The Genesis of the Global Seismographic Network

Although by the beginning of the 20th century a few seismographs had been established on all inhabited continents, global seismology on an industrial scale had its origin 60 years ago as part of the United States' project VELA Uniform designed to improve the capability for detecting and identifying underground nuclear explosions. Implemented by the US Coast and Geodetic Survey the Worldwide Network of Standard Seismograph Stations, at its peak in the early 1970s, comprised about 115 stations distributed throughout most of the non-communist world. These stations used careful shaping of the instrument response to improve the detection of surface waves from very small events and so improve the magnitude threshold for discriminating earthquakes from explosions. The WWSSN soon resulted in a significant increase in number of earthquakes detected and located illuminating the global patterns of seismicity which helped lay the foundation for the theory of plate tectonics.

During the 1970s improvements in instrumentation made it possible to measure very long period ground motions (periods of more than 100 s). While the initial impetus for this came from physicists who wished to detect the possible excitation of the earth's free oscillations by gravitational radiation, it became apparent that studies of the earth's normal modes could provide valuable constraints on earth structure and earthquake mechanisms. This realization led to Project IDA a global array of long-period, digitally recorded seismographs limited only by ambient noise.

In 1983, with encouragement from the National Academy of Sciences, a consortium of universities in the United States banded together to form the Incorporated Research Institutions for Seismology (IRIS), now with over 250 members and affiliates around the world. One of the goals of IRIS was to develop a 150-station Global Seismographic Network of modern high-quality seismographic stations.

Today the GSN operates via a long-standing and successful collaboration between IRIS, NSF and the USGS delivering continuous data in real time to users without charge or restriction. The GSN works closely with other global networks (e.g., GEOSCOPE, GEOFON, CTBTO) as a part of the International Federation of Digital Seismograph Networks (FDSN).