HR: 09:15h
AN: S21C-06    [Abstracts]
TI: Supraslab earthquakes above the Pacific-plate slab in NE Japan: A possible graveyard of detached seamounts and volcanic ridges?
AU: * Kirby, S
EM: skirby@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025 United States
AU: Okada, T
EM: okada@aob.geophys.tohoku.ac.jp
AF: Cent. Earthquake and Vol. Pred., Graduate School of Science, Sendai, 980 8578 Japan
AU: Uchida, N
EM: uchida@aob.geophys.tohoku.ac.jp
AF: Cent. Earthquake and Vol. Pred., Graduate School of Science, Sendai, 980 8578 Japan
AU: Hasegawa, A
EM: hasegawa@aob.geophys.tohoku.ac.jp
AF: Cent. Earthquake and Vol. Pred., Graduate School of Science, Sendai, 980 8578 Japan
AU: Matsuzawa, T
EM: matsuzawa@aob.geophys.tohoku.ac.jp
AF: Cent. Earthquake and Vol. Pred., Graduate School of Science, Sendai, 980 8578 Japan
AU: Hino, R
EM: hino@aob.geophys.tohoku.ac.jp
AF: Cent. Earthquake and Vol. Pred., Graduate School of Science, Sendai, 980 8578 Japan
AB: Double-difference relocations of interplate thrust and intraslab earthquakes at depths greater than 35 km under NE Japan indicate that many clusters of earthquakes occur above the interplate thrust zone and hence are no longer part of the sinking Pacific-plate slab. The best examples of such clusters are found at depths of 40 to 60 km near the depth limit of interplate thrust earthquake activity and near the intersection of the forearc Moho with the plate interface. In some clusters, small repeating earthquakes occur on the plate interface below the supraslab clusters. The largest of these clusters have earthquakes that are as much as 25 km shallower than the plate boundary and extend as much as several tens of km in the down-dip direction. Offshore multi-beam sonar bathymetry shows seafloor relief that is dominated by seamounts and guyots, representing Cretaceous intraplate volcanic activity. The Japan inner trench slope is marked by many re-entrants that record past seamount-forearc collisions. Supraslab earthquake clusters may represent earthquake activity inside seamounts that have detached from the underlying Pacific plate along the original sedimented seafloor on which these intraplate shield volcanoes were built. If this interpretation is correct, then supraslab earthquakes may represent a unique cumulative record of past seamount subduction.
DE: 7208 Mantle (1212, 1213, 8124)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 7240 Subduction zones (1207, 1219, 1240)
SC: Seismology [S]
MN: Fall Meeting 2005