An earthquake alert is then sent to Geoscience Australia’s partner in the JATWC, the Australian Bureau of Meteorology, to determine tsunami advice and publish tsunami bulletins. They are most common at tectonic plate boundaries where different plates meet.
The parameters of all other earthquakes with a magnitude greater than 3.5 are generally computed within 20 minutes. Frame houses not secured to the foundation may move. Landslips in roadside cuttings and unsupported excavations. The largest events usually happen where two plates are colliding, or colliding and sliding past one another.
Seismographs, such as the Teledyne Geotech Helicorder pictured, were used in the past to detect earthquake activity and relied on a mechanical system to record the seismic energy in the Earth onto paper.
In contrast, modern seismometers detect and convert any small movement in the Earth into an electrical signal for use in computer systems, as shown in the digital seismogram image of five seismic sensors which detected the magnitude 5.4 earthquake near Moe in Victoria on 19 June 2012.
Geoscience Australia uses data provided by the Governments of New Zealand, Indonesia, Malaysia, Singapore and China and has access to data from global seismic networks provided by the USA, Japan, Germany and France. Typical buildings of this kind are well reinforced by means of steel or ferro-concrete bands, or are wholly of ferro-concrete construction.
The Comprehensive Nuclear Test Ban Treaty Organisation’s International Monitoring System also provides seismic data for tsunami warning purposes. Frame houses not secured to the foundations shift off. All mortar is of good quality and the design and workmanship are good.
The International Seismological Centre led this project which reassessed the location and magnitude of approximately 20 000 historical earthquakes worldwide as part of an effort to extend and improve their database of seismic events. Australia's largest recorded earthquake was in 1988 at Tennant Creek in the Northern Territory, with an estimated magnitude 6.6, but it occurred in a sparsely populated area.
The system also has access to crustal velocity models which provide approximate information on how fast the various earthquake waves travel through the different layers which make up the Earth in the area between the earthquake and the seismometers.This location is also known as its focus or hypocentre which is represented by the latitude, longitude and depth below the surface.Geoscience Australia monitors seismic data from more than 60 stations on the Australian National Seismograph Network and in excess of 300 stations worldwide in near real-time, 24 hours a day, seven days a week. Visible wave-motion of the ground surface reported. If the people or buildings are on soft ground such as old river sediments, the MM intensity experienced may be one to two units higher; if on solid rock, it may be one unit lower.The size or magnitude of earthquakes is determined by measuring the amplitude of the seismic waves recorded on a seismograph and the distance of the seismograph from the earthquake.These are put into a formula which converts them to a magnitude, which is a measure of the energy released by the earthquake.