Imaging Terranes and Structure of the Southern South Island, New Zealand, With Joint Earthquake Travel-Time and Ambient-Noise Tomography

Date: 4/26/2019

Time: 11:15 AM

Room: Vashon

The South Island lithosphere consists of multiple terranes that were amalgamated during previous periods of subduction. Currently oblique collision produces major faulting, crustal thickening and subduction along the western South Island, with decreased deformation and seismicity towards the east. Local earthquake travel-time tomography has provided South Island seismic structure, and illustrated most transitions between terranes, but the sparse seismicity only allows coarse imaging in some key areas. In this study, we combine surface wave group velocity with the travel-time data to increase the resolution. We use ambient noise data from the permanent network and 47 portable broadband stations. This enhances spatial resolution in low seismicity areas, and improves resolution of shallow features. The Haast schist has distinct variation in seismic properties across the region, from a zone of ductile deformation and crustal thickening in the western South Island to a thick dry unit in the east. Although the eastern seismicity is sparse, there are numerous distributed potentially active fault structures, as well as basins which include active faults. The Matai terrane and Median batholith, which acted as backstops to Cretaceous accretion and schist development, are shown in the eastern South Island. In southwestern South Island, there is a sharp change in seismic properties and structure where the Fiordland block of Median batholith was emplaced.

Presenting Author: Donna Eberhart-Phillips

Authors