HR: 10:20h
AN: S52B-01    [Abstracts]
TI: Studying global seismicity and other phenomena with the Global Seismographic Network
AU: * Ekstr\"om, G
EM: ekstrom@eps.harvard.edu
AF: Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138
AU: Dziewo\'{n}ski, A M
EM: dziewons@eps.harvard.edu
AF: Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138
AU: Nettles, M
EM: nettles@eps.harvard.edu
AF: Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138
AU: Maternovskaya, N N
AF: Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138
AB: The Global Seismographic Network (GSN) is the primary source of data for studies of global earthquake activity. The growth of the network to more than 100 well-distributed stations has dramatically increased our ability to detect, locate, and investigate earthquakes anywhere on Earth. The Harvard centroid-moment-tensor (CMT) project was started more than 20 years ago to study global and regional seismicity using data from the global network. The CMT catalog now contains more than 21,000 moment-tensor solutions for the period 1976 to the present, providing a nearly complete record of earthquakes with magnitudes greater than 5.5. Recent progress in the mapping of crust and upper-mantle structure has translated into an improved ability to model shorter-period surface waves. Starting with earthquakes in 2004 we now use these surface waves in the CMT analysis, and are able to analyze significantly smaller earthquakes routinely. Improved station coverage, real-time data access, and new data-processing techniques now allow us to perform much of the CMT analysis automatically and in near-real time following even moderately sized earthquakes. To complement the earthquake reporting of the NEIC, we have recently developed and implemented a technique to use the GSN as a global, steerable array to search for localized sources of intermediate-period (40--150 s) Rayleigh waves. The method detects nearly all earthquakes with magnitudes greater than 5, including a substantial number of events that go unreported in standard catalogs (PDE, ISC, REB). Many of the previously undetected events are sufficiently large that we can perform a CMT analysis to determine their focal mechanisms, and most are found to be standard tectonic earthquakes. We have also identified many seismic events that appear to be non-tectonic, in particular more than one hundred M$\sim$5 earthquakes on Greenland that we attribute to sudden glacial sliding. Other unassociated events await analysis and interpretation. Results from our CMT project and real-time search for seismic events can be found on our web site, www.seismology.harvard.edu.
DE: 7230 Seismicity and seismotectonics
DE: 7294 Instruments and techniques
DE: 7200 SEISMOLOGY
DE: 7215 Earthquake parameters
SC: Seismology [S]
MN: 2004 AGU Fall Meeting