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[SCG52-P09] Topographic evolution of western Japan in the Quaternary based on the dislocation model for plate subduction
Keywords:topographic evolution, western Japan, slab configuration, dislocation model
In the last JpGU (Mori & Fukahata, 2021), by applying the dislocation model for plate subduction developed by Matsu'ura & Sato (1989), Hashimoto et al. (2004), and Fukahata & Matsu'ura (2016), we have shown that subduction of a slab along a trench axis with a bend results in subsidence around the bend, and that subduction of a slab with a ridge results in subsidence just above the ridge and uplift in the adjacent areas.
In western Japan, the paleo Setouchi low-land area extends until the east of the Nobi plain in the Pliocene. In the area, non-marine sediments deposited, which means that this low-land area was separated from the Pacific Ocean.
In the Quaternary, the stress regime has drastically changed to strong E-W compression. In the inner zone of the Kinki district, block-fault mountains, such as the Suzuka and the Ikoma mountains, have formed due to active reverse fault movements. In the outer zone, the undulation of the topography becomes larger: uplift of the Kii mountains has accelerated, while the Kii strait was opened.
The Philippine Sea slab has large undulation, which is considered to have been caused by E-W compression since 3 Ma. In other words, the large undulation of the Philippine Sea slab has developed in recent 3 Ma. Therefore, it is considered that, in response to the development of the undulation of the Philippine Sea slab, the undulation of the topography of the outer zone has become larger in western Japan. That is to say, strong E-W compression, which started 3 Ma, results in the formation of short-wavelength pairs of mountains and basis in the inner zone, and larger scale topography, such as Ise Bay, the Kii Mountains, the Kii Strait, the Shikoku Mountains, and the Bungo Channel, in the outer zone of western Japan.
In western Japan, the paleo Setouchi low-land area extends until the east of the Nobi plain in the Pliocene. In the area, non-marine sediments deposited, which means that this low-land area was separated from the Pacific Ocean.
In the Quaternary, the stress regime has drastically changed to strong E-W compression. In the inner zone of the Kinki district, block-fault mountains, such as the Suzuka and the Ikoma mountains, have formed due to active reverse fault movements. In the outer zone, the undulation of the topography becomes larger: uplift of the Kii mountains has accelerated, while the Kii strait was opened.
The Philippine Sea slab has large undulation, which is considered to have been caused by E-W compression since 3 Ma. In other words, the large undulation of the Philippine Sea slab has developed in recent 3 Ma. Therefore, it is considered that, in response to the development of the undulation of the Philippine Sea slab, the undulation of the topography of the outer zone has become larger in western Japan. That is to say, strong E-W compression, which started 3 Ma, results in the formation of short-wavelength pairs of mountains and basis in the inner zone, and larger scale topography, such as Ise Bay, the Kii Mountains, the Kii Strait, the Shikoku Mountains, and the Bungo Channel, in the outer zone of western Japan.