The Global Seismographic Network (GSN) is a 150+ station, globally distributed, state-of-the-art digital seismic network that provides free, realtime, open access data through the IRIS DMC. The map above shows the distribution of the current station network with respect to network operations.
The Global Seismographic Network is a cooperative partnership between IRIS and the U.S. Geological Survey (USGS), coordinated with the international community, to install and operate a global, multi-use scientific facility as a societal resource for Earth observations, monitoring, research, and education. The stations of the GSN attempt to obtain the best possible recording capability, balanced with global geographic coverage. GSN instrumentation measures and records with high fidelity all seismic vibrations possible from high-frequency, strong ground motions near an earthquake to the slowest global Earth oscillations excited by great earthquakes. Seismology has been the primary focus in the creation of the GSN, but the infrastructure is inherently multi-use and can be extended to other disciplines. Several GSN stations currently incorporate microbarographs, GPS, Geomag, and Meteorological packages.
Global Seismology. University of Michigan. (seismology, earth structure, earthquakes, imaging, tomography)
Using Three-Dimensional Earth Models
Global Test of Seismic Event Locations Using Three Dimensional Earth Models. By Qi-fu Chen and Raymond J. Willemann.
Greg Houseman. Geodynamics and Seismology
The Harvard Seismology Group carries out a broad range of projects with topics including mapping the interior of the earth, characterizing the seismic sources and global seismicity. The seismology group includes faculty, research associates, and students from the Department of Earth & Planetary Sciences.
The first major global tomographic study was made by Professor Dziewonski in early 70's. The idea of this study was that the travel time anomalies observed for many ray paths, criss-crossing the Earth between various points near the Earth's surface and reaching different depths in its interior, could be resolved formally into a three-dimensional (3-D) model. This is now called `seismic tomography', as it conceptually resembles the medical CAT-scan. The early results were reported orally in 1974 and 1975 by Dziewonski and a full report was published in January 1977 (Dziewonski et al., 1977). A more detailed description can be found a statement written by Professor Dziewonski. The motivation for studying 3-D structure of the Earth's interior is that it may offer the best information on the dynamic processes in the deep interior of the Earth. As the seismic wave speeds change with temperature, it is plausible to obtain 3-D snapshots of the convection pattern in the Earth. By performing waveform and travel time inversions using long period seismic records, we have obtained global models for the long wavelength 3-D velocity structure of the Earth.
The ANSS (Advanced National Seismic System) Composite Catalog is a world-wide earthquake catalog created by merging the master earthquake catalogs from contributing ANSS institutions and then removing duplicate solutions for the same event. The ANSS Composite Earthquake Catalog grew out of the efforts of the CNSS (Council of the National Seismic System). It was previously called the CNSS Earthquake Catalog.