obspy.io.sac - SAC read and write support for ObsPy

This module provides read and write support for ASCII and binary SAC-files as defined by EarthScope (https://ds.iris.edu/files/sac-manual/).


The ObsPy Development Team (devs@obspy.org) & C. J. Ammon & J. MacCarthy


GNU Lesser General Public License, Version 3 (https://www.gnu.org/copyleft/lesser.html)

The SAC implementation in ObsPy is a modified version of PySac (https://github.com/LANL-Seismoacoustics/pysac), developed under U.S. Government contract DE-AC52-06NA25396 for Los Alamos National Laboratory (LANL) and copyrighted for Los Alamos National Security, LLC under LA-CC-15-051.


Similar to reading any other waveform data format using read():

>>> from obspy import read
>>> st = read('/path/to/test.sac', debug_headers=True)
>>> st 
<obspy.core.stream.Stream object at 0x...>
>>> print(st) 
1 Trace(s) in Stream:
.STA..Q | 1978-07-18T08:00:10.000000Z - ... | 1.0 Hz, 100 samples

The format will be determined automatically. As SAC-files can contain only one data trace (as opposed to Mini-SEED or GSE2), the length of ‘st’ will be one. ‘st[0]’ will have a stats attribute containing the essential meta data (station name, channel, location, start time, end time, sampling rate, number of points). Additionally, when reading a SAC-file it will have one additional attribute, ‘sac’, which contains all SAC-specific attributes (SAC header values).

>>> print(st[0].stats)  
         station: STA
         channel: Q
       starttime: 1978-07-18T08:00:10.000000Z
         endtime: 1978-07-18T08:01:49.000000Z
   sampling_rate: 1.0
           delta: 1.0
            npts: 100
           calib: 1.0
         _format: SAC
             sac: AttribDict({...})
>>> print(st[0].stats.sac.dist)

The data is stored in the data attribute.

>>> st[0].data 
array([ -8.74227766e-08,  -3.09016973e-01,..., 3.09007347e-01], dtype=float32)


Writing is also straight forward. All changes on the data as well as in stats and stats[‘sac’] are written with the following command to a file:

>>> st.write('tmp.sac', format='SAC') 

You can also specify a byteorder keyword argument to set the endianness of the resulting SAC-file. It must be either 0 or '<' for LSBF or little-endian, 1 or '>' for MSBF or big-endian. Defaults to little endian.



SAC bindings to ObsPy core module.


obspy.io.sac.sacpz - SACPZ write support for ObsPy


SAC header specification, including documentation.


Low-level array interface to the SAC file format.


Python interface to the Seismic Analysis Code (SAC) file format.


SAC module helper functions and data.