Аннотация
In recent years, there has been an increase in the deployment of relatively
dense arrays of seismic stations. The availability of spatially densely
sampled global and regional seismic data has stimulated the adoption
of industry-style imaging algorithms applied to converted- and scattered-wave
energy from distant earthquakes, leading to relatively high-resolution
images of the lower crust and upper mantle. We use seismic interferometry
to extract reflection responses from the coda of transmitted energy
from distant earthquakes. In theory, higher-resolution images can
be obtained when migrating reflections obtained with seismic interferometry
rather than with conversions, traditionally used in lithospheric
imaging methods. Moreover, reflection data allow the straightforward
application of algorithms previously developed in exploration seismology.
In particular, the availability of reflection data allows us to extract
from it a velocity model using standard multichannel data-processing
methods. However, the success of our approach relies mainly on a
favourable distribution of earthquakes. In this paper, we investigate
how the quality of the reflection response obtained with interferometry
is influenced by the distribution of earthquakes and the complexity
of the transmitted wavefields. Our analysis shows that a reasonable
reflection response could be extracted if (1) the array is approximately
aligned with an active zone of earthquakes, (2) different phase responses
are used to gather adequate angular illumination of the array and
(3) the illumination directions are properly accounted for during
processing. We illustrate our analysis using a synthetic data set
with similar illumination and source-side reverberation characteristics
as field data recorded during the 2000-2001 Laramie broad-band experiment.
Finally, we apply our method to the Laramie data, retrieving reflection
data. We extract a 2-D velocity model from the reflections and use
this model to migrate the data. On the final reflectivity image,
we observe a discontinuity in the reflections. We interpret this
discontinuity as the Cheyenne Belt, a suture zone between Archean
and Proterozoic terranes.
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