Jun 13 2011 - Large earthquakes strike south-east of Christchurch

Two large earthquakes centred south-east of the city struck during the afternoon of Monday 13 June: a magnitude 5.6* at 1:00 pm and a magnitude 6.3* at 2:20 pm

Last updated at 10:00 am on Friday 17 June

Details of the main earthquakes

The two diagrams to the right show Peak Ground Accelerations for the earthquakes.

The diagram at the top shows both earthquakes as recorded at the McQueens Valley (MQZ) seismograph.

* The Richter magnitudes for these earthquakes were revised to 5.6 and 6.3 upon receipt of further data and analysis.

Our initial estimates are based on the data received at the time of website update, generally 15 minutes after the earthquake. The magnitude 6.3 earthquake was detected on over 250 New Zealand seismographs, and not all of the necessary waveforms used for working out the most accurate Richter magnitude were present then. Rather than wait any longer, the website is updated with the best estimate we can make at that time.

The other felt earthquakes


Earthquake characteristics


Further analysis of the waveforms show that the focal mechanism for the June 13 M6.3 earthquake is a strike-slip mechanism and is different from the February 22 M6.3 earthquake which had a reverse (thrust) faulting mechanism. The focal mechanism for the M5.6 earthquake is also primarily strike-slip but is rotated about 20 degrees counter-clockwise to the M6.3 earthquake.




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