Explosion more likely than earthquake

15 December 2008

Reports of rattling and shaking of windows as far as 25km from an earthquake reported near the nation’s capital have been reviewed by seismologists who recorded the event last Friday.

Geoscience Australia recorded a seismic event at 1:28pm Friday 12 December 2008 located between NW Canberra and Murrumbateman. Following further analysis of the recorded data, and reports submitted from the public to our "Recent Earthquakes" webpage over the weekend, an upgraded estimate of magnitude has been produced.

Analysis has also shown that the event is unlikely to have been an earthquake, as the effects described by the public are more consistent with that of an explosion rather than a naturally occurring fault. This is becasue the effects described suggest that the shockwaves felt by people travelled through the air as opposed to through the ground.

"An earthquake of this size would usually only be felt in a 5km radius from the epicentre, and as the shockwaves from this event were felt up to 25km away, it indicates some form of explosion rather than a natural event," said Senior Seismologist Dr David Jepsen.

The event was of such a small magnitude that it was recorded on only three of Geoscience Australia's seismographs, which allows location accuracy up to approximately 5km and magnitude estimates between 1.4 and 2.5.

"It can be difficult to distinguish between explosions and naturally occurring events when they are such a small size and recorded on so few instruments," said Dr Jepsen.

You can assist Australia's earthquake research by telling us if you think you have felt an earthquake. Geoscience Australia's simple online earthquake report form gathers information through a series of questions to find out about shaking windows, loud noises or any immediate building damage. This information will assist seismologists in gaining a greater understanding of this naturally occurring Earth process

Topic contact: media@ga.gov.au Last updated: October 4, 2013