Read today that the Japanese earthquake has been reclassified as a magnitude 9.0 and that they are warning of a possible 7.0 or above in the next few days. The good news was the 60 year old gentleman found clinging to the roof of his house two miles out to sea.
Large plate tectonics, unfortunately, do not give all the answers as many of the larger plates carry many smaller plates. The British Isles are formed out of the collisions of four plates and there is also an old faultline running from centeral Switzerland, through Germany, alongside Dover and up through London. Quakes along that have been found from Roman times in London up to the 1600's in Lucerne.
http://www.thisiskent.co.uk/news/Channel-tsunami-warning/article-2670790-detail/article.html