Lee M. Liberty Research Professor Boise State University

 Sort (Shots to CMP domain)  Normal moveout correction (NMO)  Stack >> Brute Stack (first look at the data!)

 Preprocessing  Clean up Shot Records  Amplitude recovery  Deconvolution  Sort to CMP  Velocity Analysis – iterative  Residual statics  NMO correction  Mutes  Stack (gains and filters often follow)  Migrate  Convert to depth

 Demultiplex (only for old data)  Vibroseis correlation  Filter to reduce noise  Spherical spreading correction  Attenuation correction  Edit bad traces  Geometry definition (assign source & receiver (x, y and elevation) values, and CMP locations into trace headers)

 Need to address ◦ How to optimally image target (model) ◦ What frequencies can you put in to the ground and get back at the geophone/hydrophone? attenuation ◦ Aliasing (spatial and temporal) – what sampling in space and time? ◦ Noise sources (how to reduce both coherent and random)

compressional wave shear wave

 Fold = no. of receivers/ (2*source positions) (relative to receivers)  Fold = geophone spacing * no. geophones / (2 * shot spacing) ◦ e.g., 120 geophone channels shot every geophone = 60 fold ◦ e.g., 120 geophone channels shot every other geophone location = 30 fold ◦ e.g., 120 geophone channels shot every ½ station = 120 fold ◦ 2-D and 3-D Fold – define bin size and place trace within a set bin

 The same seismogram should be recorded if the locations of the source and geophone are exchanged.  No matter how complicated a geometrical arrangement, the speed of sound along a ray is the same in either direction.  Source/receiver antenna design does matter

 Anything that makes a noise…  Point source, or array to suppress noise  Rapid and repeatable:  Inexpensive  Easily transported/moved, little setup time  Proper amplitude and frequency characteristics  Land: ability to create horizontal as well as vertical displacement

Seismic frequency bands of interest: Gravitational tides ~0 Hz to ~70 microHz (periods of 4+ hours) Earth's eigenvibrations~0.3 mHz to ~0.1 Hz Surface wave analysis~2 mHz to ~2 Hz Regional earthquakes~10 mHz to ~10 Hz Local earthquakes~10 mHz to ~400+ Hz Strong motion ~0.05 Hz to ~10 Hz (frequency band which usually causes structural damage during strong ground shaking)

Land seismic sources P-wave

Sourcefrequency (Hz) max depth buried 1 lb dynamite km 50 lbs dynamite km Blasting cap m surface Vibroseis km Minivib km weight drop km sledgehammer m

Land seismic sources s-wave

 Single sensor or array of receivers ◦ Each receiver often consists of a small array ◦ Easily moved/carried (lightweight, small)  Cable or telemeter back to computer  Sensitive to a range of frequencies of interest  Large dynamic range ◦ (can correctly record very large and very small signals)

 velocity transducer; measure ground motion velocity A particle velocity of 0.1 mm/s caused by a ground displacement of 160 nm at 100 Hz generates an amplitude of 3 mV (Faber and Maxwell, 1997) Spurious frequency = natural resonance of a geophone with motion normal to the natural frequency

 Geophone coupling depends upon the firmness of the soil.  The best coupling is achieved by burial of the geophones.  By changing ground conditions, earth response can be highly variable.  Longer geophone spikes produces better ground coupling best

Land Streamer on pavementSpike geophones planted at roadside. (uniform/compacted ground conditions)

Number of channels Number of values per channel (Sampling rate, Time window of sampling) Number of bytes per sampled value Example Channels:96 Sampling rate:2 ms Time window:0.8 s Format:4 Bytes per value  (800 / 2) Samples x 96 channels x 4 Bytes = MBytes

But … after correlation Number of channels Number of values per channel (Sampling rate,Time window of sampling) Number of bytes per sampled value Example Channels:9000 Sampling rate:2 ms (resampled) Time window:4 s Format:4 Bytes per value  (2000 Samples/shot) x 9000 channels x 4 Bytes = 72 Mbytes Per shot * 200 shots/day = 14 Gbytes/day 14*90 days = 1.26 Tbyte data set

Number of channels Number of values per channel (Sampling rate,Time window of sampling) Number of bytes per sampled value Example Channels:9000 Sampling rate:1 ms Time window:8 hours = 8*60*60 seconds = 28,800 s Format:4 Bytes per value  (28800*1000) Samples x 9000 channels x 4 Bytes = Tbytes Per day 1.036*90 days = 93.3 Tbyte data set

Vibroseis sources use cross-correlation to synthesize a short, zero- phase wavelet from a long source sweep.

The “Pad” and the Sweep (schematic) Time (10 s)  10 Hz 80 Hz  Watch here and  here

After Lindseth, 1968 Figure 1. Vibroseis Schematic

After Lindseth, 1968 Figure 1. Vibroseis Schematic – Cross Correlation with pilot

After Lindseth, 1968 Figure 1. Vibroseis Schematic – Cross Correlation, 1st Reflection Maximum positive correlation at this position

After Lindseth, 1968 Figure 1. Vibroseis Schematic – Cross Correlation, 2nd Reflection Maximum negative correlation at this position

After Lindseth, 1968 Figure 1. Vibroseis Schematic – Cross Correlation, 3rd Reflection Maximum positive correlation at this position

Reynolds, 1997

 For accurate velocity and depth determination, array should at least equal the target depth  For amplitude-versus-offset (AVO) determination, the receiver array should be at least twice the target depth, giving us incidence angles of more than 45 o. 45 o

 Unfiltered shot  Filtered shot

Sample rate 1 ms Nyquist=500 Hz

 Preprocessing  Clean up Shot Records  Amplitude recovery  Deconvolution  Sort to CMP  Velocity Analysis – iterative  Residual statics  NMO correction  Mutes  Stack (gains and filters often follow)  Migrate  Convert to depth

SUKILL - zero out traces sukill stdout [optional parameters] Optional parameters: key=tridheader name to select traces to kill a=2header value identifying tracces to kill or min= first trace to kill (one-based) count=1number of traces to kill Notes: If min= is set it overrides selecting traces by header.

 suwind tmax=.15 <Highland_shot.su |sugain pbal=1|suop op=neg |sukill key=tracf min=25 count=5|suxwigb perc=90 key=tracf