segyio - SEG-Y Seismic Data
Quick Reference
python
import segyio
# Read
with segyio.open('seismic.sgy', 'r') as f:
print(f.tracecount, len(f.samples))
trace0 = f.trace[0] # Single trace as numpy array
data = segyio.tools.collect(f.trace[:]) # All traces
# 3D access (specify inline/xline byte locations)
with segyio.open('seismic.sgy', 'r', iline=189, xline=193) as f:
inline_100 = f.iline[100] # 2D array (xlines x samples)
cube = segyio.tools.cube(f) # Full 3D cube
# Write
spec = segyio.spec()
spec.samples = samples
spec.tracecount = n_traces
with segyio.create('output.sgy', spec) as f:
f.trace[0] = data
Key Access Modes
| Mode | Description |
|---|---|
f.trace[i] | Sequential trace access by index |
f.header[i] | Trace header access (dict-like) |
f.iline[n] | Inline slice (3D surveys) |
f.xline[n] | Crossline slice (3D surveys) |
f.depth_slice[n] | Horizontal time/depth slice |
f.text[0] | Text header (3200 bytes) |
f.bin | Binary header |
Essential Operations
Open and Inspect
python
with segyio.open('seismic.sgy', 'r') as f:
print(f"Traces: {f.tracecount}")
print(f"Samples: {len(f.samples)}")
print(f"Sample interval: {f.samples[1] - f.samples[0]} ms")
if f.ilines is not None:
print(f"Inlines: {f.ilines}")
print(f"Crosslines: {f.xlines}")
Read Trace Headers
python
with segyio.open('seismic.sgy', 'r') as f:
header = f.header[0]
print(header[segyio.TraceField.INLINE_3D])
print(header[segyio.TraceField.CDP_X])
# Get all values for one field
inlines = f.attributes(segyio.TraceField.INLINE_3D)[:]
Read 3D Data
python
with segyio.open('seismic.sgy', 'r', iline=189, xline=193) as f:
inline_data = f.iline[100] # Shape: (n_xlines, n_samples)
xline_data = f.xline[200] # Shape: (n_ilines, n_samples)
time_slice = f.depth_slice[250] # Shape: (n_ilines, n_xlines)
cube = segyio.tools.cube(f) # Shape: (ilines, xlines, samples)
Read Unstructured Data
python
# For 2D lines or unsorted data
with segyio.open('seismic.sgy', 'r', ignore_geometry=True) as f:
data = segyio.tools.collect(f.trace[:])
Create New SEG-Y
python
import numpy as np
spec = segyio.spec()
spec.samples = np.arange(500) * 4 # 4ms sample rate
spec.tracecount = 100
spec.format = 1 # IBM float
with segyio.create('output.sgy', spec) as f:
for i in range(100):
f.trace[i] = data[i]
f.header[i] = {
segyio.TraceField.TRACE_SEQUENCE_LINE: i + 1,
}
Modify Existing File
python
with segyio.open('seismic.sgy', 'r+') as f:
f.trace[0] = f.trace[0] * 2.0
f.header[0][segyio.TraceField.CDP] = 999
Data Formats
| Code | Format |
|---|---|
| 1 | IBM 4-byte float |
| 2 | 4-byte signed integer |
| 3 | 2-byte signed integer |
| 5 | IEEE 4-byte float |
| 8 | 1-byte signed integer |
Common Issues
| Issue | Solution |
|---|---|
| Geometry not detected | Specify iline= and xline= byte positions |
| Can't read 3D slices | Use ignore_geometry=True for unstructured data |
| Wrong inline/xline bytes | Check headers with f.header[0] to find correct bytes |
| File not opening | Check file path, permissions, and SEG-Y format validity |
References
- •Trace Header Fields - Complete header field reference (bytes, types)
- •Troubleshooting - Common problems and solutions
Scripts
- •scripts/inspect_segy.py - Inspect SEG-Y file structure and geometry
- •scripts/extract_subset.py - Extract subset of traces or inlines