Source Properties of Shallow Earthquakes in New Zealand and their Tectonic Associations

Seismic moments estimated from the surface-wave parameter AR, together with local magnitudes ML have been used to determine the source parameters of 270 shallow New Zealand earthquakes between 1965 and 1973 which were well recorded on long-period seismographs at Wellington. Average displacements across the fault plane, referred to a common seismic moment, show differences several times larger than errors likely in their estimation. The displacements display a regular regional pattern. In the northern seismic zone displacements are small between the Hikurangi Trench and the east coast of the North Island and also on the continental side of the volcanic front. Between these two regions, and thus over most of the North Island, displacements are large. The whole central region of the South Island has small displacements. The Fiordland region in the south-west, which has island-arc affinities but no volcanism or active faulting, is one of predominantly large displacements.