GATE-2018
81. Consider a laterally
homogeneous and isotropic earth model with a flat horizontal surface
and three horizontal layers underlain by a half-space. A seismic
reflection survey was simulated on this model with the sources and
receivers placed on the surface. The table below lists the root mean
square (rms) velocities, Vrms and zero-offset two-way
travel times t0 for the three reflection events from the
bottom of each of the three layers observed in a prestack CDP ( CMP)
gather. The interval velocity of the second layer is _______________
m/s
|
Reflection
Event
|
Vrms
|
t0
|
|
1
|
1500 m/s
|
0.2s
|
|
2
|
1600 m/s
|
0.3s
|
|
3
|
1700 m/s
|
0.4s
|
Solution:
From Dix’s formula
Vint = √(
( v22
t2
- v12
t1)/
(t2 -t1)
)
In
above problem three layer velocities and two-way travel times are
given but we want to calculate only second layer layer interval
velocity, for this only first and second layer velocities and two-way
travel times need.
v1
= 1500 m/s
t1
= 0.2 s
v2=
1600 m/s
t2
=0.3 s
Vint
= √( (
(1600)2 (0.3)
- (1500)2
(0.2)) / (0.3
– 0.2) )
Vint
= √ (
(768000 -450000) / (0.1) )
Vint
= 1783.255 m/s
Post a Comment
Post a Comment