There is no "if." We already know that Gravity waves pass through your observatory, otherwise centrifugal force of the Earth's rotation would throw said observatory away from this planet.
Corrected caption in reply #1 follows ...
HOW A LASER INTERFEROMETER CAN CATCH THE ELUSIVE WAVES
Two super-dense neutron stars circling each other [1] are expected to emit gravitational waves that move out at the speed of light At GEO 600, a high-powered laser [2] is fired at a 'beam splitter' - a semi-transparent mirror - which divides the beam down two vacuumed tunnels Mirrors [a+b] at the far ends bounce the light back; more mirrors [c+d] extend the measuring distance, and still more [e+f] are used to recycle the power and enhance the signal The light paths from the separate arms are recombined and sent to a photodetector. If a gravitational wave has passed though the observatory, it will have changed the length of the arms and the signal should be evident when analysed by computer
There is no "if." We already know that Gravity waves pass through your observatory, otherwise centrifugal force of the Earth's rotation would throw said observatory away from this planet.