A small earthquake in the Irish Sea just off the North Wales coast shook parts of the British Isles early Wednesday, UPI reported. The British Geological Survey reported the quake came in at 3.8 on the Richter scale, while some other agencies put it at just over 4, The Irish Times reported. No damage was reported, but residents reported feeling the quake 100 miles or more away. An earthquake of that magnitude would be business as usual in California. But Robert Holdsworth, a structural geologist at Durham University, told The Guardian the British Isles get about one magnitude 4 earthquake every two years -- and can expect a strong magnitude 6 quake sometime in the next 10,000 years. Wednesday's quake was near the Llyn Peninsula, an area sometimes called the Dragon's Tail. In 1984, a 5.4 earthquake struck the peninsula, the largest recorded so far in Britain, followed by two smaller ones a month later. "This area seems to be a hotspot for tremors," Holdsworth said. "It's part of a wider band of activity that spreads from north Wales, up through northwest England into Scotland. We don't really understand what's causing them, unlike, say, the San Andreas Fault line in California, which lies on a plate boundary. And we don't understand why they localize where they do."