Intraplate seismicity of the southern part of the Pacific Plate

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Abstract
We present a compilation of all the known seismicity of the part of the Pacific plate located south of the equator. This includes historical earthquakes dating back to 1937. In addition to the Gilbert Islands swarm of 1981–1983 we identify 60 events at 32 epicenters in the magnitude range 4.3–6.9. Our results indicate that the level of seismicity of the southern Pacific plate is comparable to that of other plates, including continent‐bearing ones. Most of the seismic activity is concentrated in the youngest parts of the plate, but a few large events are present in Cretaceous lithosphere. With the exception of events from the Gilbert Islands swarm, earthquakes located in lithosphere 35 Ma and older are usually compatible with the release of horizontal compressional stress due to the gravitational process known as ridge push; in younger areas the situation is much less clear‐cut. The final geometry of the focal mechanisms is controlled by local tectonics; in particular, due to the Miocene reorientation of the spreading at the East Pacific Rise, the bulk of the Pacific plate is particularly vulnerable to ridge push, and this explains the numerous strike‐slip events and the absence of magnitude 6 events in most of the plate. Correlations of epicenters with zones of weakness or bathymetric features are frequent but not universal. Finally, a number of areas with high seismic release are identified as potential targets for future exploration.