Continuous distribution of the horizontal strain in the Tohoku district, Japan, predicted by least-squares collocation

Abstract

Least-squares prediction using two empirically deduced local covariance functions was applied to estimate the horizontal strains in the Tohoku district, Japan. The horizontal displacement vectors that cover the area of approximately 450×275 km 2 for the interval from 1979 to 1991 were used and the results were shown in the form of contour maps. In order to apply least-squares prediction for studying the horizontal strains, we first derived two covariance functions of the horizontal crustal movements, one for the E–W component and the other for the N–S component, with a Gaussian form. Then we used these functions to estimate the spatial distribution of the horizontal strains in the Tohoku district. By the present method, the results of numerical calculation are discussed with reference to the tectonics of the Tohoku district. The main conclusions are:1. The total amount of strain accumulation thus obtained does not exceed 3×10 −6 in every part of the district except the North Japan Sea coast and the area at the central part of Tohoku. We may roughly say, therefore, that the average rate of strain accumulation is mostly less than the order of 0.25×10 −6⧹a, but it is not certain whether the rate is constant or not.2. The general pattern of distribution of principal axis of strain in the Tohoku district shows compression in ESE–WNW direction.3. Comparison of the above estimated geodetic strain rates with the ones estimated by ( Kaizuka and Imaizumi, 1984) from fault data in the Quaternary period shows that the former is one order of magnitude higher than the latter.