Joint local earthquake and teleseismic inversion for 3-D velocity and Q in New Zealand

Abstract

We have developed a joint inversion of local earthquake and teleseismic data and applied it in New Zealand to obtain improved 3-D seismic velocity, Qp and Qs models. To accommodate sharper detail where there are dense local earthquake data, varied spatial resolution is enabled with linking of nodes into larger inversion elements where data are sparse. The teleseismic t∗ measurements are obtained by stacking and removing the average for the common source and path. The combined inversions used data from 126 teleseisms and 2365 local earthquakes that extend to 350 km depth. Vp results are similar to previous studies, but have enhanced detail near the slab provided by local seismicity. Sub-slab low velocity and low Q is imaged along the eastern North Island, which may represent asthenosphere with entrained water and melt. Along the western South Island, there is a high Vp, high Q feature distinct from the current slab, and interpreted to be a slab remnant from the period of Subduction-Transform Edge Propagator fault development and trench rollback. The axial South Island high Vp, high Q feature of the Hikurangi Plateau is imaged, and is bounded on the southeast by thinner lithosphere that may be related to the period of Great South Basin rifting.