Ewing Oil decides to shoot two marine seismic surveys. For the first survey, tar

Question

Ewing Oil decides to shoot two marine seismic surveys. For the first survey, targeting shallow layers, air guns are fired every 17 m, the hydrophone streamer is 2.45 km long and consists of 72 separate hydrophone sections and both the source and the streamers are towed at 5m depth. In the second survey, targeting deeper layers, air guns are fired every 50 m, the streamer is 5 km long and consists of 100 sections and both the source and the hydrophones are towed at 15 m depth. If the velocity of seawater is 1.5 km/s, what is the peak frequency of each survey? What is the fold of each survey?

Explanation / Answer

Energy travels up from the source and is reflected off the sea surface. When this energy combines with the original down-traveling energy, the waveshape is changed and the “ghost” is created.

a) Thus, to find this frequency one must calculate the two way vertical time

v= 1500m/s

depth, d1 = 5m

time = 5/1500 = 0.0033 sec

and thus notch or peak frequency is 1/0.0033 = 300 Hz

depth d2 = 15m

time = 15/1500 = 0.01

frequency = 100 Hz

b) fold = (N/2)(hydrophone spacing/shot spacing)

case 1, fold= 74.11

case2, fold = 51

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