Complex sentence: In 1909, a Chigorin Memorial tournament was played in St. Petersburg, after that many more followed, from 1947 onwards mainly in Sochi and from 1990 back in Saint Petersburg.
Split into simpler sentences: In 1909, a Chigorin Memorial tournament was played in St. Petersburg. After that many more followed: from 1947 onwards mainly in Sochi and from 1990 back in Saint Petersburg.