Correlation between Heights of Younger and Older Shorelines for Estimating Rates and Regional Differences of Crustal Movements Yoko OTA1), Sohei KAIZUKA2), Takao KIKUCHI2), and Hiroo NAITO2) The study of crrustal movements depending upon former shorelines has been one of the intersting fields of the Japanese Quaternary. Herein an attempt was made for estimating the rates and regional differences of Quaternary crustal movements in Japan by using correlation between the heights of older and younger shorelines. The method of approach is as follows: In a coastal region, the heights of former shorelines of two different ages (t1 and t2 years B. P.) are measured. Pairs of older and younger shoreline-heights in close distance are designated as h1 and h2 respectively (fig. 4). When many pairs of h1 and h2 are obtained in a coastal region, the values are compared on a correlation diagram. Six regions studied are shown in fig. 1 and 11 cases of correlation obtained from the six regions are shown in fig. 3. In four regions, Kanto, Muroto Peninsula, Nishitsugaru and Osado, shoreline-heights of three different ages were measured and two correlation diagrams were drawn for each region. From fig, 3, it can be said that the relationship between h1 (in ordinate) and h2 (in abscissa) is linear in most cases. Therefore, the regression line, was applicable to many cases, and calculated values of 'a' and 'b' are shown in each case. Under what conditions is it possible to be applicable to the above equation (1) for variables of h1 and h2? When we use the signs shown in fig. 4, h1 and h2 are expressed as follows: That is, v2 is expressed by a linear formula of v1, where the gradient and intercept are constants peculiar to the concerning region. Therefore, (4) is also expressed by the following formula, using 'm' and 'n' which are constants peculiar to the concerning region: where 'm' means how v1 is succeeded by v2, and is named, therefore, a 'successional coefficient of the rate of crustal movement'. On the other hand 'n' means the rate of crustal movement which is added after t2 years B. P. and is uniform through the whole concerning region. Therefore, `n' is named a 'regional addend of the rate of crustal movement'. A model of areal distribution of v1 and v2 is shown in fig. 5 (in case of m=3). If (5) is right in one region, (1) is also led, then 'a' and 'b' are expressed as follows; That is, 'a' is a function of 'm', and 'b' is a function of 'm' and 'n'. For the correlated two shorelines of plural regions, if 'a' of each region is equal to one another, then 'm' is the same. Moreover,
The Quaternary Research Vol. 7 No. 4 if 'a' values of many regions, having different geologic structures and different physical properties of rock, are equal, then every 'm' value can be estimated as 1, because it is improbable that 'm' As for the 11 cases shown in fig. 3, the following interpretations can be led from the above mentioned general consideration Comparing the amount of uplift during the period from one destructive earthquake to the next and 0.8 times faster than the mean rate between S (or M) and N ages, being paid no regard to 'n'. Comparing the shoreline-heights of M1 and H1 (or T2) terraces (cases 4, 5, 6, 7, 8 and 11), and M1 and H1 terraces (cases 9 and 10), it is not sure that 'm' takes 1 in any region. In cases 5, 6 and 7 or 9 and 10, 'a' and 'b' values are similar respectively. These regions, i. e., Nishitsugaru, Oga and Osado, belong to the same geologic province of the Inner Zone of Tohoku, thus the above mentioned fact is likely to indicate that the natures of crustal movements are very similar to one another. In case 2, one point (datum of Oiso, on the coast of the Sagami Bay) is isolated from others. This indicates that at Oiso the nature of crustal movement is different from other localities in the Kanto district. Generalizing this case, one region, where a linear relation can not be found between h1 and h2, may be divided into plural regions of crustal movement, each of which has a particular linear relation. be introduced. Through this, method, regional classification of crustal movement can
Fig. 1 Index map Figure shows case number in Fig. 3.
The Quaternary Research Vol. 7 No. 4
Fig. 2 Map showing marine terrace plains and heights of former shorelines in the Oga Peninsula. (after N. Katsurahara, 1968 MS.)
The Quaternary Research Vol. 7 No. 4 Fig. 3 (Erata: for 1 and 2m on the abscissa of 2 read 10 and 20m.)
Fig, 3 Correlation between heights of former shorelines at different times.
The Quaternary Research Vol. 7 No. 4 Fig. 4. Change of heights of former shorelines with the passage of time. Fig. 5. Relation between v1 and v2 (in case of m=3).
The Quaternary Research Vol. 7 No. 4
McIntire, W. G. and Morgan, J. P. (1962) Recent geomorphic history of Plum Island, Massachusetts, and adjacent coast. Coastal Studies Inst., Tech. Rep., 19-A, 44p. Kaizuka, S. (1967) Rate of folding in the Quaternary and the present. Geogr. Rep. Tokyo Metro. Univ.,