The SEG-Y standard format (Barry and others, 1975) used by the U.S. Geological Survey for seismic data consists of the following:
- A 3600-byte reel identification header with the first 3200 bytes consisting of a EBCDIC header block and a 400-byte binary header block. Both headers include information specific to line and reel number.
- The trace data block follows the reel identification header. The first 240 bytes of each trace block is the binary trace identification header. The seismic data samples follow the trace identification header. The trace data are recorded in binary format. The format that follows is that used for many of our seismic data sets. There is a new revision 1 standard (www.seg.org/publications/tech-stand/seg_y_rev1.doc )
EBCDIC Headers
Example of a 3200-byte EBCDIC reel identification header.
| Column Numbers | Description |
|---|---|
| C 1 | CLIENT COMPAGNY CREW NO |
| C 2 | LINE AREA MAP ID |
| C 3 | REEL NO DAY-START OF REEL YEAR OBSERVER |
| C 4 | INSTRUMENT: DELPH MODEL xx SERIAL NO |
| C 5 | DATA TRACES/RECORD AUXILIARY TRACES/RECORD CDP FOLD |
| C 6 | SAMPLE INTERVAL SAMPLES/TRACE BITS/IN BYTES/SAMPLE |
| C 7 | RECORDING FORMAT FORMAT THIS REEL MEASUREMENT SYSTEM |
| C 8 | SAMPLE CODE: |
| C 9 | GAIN TYPE: |
| C10 | FILTERS: ALIAS NOTCH Hz Band - Hz SLOPE - DB/OCT |
| C11 | SOURCE: TYPE NUMBER/POINT POINT INTERVAL |
| C12 | PATTERN: LENGTH WIDTH |
| C13 | SWEEP: START Hz END Hz LENGHT ms CHANEL NO TYPE |
| C14 | TAPER: START LENGHT ms END LENGHT ms TYPE |
| C15 | SPREAD: OFFSET MAX DISTANCE GROUP INTERVAL |
| C16 | GEOPHONES: PER GROUP SPACING FREQUENCY MFG MODEL |
| C17 | PATTERN: LENGTH WIDTH |
| C18 | TRACES SORTED BY: |
| C19 | AMPLITUDE RECOVERY: |
| C20 | MAP PROJECTION ZONE ID COORDINATE UNITS |
| C21 | PROCESSING: |
| C22 | PROCESSING: |
| C23 | |
| C24 | |
| C25 | |
| C26 | |
| C27 | |
| C28 | |
| C29 | |
| C30 | |
| C31 | |
| C32 | |
| C33 | |
| C34 | |
| C35 | |
| C36 | |
| C37 | |
| C38 | |
| C39 | |
| C40 | END EBCDIC |
Binary Headers
The SEG-Y binary reel identification header.
| Byte Numbers | Header Value Description |
|---|---|
| 3201 - 3204 | Job identification number. |
| 3205 - 3208 | Line number. |
| 3209 - 3212 | Reel number. |
| 3213 - 3214 | Number of data traces per record. |
| 3215 - 3216 | Number of auxiliary traces per record. |
| 3217 - 3218 | Sample interval, microseconds, this file (reel). |
| 3219 - 3220 | Sample interval, microseconds, original field recording. |
| 3221 - 3222 | Number of samples per data trace, this file (reel). |
| 3223 - 3224 | Number of samples per data trace, original field recording. |
| 3225 - 3226 | Data sample format code: 1 = floating point (4 bytes) 2 = fixed point (4 bytes) 3 = fixed point (2 bytes) 4 = fixed point with gain code (4 bytes). |
| 3227 - 3228 | CDP fold. |
| 3229 - 3230 | Trace sorting code: 1 = as recorded (no) sorting) 2 = CDP ensemble 3 = single fold continuous profile 4 = horizontally stacked |
| 3231 - 3232 | Vertical sum code: 1 = no sum 2 = two sum ... N = N sum (N = 32,767) |
| 3233 - 3234 | Sweep frequency at start. |
| 3235 - 3236 | Sweep frequency at end. |
| 3237 - 3238 | Sweep length, ms. |
| 3239 - 3240 | Sweep type code: 1 = linear 2 = parabolic 3 = exponential 4 = other |
| 3241 - 3242 | Trace number of sweep channel. |
| 3243 - 3244 | Sweep trace taper length, ms, at start if tapered. |
| 3245 - 3246 | Sweep trace taper length, ms, at end. |
| 3247 - 3248 | Taper type: 1 = linear 2 = cos 3 = other |
| 3249 - 3250 | Correlated data traces: 1 = no 2 = yes |
| 3251 - 3252 | Binary gain recovered: 1 = yes 2 = no |
| 3253 - 3254 | Amplitude recovery method: 1 = none 2 = spherical divergence 3 = AGC 4 = other |
| 3255 - 3256 | Measurement system: 1 = meters 2 = feet |
| 3257 - 3258 | Impulse signal: 1 = Upward = negative number. 2 = Upward = positive number. |
| 3259 - 3260 | Vibratory polarity code - seismic signal lags pilot signal by: 1 = 337.5 - 22.5 degrees 2 = 22.5 - 67.5 degrees 3 = 67.5 - 112.5 degrees 4 = 112.5 - 157.5 degrees 5 = 157.5 - 202.5 degrees 6 = 202.5 - 247.5 degrees |
Trace Identification Headers
Example of the SEG-Y defined 240-byte trace identification header values.
