To analysis of source mechanism of the 26 December 2004 Indian Ocean tsunami

4. Numerical Simulation of Tsunami Generation, Propagation and Run-up: Keyboard Model of the Source (Oblique, Sumatra-Andaman-Like, Subduction Zone)

[18] The above performed study was then applied under analysis of tsunami wave generation due to the 26 December 2004 Indian Ocean earthquake. The earthquake source was located west of Sumatra Island northward along the oceanic subduction zone. The extent of the source was estimated near 1000 km [see, e.g. Lay et al., 2005].

[19] In this work, there are considered two possible scenarios of seafloor motions in the earthquake source (subduction zone) for geometry close to that of oblique subduction zone (Figure 3) in the source of Sumatra-Andaman earthquake [cf. with Lobkovsky et al., 1991]. These motions were approximated by motion of several keyboard blocks with different size. The location of the source relative to the Sumatra Island and Thailand beaches, the ocean depth in the source zone, extent of the near-coast zone (slope length and shelf slope angle), as well as possible parameters of the earthquake process were taken into account at given simulation. It was considered a run-up on a plane slope. However, modelness of the problem is that it was not taken into account the real bathymetry of the ocean and estimations were made for wave propagation on the even bottom. Such approach corresponds to small-scale tsunamizonation when ocean bottom relief can be considered as smoothed one [Soloviev et al., 1977]. It was mainly considered run-up at the nearest to the earthquake source beach corresponding to the Thailand coast.

4.1. Source Consisting of Three Keyboard Blocks

Figure 12

[20] The location of the first keyboard block with size 400 km times

150 km corresponds to the region of northwest of Sumatra Island where the first strongest quake occurs. Second keyboard block 300 km long is of width decreasing from 150 km to 100 km northward. Third keyboard block is also of 300 km long, and the width is decreased from 100 km to 50 km. The keyboard blocks moves successively: first shifts upward to 9 meters, second shifts downward to 3 meters, third shifts upward to 5 meters. The entire time of block motion is equal to 330 s. Figure 12 shows the location of keyboard blocks (a) and space-time picture of the moving shoreline (b). Animation 1 (see online version) shows dynamics of wave generation, propagation, and run-up on the beach. It is well seen that to a beach it comes a wave train: two large waves which are followed by a strong sea recession. Then, in addition, three waves are followed them. First front comes in nearly 1.5 hours after the beginning of the motions in the source. Its height is not very large, up to 3 meters. Then, 20 min later, it comes the wave with height 9.5 meters. It is followed by alternating wave run-ups and run-downs with somewhat smaller height (depth).

4.2. Source Consisting of Eight Keyboard Blocks

Figure 13

[21] The location of the first keyboard block also corresponds to northwest Sumatra Island and is 300 km long while all another blocks are 100 km long and 150 km wide. The keyboard blocks moves successively in the following order:

Block	Block length, km	Vertical shift	Shift value, m	Motion time, s
1	300 km	upward	7	60
2	100 km	upward	3	40
3	100 km	downward	3	60
4	100 km	upward	4	50
5	100 km	upward	2	30
6	100 km	downward	2	60
7	100 km	upward	3	40
8	100 km	upward	2	60

Figure 13 shows the location of keyboard blocks (a) and space-time picture of moving shoreline (b). Animation 2 (see online version) shows dynamics of wave generation with scale of maximum run-up on the beach and 9 fragments of surface water wave generation. It is well seen that given parameters of keyboard blocks in the earthquake source lead to one significant wave run-up on the beach and essential run-down and then to several more weak waves. Maximum run-up in this case is equal to 11 meters.

[22] The further performed numerical simulation of the surface water wave generation by motions of keyboard blocks in the source of given earthquake demonstrates that under keyboard block motion in the source from south to north, along the subduction zone, the keyboard block sizes and velocity with which they move upward (downward), as well as velocity with which this motion comes along the subduction zone are the essential factors.