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(c) a possible crust-mantle interface of granulite (
α
=
7.3 km s
−
1
,
ρ
=
3.2
×
10
3
kg m
−
3
)over peridotite (
α
=
8.1 km s
−
1
,
ρ
=
3.3
×
10
3
kg m
−
3
).
23. Calculate the wavelengths of 20-, 30- and 40-Hz seismic P-waves in these rocks:
(a) sandstone (
α
=
3.0 km s
−
1
) and
(b) gabbro (
α
=
7.0 km s
−
1
).
What do these calculations indicate about the resolution of shallow and deep crustal
structures by seismic-reflection profiling.
24. Given the following time-distance data from a seismic-reflection survey, calculate
the depth of the reflector and a velocity for the material above it. What type is this
velocity?
Distance (km)
Travel time (s)
0.5
1.01
1.0
1.03
1.5
1.07
2.0
1.11
2,5
1.17
3.0
1.25
3.5
1.33
25. If normal-incidence reflection lines were shot over the structure shown in Fig. 4.56,
mark on record sections the arrival times of the phases that would be recorded. What
would be the relative amplitudes of the phases and by what physical factors are they
controlled?
Figure 4.56.
The vertical
cross section for Problem
25, showing P-wave
velocities in km s
−1
0
a
= 2.1
r
= 2000
and
densities in kg m
−3
.
a
= 3.7
r
= 2300
a
= 4.2
r
= 2400
α
= 4.2
r
= 2400
1
a
=
5.3
r
= 2500
a
= 5.3
r
= 2500
2
26. Using the parametric form of the travel-time and epicentral-distance equations for
earthquakes (see Appendix 3), obtain the following relation:
t
=
p
+
2
r
max
2
−
p
2
)
1
/
2
r
(
η
d
r
r
min
