Geomorphic Development and Crustal Movement of the Middle Course Basin of the Kinokawa River

Sangawa, Akira

doi:10.4157/grj.50.578

Cited by 11 publications

(5 citation statements)

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“…By contrast, dextral faulting has dominated since the earliest Quaternary period to the present time ( Kaneko 1966; Sangawa 1986). The oldest record of the dextral displacement was dated ca 2 Ma and was reported from the eastern margin of the MTL on the basis of the analysis of faults that juxtaposed confluent fans and rivers ( Sangawa 1980; Tsukuda 1990).…”

Section: Structural Geologic Eventsmentioning

confidence: 99%

Volcanic history and tectonics of the Southwest Japan Arc

Kamata¹,

Kodama²

1999

Island Arc

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Remarkable changes in volcanism and tectonism have occurred in a synchronous manner since 1.5–2 Ma at the junction of the Southwest Japan Arc and the Ryukyu Arc. Although extensive volcanism occurred in Kyushu before 2 Ma, the subduction‐related volcanism started at ca 1.5 Ma, forming a NE–SW trend volcanic front, preceded by significant changes in whole‐rock chemistry and mode of eruptions at ca 2 Ma. The Median Tectonic Line has intensified dextral motion since 2 Ma, with a northward shift of its active trace of as much as 10 km, accompanied by the formation of rhomboidal basins in Central Kyushu. Crustal rotation and incipient rifting has also occurred in South Kyushu and the northern Okinawa Trough over the past 2 million years. We emphasize that the commencement age of these events coincides with that of the transition to the westward convergence of the Philippine Sea plate, which we interpret as a primary cause of these synchronous episodes. We assume that the shift in subduction direction led to an increase of fluid component contamination from subducted oceanic slab, which then produced island‐arc type volcanism along the volcanic front. Accelerated trench retreat along the Ryukyu Trench may have caused rifting and crustal rotation in the northern Ryukyu Arc.

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Section: Structural Geologic Eventsmentioning

confidence: 99%

Volcanic history and tectonics of the Southwest Japan Arc

Kamata¹,

Kodama²

1999

Island Arc

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“…The SW Japan arc corresponds to the subduction of relatively younger part of the PHS plate (27-15 Ma, Okino et al 1994). The direction of relative motion around SW Japan is oblique (N55°W), which is considered to drive the right-lateral strike slip of the Median Tectonic Line (MTL) (e.g., Sangawa 1977;Sato et al 2015). The tectonic environment as described above continues to influence the fault development and present seismic activity in SW Japan.…”

Section: Tectonic Settingmentioning

confidence: 99%

Stress change in southwest Japan due to the 1944–1946 Nankai megathrust rupture sequence based on a 3-D heterogeneous rheological model

Hashima,

Hori,

Iinuma

et al. 2024

Earth Planets Space

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The Nankai trough has repeatedly experienced large megathrust earthquakes at intervals of 100–200 years. The inland region of southwest (SW) Japan has a seismically active period from 50 years before to 10 years after megathrust earthquakes. To assess the activities of inland earthquakes after megathrust earthquakes, we need to quantitatively evaluate the postseismic stress accumulation on the inland source faults considering plausible viscoelastic relaxation. Recent studies have shown the importance of low-viscosity layers along the lithosphere-asthenosphere boundary (LAB layer) in postseismic deformation. In the present study, we focus on the most recent ruptures, the 1944 M7.9 Tonankai and the 1946 M8.0 Nankai earthquakes, estimating the 4-year stress change on the source faults in SW Japan in a forward modeling approach. The 1944–1946 megathrust rupture sequence was followed by severe ~ M7 inland earthquakes, such as the 1945 M6.8 Mikawa and 1948 M7.1 Fukui earthquakes. For stress calculation, we used a highly detailed finite element model incorporating the actual topography and the plausible viscoelastic underground structure from past studies. The calculated inland stress field shows the dominance of the coseismic change during the 1944 and 1946 earthquakes and little contribution from viscoelastic relaxation. In contrast, viscoelastic relaxation has a significant effect on stress in the slab, indicating the importance of quantifying the viscosity of the LAB layer. Based on the calculated stress, we evaluated the change in the Coulomb failure stress (ΔCFS) on each source fault. The ΔCFS is generally positive on the strike-slip faults east of 135°E due to the 1944 rupture. In contrast, the ΔCFS on the faults west of 135°E, including the Median Tectonic Line segments, became positive due to the 1946 rupture. The occurrence of the damaging earthquakes in 1945 and 1948 can be explained by the calculated ΔCFS. The ΔCFS on the recent earthquake faults of the recent damaging earthquakes such as the 2016 M7.2 Kumamoto earthquake is generally negative, suggesting the delay in stress accumulation. The ΔCFS on the source faults of the intra-slab earthquakes differ significantly as large as tens of kilopascals depending on the viscosity of the LAB layer. Graphical Abstract

