8ο Πανελλήνιο Συμποσιο Ωκεανογραφίας & Αλιείας 553 A Marine Broadband Seismological Station with Data Transmission in realtime Papoulia J. 1, Makris J. 2, Ballas D. 1, Pagonis P. 1 1 Hellenic Centre for Marine Research, Institute of Oceanography, 46,7 Km Athinon- Souliou, 19013 Anavissos, Attiki, Greece 2 GeoPro GmbH, St. Annenufer 2, 20457 Hamburg, Germany Abstract A marine broadband seismological station with real time data transmission is developed in the frame of the operational program AMPHITRITE. The station, which is the first permanent marine seismological station in Europe, operates in the North Evoikos Gulf, offshore Atalanti, and transmits data in real time to a base station at the Monastery of St. George, in Malesina. From there, through an internet connection, a central recording unit transfers data to HCMR Headquarters, at Anavissos and to GEOPRO GmbH, in Hamburg. The station will be further equipped with the appropriate sensors, in order to provide simultaneously meteorological and oceanographic information. Περιληψη Στα πλαίσια του ανταγωνιστικού προγράμματος ΕΠΑΝ ΑΜΦΙΤΡΙΤΗ, κατασκευάστηκε ένας υποθαλάσσιος σεισμολογικός σταθμός για μετάδοση στοιχείων σε πραγματικό χρόνο. Ο σταθμός, που είναι ο πρώτος που λειτουργεί στην Ευρώπη, είναι ποντισμένος στη θαλάσσια περιοχή Αταλάντης και μεταδίδει συνεχώς σεισμολογικά δεδομένα σε ένα κεντρικό σταθμό βάσης, που έχει εγκατασταθεί στο Μοναστήρι του Αγ. Γεωργίου, στη Μαλεσίνα. Από εκεί, μέσω διαδικτύου, τα δεδομένα μεταφέρονται στο ΕΛΚΕΘΕ στην Ανάβυσσο και στην εταιρεία GEOPRO στο Αμβούργο. Ο σταθμός θα εφοδιαστεί μελλοντικά με αισθητήρες για ταυτόχρονη μετάδοση μετεωρολογικών και ωκεανογραφικών δεδομένων. Keywords: permanent marine seismological stations, real time transmission
554 8ο Πανελλήνιο Συμποσιο Ωκεανογραφίας & Αλιείας Introduction Seismological networks are landlocked and bias the definition of the foci parameters, particularly for events located offshore. This can be improved if we can establish seismological stations offshore that transmit their data in realtime to central recording stations. Thus we can significantly improve the foci location and at the same time our understanding of the velocity structure of the earth and the tectonic processes that release seismic energy. Greece is a country with very high seismic activity and most of the seismogenic faults are located in the offshore areas. It is therefore of great importance to establish seismic stations in these areas and extend the land locked seismological network by permanent broadband stations transmitting data in realtime. In the following we present the technical solution of an offshore recording broadband seismological station, specially developed in the frame of the project AMPHITRITE. The station was deployed in June 2005 in the North Evoikos Gulf, offshore Atalanti (fig. 1). It transmits earthquake data in realtime to a base station at the Monastery of St. George, in Malesina. From there, a central recording unit transfers the data through an internet connection to HCMR, Athens and GEOPRO, Hamburg. The station will be further equipped with meteorological and oceanographic sensors in order to provide additional environmental information. Methodology The buoy (fig. 2) is anchored by a wirerope and an anchor-weight of 500 kg on a fixed position at the seafloor. The seismic sensor at the seabottom is a broadband instrument, CME Model 4011, placed in a glass sphere and anchored at the seafloor close to the mooring of the surface buoy. It is connected by cable to the buoy and the seismic signals are transferred to it, digitized, processed, stored on hard disc and transferred by radio to an onshore position. The sensor is gardan mounted and a compass provides the orientation of the horizontal components. Movements or vibrations are damped by a silicon fluid that holds the sensor elements aligned along the plumpline. Power supply is provided by two car batteries that are recharged by 3 to 4 solar panels of 40W each. A GPS receiver provides continuous timing for the SEDIS IV CPU and data logger (see GEOPRO SEDIS IV User Guide, 2004). Figure 1: Location of the Seismological Station in the North Evoikos Gulf
8ο Πανελλήνιο Συμποσιο Ωκεανογραφίας & Αλιείας 555 Seismic Data T elemetr y B uoy A ntenna Solar Panel E quipment C ontainer T o B ase Station Oceanographic S ensors A nchor 500kg Seismic S ensor Figure 2: Elements of the Seismic Buoy Configuration Seismic Data T elemetr y B uoy Sensor Seismic Sensor Data I nput A /D-unit CPU S torage Sedis-IV B uoy M odem R adio Satellite GSM Data Transmission Data reception M odem R adio Satellite GSM Oceanographic Sensors 2*12V C ar B atteries Power S upply 3*40W Solar Panel C omputer I nternet Figure 3: Schematic description of the complete system indicating also the elements consisting the base station. Input sensors are indicated by green color, cpu elements by yellow, transmitting components by red and power supply by blue.
556 8ο Πανελλήνιο Συμποσιο Ωκεανογραφίας & Αλιείας Figure 4: Buoy Data from North Evoikos Gulf. The Aegean Sea Event from 23.06.05, mb=4.2 The radio modem at the present configuration connects the SEDIS IV unit to a transmitter, which at present covers offsets up to 40 km from the coast. It is possible by installing different modems to use mobile telephonic or satellite connection in order to transfer the data from the buoy to the onshore base station. This is necessary if the distance between the buoy and the onshore base station is too large. The base station consists of the radio antenna and preamplifier, the radio modem, the central PC-computer that operates in Linux 8.2 system and an internet connection (see fig. 3). This gives us the possibility to download data continuously and to communicate with the buoy through radio link between the base station and the radio installed in the buoy. The power supply of the system is provided by a SMART UPS 700 XL system that can sustain the operation for 12 hours if the external electric power supply is interrupted. Results The seismic buoy has been continuously working since June 2005, recording data directly from the sea bottom. Both local and teleseismic events are recorded and transmitted through internet in realtime. Figure 4 is an example of a buoy record from the 23 June 2005 Aegean Sea earthquake (mb=4.2). Buoy data will be combined by those recorded by 5 digital land stations deployed at selected sites onshore, in mainland Greece and Evia island, and processed using a local velocity model obtained by active seismic experiments (Makris et al., 2001). This will optimize hypocenter location and consequently the delineation of active faults and the assessment of the regional seismic hazard. Acknowledgements We are grateful to Sisters Crhistofora Rozopoulou and Theologia Kralli for their valuable help in establishing our base station and internet connection at the Monastary of St. George, in Malesina. We thank Andrei Martinenko and Nikolai Ziabko from GEOPRO GmbH Hamburg
8ο Πανελλήνιο Συμποσιο Ωκεανογραφίας & Αλιείας 557 for their valuable help in buoy construction. We acknowledge the assistance of L. Athineos from HCMR, Athens and Captain Zervas and Kiriazis, and their crew from Skala Atalanti, during the field operations and the buoy deployment. This project is supported by the General Secretariat for Research and Technology of Greece, 3 rd Framework Operational Programme. References GEOPRO GmbH Hamburg, 2004. Data Acquisition System SEDIS IV User Guide, pp. 34. MAKRIS, J., PAPOULIA, J., PAPANIKO- LAOU, D. and STAVRAKAKIS, G., 2001. Thinned continental crust below the northern Evoikos Gulf, central Greece, detected from deep seismic soundings. TECTONO- PHYSICS, 341, 225-236.