Page 156 - Whole Earth Geophysics An Introductory Textbook For Geologists And Geophysicists

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139
incidence
time section
time section, illustrating how the event in
incidence raypaths. b) Migrated
(Fig. 6.2b) to a migrated depth section (b).
time
of
;
reflector (a) is used to
to a vertical
average velocity of
time section
mimics the hypothetical situation
Profiles
its normal
the
(migrated) position.
migrated
on
Reflection
horizontal
(unmigrated) position
a migrated
Fig. 6.1¢ moves from
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igrated
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rs
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of the orientation truer a section, revealing depth the on left the to gently dips tions, plate. subducting f velocity the of knowledge accurate require conversion depth and Migration not viewing requires interpretation Thorough energy. seismic of paths travel and before appear events how seeing
Profiles aseismic trace,a Normal unmigrated time the if even ray the takes time). travel went ray a as to converted from aver- an travel two-way Nankai the of oceanic unmigrated and is cover of the side through the on in not are within the water the on appears
Reflection On a dipping interface is vertically below the common raypaths for dipping reflector, source/receiver positions. c) The seismic reflection profile is an position, it time (two-way if each thus referred be 6.3). For (Fig, from of profile top The sedimentary left wedge bottom water that faults of strata that shows than
Seismic 6.1 a) from source/receiver position. b) to several common (b) the at positions, as is section can scale section point seismic 1990). on. the profiles. The accretionary the section less.thickness
Of FIGURE reflection plotted incidence resulting from section. source/receiver appears surface the true time vertical depth a of a et.al., time, deep-marine the of an of image Likewise, apparent offsets depth far
Interpretation Incidence yideq OWL] JOACLL common event to back their to back migrated the migrated conversion V. x (T/2) for displays Moore also travel two-way and side right into distorted migration. to move profile. The
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Tectonic SM 0) = the below. The then A 6.2). migration yielding a the interface, = d section 1982; see s, 8 basement the the on deformed is the that through migration migrated material, encompasses
And Normal (T of position directly interface, seismic events (Fig. up After the three al., et above Overlying material that Notice clarified the
Structural Surface the from not reflecting moves back then section. travel time to depth, above is: (d) shows the (Nasu just imaged fill trench trench-fill folding. is section on wedge low-velocity
Sources Trace™ below was the incidence (V) depth 6.4 off Japan is sections. shows and their proper positions before is
6 Seismic to Migration down velocity to
Chapter Incidence Raypaths Unmigrated Reflection (Event) directly reflection travel to straight vertical two-way age (T) time Fig. Trough, basement migrated undeformed, section thrusting unmigrated accretionary layer, which
138 a b Normat Cc Time Section