4:15 PM - 4:30 PM
[SCG45-34] Role of folds formed along plate boundaries in subduction zones as inelastic deformation of accretionary prism
Keywords:Slow earthquake, Accretionary complex, Fold, Bedding plane slip, Subduction
We study the relationships between inelastic deformation of hanging wall and slow earthquakes in the shallow part of the subduction zone. Generally, previous studies indicate the low activity of slow-earthquake activity near the trench. Our focus is on the mechanical strength near the trench in the hanging wall (e.g., Nankai, Japan) where folds are identified. These folds partially contribute to the inelastic deformation associated with plate subduction. However, the extent of stress buildup near the plate boundary during inelastic fold deformation remains uncertain. The strain rate forming the folds matches the rate of plate movement. This deformation is steady compared to faulting. Hence, the fold deformation is non-episodic. In the case of multilayered folds, bedding-plane slip plays a role in deforming the layers.
To understanding the magnitude of shear stress stored on the plate boundary, our model on shallow slow earthquakes considers three steps. Step 1: Deposition of sand and mud on the incoming oceanic plate. Step 2: At near the trench, little stress accumulation in the accretionary prism due to inelastic fold formation. Step 3: Elastic stress accumulation in the accretionary prism at a further landward location after the completion of folding as the fold works as an elastic medium. If the strain from plate subduction are mostly consumed by folds in the accretionary prism at step 2, shear stress at the plate boundary beneath the folds will be minimally loaded, leading to low earthquake activity. At step 3, elastic strain can be stored in the accretionary zone, and the strain energy can be released by the slip on the plate boundary as an earthquake.
Preliminary, we are studying the accretionary complex exposed on land at the southern tip of the Boso Peninsula, Japan, which represents a shallow accretionary complex. At a coastal site that corresponds to a shallow accretionary prism near the trench, we measured the spacing of bedding-plane slips. The average of measured intervals was 2-3 m. The bedding-plane slip is likely responsible for the elastic energy resolution of folds in multilayers
To understanding the magnitude of shear stress stored on the plate boundary, our model on shallow slow earthquakes considers three steps. Step 1: Deposition of sand and mud on the incoming oceanic plate. Step 2: At near the trench, little stress accumulation in the accretionary prism due to inelastic fold formation. Step 3: Elastic stress accumulation in the accretionary prism at a further landward location after the completion of folding as the fold works as an elastic medium. If the strain from plate subduction are mostly consumed by folds in the accretionary prism at step 2, shear stress at the plate boundary beneath the folds will be minimally loaded, leading to low earthquake activity. At step 3, elastic strain can be stored in the accretionary zone, and the strain energy can be released by the slip on the plate boundary as an earthquake.
Preliminary, we are studying the accretionary complex exposed on land at the southern tip of the Boso Peninsula, Japan, which represents a shallow accretionary complex. At a coastal site that corresponds to a shallow accretionary prism near the trench, we measured the spacing of bedding-plane slips. The average of measured intervals was 2-3 m. The bedding-plane slip is likely responsible for the elastic energy resolution of folds in multilayers