Seismic Local Networks of the Iranian Seismological Center
The Institute of Geophysics, affiliated with the University of Tehran, constructed the first seismic station in Tehran in 1958, to record and locate earthquakes. In the 1960s, the number of seismic stations increased to five (5) analogue stations installed in the cities of Tehran, Tabriz, Mashhad, Shiraz and Kermanshah. The stations of Tabriz, Mashhad and Shiraz were a subset of the World-Wide Standardized Seismographic Network (WWSSN). The Iranian Long Period Array (ILPA) consisted of seven (7) stations installed in the south-west of Tehran in 1975. In the early 1981s, some additional analogue stations were installed at Brojen, Minoodasht, Mahabad, Ghamsar-e-Kashan and Ghaleh-Ghazi by Institute of Geophysics. Until 1995, the above mentioned analogue stations were responsible for recording and reporting earthquake events throughout the nation. Digital seismological equipment was supplied and installed in Tehran and Tabriz seismic local networks in 1995, and gradually the local networks of Semnan, Quchan, Yazd, Sari, Esfahan, Shiraz, Mashhad, Kermanshah, Birjand and Khoram-abad in turn were installed and equipped with digital instruments. The new seismic local networks of Minab, Kerman, Shahr-e-Kord and Hamedan were installed in 2010. Seismic stations are equipped with three (3) component short-period, medium-band or broad-band seismometers. Today, the Iranian seismological network comprises 108 digital seismic stations in 20 seismic local networks, 4 digital seismic stations and 1 borehole stations which cover most earthquake-prone regions (Figure 1).
Figure 1 Seismic local networks of the Iranian seismological network
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Seismic local networks are developing and expanding according to our short-term, medium-term, and long-term plans. Recorded data in all stations in the country are transmitted to the center of each seismic local network, which relays the data to the Iranian seismological center continuously by VPN or Satellite communications.
Our Short period seismic stations are equipped with SS1 seismometers, the medium- bands are equipped with Trillium-40s seismometers, and broad-bands are equipped with CMG3ESP-120s, CMG3T-360s and Trillium-240s seismometers.
The magnitude of earthquakes is reported in the corrected Nuttli (1973) magnitude scale (Rezapour, 2005):
where, is the maximum amplitude in nanometers per second and is epicentral distance in kilometers.
Nuttli, O.W., 1973. Seismic wave attenuation relations for eastern NorthAmerica. Journal of Geophysical Research,78, 876-855.
Rezapour, M., 2005. Magnitude scale in the Tabriz seismic network. Journal of the Earth&Space Physics, 31(1), 13-21.