Seismic Analysis Code (SAC) format

Format defined by the SAC software suite; supported by many other tools. The SAC data format includes waveform data, station identifier, starting time, and optionally an origin time for a seismic source; it is usually accompanied by separate metadata files in Poles and Zeros (SACPZ) format for instrumentation correction. Each signal is stored on disk in a separate SAC data file. These files contain a fixed length header section followed by one or two data sections. The header contains floating point, integer, logical, and character fields. Evenly spaced data files have only one data section which contains the dependent variable. Unevenly spaced data and spectral data files contain two data sections. For unevenly spaced data, the first data section contains the dependent variable and the second contains the independent variable. For spectral files the first component is either the amplitude or the real component and the second component is either the phase or imaginary component. https://ds.iris.edu/files/sac-manual/manual/file_format.html