Global Seismograph Network Helps Earthquake Monitoring, Research

The Global Seismograph Network (GSN) is a system of some 100 modern seismographic stations deployed worldwide to collect data for monitoring earthquakes and for research on earthquakes and the structure and processes of the Earth. The GSN is supported by a partnership of the USGS, the Incorporated Research Institutions for Seismology (a consortium of universities supported by the National Science Foundation), and the Institute for Geophysics and Planetary Physics at the University of California, San Diego.

GSN data are used daily in the routine operations of the National Earthquake Information Center. Data from a subset of GSN stations are transmitted continuously to the Center, where they are used with other data to determine the locations, depths,

USGS scientist training personnel from the University of Nairobi, Kenya, in the operation of Global Seismograph Network instruments.

magnitudes, and other measurements of earthquakes worldwide. A unique feature of the GSN data is that they can be used to estimate, within an hour, the geometric orientation and overall length of the fault that caused an earthquake. This information can be used to quickly assess the damage potential of an earthquake and its potential for generating a tsunami.

GSN data are widely used in basic research on the internal structure of the Earth and the physics of earthquakes. Recently researchers at Columbia University used GSN data to determine that the inner, solid core of the Earth rotates at a slightly different rate than the rest of the planet. This difference in the rate of rotation was detectable only with the high quality, digital data available from the GSN. This discovery provides fundamental support and substance to the "dynamo theory" used to explain the existence of and changes in the Earth's magnetic field.

Several GSN stations have been formally affiliated with the International Monitoring System being established to monitor the Comprehensive Test Ban Treaty (CTBT). Additionally, the entire GSN can contribute to the independent capability of the United States to monitor this treaty.

For example, on August 16, 1997, a small seismic event occurred near a known Russian nuclear test site on Novaya Zemlya Island in the Barents Sea. According to public reports, U.S. government experts initially identified this event as a possible underground nuclear explosion. Various additional data were used to help target the location of the suspected explosion. The improved location moved away from the island test site, out into the ocean. More importantly, data from the USGS station at Kevo, Finland, were used to show that the seismic waves recorded from the event in question were similar to those generated by earthquakes and different from those previously recorded at Kevo from explosions on the Russian test site. Additionally, GSN data are used extensively in major research programs conducted by the Department of Defense and the Department of Energy to improve CTBT monitoring.