The GEOSCOPE Program: state of the art in 2003 and perspectives

Details The GEOSCOPE Program: state of the art in 2003 and perspectives The GEOSCOPE Program: state of the art in 2003 and perspectives

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufm.u22a0028r&link_type=abstract

American Geophysical Union, Fall Meeting 2003, abstract #U22A-0028

Physics

7294 Instruments And Techniques

Scientific paper

The GEOSCOPE program was launched in 1982 by the National Institute of Sciences of Universe (INSU), a department of the French National Center of Scientific Research (CNRS), at the instigation of the Institute of Physics of the Earth of Paris (IPGP). The purpose of the GEOSCOPE program was the installation of about 25 stations well distributed worldwide, in particular in the southern hemisphere, in the standard configuration defined by the FDSN (very broad-band 24 bit, continuous recording at 20sps). The GEOSCOPE program is operating 28 digital very-broadband stations. Data from large events are teletransmitted for some stations (by phone line or through internet) and made available within one day. A satellite transmission system is now working, in cooperation with the french military agency CEA/DASE, in cooperation with CTBTO (Dzumac in New Caledonia ). An agreement between GEOSCOPE and CTBTO allows us to get data continuously and with a low gain. The next CTBTO stations to be installed are ATD (Djibouti) and MBO (Senegal) in 2004. In terms of siting locations, the aim of the GEOSCOPE program is almost fulfilled; we plan to install a new station in MARQ (Marquesas Islands), one in Russia at high latitude at VOR (Vorkouta), one in Patagonia (COY in Chile), a joint station with IRIS at TRIS (Tristan Da Cunha) in order to fill some geographical gaps in the southern hemisphere. DCC in Antarctica is a joint EOST-Strasbourg/Concordia-Italy station. Our goal is now to replace our old digitizers by Quanterra ones, and to transmit all data in near real-time. An inversion method for the fundamental mode Rayleigh wave spectra has made possible the rapid determination of the mechanism and the seismic moments.This determination is done routinely for all events with Ms>6.8 from the teletransmitted stations data. The estimate Power Spectral Density plots have been computed for each station and are available on the Web site. Some small to medium earthquakes are not detected and thus are not referenced in the earthquake catalogues. Most of these eve nts are in the southern hemisphere where the lack of seismic stations creates a detection sensitivity gap. We estimate that more than a hundred southern hemisphere events per year with magnitude between 4.5 and 5.5 go undetected by the worldwide networks. We use a surface wave analysis method to effectively detect and locate these earthquakes, particular ly near-ridge events. Most GEOSCOPE stations are equipped with STS1 seismometers, only a few ones with STS2 seismometers. We are planning to move some stations from the northern hemisphere to the southern one. We are equipping all stations with thermometers, and also with microbarometers in order to clean routinely the signal from the atmospheric pressure effect.

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