Abstract
First-arrival waveforms remain underutilized in crustal refraction-reflection
seismology by mostly reducing them to traveltime picks. However,
as in earthquake seismology, the waveforms also contain important
information about shallow near-receiver structures. We illustrate
the use of three-component waveform analysis on the records from
the ACCRETE wide-angle data set (SE Alaska and British Columbia;
1994), apply the Receiver Function (RF) methodology to the codas
of P-wave arrivals, and draw two important conclusions. First, the
P-wave polarization azimuths are found to be controlled by the near-receiver
structures and virtually unrelated to the source-receiver backazimuths,
from which they deviate by up to \~40 deg. This observation might
be important for studies of anisotropy and also for earthquake RF
studies. Second, after correcting for the polarization azimuths,
clear P/S mode conversions are reliably detected within 80-400 ms
following the primary arrivals. The conversions are interpreted as
originating at the base of the sedimentary cover of the fjord channel.
In most cases, imaging of the basement requires only several records;
however, notable exceptions are also found and interpreted as caused
by multipathing, localized scattering, and onsets of crustal and
Moho reflections. The ACCRETE example shows that RF methodology could
be useful for constraining sediment thickness and deriving P- and
S-wave receiver statics in land refraction surveys where collocated
reflection profiles are not available. In addition, RFs from repeatable
controlled sources could be useful for testing and calibration of
RF techniques.
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