wide aperture reflection refraction profiling is studied in this presentation ,\

1. Wide Aperture Reflection Refraction Profiling
Originally developed for evaluating offshore seismic data recorded by ocean seismograph
(OBS)
 Exploit the wide-angle reflected energy
 Diving wave as well as normal incident energy
 develop a velocity depth model of a seismic time section from common shot or
station gather
(Makris and Thieben, 1984; Makris et al., 1998; Dell' Aversana P. et al., 2000, Leven et al.
2004)
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Aghazde.kamal@ut.ac.ir
Aghazde.kamal@yahoo.com

2. Coparing Warrp & conventional methods
Short ranged near normal incidence long ranges large
 produce “image “ of impedance contrasts angle of incident
 Detailed structure: sediments,faults,etc produce”model” of
structure
major variation only
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3. • Long offset data:
Observe the wave field of Diving waves
&
Wide angle reflection that have penetrated deeper into section
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5. energy conversion at the interface between two layers in a simple, two layer case.
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6. energy partitioning between the p and s phases
Greater portion of energy propagate
in reflected phase at angles of
incidence beyond the critical angle.
Beyond the critical distance S-waves
penetrate and map the structure where P-
waves are no more transmitted.
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7. Warrp is modelling not a processing technique.
• Warrp is based on:
 first break tomography
 none linear tomography by exploiting later arrival
 forward modelling by ray tracing or finite difference calculation
Velocity model is used to time and depth migrate the common shot
gathers
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8.  Effective under conditions where CDP approach fails to reveal
subsurface structure.
 essential to observe offsets significantly larger than the depth of the
target zone.
 penetrate the geological structures with sufficiently redundant
seismic energy.
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10. Invert for velocity structure on a grid (akin to medical tomography)
Can formulate problem as:
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11. • First break picks: an initial estimate of velocity structure of any
seismic profile
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12. First break for tomography inversion
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13. Defining velocities for the different layers that are identified
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15.  the spatial of a warrp model depends on the density of shots and
receivers and the redundancy of the seismic energy that penetrates
the different parts of the model.
 The advantage of WARRP mapping over a standard CDP or CRS-
survey is that since CDP or CRS-stacking is not needed we can map
the subsurface using less shots (i.e. one out of three).
Also modeling is accomplished on the real topography and static
corrections are not needed.
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16. In order to improve the velocity model derived by the first break
inversion and define the boundaries of the velocity layers, first order
discontinuities are introduced in the zones of steep velocity
gradients.
 The v(x,z)-functions within these layers are basically substantiated
by the apparent velocities of reversed observations over identical
parts of a line, as directly derived from CSG observations and the
velocity gradient model that first break tomography has produced.
 The identification procedure is based on a cross-correlation
procedure using amplitudes and waveform characteristics.
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17. • In order to improve the velocity model derived by the first break
inversion and define the boundaries of the velocity layers, first order
discontinuities are introduced in the zones of steep velocity gradients.
The v(x,z)-functions within these layers are basically substantiated by
the apparent velocities of reversed observations over identical parts
of a line, as directly derived from CSG observations and the velocity
gradient model that first break tomography has produced. The
identified arrivals for first breaks and reflected phases are presented
in below 2 figures . The identification procedure is based on a cross-
correlation procedure using amplitudes and waveform characteristics.
Wrongly picked and correlated arrivals are manually corrected.
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identification arrivals for first breaks and reflected phases

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27. • The P-wave speed-depth structure is finalized by iterative forward
modeling as stated above using a modified and optimized ray tracing
software program.
• The starting P-wave speed-depth model is derived from correlated
travel times in the WARRP sections by evaluating apparent velocities
and depth of shallow structures.
The P wave speed model is finalized when the observed arrival times of
reflected and refracted energy and the observed amplitudes are
reproduced by the model within acceptable limits defined by the
picking accuracy of the first arrivals.
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28. simplified schema of the ray paths explioted in this procedure
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Similar to first arrival
tomography but now we can
include wide-angle
reflections, which tell us
about “velocity
discontinuities"
Reflection-refraction tomography

29.  Guess velocity structure (based on graphical fit, 1D models etc)
 Calculate expected travel times for this model
 Compare expected travel times with observed travel times
 Refine model and repeat
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30. One example of a ray traced CSG and its synthetic amplitudes
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31. • to delineate small scale structures, smoothed usually by ray-tracing,
and resolve faults and tectonic details, prestack migration is
necessary. Algorithm described in details by:
• Pilipenko, V.N. and Makris, J. (1997) and Pilipenko, V.N. (1982).
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