When an anchor can sever an undersea cable

Could a five-centimeter undersea cable at thirty meters depth be cut accidentally, or would the damage probably be deliberate?

Either is possible. An anchor can cut it, but the cable's position relative to shipping lanes and anchorages determines how suspicious repeated incidents should appear.

A 5 cm cable at roughly 30 m depth can plausibly be cut by a vessel dragging an anchor. Repeated breaks need comparison with the amount of shipping: two incidents among only a dozen annual ship movements would be more suspicious than accidents in a busy area. An anchor dropped early or left down a few miles outside a roadstead offers a plausible accidental explanation. Damage some 50 miles offshore, near the edge of the continental shelf, is harder to explain that way. The physical possibility of anchor damage does not by itself settle whether a particular incident was accidental or deliberate.