of all we examined the physical properties of the polyester film made in our country to know whether the material is available for use in a stable horizontal floating balloon. The modulus of elasticity in M-direction was found to be (3∼6) × 108 kg/m2 at 15°C,and the total creep to be 5% per 10,000 psi (Table 1).These values are almost similar to those of the mylar film which has been used sofar by U.S. research groups (see Table 1). The balloon we designed is about 1.7 m in diameter, made of films 50 microns thick. The sphere consists of 12 segments. The size was determined to meet the purposes of measuring airflows at a hight of about 2∼5 kms above m.s.l., with a payload of about 1 kg. The changes of volume in the balloon thus constructed du e to the superpressure were measured and the results are shown in Fig. 2 on three samples of the balloon. We find that the rate of the volume change (ΔV/V0 in %) is about 2% for a superpressure of 50 mb. The rate of the volume change can also be estimated analytic a lly by eq. (7) and as for the balloon we made, which has a radius of 0.82 m, thickness of 50 microns and modulus of elasticity of (3∼6) × 108 kg/m2, we can get ΔV/V0=0.02∼0.04 for a superpressure of 50 mb. Thus the observed and the calculated values of the rate of volume change may be said to coincide well. The solid lines in Fig. 2 show the calculated values.