HR: 13:40h
AN: G22D-01 INVITED     [PDF]
TI: Secular Subsidence and Deep Basal Subduction Erosion at the Northeastern Japan Forearc
AU: * Heki, K
EM: heki@miz.nao.ac.jp
AF: Div. Earth Rotation, National Astron. Obs., 2-12 Hoshigaoka, Mizusawa-city, Iwate, 023-0861 Japan
AB: Subduction erosion has two basic mechanisms, (1) material collapsed from the landward slope is trapped in horst-graben structure of the subducting plate (frontal erosion), and/or (2) materials at the base of the upper plate are scraped off by the subducting slab (basal erosion). These processes let the upper plate material subduct with the slab, and make the trench retreat landward and cause forearc subsidence. Subduction erosion in Northeast Japan (NEJ) has been investigated by many geologists since ocean drilling at the continental slope of the Japan Trench discovered evidence of past erosion, i.e. unconformity over Cretaceous subaerial strata several kilometers deep. Tide gauge data of the last few decades in NEJ forearc also show that both interseismic and coseismic vertical movements are downward, suggesting secular subsidence of the forearc currently goes on. On the other hand, subduction erosion does not take place in Southwest Japan (SWJ); it has a well-developed accretionary prism, and sediment accretion is considered to occur there. Direct observation of the erosion has been difficult as it leaves little geological and geophysical evidence. In the present study, we compare horizontal and vertical velocity profiles across NEJ and SWJ, and investigate geodetic signatures of subduction erosion and accretion with modern satellite geodesy. The horizontal velocities agree well with those predicted by the elastic loading of the subducting slabs. However, vertical velocities in the NEJ forearc show significant negative deviation (subsidence). This may indicate loss of material at the plate interface, due to the erosion of the upper plate by the slab (basal subduction erosion). The estimated rate (15 mm/yr down to 90 km) is somewhat faster than the geological average, and the erosion speed may be variable being controlled by the surface roughness of subducting slabs.
DE: 1206 Crustal movements--interplate (8155)
DE: 1213 Earth's interior--dynamics (8115, 8120)
DE: 1243 Space geodetic surveys
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 8105 Continental margins and sedimentary basins
SC: Geodesy [G]
MN: 2003 Fall Meeting