31 July 2009
On 15 July 2009 the first tsunami warning from Australia's now fully operational Tsunami Warning System was issued for the east Australian coast, following a large undersea earthquake. The threat didn't come from the great Sumatra subduction zone that caused the Indian Ocean tsunami in 2004, but from the relatively unknown Puyseger subduction zone off the coast of New Zealand.
Click to see location map showing
earthquake in proximity to Australia.
A magnitude 7.9 earthquake occurred in the Fjordland region along the southwest coast of the South Island of New Zealand at approximately 7:30pm AEST and was widely felt throughout the region though no major damage was reported.
The earthquake occurred along the boundary where the Australian and Pacific tectonic plates meet. At this plate boundary, the Australian plate is being forced under the Pacific plate ('subducted') at a rate of about 40mm a year, resulting in the uplift of the Southern Alps of New Zealand and causing the deep Puyseger trench in the sea floor to the south.
"The subduction of the Australian plate causes stresses to build up where the plates slide past each other. Periodically, the rocks give way under this stress causing earthquakes, and we observe the effects on land such as ground shaking and displacement of the ground surface", said Clive Collins, a senior seismologist at Geoscience Australia.
Click to see digital seismogram
of the 7.9 magnitude earthquake
Earthquakes which occur along the Puyseger subduction zone, which runs southwards from southwest New Zealand, can potentially generate tsunamis which will reach the Australian coastline. They are typically thrust earthquakes, in which the upper Pacific plate 'thrusts' up over the downgoing Australian plate when the boundary between the plates slips during an earthquake. This has the effect of suddenly pushing upwards all the water above and spawning a tsunami wave.
"When these type of large, shallow earthquakes occur in this area off the South Island, such as this one, they do have the potential to create tsunami which propagates towards the eastern seaboard of Australia", said Mr Collins.
A small tsunami was generated during the earthquake and was recorded on tide gauges. In New Zealand, a tide gauge at Jackson Bay measured the height of the tsunami wave at 50cm. A tsunami warning was issued for the marine areas of New South Wales, Victoria, Norfolk Island and Tasmania, and a land inundation warning for Lord Howe Island. No visible effects were reported at any of these locations, but tide gauges measured a 15cm wave at Port Kembla in New South Wales and a 12cm wave at Spring Bay in Tasmania.
"What's also interesting is according to GPS measurements following the earthquake, the southwest tip of New Zealand shifted westwards towards Australia by about 30cm during the earthquake, and south by about 7cm. So now our neighbours are a little closer", he said.
31 July 2009
Geoscience Australia graduates
undertaking fieldwork at Twofold Bay
(© Geoscience Australia)
Geoscience Australia's 2009 graduates are undertaking their field-based project in partnership with the Sapphire Coast Marine Discovery Centre.
The graduates' week-long field trip took them to Eden and Twofold Bay in New South Wales. During their trip, they surveyed the local beach, collected sediment and rock samples and took seabed video footage from around Twofold Bay.
Over the next two months the graduates will use the data they collected to prepare four educational posters which will become permanent exhibits at the Marine Discovery Centre. The posters explain the geology, geomorphology, land-use and seabed environments within the region. The posters will be delivered to the Centre in time for the peak summer holiday season.
The Marine Discovery Centre has a strong educational focus and uses a wide range of interactive exhibits that help visitors to explore the coastal and marine environments of the region.
28 July 2009
Amery Ice Sheet, Antarctica
(Reproduced with permission from
Australian Antarctic Division)
Geoscience Australia geologist Dr Alix Post recently participated in Fresh Science 2009. Fresh Science is an annual national media competition and training program that highlights new and interesting research being undertaken by early-career scientists from around Australia.
Dr Post presented research on the history of colonisation of a unique 9000 year old seafloor ecosystem found beneath the Amery Ice Sheet in east Antarctica. Scientists from Geoscience Australia, working in collaboration with the Australian Antarctic Division, studied the sediment samples to determine their age and to look for clues to changes in the environment over time. They also studied shell fossils within the core samples looking for clues about changes in the environment over time.
Studying habitats such as these can help to improve understanding about changes in species diversity over time, and allow us insight into how ecosystems are able to survive and prosper in such hostile environments.
Further information about Dr Post's work is available on the Fresh Science website.