NEW_Accomplishments.indd - IRIS

2006 IRIS 5-YEAR PROPOSAL UPWELLING AND DOWNWELLING
Finite Difference Synthetic Test for Kirchhoff Migration of Receiver Function on
Subducting Slab
Sangwon Ham, Alan Levander, Fenglin Niu • Rice University
Receiver function imaging enables higher resolution imaging than traveltime tomography, and dense and portable seismic
array deployments permitting the migration techniques are possible with the Japanese seismic networks and IRIS PASS-
CAL deployments. We conducted Kirchhoff migration for the synthetic data generated from two-dimentional elastic wave
finite-difference modeling to verify the imaging quality of the migration code and to understand the relationship between the
physical parameters of the subsurface and the migrated image (Levander, 1988; Levander 2005). The slab geometry from
High-Resolution tomography in Japan (Zhao et al., 1994) was used to construct a synthetic model. We set up the parameters
for the synthetic modeling, receiver function generation, and migration to simulate the geometry of the earthquake on February
26, 2001, in India.
We can verify that migration with a smoothed 2D version of the velocity distribution gives an improved image of the slab
geometry than that with a 1D velocity model (Figure 1). We simulated the effect of various model parameters like epicentral
distances (i.e. incidence angle of the incoming wave) on the migrated image. We found that the conversion coefficient in the
migrated image is strongly dependent on the P-wave incidence angle, hence the epicentral distance (Figure 2). We will get
more quantitative results for the effect of the subsurface parameters on the migrated image that are the subject of a forthcoming
publication.
Figure 1. Effect of velocity model on
the migrated image. Migration with
2D velocity model (right) shows
better top boundary constraint of
the slab geometry than that with 1D
velocity model (left).
Figure 2. Effect of epicentral
distance on the migrated image. Migration
with 55° epicental distance
(right) shows stronger boundary
constraint of the slab geometry than
that with 45° epicental distance
(left).
Zhao, D., A. Hasegawa, and H. Kanamori, Deep structure of Japan subduction zone as derived from local, regional, and teleseismic events, J. Geophys. Res.,
99, 22,313-22,329, 1994.
Levander, A., F. Niu, C.-T.A. Lee, and X. Cheng, Imag(in)ing the Continental Lithosphere, Physics of the Earth and Planetary Interiors, accepted, 2005.
This research is supported by NSF CMG 0222270
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