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## Making CMP’s

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**Making CMP’s**From chapter 16 “Elements of 3D Seismology” by Chris Liner**Outline**• Normal Moveout • Stacking**Normal Moveout**Hyperbola: x T**Normal Moveout**x T “Overcorrected” Normal Moveout is too large Chosenvelocity for NMO is too (a) large (b) small**Normal Moveout**x T “Overcorrected” Normal Moveout is too large Chosenvelocity for NMO is too (a)large (b) small**Normal Moveout**x T “Under corrected” Normal Moveout is too small Chosenvelocity for NMO is (a) too large (b) too small**Normal Moveout**x T “Under corrected” Normal Moveout is too small Chosenvelocity for NMO is (a) too large (b) too small**Vinterval from Vrms**Dix, 1955**Vrms**V1 V2 Vrms < Vinterval V3**Multiples and Primaries**x M1 T M2**Conventional NMO before stacking**x M1 NMO correction V=V(depth) e.g., V=mz + B T M2 “Properly corrected” Normal Moveout is just right Chosenvelocity for NMO is correct**Over-correction (e.g. 80% Vnmo)**x x M1 M1 NMO correction V=V(depth) e.g., V=0.8(mz + B) T T M2 M2**f-k filtering before stacking (Ryu)**x x M1 NMO correction V=V(depth) e.g., V=0.8(mz + B) T T M2 M2**Correct back to 100% NMO**x x M1 M1 NMO correction V=V(depth) e.g., V=(mz + B) T T M2 M2**Outline**• Convolution and Deconvolution • Normal Moveout • Stacking**NMO stretching**T0 V1 V2 “NMO Stretching”**NMO stretching**V1 T0 V2 “NMO Stretching” V1<V2**NMO stretching**V1 V1<V2 NMO “stretch” = “linear strain” V2 Linear strain (%) = final length-original length original length X 100 (%)**NMO stretching**original length = final length = V1 V1<V2 V2 X 100 (%) NMO “stretch” = X 100 (%)**stretching for T=2s,V1=V2=1500 m/s**Green line assumes V1=V2 Blue line is for general case, where V1, V2 can be different and delT0=0.1s (this case: V1=V2) Matlab code X 100 (%)**Stacking**+ + =**Semblance Analysis**X + + = Twtt (s) “Semblance”**Semblance Analysis**X V + + = V1 V2 Twtt (s) V3 Peak energy