|Observatories and Research Facilities for EUropean Seismology|
|Volume 1, no 1||January 1999||Orfeus Newsletter|
The GEOFON ProgramWinfried Hanka
Broadband seismology has a long tradition in Germany. The Graefenberg Array (GRF) was the world's first major broadband installation. It is operational since 1976 and many scientific studies demonstrated the benefit of broadband digital recording since then. Between 1991 and 1993, 12 stations of the German Regional Seismic Network (GRSN) were installed performing a modern national seismograph network. Following that tradition, the GEOFON Program has been founded by GFZ in 1992. The program consists of three major components: a permanent network, a mobile broadband network for longterm temporary installations and a data center. Presently (January 99) alltogether 47 stations contribute to the GEOFON networks. Innovative and resources saving concepts and comprehensive cooperation with other programs and institutions allow the installation, operation and maintenance of these stations on a very cost and personel effective basis.
The permanent network presently consisting of 31 stations (25 in the ORFEUS/EMSC area) became meanwhile a multinational initiative. A number of institutions from different countries joint the GFZ efforts to set up a permanent seismological network in Europe and the Mediterranean as well as to fill some gaps in the global broadband network. Cooperations on different levels with other programs like IRIS, Pacific21, MedNet and GRSN and individual geophysical institutes in Israel, Spain, Hungary and Germany led to the fact that the GEOFON network is growing much faster than expected. The GFZ part of both networks belong formally to the GFZ instrument pool, which holds more than 200 stations mainly for mobile use. GEOFON stations are normally equipped with Streckeisen STS-2 VBB seismometer with a special shielding and Quanterra Q380 or Q4120 datalogger which allow the recording of all relevant seismic signals from high frequency local events to the earth tides. In several "global" sites STS-1 seismometers are used. The stations are normally accessible through telephone lines, Internet or other means for remote control and data retrieval. In several stations a newly developped PC based GEOFON station processor providing increased data processing and communication means is installed in addition to Quanterra data aquistion systems.
The temporary GEOFON network presently consists of 11 stations in Central Europe, Greece, and Namibia installed for periods between one and three years. Several projects in Chile, Southern and Northern Tibet, Alaska, Yakutia, Brazil and Germany were carried out already since 1993. In addition, a large scale American-German project GEDEPTH II-INDEPTH III is presently carried out in Northern Tibet. Common goal for these projects is the investigation of the structure of the lower crust and upper mantle preferably in subduction and collision zones with sparse networks of 3-5 stations only. Beside the STS-2, also Guralp CMG-3T and 40T seismometers are in operation. Depending on the site infrastructure, either Quanterra Q4120 datalogger with remote control by GSM or Reftek 72A systems with extra large disks and independent power supply by solar panels are used for longterm unattended operation. A mobile data collection center was developped on laptop basis for infrequent station visits. Other more short term experiments with larger number of instruments ( PISCO94, GEDEPTH-INDEPTH II, Vogtland, TOR, Eifel Plume, SVEKALAPKO) were also supported The GEOFON data center consists of four components: the near-realtime event oriented SPYDER online pool, the continuous near realtime online data base OnDB, the continuous GEOFON DIRTS data archive and the FARM event volumes. The GEOFON SPYDER node presently regularly retrieves the data from more than 30 stations e.g. nearly all permanent GEOFON stations and a set of other stations in Central Europe for all global events larger than mb 5.5. This system is a common effort with IRIS DMC, ORFEUS DC and several other SPYDER nodes worldwide triggered by NEIC alerts. From GFZ, the GEOFON SPYDER data are distributed to ODC and IRIS DMC by Internet and their data are copied to Potsdam the same way. Therefore several hours after origin time the event data for up to over 100 stations become available at the GEOFON DC for all major global events. Moreover, in 1995 a regional EuroSPYDER system for smaller events (5.0 < mb < 5.5) in Europe and the Mediterranean was introduced triggered at first internally and since summer 1997 also by the EMSC alerts. This system, also operated in cooperation with ODC, provides data for the regional source parameter determination carried out at GFZ as a key node in the European Mediterranean Seismological Center (EMSC) framework. Access to SPYDER, EuroSPYDER and OnDB is provided by DRM and AutoDRM (presentlly OnDB only). More sophisticated web interfaces are under construction.