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“…These differences are considered to come from the age of the subducting plate; the subducting slab under the SW Japan arc is younger (27 − 15 Ma, Okino et al, 1994) than that under the Ryukyu arc (120 − 30 Ma, Lallemand, 2016). The direction of relative motion around SW Japan is oblique (N55°W), which is considered to drive the right-lateral strike slip of the Median Tectonic Line (MTL) (e.g., Sangawa, 1977;Sato et al, 1995). The tectonic environment as describe above in uences the fault development and present seismic activity in SW Japan.…”

Section: Tectonic Settingmentioning

confidence: 99%

Stress change in southwest Japan due to the 1944–1946 Nankai megathrust rupture sequence based on a 3-D heterogeneous rheological model

Hashima

Hori

Iinuma

et al. 2023

Preprint

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The Philippine Sea plate subducts under the southwest (SW) Japan arc at the Nankai trough, repeatedly causing large megathrust earthquakes at intervals of 100 to 200 years. According to the studies of historical earthquakes, the inland region of SW Japan has a seismically active period from 50 years before to 10 years after megathrust earthquakes. To assess the activities of inland earthquakes, we need to quantitatively evaluate the stress accumulation on the inland source faults. For the periods before megathrust earthquakes, we can calculate inland stress accumulation rates from a nearly steady locking pattern. For the periods after megathrust earthquakes, however, we need to consider the various rupture patterns of past events and postseismic viscoelastic relaxation. In this study, we focused on the most recent ruptures, the 1944 Tonankai and the 1946 Nankai earthquakes, estimating the 4-year stress change on the source faults in SW Japan. This rupture sequence was followed by severe ~ M7 inland earthquakes, such as the 1945 Mikawa and 1948 Fukui earthquakes. For realistic stress calculation, we used a highly detailed finite element model (FEM) incorporating the actual topography and the plausible viscoelastic underground structure from past studies. The computation cost of the FEM was reduced by the analysis method optimized for crustal deformation. The calculated inland stress field shows the dominance of the coseismic change during the 1944 and 1946 earthquakes and little contribution from viscoelastic relaxation. In contrast, viscoelastic relaxation has a significant effect on stress in the slab, indicating the importance of understanding the viscosity structure. Based on the calculated stress with an effective friction coefficient of 0.4, we evaluated the change in the Coulomb failure stress (ΔCFS) on each source fault. The ΔCFS is generally positive on the strike-slip faults east of 135°E due to the 1944 rupture. In contrast, the ΔCFS on the faults west of 135°E, including the Median Tectonic Line segments, became positive due to the 1946 rupture. For faults in Kyushu, the westernmost part of SW Japan, the ΔCFS remained negative. The occurrence of damaging earthquakes such as the 1945 Mikawa and 1948 Fukui earthquakes can be explained by this basic trend. This trend is less dependent on the viscosity structure and the variation of the slip distribution of the megathrust earthquakes. However, if the viscosity in the thin layer along the lithosphere-asthenosphere boundary is extremely low, the ΔCFS on the eastern source faults, including that of the 1891 M8.0 Nobi earthquake, was positive immediately after the 1944–1946 rupture sequence but decreased gradually due to viscoelastic relaxation, which is not consistent with earthquake occurrence. Also, some faults, including that of the 1995 M7.3 Kobe earthquake, exhibit behavior more sensitive to the slip distribution on the megathrust than to viscoelastic relaxation. These results imply the usefulness of the stress calculation combined with seismicity for determining the constraints of the viscosity structure and the slip distribution.

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Geomorphic Development and Crustal Movement of the Middle Course Basin of the Kinokawa River

Cited by 11 publications

References 0 publications

Volcanic history and tectonics of the Southwest Japan Arc

Volcanic history and tectonics of the Southwest Japan Arc

Stress change in southwest Japan due to the 1944–1946 Nankai megathrust rupture sequence based on a 3-D heterogeneous rheological model

Stress change in southwest Japan due to the 1944–1946 Nankai megathrust rupture sequence based on a 3-D heterogeneous rheological model

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