Hi @karina_F,
This usually implies that you are running out of memory. Typically, anywhere from ~24 - 64 GB or RAM is required for full length Small-Sub-Unit (SSU) rRNA gene sequences.
You can save memory usage by trimming your SILVA reference sequences such that it only spans your amplicon region. I've been able to get away with 16 - 32 GB of RAM, depending on the marker gene. You can use RESCRIPt to help make your own SILVA amplicon reference database. You can look through these tutorials:
If you still observe Segmentation faults, then you'll need to find a machine with more memory.
-Good luck!
-Mike