U.S. Geological Survey Data Series 420

SEG-Y Format

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The seismic data are stored in SEG-Y, integer, Motorola format. The SEG-Y files on this disc conform to the SEG-Y standard format (Barry and others, 1975) with the exception of the first 3,200 bytes of the reel identification header, which are in ASCII format. Standard SEG-Y uses an EBCDIC format. The Delph Seismic version of SEG-Y consists of the following:

A 3,600-byte reel identification header consisting of a 3,200-byte ASCII header block and a 400-byte binary header block. Both headers include information specific to the line and reel number.
The trace data block follows the reel identification header. The first 240 bytes of each trace block are the binary trace identification header. The seismic data samples follow the trace identification header.

Example of a 3,200-byte ASCII reel identification header created with Delph Seismic software.

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 1500 HZ 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

Example of a 400-byte binary reel identification header.

The values in bold are assigned in the SEG-Y output from Delph Seismic.

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 = M-1 sum (M = 32,767).
3233 - 3234	Sweep frequency at start.
3235 - 3236	Sweep frequency at end.
3237 - 3238	Sweep length, milliseconds.
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.

The SEG-Y defined 240-byte trace identification header values.

The values in bold are assigned in the SEG-Y output from Delph Seismic.

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 (in meters).
65 - 68	Water depth at group.
69 - 70	Scalar to be applied to all elevations and 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 or longitude.
77 - 80	Source coordinate - Y. UTM Northing coordinate or latitude.
81 - 84	Group coordinate - X. UTM Easting coordinate or longitude.
85 - 88	Group coordinate - Y. UTM Northing coordinate or latitude.
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 milliseconds 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 that may be recorded on an auxiliary trace or as otherwise specified by the recording system.
107 - 108	Lag time B. Time in milliseconds between the time break and the initiation time of the energy source. May be positive or negative.
109 - 110	Delay recording time. Time in milliseconds 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 (decibels).
125 - 126	Correlated: 1 = no 2 = yes.
127 - 128	Sweep frequency at start.
129 - 130	Sweep frequency at end.
131 - 132	Sweep length, milliseconds.
133 - 134	Sweep type: 1 = linear 2 = parabolic 3 = exponential 4 = other.
135 - 136	Sweep trace taper length at start, milliseconds.
137 - 138	Sweep trace taper length at end, milliseconds.
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,...,32767).
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	Gap 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.

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