| Abstract: | New Zealand earthquakes rarely cause significant tsunamis. In 1947 two tsunamis reaching a height of about 10 m were associated with earthquakes of less than magnitude 6. Their records have the predominantly low-frequency character of the tsunami-generating shocks on the inner margin of the Japan Trench, but they originated beneath a shallow coastal platform, and not close to the Hikurangi Trench. The platform consists of weak folded sediments penetrated by diapiric intrusions from which large quantities of mud and breccia have been explosively expelled from time to time. The mechanical behaviour of this extruded material is believed to be responsible for the character of the shocks, and to provide a mechanism for the generation of tsunamis. |
