Seismology - Is the Inner Core Moving Faster or Slower?

Scientists are trying to work out if the inner core is moving faster or slower. Seismologists look at a record of an earthquake wave, which has gone through the Rocky mantle and into the inner core. And then they try for another earthquake that happened in nearly exactly the same place as close as possible. But earthquakes aren't in exactly the same places each time. They're in slightly different places. If you don't take that into account really carefully, you can come out with some really weird looking results.