Abstract

The purpose of the GEOSCOPE program was the installation of about 20 stations well distributed worldwide (in particular in the southern hemisphere), in the standard configuration defined by the FDSN (VBB 24 bit, continuous recording at 20 samples/s). The installation is almost complete. The effort has been focused on the accessibility of data from our Data Center. Data can be obtained either on line through the WWW server, or through our anonymous ftp, or through CDROM production or through the SPYDER system for large earthquakes. In the near future easier ways will be available, such as autoDRM ( automatic Data Request Management) and NetDC requests (protocol proposed by the IRIS DMC).

Present status of the network

The Data Center of Paris is archiving data from 29 stations :

• twenty-six permanent « Geoscope » stations
  • 20 Stations maintained by the Technical Division of IPGP (Saint-Maur, near Paris). All of them are operating in VBB configuration (BH channel at 20 sps, LH channel at 1 sps, VH channel at 0.1 sps).
  • 4 stations maintained by EOST (Strasbourg), in VBB configuration.
  • 2 stations maintained by ORSTOM in Africa in VH/LH/MH configuration (VH in m/s/s with continuous recording at 0.1sps, LH in m/s/s with continuous recording at 1s ps, MH in m/s and triggered at 5sps).
• three « contributing » Geoscope stations (in VBB configuration):
  • 1 station maintained by ORSTOM and EOST in Vanuatu Islands, PVC.
  • 1 station maintained by IPGP (Seismotectonic group) in Chile, ICC.
  • 1 station maintained by Centro de Geofisica de Universidad de Lisboa (Portugal), EVO.

Sixteen stations are remotely accessible (teletransmitted by phone). In case of large events, data from these stations are recovered in St Maur (Figure 1, green dots) and made available at the Data Center in Paris within one or two days. In parallel to the classical recording in station (VBB configuration), seismic data are continuously recorded on a magneto-optical disk at 20sps. This method designed by the Technical Division has been implemented since 1992 in twelve stations (Figure 1, red dots). In all stations the time reference is given by a GPS clock. In the future, a satellite transmission system will be installed in ten stations, in cooperation with the french military agency CEA/DASE (see the white dots in Figure 1). In terms of siting locations, the aim of the GEOSCOPE program is almost fulfilled; we plan to install only one new station: Vorkouta with our colleagues of IIEPTMG. (Moscow). After the installation of this last station, our goal is to install in each station, a new acquisition chain defined by Agecodagis manufacture (in Toulouse) and DT/IPGP in order to improve their quality.

The GEOSCOPE data center

GEOSCOPE activities and facilities

1. The GEOSCOPE station book
   On the WWW server the totality of the GEOSCOPE station-book is provided; it is updated as soon as there is a modification. Each station is described since its beginning with information about the parent organization, the network affiliation, the vault conditions, the site description, the instrumentation, the sensors, the channels, the dates of upgrade, the sensitivities in the flat part of the band-pass of the instrumental responses. You can find the curves of instrumental responses of the stations, for each component, for each channel, each period of time since the beginning of the network.
2. Continuous VBB (BH) channels
   In parallel to the classical recording in a station (triggered BH channel), seimic data are also continuously recorded on a magneto-optical disk at 20sps. This method, designed by the Technical Division at Saint Maur in cooperation with the CEA/DASE is now implemented in twelve stations allowing to be sure not to loose some data with the triggering system. The PVC station located in the Pacific Ocean and maintained by our colleagues of EOST in Strasbourg and ORSTOM in Nouméa (New Caledonia) also corresponds to a continuous recording of BH channel at 20sps.
3. The GEOSCOPE noise level plots
   The estimate Power Spectral Density plots have been computed for year 1995. The annual seismic noise level is presented for the 3 channels VH, LH and BH, for the 3 components, Vertical , North-South and East-West. The diurnal and seasonal seismic noise plots are presented for the 3 components, and respectively for both channels BH and LH (for the diurnal variation) and for the three channels BH, LH and VH (for the seasonal variation).
4. The French SSB station recorded in Quasi real-time data
   Data are received from the GEOSCOPE SSB station located in France at the Data Center in Paris in quasi real-time. Every hour we get data for three 20 minutes length files, for the MH channel (in fact the BH channel decimated at 5sps). The data are immediately and automatically stored on a disk, and the corresponding plots available on the WWW server. The interest is to get immediately and continuously data from the french station.
5. GEOSCOPE CMT determination
   A simple inversion method for the fundamental mode Rayleigh wave spectra has made possible the rapid determination of the mechanism and the seismic moments. The demonstration is done that a correct CMT can be retrieved by using few stations, and that in a laterally heterogeneous Earth.
6. The NetDC procedure
   The necessity for dissemination of large datasets to the seismic community leads to the need of a new form of distribution with cooperative environment between the different participating data centers. The NETDC (Networked Data Centers) idea (designed by IRIS in cooperation with other Data Centers, GEOFON, ORFEUS, UC Berkeley) is to make the access to data transparent to users, who should not bother about where to ask for data ; the routing of the data request should be solved by the coordinating data centers. The INVENTORY protocol is already working in our Data Center (netdc@ipgp.jussieu.fr) and we will install the Instrumental responses as soon as possible
7. The future with GEOSCOPE 2000
   In the future all GEOSCOPE stations will be equipped with seismometers but also with POS sensors, microthermometers, microbarometers, inclinometers, short period seismometers, GPS. The new acquisition chain designed by DT/IPGP and the manufacturer AGECODAGIS in Toulouse (France) will provide recordings from 22 channels, 6 main channels (24bit) for ground velocity and POS measurements (recorded continuously at 20sps and triggered at 80sps for the STS2 seismometer), and 16 auxiliary channels in 16bit (1,6s). In the framework of the Test Ban Treaty, some GEOSCOPE stations have been chosen to be teletransmitted by satellite in real-time, and ten stations will be equipped in that purpose with help of CEA/DASE. WUS station equipment has been installed through a direct cooperation between GEOSCOPE and the SSB (State Seismological Bureau) of Beijing in China. AIS station in the Indian Ocean has been equipped during 1998 in the framework of the cooperation between IRIS and GEOSCOPE.

Conclusion