HR: 0830h
AN: S21D-0320    [PDF]
TI: Cross-Correlation-Based Relocation of Intermediate-Depth Subduction Seismicity in Japan
AU: * Shelly, D R
EM: dshelly@pangea.stanford.edu
AF: Department of Geophysics, Stanford University, 397 Panama Mall, Stanford, CA 94305-2215 United States
AU: Beroza, G C
EM: beroza@pangea.stanford.edu
AF: Department of Geophysics, Stanford University, 397 Panama Mall, Stanford, CA 94305-2215 United States
AU: Ide, S
EM: ide@eps.s.u-tokyo.ac.jp
AF: Department of Earth and Planetary Science, University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo, 113-0033 Japan
AB: We present very high precision hypocenter relocations of intermediate-depth subduction earthquakes off the Ibaraki Prefecture of north-central Honshu, Japan and analyze their implications for subduction mechanics and the mechanism of intermediate-depth earthquakes. Our relocations are obtained using cross-correlation-derived differential arrival times and the double-difference algorithm of Waldhauser and Ellsworth (2000). Cross-correlation-based relocation of subduction seismicity substantially increases the location precision over relocations using only catalog phase picks and dramatically improves routine catalog locations. Our previous relocations in neighboring regions using the double difference method on catalog arrival times have shown a substantial increase in organization of seismicity, compared with the catalog locations. In particular, we observed a narrowing of the seismogenic zone at depth and a narrowing of each limb of the double seismic zone when viewed in cross-section. We have also observed unusual events that appear to be within the mantle wedge above the slab and substantial seismicity within the slab between the two planes of the double seismic zone. We chose the Ibaraki region for its high rate of slab seismicity, its relatively simple geometry, and for the presence of an intermediate-depth double seismic zone. We relocate nearly 5000 mostly intermediate-depth events occurring in this region between June 2002 and May 2003 using more than 100,000 waveforms from the JMA unified catalog. Many of these waveforms are from stations in Hinet, a recently installed national borehole network that provides particularly high-quality data.
DE: 7209 Earthquake dynamics and mechanics
DE: 7230 Seismicity and seismotectonics
DE: 8123 Dynamics, seismotectonics
SC: Seismology [S]
MN: 2003 Fall Meeting