5:15 PM - 7:15 PM
[SCG61-P13] Effect of westward motion of the Philippine Sea plate on the east-west compression in the Japanese islands
Keywords:Stress loading, Philippine Sea plate, Northeastern Japan, Plate subduction, Viscoelasticity
1. Introduction
At present, northeast Japan is under east-west compressive tectonics. To explain this, Takahashi (2006) examined the relationship between the deformation of Northeast Japan and the movement of the surrounding plates. He concluded that the westward movement of the Philippine Sea Plate results in east-west compression of the Japanese Islands. However, he did not consider if its westward motion actually produces the stress enough to compress the northeast Japan. This study aims to quantitatively verify the qualitative considerations of Takahashi (2006) by the modeling approach.
2. Method
This study computes deformation rates due to the plate-to-plate interaction of the three plates involved. The plate-to-plate interaction can be expressed by the slip motion over the plate boundary. We simplify the geometry of the plate boundaries so as to keep the essence of the model by Takahashi (2006): the north-south straight line as Japan-Izu-Bonin trench and east-west vertical strike-slip fault as the Nankai-Sagami trough. Relative motions are set 10 cm/yr between the Pacific-Eurasia plates, 7 cm/yr between the Pacific-Philippine Sea plates, and 3 cm/yr between the Philippine Sea-Eurasia plates. The above setting enables to produce the Takahashi (2006) model. In the actual computation, we superpose computational results of the 7-cm/yr laterally uniform Pacific plate subduction, the 3-cm/yr Pacific plate subduction under the Eurasia plate, and the 3-cm/yr strike-slip motion between Philippine Sea–Eurasia plates.
3. Results
The computed velocity fields show overall rigid motion in each plate. In the proximity to the triple junction, however, we found small velocity of several mm/yr with respect to the fixed point in the Eurasia plate, which means non-rigid motion due to each plate-to-plate interaction. To quantitatively find the amount of deformation, we compute east-west strain rates. The results shows the distribution of east-west compression near the triple junction, though the amount is the order of 10^-9 /yr.
4. Discussion
We confirmed formation of compressive strain in the Eurasian plate due to interaction between three plates. However, the compressive occurred within the distance of 300 km from the triple junction. Also, the computed strain rates were of the order of 10^-9 /yr, which are 1/10 of the strain rates obtained by geological methods. Thus, we cannot conclude that the westward motion of the Philippine Sea plate is the main cause of the present east-west compression in the northeast Japan. The other candidates such as the collision of the Izu Peninsula or the partial collision along the Japan trench (Hashimoto and Matsu’ura, 2006) should be examined in the future.
At present, northeast Japan is under east-west compressive tectonics. To explain this, Takahashi (2006) examined the relationship between the deformation of Northeast Japan and the movement of the surrounding plates. He concluded that the westward movement of the Philippine Sea Plate results in east-west compression of the Japanese Islands. However, he did not consider if its westward motion actually produces the stress enough to compress the northeast Japan. This study aims to quantitatively verify the qualitative considerations of Takahashi (2006) by the modeling approach.
2. Method
This study computes deformation rates due to the plate-to-plate interaction of the three plates involved. The plate-to-plate interaction can be expressed by the slip motion over the plate boundary. We simplify the geometry of the plate boundaries so as to keep the essence of the model by Takahashi (2006): the north-south straight line as Japan-Izu-Bonin trench and east-west vertical strike-slip fault as the Nankai-Sagami trough. Relative motions are set 10 cm/yr between the Pacific-Eurasia plates, 7 cm/yr between the Pacific-Philippine Sea plates, and 3 cm/yr between the Philippine Sea-Eurasia plates. The above setting enables to produce the Takahashi (2006) model. In the actual computation, we superpose computational results of the 7-cm/yr laterally uniform Pacific plate subduction, the 3-cm/yr Pacific plate subduction under the Eurasia plate, and the 3-cm/yr strike-slip motion between Philippine Sea–Eurasia plates.
3. Results
The computed velocity fields show overall rigid motion in each plate. In the proximity to the triple junction, however, we found small velocity of several mm/yr with respect to the fixed point in the Eurasia plate, which means non-rigid motion due to each plate-to-plate interaction. To quantitatively find the amount of deformation, we compute east-west strain rates. The results shows the distribution of east-west compression near the triple junction, though the amount is the order of 10^-9 /yr.
4. Discussion
We confirmed formation of compressive strain in the Eurasian plate due to interaction between three plates. However, the compressive occurred within the distance of 300 km from the triple junction. Also, the computed strain rates were of the order of 10^-9 /yr, which are 1/10 of the strain rates obtained by geological methods. Thus, we cannot conclude that the westward motion of the Philippine Sea plate is the main cause of the present east-west compression in the northeast Japan. The other candidates such as the collision of the Izu Peninsula or the partial collision along the Japan trench (Hashimoto and Matsu’ura, 2006) should be examined in the future.