Among effects of various factors on monthly mean sea level, barometric pressure, water temperature and oceanographic conditions are predominant. For the correction of barometric pressure, the theoretical value of -10 mm/mb instead of the actual ones can be adopted. The water temperature during the same month is conventionally used for the temperature correction of monthly mean sea level in a month. Considering the irregular seasonal variation of the thermocline, the modified tem perature at lm below sea surface is proposed. As its application, a method of temperature correction in which the water temperature is shifted in phase, is derived in this paper. This method can be considered as an approximation to the dynamic depth anomaly, of which determination is very difficult because of scantiness of oceanographic data. The following are clarified. 1) The change of monthly mean sea level has the time lag of 1-2 months for the change of water temperature at lm below sea surface, showing the maximum time lag at Abratsubo, as shown in Table III. 2) The temperature coefficients rather vary year by year at each tide gauge station, as shown in Table IV. 3) The standard deviation of noises left after the present correction reduces by 20-35% comparing with that of the conventional correction. The noises remained after the correction seem to be caused by the oceanographic conditions. So long as the effect of oceanographic conditions on monthly mean sea level is not clarified, it seems likely that the vertical displacement of the earth's crust within a few months can not be discussed with confidence.

抄録全体を表示

In order to improve the accuracy of magnetic survey and to clarify the locality of conductivity anomalies of the earth, the variations H, Z and D of geomagnetic daily mean values are examined using the data of 47 magnetic observatories in the world during the period of IGY, 1958. It is clarified as follows. 1) The variations of daily mean values may be caused by the disturbing field due to the ring current around the earth . 2) The coefficients of the geomagnetic potential in the development of spherical functions are shown in (11). The first terms (global effects) of H, Z are proportional to cos θ and sin θ(θ: geomagnetic latitude), and that of D shows rather complicated patterns. The terms up to m = n = 2 except the first term (regional effects) are estimated as 2 % in maximum, comparing with the first term. 3) Excluding the global and regional effects, the local anomalies of H, Z and D are found in Eurasia, South Africa, Melanesia, Oceania and Central America, as shown in Figs. 810. 4) The ratio of the potential coefficients due to the internal and external origins is estimated as 0.27±0.01, because Z'/X' = (0.36±0 .01) tan θ holds. The result coincides with that obtained from the analysis of geomagnetic variations with the period of 27-day. It seems unlikely that the conductivity near the depth of 1, 200 km below Japan is abnormal.

抄録全体を表示

The new first order levelling along the coast of Izu Peninsula was carried out by the Geographical Survey Institute during the period from 1967 to 1968. This survey was done after 30 years since the former similar survey had been finished. The author tried to summarize the studies of the vertical movement of crust in this peninsula on the occasion of the new levelling work. It is well known fact that some peninsulas toward the Pacific Ocean are gradually inclined to the ocean. T. Terada and N. Miyabe stated that this trend can be found also in Izu Peninsula. But, the comparison of the results of several repeated levellings can not prove this trend so cleary. We can observe this trend only for the period from 19301931 to 19671968 at the most southern part of peninsula, and the rate of this inclination is so small that we can not subject this trend to be closely associated to occurence of great earthquake. In nothern part of peninsula, we can notice the uplift zone that runs from northwest to south-east. Mean rate of uplift during the period from 19301931 to 19674968 is approximately +2.2 mm/year. Along this uplift zone several earthquake swarms were observed during the seismic activities of 1930 in this peninsula. At the region of Ito earthquake swarm of 1930, upheaved bench marks show only a small subsidence after earthquake swarm. We tried to apply subsidence effect corrections to the displacement of bench marks in order to get the vertical movement closely associ ated only to the activities of the earthquake swarm. This can be possible, because subsidence seems to be a secular change. By this analysis, it is proved that the crust responses as a plastic substance rather than elastic to the earthquake-generating forces. Relative height change of bench marks on both side of Tanna Fault seems to be very stable at present. But, at the western region of Tanna Fault, a remarkable, local upheval can be observed. This part is quite the same as one of fore-shocks areas of Kita-Izu earthquake of 26 Nov. 1930. The rate of upheval had became very large before the occurence of Kita-Izu earthquake and then small. Furthermore, at this region, change of gravity of +0.14 mgal was observed by comparison of the gravity values observed in 1955 and 1968 by the Geographical Survey Institute. Formerly, Prof. N. Yamazaki explained the topography near Tanna Fault by two tilted blocks, one of which is inclined to southward and other is northward. Vertical movement of triangulation points before and after the Kita-Izu earthquake and the distri bution of Bouguer anomalies around Tanna Fault show that Prof. N, yamazaki's consideration seems to be appropriate.

