Horizontal Crustal Movement in KANTO-TOKAI District (VIII):—Tectnic Strain Field—

概要

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Secular strain field in the Kanto-Tokai district is deduced from the observed crustal strains in various regions and for different periods. Deduced tectonic strain will be contaminated by some unexpected anomalous crustal movement such as post-seismic and preseismic one, even though earth's strains during the period without any large earthquake are taken into consideration. The longest survey intervals are adopted in order to make larger the accumulated strains and smaller the unexpected effects. Line of contraction is defined as a curved line, tangent of which at any point on the line coincides with the principal axis of contraction at that point, and shown in the Fig. 5. This indicates tectonic line of contraction in the Kanto-Tokai district. Frequency distribution of maximum shear strain rates is calculated in order to estimate representative strain rate in the district. When the mode of frequency distribu tion is adopted as the representative value, these are ;4.0×10-7/yr for the Kanto district, 1.6 ×10-7/yr for the Tokai district, and 5.3×10-7/yr for the Izu peninsula.These obtained strain rates are the same order, except for the Tokai district, as the strain rate in the other tectonic area, when the geodetic observations are carried out across or close to the plate boundary. The obtained small strain rate in the Tokai district will be contaminated by the occurrence of the 1944 Tonankai earthquake.
日本測地学会の論文