Abstract
At first, the term “neotectonics” is examined. The term seems to have been used for the first time by SCHULTZ (1939) and is defined by NIKOLAEV (1962) as a science of crustal movements that have given rise to the present relief of the earth's surface. On the other hand, ICHIKAWA (1958) defined it as the tectonics of Neogene and Quaternary periods, this definition showing the coincidence with the view of Nikolaev and his colleagues. The Neotectonics Commission is established in INQUA and works for neotectonic maps. In this Commission, the Pacific Regions Working Group was organized in 1965. The activity of this Working Group is described in vol. 6 (1967) no. 1 of this journal in English. The National Committee on Neotectonics corresponding to the Commission and to the Working Group was organized in Japan. Moreover, we have the research team for Quaternary tectonic map of Japan, the results being summarized in this issue. Besides, there are some research teams for studying neotectonics in the Geological Survey, the Earthquake Research Institute, and other organizations. Each of these “neotectonics” is one of or a combination of three different meanings: Neogene tectonics, Quaternary tectonics, and present-day tectonics (Lebende Tektonik). In this article, the author limits himself to discuss only the Quaternary tectonics.
Secondly, methods and characteristics of the study on Quaternary tectonic movements are made clear by comparing recent tectonic movements detected by geodetic means (A), Quaternary tectonic movements (B), and past tectonic movements detected by geologic survey (C), with each other. Table 1 is for the comparison. The means to know vertical displacements are bench marks for leveling, ancient shore-line and geomorphologic surface, and marine sedimentary formation, respectively. For all these means, the sea-level is employed as a criterion. The sea-level oscillates with different periods however the term considered is short or long, the changes being caused by ocean current and atmospheric pressure, glacial control, and epirogenic movements, respectively. To get the amount of vertical tectonic movements (other than epirogenic ones), it is necessary to separate it from the amounts of those factors. Horizontal displacements associated with recent tectonic movements can be detected by triangulation, and displacements associated with past geologic time can be inferred from paleomagnetic data. For Quaternary there is no effective method, except geomorphologic means including a clue using horizontal offsets of river courses and other features. The adequacy of these various techniques for describing tectonic movements in space and time is quite different. The geodetic technique gives complete coverage in space but little or no information about time variations. The geological techniques give a fairly adequate description of the variations over time, but cannot give a complete picture for all areas. The geomorphological techniques are intermediate to the geodetic and geologic ones in both time and space coverage. The development of submarine geology and isotope chronology are expected for future studies to diminish these defects in (B). However, the basic knowledge for Quaternary tectonics is in geomorphology and Quaternary stratigraphy.
Thirdly, emphasis is put on relationships between sea-level changes and tectonic movements. Fig. 1 is an example of consideration on the relationship between them, published before the glacial eustasy began to be favoured. Fig. 2 is an example that indicates the correlation between the regional distribution of the amount of vertical displacements since the time of the highest sealevel after the post-glacial transgression, and the one of vertical displacements at a major earthquake. Persistency in tectonic movements is expected from this relation.
