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Processing and Binning Overview From chapter 14 “Elements of 3D Seismology” by Chris Liner

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Outline Justification for Processing Processing Flow Bins

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Justification Field data representation of the data is distant from a distance-depth representation of data.

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Categories of Processing Adjustments to wavelets, or short-pulse adjustments e.g., frequency filtering phase shifts (rotation) vibroseis correlation Traveltime Corrections (fig. 14.1) : Statics Normal Moveout Dip Moveout Migration

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Categories of Processing Amplitude Corrections Geometric spreading Automatic Gain Control Noise Reduction Vertical stack Muting CMP stack filtering (f, f-k, tau-p (or radon) multiple suppression

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Xia et al., 2004 An example of analysis for near-surface seismic structure

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Seismic data “Multiple universes for seismic data” Shotpoint gathers (distance versus time) CMP gathers (distance versus time) Tau-p (horizontal slowness versus intercept time) f-k (frequency versus wavenumber)

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Distance between shot and the receiver (m) Two-way traveltime (s)

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Distance between shot and the receiver (m) Two-way traveltime (s) dT/dx = 1/V (s/m) Velocity (m/s) T 2 = T 0 2 + x 2 / V 2 T0T0

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Distance between shot and the receiver (m) Two-way traveltime (s) dT/dx = 1/V (s/m) Velocity (m/s) T 2 = T 0 2 + x 2 / V 2 T0T0

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dT/dx = 1/V (s/m) x 1/V = 0 ( s/m) 1/V = p (ray parameter) V

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Distance between shot and the receiver (m) Two-way traveltime (s) dT/dx = 1/V (s/m) Velocity (m/s) T 2 = T 0 2 + x 2 / V 2 T0T0

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dT/dx = 1/V h (s/m) x 1/V h = 1/[V/ sin(angle) ] ( s/m) 1/V h = p (ray parameter) angle V

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Distance between shot and the receiver (m) Two-way traveltime (s) dT/dx = 1/V (s/m) Velocity (m/s) T 2 = T 0 2 + x 2 / V 2 T0T0

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x 1/V h = 1/[V/sin(angle) ]( s/m) 1/V h = p (ray parameter) angle V

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x (m) Two-way traveltime (s) T0T0 p (s/m) p=0 tau (intercept time) s Add amplitude

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x (m) Two-way traveltime (s) T0T0 p (s/m) p=0 tau (intercept time) s Add amplitude

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x (m) Two-way traveltime (s) f (1/s) p=0 k (wavenumber - 1/m) V=f/k (m/s) 100 Hz 1000 m/s 1/10 m

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x (m) Two-way traveltime (s) f (1/s) p=0 k (wavenumber - 1/m) V=f/k (m/s) 100 Hz 1000 m/s 1/10 m

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x (m) Two-way traveltime (s) f (1/s) k (wavenumber - 1/m) V h =inf (m/s) V h =1000 (m/s) V h =inf (m/s) V h =1000 (m/s)

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P-wave & Sv - wave SzSz SxSx

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“skin depth” = 1/2 longest wavelength V h ~= 90% shear wave velocity

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Dispersion t0t0 t1t1 t2t2 t1t1 t2t2

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Xia et al., 2004

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x (m) Two-way traveltime (s) f (1/s) p=0 k (wavenumber - 1/m) V=f/k (m/s) 100 Hz 1000 m/s

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Outline Bins Calculated common midpoints “CMP bin center” Length and width of bin <= spatial aliasing dimensions

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To prevent aliasing: max dimension = V/4f max For GOM: V = V 0 + 0.4 x depth Rule of Thumb: 12.5m by 12.5 m for > 2000 m IDEAL BIN SIZE: 5m by 5m for seafloor and deeper

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The “best” bin: SMALL ALL OFFSETS ALL AZIMUTHS LARGE FOLD

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Outline Justification for Processing Processing Flow Bins

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