If you run a search for Colchester and earthquake, you'll see that we do get quite strong quakes. Not often. But in the South East, where no effort has been made to make modern buildings earthquake proof, and most building has taken place. On flood plains, and sometimes landfill. And as you can find in some accounts, the movement travels some distance because of the land structure - if there's a quake in Canterbury or Colchester, London knows about it. We can also pick up on continental quakes - in the 30s a Brussels quake had people leaving buildings in Brighton. And we get frequent small tremors in other parts of the country.