| dc.description.abstract | Historically, literature had shown that eastern Taiwan had been attacked by tsunamis at least 14 times since 1771. For the location of Taiwan as in the Circum-Pacific Seismic Belt, many large earthquakes occurred in and offshore Taiwan, especially in eastern Taiwan, with frequent events for the magnitude of 6 or larger. To examine the tsunami threat in eastern Taiwan, through numerical simulating, we assess the tsunami potential to help on the precaution against tsunami calamities. To model the possible tsunami occurred in eastern Taiwan, we divided the eastern offshore Taiwan into 70 different source regions of latitude of 21o to 26 o, and longitude of 121 o to 125 o to examine the tsunami propagation characteristics (path effects) from finite-difference method by solving linear shallow water wave equation in spherical coordinates. The source region has a dimension of 0.5 degree by 0.5 degree. We gave an area of 8km by 8km with 10m uplift for the tsunami source in the region, individually, to examine how the tsunami propagating toward Taiwan from each source region. A grid size of 2 km is utilized in the tsunami simulation with 1 minute high resolution bathymetry. By analyzing the maximum amplitudes and the arrival time for the assumed stations around the coastal of Taiwan, we select special cases those have significant effect toward Taiwan to discuss the path effects and bathymetry affections. We found that the most possible tsunami threat region in eastern Taiwan is Ilan. Ilan plain located close to the end of the Okinawa trough, tsunami waves tend to lead to Ilan by following the trough structure. The Gagua Ridge in eastern offshore Taiwan, actually, diverts the wave to prevent the tsunami threat from long distance. Considering the deep water depth in eastern Taiwan, we also try to discuss about the dispersion effect on tsunami propagation for deeper water events to the south of Ryukyu trench. The results show that the dispersion effect from the deep ocean is not significant for the tsunami modeling in eastern Taiwan. Our simulations also show that the tsunami speed in eastern Taiwan can be divided into three regions, north of latitude 24.5 o, the Ryukyu arc region, and the south region of the Ryukyu arc. The average tsunami speed in these three regions are：8.1km/min, 10.2km/min, and 13.9km/min, respectively. These values and the amplitude attenuation characters can be used for the future tsunami warning. The identified tsunami potential regions in offshore Taiwan could also be examined with the background seismicity and possible marine landslide to further investigate the possibility on the occurrence of the larger events (6 or larger) for the future studies. The overall survey on the tsunami potential in Taiwan region will toward the goal for future tsunami warning, together with recent developing earthquake warning system in Taiwan. | en_US |