抄録全体を表示

Recent development of electro-optical distance measuring (EDM) techniques has enabled us to repeat precise base-line surveys very easily . Among the various models now available in the market, an AGA Geodimeter is regarded as one of the most responsible instruments. From this point of view, the authors have been conducting patrolling Geodimeter surveys since 1963, in order to establish an effective monitoring system of crustal movements .Thus, there have been constructed fifteen base-line networks in central Honshu, Japan. The present paper introduces the authors' scheme of field work and of data analysis as well as a summary of the observational results at these sites . In the Matsushiro area, for example, they observed abnormally high rate of strain accumulation associated with the swarm activity. During the period October 1965October 1966, the three base-lines of Sorobeku, Nishiterao and Zozan changed their lengths for +116, +72 and -40cm, or, +3.7×10^-4, +2.5×10^-4 and -0.9×10^-4 in strain, respectively. Strain accumulation to the peak values and its gradual decay following them harmonizes very well with the uphe aval and tilt of the ground there, in respect to their mode of development . It seems to suggest that the observed horizontal deformations have essential bearing on the processes in the focal region.

抄録全体を表示

En un point sur la surface terrestre, it existe deux lignes de réferénce; la ligne de verticale vraie et celle de normale sur 1' ellipsoide. On pent donc constituer sur un point deux systemes de coordonness rectangulaires selon les deux lignes. Ces deux triédres peuvent se transformer de 1' un a 1' autre par la matrice de transformation dont les composants sont ξ, ζ, et on voit que 1' equation de Laplace et les relytions des angles apparaitre dans cette transformation. De ce point de vue, les procédés de calcul que nous effectuont actuellement, sans tenir compte de la déviation verticale, correspond a la transformation par la matrice dont les composants non diagonaux sont zero. Comme on voit Bans le tablau ce procédé produit des erreures asset considerables par rapport de la transformation rigoureuse.

抄録全体を表示

Using the data of the time observations reduced to an uniform system, the secular variations of longitudes for some observatories were determined . The existence of significant variations are shown for some observatories, however, in order to determine the continental drift from the variations of longitudes, the local systematic errors in the time observations must be made clear. A few of these errors are discussed.

抄録全体を表示

The first order triangulation in Japan had been carried out twice for 1882-1911 and 1948-1967. Change in angle for the above period at every station is illustrated in Fig. 2. Changes of all sides are illustrated in Fig. 3. Such areas as changes in angles are more than 3".0 correspond to the areas deformed violently by the destructive earthquakes that exceed 7.0 in magnitude. Change in angle is about 1".0 at half of the stations. The standard deviation of an observed angle is 0".7. Accordingly, there is perhaps very 19ttle deformation of the crust in these areas. The figure of deformation vectors found in the case that the triangulation is adjusted whole Japan as a single net is already reported in Fig. 8 in [1]. The very remote vectors from the datum station in the figure are influenced uniformly by accumulated errors. Consequently, we cannot know intuitively minute relative deformation of the crust in these areas. In order to avoid the above inconvenience we choose five stations whose numbers are written in Fig. 2 from the quiet zones of crust movement, and give forcibly their positions old results and adjust again whole Japan as a single net. The vectors obtained by the above method are shown in Fig. 4, five fixed stations are indicated with circles in the figure. The figure expresses clearly the movement of the crust caused by destructive earthquakes. Fig. 4 shows also the fact that there are many blocks of various sizes in horizontal movement of the crust.

抄録全体を表示