## 7 KOERI-TSP Decision Support System  
The KOERI-TSP system relies on the fast and reliable determination of the location, magnitude and depth of an earthquake to assess its tsunamigenic potential through a decision matrix (Figure 3). KOERI-TSP disseminates tsunami messages to its subscribers based on the alert level and guided by this decision matrix. The target time of the dissemination of the first message is set as 7 min after the earthquake origin time because of the seismologically unavoidable trade-off between accuracy and the timely availability of the earthquake magnitude information to the duty officer on shift. KOERI-TSP's decision support system was initially based on the NEAMTWS Operational Concept Decision Matrix presented in [4]. Nevertheless, KOERI modified this initial decision matrix over time based on supporting scientific studies, such as [20; 21], and its operational experience--so-called \"best practices\". The current decision matrix in operation (Figure 3) is less conservative in comparison to the NEAMTWS Decision Matrix for the Mediterranean in terms of Mw thresholds, although associates the 'information' alert level with \"low tsunami potential\" on the grounds of the possibility of a triggered submarine landslide. Basin-wide 'watch' (highest alert level) messages are issued only for events with Mw \(\geq\) 7.5. The decision support matrix, which translates alert levels into anticipated wave amplitude and run-up values, is implemented in accordance with [4]. The message content conforms to the various message types defined by [4]. A slight modification indicating the possibility of a tsunami being caused by a submarine landslide generated by an earthquake was introduced in the 'information' message in 2015. In 2018, a statement was added to the initial message addressing the magnitude uncertainty by stating that the magnitude as the basis of the initial bulletin may be subject to further revision upon availability of additional seismic data, which may differ from the final magnitude estimation. The messages clearly indicate that the alerts apply to countries subscribed to the services of KOERI-TSP and within its monitoring area, and all prescribed parameters are contained in the message. For tsunamigenic events, the duty officer (staff responsible for sending the tsunami alert messages according to the decision matrix) on shift starts monitoring the tsunami propagation after the dissemination of the first message via real-time sea level data transmitted from tide gauge stations to KOERI servers. In the meantime, if the earthquake magnitude has been revised in such a way that the alert level in the initial message needs to be raised, a second message with the revised earthquake magnitude should be sent within 15 min of the earthquake origin time. If a tsunami is observed at any tide gauge station in the event area, an 'ongoing' message is prepared by the duty officer, including the measured sea level data, such as the name and coordinates of tide gauge station, the arrival time of the first wave, the maximum wave amplitude and the period of the observed wave. As stated in [4], the watch level indicates the potential for a tsunami along the coast with a wave height higher than 0.5 m, while the advisory level corresponds to wave heights between 0.2 m and 0.5 m. However, the tsunami watch alert level is not downgraded to the advisory level by KOERI-TSP if the measured sea level at the tide gauge station is less than 0.5 m, simply because of the fact that the sea level measured at the second closest tide gauge station may very well exceed 0.5 m, especially considering the limited availability of coastal tide gauge stations. The duty officer proceeds to monitor tsunami propagation and whether tsunami waves are observed at any other station or set of stations, then the next ongoing message is disseminated. The process of  
Figure 3: KOERI–RETMC decision matrix (top) and NEAMTWS decision support matrix used in KOERI–TSP operations.