Reflectivity imaging of local earthquake seismograms has revealed
the structure of the Hikurangi subduction interface at the location
of two strong earthquakes that occurred in 1990. The earthquakes
originated within the continental plate of the North Island of New
Zealand and below in the subducting Pacific slab. We used seismograms
from 500 well-located events in two earthquake sequences recorded
by a small temporary seismograph deployment to directly image the
structure and multiphase reflectivity of the plate interface. Synthetic
tests of the imaging method show the effects of the poor 3-d geometric
coverage afforded by the seismometer array. Kirchhoff summation image
sections computed from synthetics show accurate depth imaging of
backscattering interfaces. Phase-converting interfaces imaged with
forward-scattered waves are smeared by poor ray coverage to 5-km
depth inaccuracy and are only imaged over a small range of their
horizontal extent. From the data, we computed image sections for
P-P, P-S, S-P and S-S scattering. We mitigated imaging artifacts
due to poor ray coverage with an obliquity factor, an antialiasing
criterion and enhancement by resampling statistics. Imaging used
a sharply layered velocity model. We tested for the effects of imaging
with first-arriving headwaves by imaging through smoothly varying
velocity models. For our ray geometry, early-arrival headwaves contribute
little to the images.The plate interface appears as a 3-5-km thick
P-P and possibly S-S backscatterer with 5 deg NW dip, offset 5 km
down-to-the-NW above a normal fault in the slab. When illuminated
from below, a wedge of the interface on the downdip side of the slab
fault forms a very prominent P-P forward scatterer. The edges of
the wedge forward-scatter some S-P and S-S energy, but an order of
magnitude less than the P-P forward scattering. The imbalances between
forward scattering of P and S energy suggest a wedge of subducted
sediment retaining significant porosity but with rigidity close to
that of surrounding rocks.
%0 Journal Article
%1 louie_etal:2002
%A Louie, J.
%A Chávez-Pérez, S.
%A Henrys, S.
%A Bannister, S.
%D 2002
%J Tectonophysics
%K geophysics seismology
%N 1-4
%P 227--246
%R 10.1016/S0040-1951(02)00144-0
%T Multimode migration of scattered and converted waves for the structure
of the Hikurangi slab interface, New Zealand
%U http://dx.doi.org/10.1016/S0040-1951(02)00144-0
%V 355
%X Reflectivity imaging of local earthquake seismograms has revealed
the structure of the Hikurangi subduction interface at the location
of two strong earthquakes that occurred in 1990. The earthquakes
originated within the continental plate of the North Island of New
Zealand and below in the subducting Pacific slab. We used seismograms
from 500 well-located events in two earthquake sequences recorded
by a small temporary seismograph deployment to directly image the
structure and multiphase reflectivity of the plate interface. Synthetic
tests of the imaging method show the effects of the poor 3-d geometric
coverage afforded by the seismometer array. Kirchhoff summation image
sections computed from synthetics show accurate depth imaging of
backscattering interfaces. Phase-converting interfaces imaged with
forward-scattered waves are smeared by poor ray coverage to 5-km
depth inaccuracy and are only imaged over a small range of their
horizontal extent. From the data, we computed image sections for
P-P, P-S, S-P and S-S scattering. We mitigated imaging artifacts
due to poor ray coverage with an obliquity factor, an antialiasing
criterion and enhancement by resampling statistics. Imaging used
a sharply layered velocity model. We tested for the effects of imaging
with first-arriving headwaves by imaging through smoothly varying
velocity models. For our ray geometry, early-arrival headwaves contribute
little to the images.The plate interface appears as a 3-5-km thick
P-P and possibly S-S backscatterer with 5 deg NW dip, offset 5 km
down-to-the-NW above a normal fault in the slab. When illuminated
from below, a wedge of the interface on the downdip side of the slab
fault forms a very prominent P-P forward scatterer. The edges of
the wedge forward-scatter some S-P and S-S energy, but an order of
magnitude less than the P-P forward scattering. The imbalances between
forward scattering of P and S energy suggest a wedge of subducted
sediment retaining significant porosity but with rigidity close to
that of surrounding rocks.
@article{louie_etal:2002,
abstract = {Reflectivity imaging of local earthquake seismograms has revealed
the structure of the Hikurangi subduction interface at the location
of two strong earthquakes that occurred in 1990. The earthquakes
originated within the continental plate of the North Island of New
Zealand and below in the subducting Pacific slab. We used seismograms
from 500 well-located events in two earthquake sequences recorded
by a small temporary seismograph deployment to directly image the
structure and multiphase reflectivity of the plate interface. Synthetic
tests of the imaging method show the effects of the poor 3-d geometric
coverage afforded by the seismometer array. Kirchhoff summation image
sections computed from synthetics show accurate depth imaging of
backscattering interfaces. Phase-converting interfaces imaged with
forward-scattered waves are smeared by poor ray coverage to 5-km
depth inaccuracy and are only imaged over a small range of their
horizontal extent. From the data, we computed image sections for
P-P, P-S, S-P and S-S scattering. We mitigated imaging artifacts
due to poor ray coverage with an obliquity factor, an antialiasing
criterion and enhancement by resampling statistics. Imaging used
a sharply layered velocity model. We tested for the effects of imaging
with first-arriving headwaves by imaging through smoothly varying
velocity models. For our ray geometry, early-arrival headwaves contribute
little to the images.The plate interface appears as a 3-5-km thick
P-P and possibly S-S backscatterer with 5 deg NW dip, offset 5 km
down-to-the-NW above a normal fault in the slab. When illuminated
from below, a wedge of the interface on the downdip side of the slab
fault forms a very prominent P-P forward scatterer. The edges of
the wedge forward-scatter some S-P and S-S energy, but an order of
magnitude less than the P-P forward scattering. The imbalances between
forward scattering of P and S energy suggest a wedge of subducted
sediment retaining significant porosity but with rigidity close to
that of surrounding rocks.},
added-at = {2012-09-01T13:08:21.000+0200},
author = {Louie, J. and Ch\'{a}vez-P\'{e}rez, S. and Henrys, S. and Bannister, S.},
biburl = {https://www.bibsonomy.org/bibtex/26c6de4066f955342b09eacecbb7f71d8/nilsma},
day = 30,
doi = {10.1016/S0040-1951(02)00144-0},
interhash = {89e3a940a64ef5477ce22fa8a9b2c839},
intrahash = {6c6de4066f955342b09eacecbb7f71d8},
issn = {00401951},
journal = {Tectonophysics},
keywords = {geophysics seismology},
month = sep,
number = {1-4},
pages = {227--246},
timestamp = {2021-02-09T13:27:42.000+0100},
title = {Multimode migration of scattered and converted waves for the structure
of the Hikurangi slab interface, New Zealand},
url = {http://dx.doi.org/10.1016/S0040-1951(02)00144-0},
volume = 355,
year = 2002
}