The very first and basic problem to solve in seismology is to locate of the seismic events. For that purpose we generally need at least 3 stations (Figure 8.1). We therefore define a seismic network as being a group of stations working together jointly for data collection and analysis.
Before 1960, there were in general only individual seismic stations operating independently. Each station made its observations, which were usually sent to some central location, if several stations were operating in a country or region. In that sense it was possible to talk about networks, however the time lag between recording and manual processing was so long that such networks are not considered as seismic networks in the modern sense. In the 1960's, ‘real’ seismic networks started operating. These were mainly networks made for micro earthquake recording and the distance between stations was a few kilometers to a couple of hundred kilometers. The key feature, used to define them as networks, was that the signals were transmitted in real time by wire or radio link to a central recording station where all data was recorded with central timing. This enabled very accurate relative timing between stations and therefore also made it possible to make accurate locations of local earthquakes. Recording was initially analog and has over the years evolved to be nearly exclusively digital. Lee and Stewart (1981) made a good general description of local networks. With the evolution of communication capabilities to cover the whole world, seismic networks are now not limited to local networks but can be either regional or global too. The distinction between them is primarily no longer the differences in data transfer, accuracy of timing, time lag between data acquisition and analysis, etc, but the scope of investigation, spatial resolution, and quality of data in terms of frequency content and dynamic range.
KeywordsEurope Attenuation Expense Refraction Azimuth
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