A rapid determination network in Turkey: Towards an early warning system in the Marmara Region

Niyazi Turkelli, Ali Pinar, Serafettin Ince
Kandilli Observatory and Earthquake Research Institute, Bogazici University, 81220, Cengelkoy, Istanbul, Turkiye.
Tel. : +90-216-332 9702, Fax: +90-216-308 3061,
E-mail: turkelli@boun.edu.tr

The Seismological Laboratory of the Kandilli Observatory and Earthquake Research Institute (KOERI) of Bogazici University decided to upgrade its network in the Marmara region, the so-called MARNET, from analog telemetry to digital telemetry in 1997. Therefore, five remote RF full-duplex, two-way telemetry, 24-bit digital systems equipped with CMG-40T broad-band seismometers were purchased. They will provide in excess of 131 dB of dynamic range at 100 sps. According to an agreement. the GFZ Potsdam will replace three stations of MARNET and add two more with exactly the same equipment except of the seismometers in addition to the five digital stations. So, GFZ Potsdam will extend their 15 stations network in Mudurnu valley by adding 5 station for monitoring the seismic activity along the northern branch of the North Anatolian Fault Zone (NAFZ) towards the west. A start was given to the site preparation and it is planned that the installation should be finished by the end of 1998. KOERI already replaced its central analog station ISK with a 24-bit, CMG-3T VBB system. In parallel with the monitoring of the seismic activity in the region a GPS project, consisting of a network of 10 continuously recording GPS stations for monitoring strain accumulation and 5 VBB seismic stations, will be conducted by TUBITAK, General Command of Mapping, KOERI, ITU, and MIT.

There are two aims for the above projects: a) To monitor seismic activity and tectonic deformation continuously in the Marmara region. Also, to allow the determination of hypocentres in a short time with high accuracy. These projects would be extended to an early warning system in the region. b) To enable scientists to the use advanced methods of studying teleseismic and regional waveform modelling, travel time tomography, hypocentre location inversion, shear wave splitting analysis, seismic risk analysis and forecasting future earthquake locations.

These projects are important for the Marmara region, having 20 million population and 40% of industrial investment of Turkey, and at the same time a great potential for earthquakes. As a result, the Marmara region will be monitored by a network of 13 high quality digital seismographs. The central data acquisition in Istanbul, Kandilli will have real-time data link with the central data acquisition system in the city of Adapazar which monitors the seismic activity in Mudurnu valley. We believe that these two networks will remarkably increase the earthquake dedectibility in the region.

The seismicity in the Marmara region is the result of tectonic movements along three possible westward extensions of the NAFZ beyond the Mudurnu valley where the influence of the Aegean extensional tectonic regime has been recognised (Barka and Kadinsky-Cade, 1988). The number of earthquakes identified in this region for the historical period (AD 1 to 1899) is around 600. Thirty-eight of them are estimated to have been relatively large shocks of magnitude Ms > 7.0 ( Ambraseys and Finkel, 1991). According to Soysal et al., (1981), 124 damaging earthquakes occurred with widespread damages in Istanbul, in places even very serious. The average intensity was about VIII. Many public buildings, mosques and houses were shattered and left on the verge of collapse, while most of the older constructions fell down. Water distribution was disrupted. Deaths are estimated at a few thousand (about 0.30.4% of a total population of 900,000). For the instrumental period (after 1900), the earthquake activity in the Marmara Sea region shows typical swarm-type activities.