Frequency-magnitude relationships for seismic areas around the capital citie s of Solomon, Vanuatu, Tonga and Fiji Islands

We studied the relationships between the frequency of occurrence and the magnitudes in seismogenic areas that will affect four capital cities in the South Pacific, namely: Honiara in Solomon Islands, Port Vila in Vanuatu, Suva in Fiji and Nuku'alofa in Tonga. We used the NEIS catalogues for the period 1973-1997, for magnitudes greater than about 5, in the proximity to the city under investigation. The definitions of the geographic boundaries of the seismogenic zones are based on the classical concepts of the distribution of the tectonic plates, the overwhelming number of studies that describe the seismotectonics in those active regions and on the observed seismicity and studies of the local people. Co mpleteness of the catalogue is assumed because of the high seismicity in these areas, despite the relatively short time span. We have used a hybrid process combining least squares fitting and Newtonian search process to find the best fit of the statistical parameters. The characteristic b value is 1.27, and seems to be irrespective of the depth and/or region.