A shallow 4.3-magnitude earthquake has shaken Christchurch in New Zealand. The tremor, centred 15 kilometres east of the city, struck on Friday followed by a lighter tremor. Geonet ranked its intensity as ‘strong’. Aftershocks have become less frequent recently following the powerful 6.3 magnitude quake on February 22, 2011 which killed 185 people and cause widespread damage in Christchurch.