Maybe subterranean just means underground? As in, not main stream?
Alien was pretty mainstream back in 79. Even more so now.
From that Facebook page......."From writer Dan O’Bannon’s original script Star Beast, to H. R. Giger’s startling designs, the influences of Egyptian and Greek mythology
I thought O'Bannon's influences was the old sci-fi/horror films, but Dan does reference Greek drama several times in his book albeit mainly for historical purposes. I suppose this is where Phillipe sees Greek mythology as one of Dan's driving influences.
However, never once does Dan mention Greek mythology in his book. As for connecting from the influence of Greek drama (or in this case, mythology) for historical purposes to modern script writing, this could be said for countless screenwriters.
Okay, I think I got it sorted it out. It's a matter of applying the 'Seven Degrees of Kevin Bacon' game . . . sorta.
Influenced by numerous old sci-fi/horror films, O'Bannon created the Alien universe, which Giler and Walter Hill, who is largely influenced by Westerns, gave Dan's script a "complete makeover" (contested by O'Bannon). In turn, Ridley Scott was tasked with bringing it to the box office.
In creating the chestburster, Ridley was influenced by Francis Bacon. And in turn, Francis was influenced by Greek mythology for his Crucifixion triptych paintings. So Ridley tasked Giger to create the chestburster with the influence of Francis Bacon, which in turn is influenced by the Greek Furies, though Giger's strongest influences were surrealists Dado and Dali.
So if you go back far enough, eventually you will bump into Greek drama or mythology . . . . though you could pretty much apply that to any modern story. Phillipe decided to hoist the Furies from the back row of influences to a front row showcase of his documentary......and that's why we see wicked witches of the mess rising from the Alien 79's illuminated blue mist.
And there you have it.....The Seven Degrees of Francis