|
Byte Numbers |
Header Value Description |
|---|---|
|
1 - 4 |
Trace sequence number within line. |
|
5 - 8 |
Trace sequence number within file (reel) |
|
9 - 12 |
Original field record number |
|
13 - 16 |
Trace number within original field record |
|
17 - 20 |
Energy source point number. |
|
21 - 24 |
CDP ensemble number. |
|
25 - 28 |
Trace number within the CDP ensemble. |
|
29 - 30 |
Trace identification code: 1 = seismic data |
|
31 - 32 |
Number of vertically summed traces yielding this trace |
|
33 - 34 |
Number of horizontally stacked traces yielding this trace |
|
35 - 36 |
Data use: 1 = production 2 = test |
|
37 - 40 |
Distance from source point to receiver group. |
|
41 - 44 |
Receiver group elevation - above sea level are positive, below sea level are negative. |
|
45 - 48 |
Surface elevation at source. |
|
49 - 52 |
Source depth below surface (positive number). |
|
53 - 56 |
Datum elevation at receiver group. |
|
57 - 60 |
Datum elevation at source. |
|
61 - 64 |
Water depth at source (this is the Fish depth below the sea surface in meters*10) |
|
65 - 68 |
Water depth at group. |
|
69 - 70 |
Scalar to be applied to all elevations & depths, specified in bytes 41 - 68 to give the real value. Scalar = 1, +/-10, +/-100, +/-1000, or +/-10,000. If positive, scalar is used as a multiplier; if negative, scalar is used as a divisor. |
|
71 - 72 |
Scalar to be applied to all coordinate specified in bytes 73 - 88 to give the real value. Scalar = 1, +/-10, +/-100, +/-1000, or +/-10,000. If positive, scalar is used as a multiplier; if negative, scalar is used as a divisor. |
|
73 - 76 |
Source coordinate - X. UTM Easting coordinate |
|
77 - 80 |
Source coordinate - Y. UTM Northing coordinate |
|
81 - 84 |
Group coordinate - X. UTM Easting coordinate |
|
85 - 88 |
Group coordinate - Y. UTM Northing coordinate |
|
89 - 90 |
Coordinate units: 1 = length (meters or feet) 2 = seconds of arc |
|
91 - 92 |
weathering velocity. |
|
93 - 94 |
Subweathering velocity. |
|
95 - 96 |
Uphole time at source. |
|
97 - 98 |
Uphole time at group. |
|
99 - 100 |
Source static correction. |
|
101 - 102 |
Group static correction. |
|
103 - 104 |
Total static applied. |
|
105 - 106 |
Lag time A. Time in ms between end of 240-byte trace identification header and time break. positive if time break occurs after end of header, negative if time break occurs before end of header. Time break is defined as the initiation pulse which may be recorded on an auxiliary trace or as otherwise specified by the recording system. |
|
107 - 108 |
Lag time B. Time in ms between the time break and positive or negative. |
|
109 - 110 |
Delay recording time. Time in ms between initiation time of energy source and time when recording of data samples begins. |
|
111 - 112 |
Mute time - start. |
|
113 - 114 |
Mute time - end. |
|
115 - 116 |
Number of samples in this trace. |
|
117 - 118 |
Sample interval, in microseconds, for this trace. |
|
119 - 120 |
Gain type of field instruments: 1 = fixed, 2 = binary, 3 = floating point, 4 = --- N = optional use |
|
121 - 122 |
Instrument gain constant. |
|
123 - 124 |
Instrument early or initial gain (db). |
|
125 - 126 |
Correlated: 1 = no 2 = yes |
|
127 - 128 |
Sweep frequency at start. |
|
129 - 130 |
Sweep frequency at end. |
|
131 - 132 |
Sweep length, ms. |
|
133 - 134 |
Sweep type: 1 = linear 2 = parabolic 3 = exponential 4 = other |
|
135 - 136 |
Sweep trace taper length at start, ms. |
|
137 - 138 |
Sweep trace taper length at end, ms. |
|
139 - 140 |
Taper type: 1 = linear 2 = cos 3 = other |
|
141 - 142 |
Alias filter frequency. |
|
143 - 144 |
Alias filter slope. |
|
145 - 146 |
Notch filter frequency. |
|
147 - 148 |
Notch filter slope. |
|
149 - 150 |
Low cut frequency. |
|
151 - 152 |
High cut frequency. |
|
153 - 154 |
Low cut slope. |
|
155 - 156 |
High cut slope. |
|
157 - 158 |
Year data recorded (four digit integer). |
|
159 - 160 |
Day of year. |
|
161 - 162 |
Hour of day (24 hour clock). |
|
163 - 164 |
Minute of hour. |
|
165 - 166 |
Second of minute. |
|
167 - 168 |
Time basis code: 1 = local 2 = GMT 3 = other |
|
169 - 170 |
Trace weighting factor - defined as 2-N volts for the least significant bit. (N=0, 1,...,32,767) |
|
171 - 172 |
Geophone group number of roll switch position one. |
|
173 - 174 |
Geophone group number of trace number one within original field record. |
|
175 - 176 |
Geophone group number of last trace within original field record. |
|
177 - 178 |
Gape size (total number of groups dropped). |
|
179 - 180 |
Overtravel associated with taper at beginning or end of line: 1 = down (or behind) 2 = up (or ahead) |
| 181 - 240 | Unassigned - for optional information. |
