A network of permanent seismographic stations (see seismograph) deployed evenly over the Earth’s surface. The GSN comprises more than 150 stations, continuously recording seismic data at a rate of 20 samples each second, with real-time access for users. The GSN is a cooperative partnership between the Incorporated Research Institutions for Seismology (IRIS) and the United States Geological Survey.

http://earthquake.usgs.gov/monitoring/gsn/ The Global Seismographic Network (GSN).