Tonga Tsunami at Lyttelton Harbour 

Data kindly supplied by Lyttelton Port Co. Ltd.

Commentary

Lyttelton is in a sheltered harbour. The harbour has a seiche period of 11 minutes and although the open coast is strongly affected by far infra gravity ( FIG ) waves, only waves with periods of around 11 minutes penetrate the harbour to the tide gauge. The tsunami arrived about 6 h after the earthquake, but the peak waves did not arrive until 18 h after the earthquake. The tsunami caused harbour resonance at 11-minute periods and this is probably why the longer period waves in the tsunami are not apparent. They are there, but they have been swamped by the harbour resonance.

Figure 1. Tonga tsunami at Lyttelton Harbour showing: A. long wave record; B. significant (red) and maximum (blue) wave heights, and high tide times (green diamonds); C. period of significant waves; and D. distribution of significant wave height with time and period. EQ denotes the time of the earthquake. Times are in NZST (UTC + 12).

How were these calculated?
Return to top
Back to Map