This report has been prepared to provide information to organizations that may be asked to participate in a program to upgrade the global seismographic network. In most cases, the organizations that will be offered new instrumentation by the U.S. Geological Survey currently operate stations in the World-Wide Standardized Seismograph Network (WWSSN) or the Global Digital Seismograph Network (GDSN).

The deployment of the WWSSN in the 1960's and the subsequent equipping of some WWSSN stations with digital equipment and borehole seismometers during the 1970's has been a remarkably successful program that generated the high- quality data needed to fuel an unprecedented period of progress in earthquake and tectonic research. The success of the WWSSN can be attributed to the importance of the data, to the strong commitment by participating organizations to international scientific cooperation, to the dedication and skill of the station operators, and to the resourcefulness of the staff supporting the network. Benefits have been widespread. The community of scientists world-wide has benefited from unrestricted access to a standardized base of calibrated data, and the participating stations have benefited from the donation of modern observatory instruments that have been useful for local earthquake studies and for the training of scientists and engineers.

Now, an exciting opportunity has arisen to deploy a new generation of seismograph systems to replace the outdated equipment at many of the WWSSN and GDSN stations. The U.S. Geological Survey (USGS) is cooperating with the Incorporated Research Institutions for Seismology (IRIS) in a program to upgrade the global seismograph network. The equipment development phase is nearly complete with a prototype of the new broadband seismograph system currently undergoing final testing at the USGS Albuquerque Seismological Laboratory. Deployment of the new equipment is expected to begin in early 1990.

As this report will demonstrate, the IRIS broadband seismograph system combines the very latest data acquisition and computer technology to produce seismic data with unprecedented bandwidth and dynamic range. Moreover, the system has been designed so that the high-quality digital data are accessible for local display and analysis. The functional design of the new system, which uses off-the-shelf modules and a standard computer bus, will make it much easier than it has been in the past to modify and upgrade the data acquisition system as improvements in technology become available. With adequate support for the program, the new IRIS seismograph system need never become obsolete.

We want you to be aware of our plans and the possibility that you may be asked to participate in this ,program. The schedule for upgrading WWSSN and GDSN stations depends on the level of funding earmarked for the program by our National Science Foundation. We hope to deploy at least ten new GSN data systems each year. If you have any questions concerning this program, please contact the Albuquerque Seismological Laboratory, U.S. Geological Survey, Albuquerque, New Mexico 87115-5000.

This report was revised in February 1992 in order to update information concerning the current program and instrumentation. The amp in Figure 1 was revised in June 1993, April 1994, December 1994, and September 1996 to reflect updated siting information. In September 1996 a composite photo of standard and optional components of the IRIS-2 GSN system hardware was added as a separate page between Figures 9 and 10.