102.
A seismic survey is carried out over a region comprising of a
sequence of alternating horizontal layers of shale and sandstone,
each having a thickness of 0.5 km with the shale layer at the top of
the sequence. The P wave velocities in shale and sandstone are 2 km/s
and 4 km/s respectively. The stacking velocity for a reflection from
the base of the 5th layer from the top is
A)
0.64 km/s
B)
1.64 km/s
C)
2.64 km/s
D)
3.64 km/s
Solution:
For
horizontal layers and small offsets Vstack is equal to the
Vrms
Formula:
Velocities
of the first and second layer is V1= 2 km/s and V2=
4 km/s
Thickness
of the layer Z = 0.5 km
Travel
time of the first layer is t1 = Z / V1
= 500 / 2000
=
0.25 s
Travel
time of the second layre is t2 = Z / V2
=
500 / 4000
=
0.125 s
The RMS Velocity formula (Vrms)=$${\sqrt{\frac{v_1^2t_1+v_2^2t_2+v_3^2t_3+v_4^2t_4+v_5^2t_5}{t_1+t_2+t_3+t_4+t_5}}}$$
Substitute
above values in the equation (1)
Vrms=$${\sqrt{\frac{2^2\times0.25+4^2\times0.125+2^2\times0.25+4^2\times0.125+2^2\times0.25}{0.25+0.125+0.25+0.125+0.25}}}$$
Vrms
= √7
Vrms
= 2.64 km/s
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this is been a great help to me. can you please solve some gravity anamaly sums of different shapes. thankyou in advance.
ReplyDeleteThanks bro a great help to me
ReplyDeleteWelcome sandip prajapati ji....
ReplyDelete2012 june net 101)(3)-for a two layer case the reflection coefficient of upper and lower layers respectively are -0.1 and 0.1,separated by 6ms and the source pulse is given as(1,-2,5,-2,1).if the sampling interval of seismic trace is 2ms,the composite wavelet is A)(-0.1,0.2,-0.4,0,0.4,-0.2,0.1)
ReplyDeleteB)(0,0,0,5,0,0,0)C)(-1,2,-5,2,1,0)
C)(-1,2,-5,2,1,0)D)(1,0,0,0,0,0).