Description of sac
http://ds.iris.edu/files/sac-manual/sac_manual.pdf

The header part of the sac file is described startinc on page
40

Specifically

Name
Type
Description
LCALDA
L
TRUE if DIST, AZ, BAZ, and GCARC are to be calculated from station and event
coordinates.
LOVROK
L
TRUE if it is okay to overwrite this file on disk.
