Wednesday, April 4, 2012

GeoNet Rapid - Why Now?



One of the obvious questions to ask about the launch of GeoNet Rapid (Beta) is - why now? Why didn’t we have it before the Canterbury earthquakes began? There are three factors to consider when answering these questions: the coverage of the GeoNet sensor networks, the rapid development of the systems and technology used to locate earthquakes and the long thin and plate boundary nature of New Zealand. GeoNet Rapid is the “tip of the iceberg”, and relies on an extensive sensor network throughout New Zealand, a real-time data communications network (like a private version of the Internet), a high technology earthquake analysis system and a state-of-the-art information delivery system.

To explain this a bit more let’s look at the evolution of GeoNet by traveling back a decade or so in time to before GeoNet existed (see Figure 1). Back then there were just four real-time earthquake recording stations, two radio networks and a small number of "dial-up" stations in the whole of New Zealand. The rest of the stations (the small black squares) recorded on cassette tapes and paper printouts which were mailed in weekly for processing. In the best case it would take an hour to get an approximate earthquake location, and weeks to months to get a “final” location. Sometimes we needed to ring up the local farmer who would read off earthquake data from the printouts! Estimates of shaking intensity from the (film recording) strong shaking instruments took up to a year to become available.


Figure 1: The Pilot network existing before the start of GeoNet in July 2001
(diagram from the original GeoNet proposal dated 16 March 2000)

Contrast that situation with the current GeoNet network (see Figure 2) which has more than 550 sensor sites and real-time (or near real-time) data communications. The GeoNet sensor network grew from almost nothing to its current size over the decade following the launch of GeoNet in 2001, but only in the last few years has it been at the size and density required to give reliable automatic earthquake locations. GeoNet was developed as a long term sustainable system and much of the effort in the first decade went into the development of the sensor networks, and it was only when they were in place that GeoNet Rapid became feasible.


Figure 2: The current GeoNet sensor network - to prevent
clutter only the earthquake recorders are shown.
For more information about the GeoNet network see
http://www.geonet.org.nz/resources/network/netmap.html

Locating an earthquake and estimating its depth and magnitude  is a complex process involving many calculations once the earthquake shaking waves arrive and are measured at a minimum number of sites (I will cover this in more detail in a later blog). Although the theory of earthquake analysis has not changed greatly, the available systems and technology have developed considerably in the last decade, receiving an extra boost following the Indian Ocean tsunami at the end of 2004. This has greatly improved the availability of software for the rapid characterisation of earthquakes. There have also been big advances in the ability to feed this information quickly to websites (and as you are now seeing to mobile devices).

New Zealand is not an easy place to locate earthquakes because it is a country made up of two long thin islands. It lies on the plate boundary between the Pacific and Australian plates and experiences many shallow and deep earthquakes. To locate an earthquake it must be almost surrounded by earthquake recorders - hard to achieve in many parts of New Zealand. A very effective earthquake recording network for New Zealand would have many offshore (undersea) instruments costing many times the current resources of GeoNet.

So GeoNet Rapid was not possible until the GeoNet sensor network was near completion and the world had made the fast advances in technology in the last few years. Even with the current network and technology earthquakes in some parts of New Zealand (where there are fewer stations) and those offshore will sometimes be mis-located and need seismologist intervention. GeoNet Rapid (Beta) can now, in most cases, produce good locations very quickly, but will still sometimes give less reliable estimates. We are working to improve this as we move through the beta process to the final release later this year.

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