M4.3. This is not an unusual size for a mining area, even the previous M5.4. They are unloading a tremendous volume on a highly stressed crust. The Sudbury area has had these for years, although most can be traced to deep rockbursts. It was never any great significance in Sudbury, since most houses are on rock or firm ground. This size of earthquake can only affect old brick houses on swamp, as we have in Christchurch.