Most countries and local governments provide earthquake services in the public domain, and they must have high accuracy. If a missed alarm of the Earthquake Early Warning (EEW) system causes many casualties, or if the industrial system is temporarily suspended owing to a false alarm, causing economic losses, it inevitably becomes the responsibility of the government. Therefore, most countries approach the technological improvement of EEW systems carefully by performing simulations and conducting long-term tests to ensure their reliability. In this study, we extract characteristics of the initial P-wave amplitude from an earthquake on the Korean Peninsula and perform trend analysis. We found a common optimal threshold on the Korea Meteorological Administration's seismic observatory network from trend analysis. We then evaluated the performance of the optimized algorithm based on the simulation. The performance evaluated the actual events recorded corresponding to the number of matched, missed, and false events. As the result of the evaluation, the optimized module combination had a significantly lower occurrence of false events than the previous version. Therefore, we expected that the proposed optimization should contribute to improving alarm stability in real-time EEW.

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We performed seismic imaging based on relative S-wave travel times to examine S-wave velocity of upper mantle structure beneath East Asia. We used teleseismic events recorded at 129 broadband stations of the Korea Institute of Geoscience and Mineral Resources (KIGAM), Korea Meteorological Administration (KMA), and National Research Institute for Earth Science and Disaster Prevention (NIED). Relative travel time residuals were obtained by a multi-channel cross-correlation method designed to automatically determine accurate relative phase arrival times. The resulting images show high-velocity anomalies along plate boundaries around the Japanese islands region. These anomalies may indicate subducting Pacific and Philippine Sea plates. On the other hand, a low-velocity anomaly is revealed beneath east of the Korean peninsula down to around 300 km depth, which is thought to be related to the formation of the Ulleung basin and the Ulleung island. Low-velocity anomalies revealed beneath the Jeju island may imply that the formation and volcanism of the Jeju island have been caused by magmatic sources from the deep mantle.

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