Abstract

This study develops a preliminary probabilistic seismic hazard model for Vanuatu. The area of investigation, formerly referred to as the New Hebrides, lies in the center of a chain of partly vulcanologically active islands that mark the present-day boundary between the Australia-India plate and the microplate of the North Fiji basin. The seismicity of the Vanuatu arc is dominated by an east-dipping subduction zone, which shows striking structural anomalies in the central part between 14° and 18° S. Our historical catalog contains 7519 events within the Vanuatu region for the period from 1964 to 2003, drawn from the global teleseismic catalogs by the United States Geological Survey/National Earthquake Information Center (USGS/NEIC, see Data and Resources section) and Engdahl et al. (1998). As a measure of seismic hazard, we use horizontal peak ground acceleration (PGA) and horizontal spectral ground acceleration (SGA) at a period of 1 sec. The hazard estimates are based on a logic-tree approach to account for the epistemic uncertainties associated with our analysis. Our results suggest that the entire island arc experiences a high and uniform seismic hazard. Typical values for PGAs range from 0.65g to 0.77g with a 10% probability of exceedence in 50 yr. For Port Vila, the capital and largest city in Vanuatu, we additionally present a PGA hazard curve and a uniform hazard spectrum over the period range 0.1–2 sec.

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