RTTY is radio teletype. It's a different modulation technique used to transmit data.
We have no way to know what it means. These messages are coded, probably using one-time pads, meaning there's no way to decode unless you have the military code book.
I've never seen EAMs using RTTY before though.
No, ELF signals are sent on very low frequencies.
Extremely low frequency (ELF) is the ITU designation for electromagnetic radiation (radio waves) with frequencies from 3 to 30 Hz, and corresponding wavelengths of 100,000 to 10,000 kilometers, respectively.
The report of the EAM was on the regular HF bands used by the military.
Primary HFGCS Frequencies 24 Hours: 8992 and 11175 kHZ
Back up HFGCS Frequencies Day: 13200 15016 kHz
Back up HFGCS Frequencies Night: 4724 6739 kHz
Some ham radio operators use RTTY.
That is the source of my knowledge.
I have never used RTTY myself although muh rig is capable of it.
I know what it sounds like on the air to recognize and where to look for it on the dial.