The Algorithm Development of the Tsunami Impact Intensity Analysis and the Application to the 1867 Keelung Tsunami Event

Abstract:

As a tsunami scientist, I’ve been frequently asked where the tsunami will/did come from? The conventional answer to this question is based on the understanding of trench and bathymetry distributions. Sometimes, for a precise answer, a series of scenario studies have to be performed in priori. Even hundreds of scenarios are created and studied, however, potential tsunami sources could be neglected unintentionally.. For this, I’ve created a new algorithm to efficiently locate the possible tsunami sources, which is called Impact Intensity Analysis (IIA). Briefly speaking, this algorithm scans the entire computational domain and find out the distribution of maximum wave height of each unit source. After that, the result presents a clear view of potential tsunami energy transport pattern. For example, the result of IIA shows that the southern east of Taiwan is under the threat of tsunamis sourcing from the northern segment of Yap Trench; and so is the northern segment of Manila Trench. A clear energy path can be seen, linking Taiwan and the Yap Trench. The result matches the scenario study of potential Yap tsunami very well (Figure 1). This indicates that once the tsunami source is located in the energy path, with a proper wave direction, the tsunami energy can be transported to the study site with relatively less energy loss. Therefore, this algorithm can help us analyze the potential tsunami source systematically; and more importantly, get rid of the impossible source candidates quickly.

In this paper, we present the detailed validation of this algorithm, including the directionality and the effect of on and off the energy path. At the end, we employ this algorithm to analyze the potential tsunami source of 1867 Keelung tsunami event. The result shows that this event was possibly caused by a submarine landslide generated tsunami and the landslide occurred in the north-east offshore Taiwan.

Figure 1. The Impact Intensity Analysis (IIA) of the south-east Taiwan (left), and the distribution of the maximum wave height of the potential Yap tsunami (right). The result of IIA shows a clear energy path between Taiwan and Yap Trench, and the Yap tsunami projects the tsunami energy to Taiwan right in this path.