In Doctor Who, a so called "rift" in the fabric space-time is created every so often usually as a direct or indirect result of the Doctor's own adventures. My question is that, as a tear in the very fabric of the Universe, how these rifts have a constant position on Earth (to name a couple, the Cardiff Space-Time Rift and the Coal Hill Space-Time Rift). As the Earth is always moving (it goes around the Sun, the Sun goes around the galaxy, etc.) surely it should leave these rifts in their place in space-time as it continues its journey and leave them behind?
How does anything keep its position constant on Earth? Earth's gravity.
There is no universal frame of reference, only relative frames of reference. So "in place" must be relative to something, and just like everything else we observe on Earth's surface, "in place" means - and can only mean - relative to the Earth, whose gravity dominates.
Perhaps the rift is relative to Cardiff. Not the specific location but rather the idea of Cardiff.