Reliable measurements of evaporation are of importance in many scientific fields. In the worldwide routine meteorological observation the evaporation rate per day is frequently measured by the evaporimeter pan. The amount of evaporation can be roughly obtained by measuring water depth in the pan and this has been done by a hook gauge up to the present. In this method the wind often influences the measurement, and a small amount of evaporation for short periods of time could not be measured. Recently, accuracy in measuring salinity was improved by use of an electric conductivity technique and it has become possible to measure salinity within an accuracy of ±0.003‰. Then, even a trace amount of evaporation during a short time interval can be detected by measuring salinity change in the salt water pan. The relative error is kept under about 2.5% by this method. The sampling error of salinity was estimated not more than 4×10-4‰ and the fallout of salt particles near the seashore was about 3.6×10-5‰. The amount of evaporation from two salt water pans of the same type showed a good agreement. Moreover, the difference between the amounts of evaporation from the salt water pan and the fresh water pan is not appreciable for long periods of time. However, the amount of evaporation from fresh water is apt to become larger as the observation time interval is shortened. It was found that the amount of evaporation from the salt water pan had a linear relationship to the vertical vapor fluxes estimated by the bulk method. The proportional coefficient of vapor fluxes to the amounts of evaporation from the pan was about 0.67. It is a temporary value and should be determined from further experiments at various places and in various atmospheric conditions in future.
The origin of the stress field concerning earthquake occurrence is studied, and it is suggested that the concept of antidislocation or passive dislocation is useful for the understanding of the formation of a focal region. This view means that the earthquake occurrence is the release of a locally accumulated elastic strain field. It is shown that some features of the earthquake such as stress concentration on the focal region before an earthquake and aftershocks occurrence are naturally explained with the use of the idea of antidislocation.
Seismically quiescent areas are observed for a long period of time in a part of the focal regions before and after great earthquakes which occur along the zone of plate boundary. A number of studies about the so-called “seismic gap” preceding earthquake occurrence have been performed by many investigators for various earthquakes. The seismic gap treated here, however, differs from those of previous investigators in that the gap refers to a comparatively narrow area in a focal region, and appears not only before the earthquake occurrence but also after the event. In this paper, the seismic gap before an earthquake is called “the Gap-B” and the seismic gap after an earthquake is called “the Gap-A”. The area of Gap is also named “the core of the focal region”, since it should be considered to play a special part in the formation of the focal region of a great earthquake. The change in seismic activity in and around the core of a focal region is well understood on the assumption that it reflects the different stages of the tectonic process by which the focal region develops, that is, it represents the coupling conditions between the oceanic lithosphere and the island arc block, and the state of strain accumulation in the core region. The process of focal region development can be divided into the following five stages according to change in the pattern of seismicity.
Stage I; The growing of the core of the focal region (normal seismic activity) Stage II; The formation of the core of the focal region (seismic gap before an earthquake—Gap-B) Stage III; The approaching to the ultimate state (precursory seismic activity and foreshocks) Stage IV; The occurrence of a great earthquake (main shock and aftershocks) Stage V; The decoupled state (seismic gap after an earthquake—Gap-A)
The present stage of the focal region of the Tokachi-oki Earthquake of 1952 may be defined as Stage II and that of the Tokachi-oki Earthquake of 1968 as Stage V. The relatively low stress drop associated with the interplate earthquake compared to the intraplate earthquake seems to be interpreted by the fact that the ratio of the core of the focal region to the whole fault area is smaller for the interplate earthquake. Furthermore, the smaller rate of seismic slip than is expected from the motion of the oceanic plate might also be explained by the existence of the decoupled state of Stage V and the imperfectly coupled state of Stage I in an earthquake cycle.
Two formulas estimating the sea surface temperature from the air are derived. In the first formula, the measurements of radiations from the sea surface in the atmospheric window region in two directions are used. In the second, which is based on the idea of Anding and Kauth, the measurements of radiations in two channels in the atmospheric window region are used. Using these formulas, the atmospheric effects can be automatically removed and the sea surface temperature is properly estimated. Applying the first formula to field observations, the sea surface temperature is obtained with an error of 0.4°C on average.
There has always been seen a warm water region south of the Kuroshio off Honshu. It is located off Shikoku or Tokaido, according to whether the Kuroshio takes a path with or without meander. These warm water regions have lens-shaped thermostads in the subsurface layer above the main thermocline, which have a thickness of 200 to 400 m at the center and diameters more than 100 km. The lens-shaped thermostads have temperature of 19°C and a thermosteric anomaly of 300 to 320 clt-1 when the Kuroshio takes a meandering path, and 17° and 260 to 280 clt-1 when it takes a straight path. A detailed analysis of the water regions observed during two periods when the Kuroshio was meandering, which began in 1959 and 1975 respectively, shows that the warm water regions do not have a lens-shaped thermostad structure in the first years of the periods, but have it in the following years. There are some differences, however, between the two cases. The thermosteric anomalies in the thermostad gradually decrease with time in the former case and increase in the latter. The geographical location of the center of the warm water region off Shikoku is rather stationary in the former case and fluctuates with time in the latter.