**4. Conclusions**

Shown in **Figure 22(a)**, and **22(b)**, are the numerical results for the water surface displacements at Point A, and Point B, indicated in **Figure 20**, respectively. The tsunami height for not only the first wave, but also the several following waves, is larger than 1.0 m at Point A, where it takes a longer time for the oscillation to attenuate because of multiple reflections of tsunamis

Although Point ➂ is more distant from Point B than Point ➁, the maximum tsunami height at Point B, near the highest population area, is larger in the case where the crater is located at Point ➂ than that in the case where the crater appears at Point ➁; for in the former case, the wave energy is large for the wave component approaching Sakurajima in a direction oblique, or parallel, to the seashore of Sakurajima, resulting in a tsunami traveling along the shoreline

The numerical results for the distributions of the maximum water level *η*max for 0.0 s ≤ *t* ≤ 2.0 ×

value of the submarine explosive index concerning tsunami generation, *V*w, is about 4.5 × 104

locations depicted with white circles, are as follows: (a) off the north of Sakurajima, (b) off Hayato, (c) off Ryugamizu,

 s, are shown in **Figure 23(a)**–**23(d)**, where the crater locations are depicted with white circles off the north of Sakurajima, off Hayato, off Ryugamizu, and off Kurokami‐cho, respectively.

m in all the cases, such that the

s, for different crater locations. The crater

at the bay head.

54 Tsunami

103

of Sakurajima toward the west.

*3.2.4. Distribution of the maximum water level*

The still water depth at the crater, *h*, is assumed to be 1.0 × 102

**Figure 23.** The distributions of the maximum water level for 0.0 s ≤ *t* ≤ 2.0×103

and (d) off Kurokami‐cho.

First, several characteristics of tsunami generation due to a landslide, or a sector collapse, were studied, with the tsunamis simulated using the MPS model, that represents their generation through an interaction between the falling bodies, and the seawater, in two vertical dimensions. The falling body was assumed to be a fluid, or a rigid body, which moved down a slope with a constant gradient.

Second, the mechanism of tsunami generation due to a submarine volcanic eruption, was discussed, focusing on a phreatomagmatic explosion. A submarine explosive index concerning tsunami generation, was developed, by assuming the relationship between a phreatomagmatic explosion, and the resultant initial tsunami waveform. A numerical simulation was also generated, for the propagation of tsunamis due to a submarine volcanic eruption, with the specific value for this index, agreeing with the observed data from the submarine explosion leading to a tsunami generated in Kagoshima Bay.
