[Bob]

Unusual image. No blast marks or debris, just a hole (deep underground explosion?) No indication of recovery operation.

To me, it looks like a massive sinkhole, something that you'd see on the surface that was caused by a huge subterranean collapse.

[PA Engineer]

To me, it looks like a massive sinkhole, something that you'd see on the surface that was caused by a huge subterranean collapse.

I agree and a collapse may be consistent with a lack of any major seismic activity.