Why are there giant concrete tunnels in the desert?

Dianna,  I would like to make a suggestion, or at least ask a serious question to the LIGO people.  Maybe you can ask it for me.  It seems to me that the long path of the laser is creating a time delay between propagation and detection. This delay might be useful for detecting waves of lower frequency if LIGO compares a wave at the detector with a fresh new different wave from the laser.  Has this been attempted?  Does it detect lower frequency waves?
At first glance, I don't see how LIGO works. Wouldn't the laser beam suffer the same distortion as the Earth as the GW passed through?  If true, then the delay creates the signal.  Make sense?  Thanks for a great video!