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SEISMIC DATA FORMAT (SEG-Y Format)
Note: The web version of this archive does not contain the SEG-Y Trace files. These files are very large and would require extremely long download times. To obtain the complete CD-ROM archive, contact USGS Information at (888) ASK-USGS.
The seismic data is stored in SEG-Y, Integer, Motorola format. The SEG-Y files on these CD-ROMs conform to the SEG-Y standard format (Barry, et al., 1975), with the exception of the 3600-byte reel identification header that is ASCII. Standard SEG-Y uses an EBCDIC 3600-byte reel identification header. The Delph Seismic version of SEG-Y consists of the following:
| C 1 CLIENT COMPANY CREW NO |
| C 2 LINE line1dS 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 1 AUXILIARY TRACES/RECORD 0 CDP FOLD |
| C 6 SAMPLE INTERVAL 333 SAMPLES/TRACE 1496 BITS/IN 16 BYTES/SAMPLE 2 |
| C 7 RECORDING FORMAT FORMAT THIS REEL MEASUREMENT SYSTEM |
| C 8 SAMPLE CODE: FIXED PT |
| C 9 GAIN TYPE: FIXED |
| C10 FILTERS: ALIAS 1500HZ NOTCH HZ BAND - HZ SLOPE - DB/OCT |
| C11 SOURCE: TYPE NUMBER/POINT POINT INTERVAL |
| C12 PATTERN: LENGTH WIDTH |
| C13 SWEEP: START HZ END HZ LENGTH MS CHANEL NO TYPE |
| C14 TAPER: START LENGTH MS END LENGTH 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: RECORD |
| C19 AMPLITUDE RECOVERY: NONE |
| 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 |
|
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 |
|
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. |