ＧＰＳ時系列データのウェーブレット解析から求めた関東・東海地方の経年的地殻変動場の特徴とそのテクトニクス解釈

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  • Characteristics of Secular Crustal Deformation in the Kanto and Tokai Regions, Deduced from the Wavelet Analysis of GPS Time-Series Data, and Their Tectonic Implications
  • GPS ジケイレツ データ ノ ウェーブレット カイセキ カラ モトメタ カントウ トウカイ チホウ ノ ケイネンテキ チカク ヘンドウバ ノ トクチョウ ト ソノ テクトニクス カイシャク

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Secular crustal deformation in the Kanto and Tokai regions, central Japan was deduced from the wavelet decomposition analysis of the GPS time-series data acquired by Geographical Survey Institute, Japan. The time-series data during the period from April 1996 to March 2002 were assumed to be composed of several trends, i.e., seasonal, transient and secular(linear) trends along with discontinuities (co-seismic or artificial jumps) and white noises. The north-south (NS), east-west (EW) and up-down (UD) components of the time-series data were also assumed to be mutually independent. After removing data-jumps, we decomposed each of the NS, EW and UD components to the desired level of 8 by using the orthogonal Daubechies wavelets. We could recognize a seasonal variation clearly in the detail component at level 8, and could estimate a secular velocity from the approximation component at the same level. <BR> We estimated secular horizontal velocities at about 540 GPS sites in central Japan on the basis of the wavelet decomposition analysis, and then evaluated horizontal velocities at 7 km × 7 km grid points by applying the least-square collocation method. We also estimated distributions of dilatational, maximum-shear, and principal strain rates. We could find out the following characteristics concerning the secular crustal deformation in the Kanto and Tokai regions, central Japan: (1) the entire region is generally under a compressive regime, (2) there exists a remarkably compressed area with a strain rate of 0.2×10-6/yr near the Boso peninsula, (3) higher maximum-shear strain rates of about 0.2 × 10-6/yr are shown near the Boso peninsula and off the eastern coast of the Izu peninsula, and (4) there exists a slight dilatational area near Mt. Fuji, corresponding to the collision zone at the northern end of the Izu peninsula. The observed features of the secular crustal deformation in the Kanto and Tokai regions were approximately explained on the basis of the back-slip fault model and the antiextensional fault model. The present back-slip fault model was assumed to consist of the multiple-fault systems along the subduction boundaries, i .e., the Sagami and Suruga-Nankai troughs. The anti-extensional fault model was also presumed to locate at the collision zone between the Sagami and Suruga troughs, i.e., the area near Mt. Fuji.

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