2.2.4. Permanent Seismic Monitoring with LOFAR/BEL
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| Fig. 13. The LOFAR (Low Frequency Array) radio telescope and infrastructure in the Netherlands. A synthetic, 300km radius radiotelescope is created by connecting a large number of small radio antennas through a fibre optic data transport network to a central supercomputer facility. The LOFAR infrastructure can simultaneously be used for a range of other sensor applications, including wireless sensors for agricultural use and 3D geophones for permanent seismic monitoring. Lower left inset shows extent of the European GÉANT network that may be employed in a similar fashion (courtesy LOFAR). |
The Dutch astronomical community has recently received funding to build a synthetic radio telescope with a diameter of some 350 km in the Netherlands. This telescope, referred to as LOFAR (Low Frenquency Array) will consist of a wide network of small antennas that are linked via an ultra fast data transmission network (~10 Gbit/s) to synthesize the telescope. The LOFAR network has provided a unique opportunity to develop a PERmanent Seismic IMaging and MONitoring network (PERSIMMON), designed for monitoring 3-D structures and processes in the subsurface of the Netherlands, by connecting a large number of 3-component geophones to the LOFAR network. Initial research on the set-up of the network has shown that ‘background noise’ from the Earth could possibly be used for imaging and monitoring purposes in the light of PERSIMMON (‘acoustic daylight imaging’). So far, its success has only been shown on synthetic data. Further investigations are required and, above all, field observations are needed to show whether this method can be applied successfully to PERSIMMON data.
In the first instance, the network will be used for monitoring the dynamic behaviour of the Netherlands’ subsurface in two regions: 1) in the north-eastern Netherlands where earthquakes and subsidence result from major gas extraction; and 2) in the south-eastern Netherlands where earthquakes are related to the subsidence in the Roer-Valley Graben. In addition there are plans to further use the opportunities offered by LOFAR to connect low-frequency geophones (<1Hz.) to the network. These can be used to image the deep crustal structure of the Netherlands down to the Moho discontinuity, the position of which is still poorly defined in large parts of the Netherlands. The network also offers opportunities to connect other types of sensors and generate real-time data. Options include e.g. atmospheric and GPS sensors (Fig. 13).
On a European scale, the GÉANT glass fibre network that is currently being rolled out over Europe offers similar possibilities as the LOFAR network. The Dutch astronomical organisation Astron is developing a European initiative to achieve this.