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

Outline Justification for Processing Processing Flow Bins

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

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

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

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

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)

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

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

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

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

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

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

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

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

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

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

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

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

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)

P-wave & Sv - wave SzSz SxSx

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

Dispersion t0t0 t1t1 t2t2 t1t1 t2t2

Xia et al., 2004

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

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

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

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

Outline Justification for Processing Processing Flow Bins