1994 年 103 巻 5 号 p. 576-590
Izu Peninsula and adjacent areas, which are located on the northern tip of the Izu-Bonin volcanic arc, are characterized by intense crustal movements and volcanic activity. Many geomorphological, geological, and geophysical data were collected from this area and various tectonic models were proposed to explain them systematically. These tectonic models can be classified into two categories : models 1 and 2. While model 1 regards the area as a single tectonic province, model 2 proposes two or more tectonic provinces, which are bounded by tectonic lines. Models 1 and 2 can be classified into models 1A and 1B, models 2A, 2B, 2C, and 2D, respectively. Model 1A hypothesizes an anticlinal bend of the Philippine Sea plate, which is being generated by the subductions along the Suruga and Sagami troughs. Model 1B emphasizes the crustal stress field generated by the collision of the Izu-Bonin volcanic arc with Japan arc and the slab-pull force along the Sagami trough. Since there are many local tectonic features that cannot be explained by model 1A or 1B, models 2A-2D were proposed. Model 2A divides the study area into two tectonic provinces : the northern province of compressive deformation by conjugate faults and the southern province of right-lateral shearing deformation. Model 2B divides the area into the eastern and western provinces, which are defined by sharp contrasts in the geologic structure, seismicity, crustal stress field, crustal movements, focal mechanisms of earthquakes, paleomagnetic directions, and volcanic activity. Many observations support the validity of the model 2B tectonic provinces. Model 2C introduces the hypothesis that the Izu-Bonin arc is being fractured into the inner and outer arcs because of a contrast in buoyancy. The existence of the estimated model 2C fracture, W est Sagami Bay Fracture, is still under debate. Model 2D regards the Higashi-Izu monogenetic volcano field, located in the eastern Izu Peninsula, as a field of crustal spreading. Model 2D proposes a key to understanding a sharp contrast in tectonic features between the eastern and western provinces of model 2B as well as the complex geometry of the Philippine Sea slab beneath the Japan arc.