This paper describes observation and quantification of tidally synchronous earthquake incidence in the period around the 26 December 2004 Sumatran earthquake/tsunami event. In addition, three other recent catalogued Indonesian earthquake/tsunami events are examined, as is the 01 April 2007 Solomon Islands event which occurred during the preparation of this paper.
For the 26 December 2004 event, the relationship indicates earthquake inducement via ocean tidal loading and, during the ten-month period of high earthquake activity in this region, earthquake incidence associated with tidal-loading maxima was (a) 38% and (b) 86% higher than the period averages for the full and declustered earthquake catalogues respectively. A preliminary investigation of the Solomon Islands event indicates a similar relationship, although the inducement appears to be via earth tides in this case, and incidence associated with earth-tide maxima in this region was (a) 70% and (b) 50% higher than the period averages for the full and declustered major-earthquake catalogues respectively. It is concluded that the 26 December 2004 earthquake/tsunami event was tidally triggered, and the 01 April 2007 Solomon Islands also on the basis of the preliminary investigation, but that the three other Indonesian events investigated were not, with two of these displaying no tidal influence.