Excitation of T Phases from Shallow and Intermediate-Depth Earthquakes in the Southten Vanuatu (New Hebrides) Arc

摘要

In this paper, we present observations on the excitation of T phases from shallow and intermediate-depth earthquakes located along the southern Vanuatu (New Hebrides) Island arc and recorded at short-period, vertical-component seismic stations on the Loyalty Islands of Lifou and Mare. Most of these earthquakes are part of the northeasterly dipping Benioff zone that defines the descending Australian plate in the upper 300 km of the mantle beneath the Vanuatu arc. The Loyalty Islands are uniquely situated on the oceanic Australian plate at distances of about 100 to 200 km in front of the southern Vanuatu trench axis. The main objectives of this study are: (1) to investigate in detail the nature and pattern of the excitation of T phases from sources of considerably varying depths, and (2) to study the effects of submarine physiography on the observed pattern. This study was particularly desirable because of the relatively unique geometry of the sources and the recording stations and because the events used in this study are well-located using local land and ocean-bottom seismic networks (Coudert et al., 1981).