The GEOSCOPE Program : state of the art in 2004
Abstract
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 2005. 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), in order to fill some geographical gaps in the southern hemisphere. We installed in 2004 a joint station with IRIS and the CTBTO at TRIS (Tristan Da Cunha), in the southern Atlantic ocean. 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. At present 4 stations are sending their data in quasi-real time (DZM, ECH, SSB, FDF and RER). 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 > 6.5 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 events 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, particularly 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, inorder to fill a geographical instrumental gap. We are equipping all stations with seismometers but also with microthermometers, microbarometers, in order to clean the seismic signal and to study potential correlations between the seismic signal and these environmental parameters. Some of our stations have long seismic time series (SSB in France and TAM in Algeria). Removing the atmospheric pressure effect is absolutely necessary for scientists using low frequency free oscillation modes, helping studies on the 'hum'.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2004
- Bibcode:
- 2004AGUFM.S53B0214R
- Keywords:
-
- 7294 Instruments and techniques;
- 7200 SEISMOLOGY