Jun 22 2011 - Overnight earthquake proves troublesome to locate

Last night's big shake was originally located 10 km west of Akaroa. The location has been revised and it has been relocated 10 km south-west of Christchurch CBD.

Peak Ground Accelerations for the magnitude 5.4 earthquake.

Peak Ground Accelerations for the magnitude 5.4 earthquake.

The magnitude 5.4 earthquake (revised from 5.3) once again registered on many of our instruments, and the GeoNet Duty Officer found that it was difficult to get a reliable location with the data that was to hand at the time. Due to the importance of getting preliminary information sent out, the best estimate, near Akaroa, was published on the website. Subsequent analysis of data that has been received, especially from the close seismographs, has shown that location to be wrong. The updated details are at:

We apologise for the error and we will keep trying to be better.

The map of recorded Peak Ground Accelerations is shown at right. Contrast it with the maps from last weeks 5.6 and 6.3 earthquakes east of the city. The station near Lincoln experienced 30.7 %g last night, 8.1 %g last week. The seismograph at Templeton recorded the strongest shaking at 62.0 %g, whereas last week it received shaking of 7.0 %g. Conversely, the badly shaken site in the M6.3 earthquake near the Heathcote and Avon estuary went down from 77.1 %g to 5.5 %g. It's not all about magnitude - it's your proximity to the epicentre, the depth of the earthquake and the soils you're built on that affect how it feels for you.

There have been two other earthquakes over magnitude 5.0 since last September in this vicinity: