Quaternary and geodetically measured crustal movements in the Tokai District, Central Honshu, Japan.

Geodetic measurements made in this century demonstrate that modern movements correlate well with deformation that has occurred during the past 2 Ma. Both show effects of subduction and of the Quaternary collision of Izu Peninsula with Central Honshu. Westward from Suruga Bay, deformation is greatest near the coast, decreases markedly towards the uplifting Akaishi Mountains, and then increases again in the conjugate block-faulted terranes of Chubu district. Quaternary faults, historic earthquakes, and the distribution of horizontal shear since approx 1880 all reflect this deformation pattern. Since 1900 the W coast of Suruga Bay has undergone secular subsidence, horizontal contraction and tilting towards Suruga Trough, all typical of the strain buildup process that occurs landward of subduction zones. However, futher westward, active mountain building is occurring, and the Akaishi Ranges are rising 3mm/a. Unlike the episodic aseismic uplift of the Transverse Ranges of southern California, movements here have been relatively uniform. It seems likely that an increase in the tilt rate of the Suruga coast recognized since approx 1973 is part of a long-term readjustment to the great Tonankai earthquake. Data show that a monotonic increase has occurred since at least 1949, and similar effects are seen adjacent to the 1944 rupture zone over 200km SW along the Nankai Trough. -Authors