Australia seismicity

The Earth is a dynamic planet consisting of an outer crust riding on so called lithospheric plates that are roughly 100 km in thickness. Australia lies within one of these plates. The lithospheric plates move relative to one another at rates that are typically around several cm per year. In some places, oceanic plates are gradually plunging into the Earth's mantle such as under Japan and Chile whereas at mid-ocean ridges, new crust forms as the plates move apart. It is the movement of the lithospheric plates that induces stresses in the crust and causes mountains and faults to be created both at plate margins and within plates. The Australian plate has been subjected to enough stress for mountain ranges to have formed and the present stresses are sufficient for earthquakes to occur.



On 28 December 1989, an earthquake measuring 5.6 on the Richter scale hit Newcastle. The epicenter was 15 km south-southwest from the city center. This earthquake caused widespread damage, damaging 50 000 buildings and killing 13 people. Damages are estimated to have cost $1.5 billion. The death toll from the earthquake could have been a lot worst. Fortunately, school was not in session at the time, as many schools were badly damaged.Although 5.6 is generally considered to be only a moderately strong earthquake, many buildings were destroyed. This was due to a number of factors. Newcastle was considered to have a low seismic risk, so buildings were not expected to adhere to earthquake standards. Many of the damaged buildings were built on alluvial land, or land deposited by water, which is affected more strongly by earthquake waves. The shaking went on for a very long time, 35-40 seconds. Finally, the focus was very shallow at only 11 km below the surface of the Earth. While the earthquake's measurement on the Richter scale was moderate, its measurement on the Mercalli scale would have been much higher.This paved the way for new building codes and tighter enforcement. 





Sources: http://en.wikipedia.org/wiki/Queensland
http://www.ses.sa.gov.au/site/community_safety/earthquake_information.jsp
http://www.seismicity.see.uwa.edu.au/welcome/seismicity_in_australia