History

The seismological observations on the territory of Bulgaria have traditions of more than 100 years. The beginning of Bulgarian seismology dates back to 1891. At that time Spas Vatzof, the director of Central Meteorological Station in Sofia, organized a network of correspondents for observation of felt earthquakes in Bulgaria. Vatzof formed a proto-type of macroseismic bulletin containing: time of perceived shaking, locality, direction of impact, observed effects, intensity assessed by Rossi-Forel scale till 1912 and Forel-Mercalli since then. The period of Bulgarian historical era ends in 1905 when the seismograph of Omorri-Boch type was installed in the first Seismological Station in the town of Sofia. The same year four seismoscopes of Agamenonne type were installed in Sofia, Petrohan, Rila Monastery and the town of Kazanlak.

The Bulgarian seismological network-NOTSSI (National Operative Telemetric System for Seismological Information) was founded at the end of 1980. The objective of NOTSSI is continuous monitoring of seismic activity in the territory of Bulgaria and adjacent areas within the Balkan region. The network consisted of 21 stations spanning the entire territory of the country. 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 on 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.

Recently a modernization process has been initiated for the Seismological Network. Modernization of NOTSSI started in 1996. First, station Vitosha (VTS, since 1979) was included in the MEDNET project and was updated with STS-1 and Quanterra 380. The VTS-MEDNET station became fully operational since May 13, 1996.

Then, in 2003, two stations: Plovdiv (PLD since 1977) and Jambol (JMB since 1982) were equipped with Quanterra 330 data loggers and Guralp CMG-40T broad-band sensors with government funding.

The EC project MEREDIAN-2 involves NOTSSI in a broadband European network. The network upgrading was done in close consultation with ORFEUS and the MEREDIAN consortium members INGV, Roma, Italy and GFZ, Germany. Since 2004, the real-time data transmission from stations Vitosha, Plovdiv and Jambol became available via leased digital telephone lines. Data from VTS, PLD and JMB stations were collected in real (near-real) time using the SeisComp/SeedLink software. The MEREDIAN-2 project initiates the rebuilding of a much-needed European and regional data exchange infrastructure. A real-time data transfer to INGV, Roma and ORFEUS Data Centers was implemented. Regional real-time data exchange between Bulgaria and Romania, Slovakia, Slovenia, Austria and Czech Republic was established.

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. At the beginning of December 2005 all stations located around the country were installed and transmitted data in real-time to the NSDC using the VPN and MAN networks of the Bulgarian Telecommunication Company.

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 DAS 130-01/3, 3 Quanterra recorders - models Q330 (two stations) and Q380 (one station).

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.