With the release of the version 7.0 of the Fortran compiler, .mod files can be stored into an archive (.a) file. An archive must be explicitly specified in a -Mpath flag on the command line for it to be searched for modules. The compiler does not search archive files by default.
Only .mod files with the same names that appear on USE statements will be searched. For example, the Fortran statement USE mymod causes the compiler to search for the module file mymod.mod by default.
While searching, the compiler gives higher priority to the directory where the module files are being written. This can be controlled by the -moddir=dir option flag and the MODDIR environment variable. This implies that if only the -Mpath option is specified, the current directory will be searched for modules first, before the directories and files listed on the -M flag.