Geoscience Australia monitors, analyses and reports on significant earthquakes to alert the Australian Government, State and Territory Governments and the public about earthquakes in Australia and overseas.
Earthquakes are detected by scientific instruments called seismometers. The word seismo originates from the Greek word seismos which means to shake or move violently and was later applied to the science and equipment associated with earthquakes. 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.
Determining the location of an earthquake
The accurate locations of seismometers are stored in a database accessible by an earthquake monitoring computer system. 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. The times at which the differing seismic waves arrive at various seismometers are identified by Seismic Analysts or by a computer system. The arrival times of the seismic waves at the seismometers, together with the locations of the seismometers and the speed at which the seismic waves travel to the seismometers are all used to determine the location of the earthquake. This location is also known as its focus or hypocentre which is represented by the latitude, longitude and depth below the surface.
How Geoscience Australia monitors earthquakes
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. Most of the 40 samples per second data are delivered within 30 seconds of being recorded at the seismometer to Geoscience Australia’s central processing facility in Canberra through various digital satellite and broadband communication systems.
Seismic data are also provided by overseas Governments which have national seismic networks. 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. The Comprehensive Nuclear Test Ban Treaty Organisation’s International Monitoring System also provides seismic data for tsunami warning purposes.
The seismic data are collected and analysed automatically and immediately reviewed by Geoscience Australia’s Duty Seismologist.
As part of the Joint Australian Tsunami Warning Centre (JATWC), Duty Seismologists also are responsible for analysing and reporting within 10 minutes of the origin time, on earthquakes which have the potential to generate a tsunami. 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.
The parameters of all other earthquakes with a magnitude greater than 3.5 are generally computed within 20 minutes. The analysis includes its magnitude, origin time and date of the earthquake and the location of its hypocentre. Smaller earthquakes that are not detected by many seismometers are difficult to locate in real-time and, consequently, are located by Seismic Analysts using computer programs.