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In September, 2005 the Geophysical Institute Bulgarian Academy of Sciences selected REF TEK to upgrade the existing national seismological network to a modern technology digital network.

The original Bulgarian seismological network - NOTSSI (National Operative Telemetric System for Seismological Information) was established at the end of 1980. The objective of NOTSSI was continuous monitoring of seismic activity in the territory of Bulgaria and adjacent areas within the Balkan region. The network consisted of 20 stations spanning the entire territory of the country. The data from all stations was transmitted in real time to the Seismic Center installed in the Geophysical Institute. NOTSSI is the only organization in Bulgaria in charge of acquisition of seismological information and is the national information center of rapid earthquake information and seismic hazard mitigation. In the case of a felt earthquake in the territory of Bulgaria , the information is transmitted to the Council of Ministers, the Governmental Commission of Disasters, the State Agency Civil Protection and other interested organizations, including mass media and general public. In close relationship with Civil Defense and other governmental institutions, NOTSSI and the Geophysical Institute are responsible for earthquake disaster mitigation.

Modernization of the NOTSSI started several years ago. First, in 1996, station Vitosha was included in the MEDNET project and was updated with STS-1 and Quanterra 380. Then, in 2003, in frame of MEREDIAN II project, two stations ( Plovdiv and Jambol) were equipped with Quanterra 330 data loggers and Guralp CMG-40T broad-band sensors with government funding. Since 2004, the real-time data transmission from stations Vitosha, Plovdiv and Jambol became available via leased digital telephone lines.

As of September 2005 NOTSSI comprised 14 permanent seismic stations: 3 broadband digital seismic stations, 11 with analog telemetry via leased telephone lines, and two local networks. The Center for Data Collection and Analysis (CDCA) is located in Sofia . Analog telemetry data from S13 seismometers were recorded on drums at the CDCA. The NOTSSI network provided reliable estimation of the main parameters of all seismic events in Bulgaria with a magnitude greater than 2.5.

In 2005, the Permanent Commission for Prevention of the Population from Natural Disasters and Catastrophes (now Ministry of State Policy for Disaster Management) supported the Geophysical Institute for overall modernization of the seismological network. After evaluation of competitive bids, REF TEK was awarded the contract to upgrade the existing national seismological network to a modern technology digital network.  The contract was signed on September 6, 2005.  The equipment was delivered to the Geophysical Institute by the middle of November with the turn-key network installation being started at the end of November by REF TEK field support and SYNAPSE software engineers. In less than 10 days, all 11 stations located around the country were installed and transmitted data in real-time to the CDSA using the VPN and MAN networks of the Bulgarian Telecommunication Company.  Quick and successful installation of the network was achieved by the great support provided by the Geophysical Institute personnel.  Thanks to Dr. Svetlana Nikolova and Dr. Dimo Solakov for professional organization of the installation process.

After the installation of REF TEK equipment, the upgraded NOTSSI network now consists of 14 stations equipped with 11 REF TEK High Resolution Broadband Seismic Recorders, model 130-01/3, 3 Quanterra recorders, models Q330 (two stations) and Q380 (one station). The network is equipped with a very broadband sensor (one station), broadband (8 stations), and short period seismometers (3 stations).  Real-time data acquisition is performed using REFTEK’s full duplex error-correction protocol RTPD. The data from the Quanterra recorders are fed into RTPD in real-time via SeisComp/SeedLink protocol.  Real-time and interactive data processing performed by the Seismic Network Data Processor (SNDP) software package running on two clustered SUN Fire V240 Servers.  Network command/control and monitoring are performed by RTCC and RTPMonitor user interfaces which are running on two SUN Blade 1500 Workstations.  Both RTCC and RTPMonitor serve up html pages that can be displayed in any standard web browser allowing the end-user to monitor the network status and control the acquisition parameters anytime and anywhere from any computer connected to the Internet.

After modernization, NOTSSI became a world-class digital network providing reliable real-time seismic monitoring and rapid earthquake information to both scientific communities and authorities in Bulgaria for seismic hazard mitigation.
On March 22, 2006, REF TEK was selected to supply 5 more stations to the NOTSSI network.

Please click here to see some photos from the installation sites.

Picture 1. National Operative Telemetric System for Seismological Information
Picture 2. Geophysical Institute - National Center for Seismological Information (NDC.BS)
Picture 3. Seismic Network: Data analyses.
Picture 4. Advanced Digital Seismic Network for Earthquake Hazard Mitigation in Bulgaria.
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