A tsunami is a significant coastal hazard that causes destructive damage to coastal cities in the world. Besides, tsunamis, generated on the west coast of Japan, damaged coastal cities on the east coast of Korea in 1983 and 1993. In recent years, there has been increasing interest in the potential tsunami zone near the west coast of Japan. Therefore, it is important to have tsunami observation instruments in proper locations for tsunami detection and warning aspect. This study proposes the optimal region for offshore tsunami observation instrument deployment under the limited condition that the tsunami source in out of the territorial sea by investigating areas with the highest tsunami detection probability along with maximum evacuation time and bottom slope. Using the Cornell Multi-grid Coupled Tsunami (COMCOT) numerical model and a probabilistic approach, this study suggests the optimal region for offshore tsunami detection instrument deployment to be the northeast area of Ulleung-do Island in the eastern sea of Korea.

The past few decades witnessed rapid population and socioeconomic development in coastal areas. However, low-lying coastal regions have been prone to extreme surges and high waves during hurricanes and tsunami events (Sun et al., 2020). Sweet et al. (2017) reported that the frequency and intensity of hazard events have increased significantly due to climate change, causing low-land areas to face unforeseeable damage. For instance, Hurricane Katrina (2005) resulted in destruction and severe damage to 133,000 houses in only the Mississippi area (Eamon et al., 2007). Hurricane Harvey (2017) severely damaged over 200,000 homes and businesses and induced massive rainfall that displaced over 30,000 people (Aghababaei et al., 2018). Significantly, the 2011 Japan earthquake-induced tsunami (M w = 9) damaged most countermeasures along the coasts and inundated further inland areas, ultimately causing a massive loss of approximately 15,844 human lives, 128,753 destroyed houses, and 245,376 partially destroyed houses (Aarup et al., 2012). Therefore, investigating mechanisms of overland flow driven by large waves and high surge levels in coastal regions is of great importance for minimizing its impacts and enhancing the resilience of coastal communities. The hydrodynamic characteristics of coastal communities under inundation flow impacts have caused extensive concern over the last decade. Several previous studies have been conducted to investigate the flow patterns surrounding buildings under overland flow impacts. Park et al. (2013) used a 1:50 scaled physical model to represent an idealized coastal community in Seaside, Oregon. This study experimentally investigated the transformation of free surface elevation, velocity, and momentum flux in the built environment and compared them with the results of numerical modeling. Qin et al. (2018) performed a high-resolution computational fluid dynamics (CFD) model based on OpenFOAM to simulate the tsunami inundation in an idealization of Seaside, Oregon, which was validated