2006 Fiscal Year Final Research Report Summary
Mechanism of deep focus earthquakes: numerical simulation of physical process and deformation in subducted slabs
| Project/Area Number |
16540388
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Solid earth and planetary physics
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| Research Institution | Hiroshima University |
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Principal Investigator |
NAKAKUKI Tomoeki Hiroshima University, Graduate School of Science, Research Associate, 大学院理学研究科, 助手 (10263667)
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| Project Period (FY) |
2004 – 2006
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| Keywords | deep focus earthquake / subducted slab / subduction zone / stress field / rheology / numerical simulation / mantle convection |
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| Research Abstract |
We have investigated deformation and physical processes in subducted slabs. We concentrated our efforts to construct dynamic model of the subduction integrated into the mantle convection system in FY2004. For this purpose, we require a numerical code to calculate the mantle convection system with 1 to 2 km resolution. We therefore developed a new code for mantle convection utilizing a 2-layer system of numerical grid. We next developed 2-D dynamic subduction model spontaneously integrated into the mantle convection. The rheological parameters are examined comparing strain and stress field of the subducting lithosphere. Based on this self-consistent subduction model, we investigated interaction of the slab with the mantle transition zones in FY2005 and FY2006. We focused on the effects of (1) effects of free trench motion on the structure of the subducted slab, (2) viscosity layering at the 660 km phase boundary, (3) weakening by the grain-size reduction associated with the 410 and 660
… More
km phase transitions. We also consider effects of temperature-and pressure-dependent thermal expansivity on the buoyancy of the subducted slab.
In this study, we have revealed the mechanism to generate the slab stagnating in the mantle transition zone. The motion of the trench unbend the subducted slab so that it makes a dip angle of the deep slab shallower. The shallow angle and the shear stress by the backward trench motion reduce downward stress at the tip of the slab interacting with the 660 km phase transition. The viscosity jump is essential to generate stress filed in the transition zone slab resembling that obtained by the seismic observation. In the case with no viscosity jump, the bending of the slab determines the stress in the slab. A couple of compressional and tensile stress always appears in the location with strong stress. The viscosity jump at 660 km phase boundary is needed to generate stress field of down-dip compression in the transition zone stab. The viscosity jump, however, slows the motion of the surface plate. Non-Newtonian deformation mechanism in the transition zone slab may be important to fill this discrepancy. Less
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Research Products
(5 results)
