DDS supports the sep (Stanford Exploration Project) format as "sep". It is handled in DDS as a subset of DDS's generic asp format without any Line Headers or Trace Headers. There are no attributes for sep output. Since it has no Line Header and no Trace Header it requires a Dictionary to define it's attributes. As such, DDS cannot automatically detect the format without it's Dictionary. The datatype is picked up the the "esize" Definition.

The sep seismic format is described only by the Trace structure, SEP_TRACE from the asp "${DDSROOT}/asp.fmt.dds" Dictionary. And since there are no Trace Headers there are no Trace Header mapping Definitions.