Level 9 gravimetric distortions were fluctuations in space from a graviton ellipse.

In 2376, Ensign Harry Kim asked Captain Kathryn Janeway to report to the bridge of the USS Voyager very early in the morning, something that she wasn't pleased about. Kim told her she wouldn't be disappointed, as the ship's sensors were reading level 9 gravimetric distortions. Soon after, the graviton ellipse emerged from subspace and nearly enveloped Voyager. (VOY: "One Small Step")