Page 152 - Whole Earth Geophysics An Introductory Textbook For Geologists And Geophysicists

135
Hz
Hz
coef-
criti-
80
40
reflection
Rayleigh; iii)
of 20 10
of 10 10
Exercises

trace.
trace.
1000
1000
re

50
50
wavelet
resulting seismic
seismic
wavelet
impedance, and
=
h=
h=
h=
direct
fl
h
m/s»
resulting
zero-phase
zero-phase
=2.4;
2.1;
2.2;
2.2;
ont
ii)
m/s
5-7
P;
p =
=
ft
=
direct
scale.
the
p
p
the
velocity, density. acoustic
Vp = 2500;
p
5-2
Exercise
above.
a
a
2500
3000
3800;
3000;
and plot
plot
= 2500;
with
with
ms
vertical
i)
fi
L7
Exercise
the:
and
series
model
series
=
V,=
for
center frequency)
center frequency)
the
=
=
vy,
p
V,
for
coefficient
coefficient
i
distance graph
layered
V,
as
V2
nvo-way travel time
Sandstone
Model
Sandstone
for
simple, horizontally
of seismic
it
Model
reflection
reflection
Shale
Shale
Hz
Hz
vs.
500m
travel time
it
= 25
~ 50
Porous
logs
Tight
the
the
ficient, with
(
(
well
frequency
Convolve
Convolve
frequency
the
i
Draw
a
Plot
Surface
Given
d)
a)
c)
e)
_
5-2
cally refracted reflection. multiple P reflection; v) first primary P P; iv) arrivals at of these velocity of each the apparent is What b) of zero m, 500 m, distance a source? the from and 20,000 m 2000 m, 6000 m, with (b), but and (a) Repeat c) of 500 m. instead depth at 5000 m interface the
Analysis the Middle America Trench no interpretation; the uppermost 4.$ km of the turbidites side of right have turbidites water strong imped- acoustic sediments very to of regions sec- of the side more a have seismic of logs the as depth
Waveform turbidites on trench a to Hemipelagic homogeneous, leading Two zone). on the right regions wave velocities (V,), densities (p) well Draw with
And from section the water layer (zero amplitude); trench (“chaotic”). From G. F. Moore and T. H. Shipley. Mechanisms D. C. section, leading contrasting those strata. model}. coefficient,
Processing, CA mene top figure shows the seismic traces with interpretations superimposed. Note that the Union, Washington, the of the water, of layérs reflections. more “transparent” turbidites crust; oceanic sedimentary layer. the of reflection and
Acquisition, UATE migrated a on packages include of sediment accretion in the Middle America Trench off Mexico, in Journal of Geophysical Research, v.93, pp.8911-8927, Geophysical side left the than velocity have turbidites high-amplitude much are crust seismically trench deformed the of on the following page shows compressional of horizontal each for bottom the to
Reflection: eee io reflection amplitude); hemipelagic sediments (Jow amplitude, “transparent” zone); deformed On results. seismic and trench of sequence oceanic (a the basement layers for the acoustic impedance drilled is acoustic
Seismic SESS y? sigan Seismic waveform packages observed Mex-2; Moore and Shipley, 1988). The the bottom, but with (“chaotic” seismic expression): and oceanic crust traces density reflection. The a to the of top reflections layering include the crystalline random or “chaotic” seismic appearance. (h) thicknesses Calculate well a density, scale.
5 is shown on is not shown. Prominent © 1988. Redrawn with permission of the American seismic higher leading on amplitude and The model and a) Pretend b) velocity, vertical
Chapter at i i a Ser te ae blank much bottom ance, deposited low complex tion, 5-1
5.36 off Mexico (Line same section water column EXERCISES
134 FIGURE section
5.0 6.0 5.0 6.0 (high