## 4 Seismic Monitoring  
Earthquake observation at KOERI dates back to the 1894 Istanbul earthquake. Seismic monitoring facilities have continued for more than a century since the installation of the first seismometer in 1895. Details of KOERI earthquake catalogues [5; 6] and seismic network evolutions [6; 7] have been presented in earlier studies. In order to obtain reliable  
Figure 1: KOERI–TSP service area (which excludes the Western Mediterranean and Corinth Gulf), tsunami forecast points (TFPs—shown as white triangles) included in its messages and tide gauges (shown as colored dots) available to KOERI-RETMC in its TSP operations.  
earthquake parameters, today REMTC operates a seismic network including 256 sensors that comprise broadband (BB), accelerometer (SM) and short-period (SP) seismometers. Sensor numbers exceed 350 when including other national and international institutes operating and distributing data around the Mediterranean Region (e.g., AC: Albanian Seismological Network (AC); BS: National Seismic Network of Bulgaria (BS); GE: GEOFON; GO: National Seismic Network of Georgia; HL: National Observatory of Athens Seismic Network; HT: Aristotle University of Thessaloniki Seismological Network; HU: Hungarian National Seismological Network (HSN); II: Global Seismograph Network-IRIS/IDA (GSN); IMS: International Monitoring System (CTBTO-IDS); IS: Israel National Seismic Network; IU: Global Seismograph Network-IRIS/USGS (GSN); IV: Italian National Seismic Network (INSN); MN: Mediterranean Very Broadband Seismographic Network (MedNet); OE: Austrian Seismic Network; OX: North-East Italy Seismic Network; RO: Romanian Seismic Network (NIEP); TU: Turkish National Seismic Network (TNSN)). The average data availability performance of the KOERI seismic network is around 80% annually.  
The earthquake detection threshold of the KOERI seismic network was studied over different time periods using the KOERI earthquake catalogue. Magnitude of completeness (Mc) values ranging between 2.6 and 2.9 [8] were obtained by using the earthquake catalogues for the period 1975-2015. As a result of the increased sensor number, an Mc value of around 2.0 was computed [5] with the use of the earthquake catalogue for the period 2013-2017. In order to present the detection capability in the tsunami service provider monitoring area, seismic network distribution and noise levels were used as described in the SN-CAST software [9]. According to the use of seismic station coordinates and noise levels in the KOERI network, the geographical distributions of the minimum detectable magnitude (MI) in Turkey and surrounding regions were computed (Figure 2). The results showed that the minimum detectable threshold mainly changes between 1.0 and 2.0 inside the landmass of Turkey and in the range of 2.0 to 4.0 in most of the neighborhood areas outside the country. This provides sufficient detection magnitude for possible tsunami warnings, not only inside the country's borders but also inside the whole tsunami service provider monitoring area.  
Figure 2: Regional seismic stations available to KOERI-REMTC within its TSP operations area and regional earthquake magnitude threshold map of KOERI-TSP. Red upwards pointing triangles show KOERI’s own seismic stations, whereas black downwards pointing arrows show stations available from other networks. The earthquake monitoring area (dotted line until 2019) is shown with green rectangles.