HR: 1340h
AN: T33A-1345 [Abstracts]
TI: Waveform Modeling Of The Subducting Slab Beneath Japan
AU: * Chen, M
EM: mchen@gps.caltech.edu
AF: Seismo. Lab., California Institute of Technology, 252-21, Caltech,
1200 E. California Blvd., Pasadena, CA 91106
United States
AU: Tromp, J
EM: jtromp@gps.caltech.edu
AF: Seismo. Lab., California Institute of Technology, 252-21, Caltech,
1200 E. California Blvd., Pasadena, CA 91106
United States
AU: Helmberger, D
EM: helm@gps.caltech.edu
AF: Seismo. Lab., California Institute of Technology, 252-21, Caltech,
1200 E. California Blvd., Pasadena, CA 91106
United States
AU: Kanamori, H
EM: hiroo@gps.caltech.edu
AF: Seismo. Lab., California Institute of Technology, 252-21, Caltech,
1200 E. California Blvd., Pasadena, CA 91106
United States
AB:
Deep earthquakes ($400-600$ km) occurring in the down-going
Pacific plate produce detailed waveform patterns recorded by
the Japanese Hi-net array ($>500$ stations), at distance from
about $7^\circ$ to $12^\circ$, with ray paths densely and
uniformly sampling the vicinity of the subducting slab. Most P-wave
direct arrivals are well predicted by a 1-D model. However,
observations along paths sampling the slab are
advanced by up to 4 seconds and many show strong multipathing
over patches of about 100 km in width. Observed P-wave seismograms
from stations in these patches can be well aligned by a time-shift
from a preferred combination involving epicentral distance and azimuth
by which the multipathing becomes well-organized.
The P-wave 3-D tomographic model proposed
for this region by Zhao (1993) has a well-developed slab
with velocities $3-6%$ higher than the normal mantle and a
thickness of about 90 km, and low velocity zones with anomalies
up to $-6%$ in the mantle wedge. Synthetics calculated based upon
2-D finite-difference and 3-D spectral-element methods are
compared with Hi-net data (vertical component)
and F-net data (3 components) for regional deep earthquakes.
The comparisons show that synthetics generated
from Zhao's P-wave model can predict some of the data
in terms of both timing and waveform complexity as measured by
cross-correlation, but discrepancies also exist.
Waveforms in certain azimuth and epicentral distance
ranges are very complex, suggesting stronger 3-D model variations.
DE: 8150 Plate boundary--general (3040)
DE: 7203 Body wave propagation
DE: 7218 Lithosphere and upper mantle
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting