Time-dependent Deformation of the South Island, New Zealand, from Inversion of GPS and InSAR Data

Abstract:

Using continuous and survey-mode GPS time series and InSAR interferograms we develop a time-dependent model of the active deformation of South Island, New Zealand, from 1996-2015. The model takes into account steady motions, co-seismic and post-seismic slip from earthquakes in addition to slow-slip events at the southern end of the Hikurangi subduction zone. Initially, the GPS time series and interferogram data are used to estimate the transient (earthquake and slow-slip) parameters together with estimates of the secular velocities at the GPS sites. The steady tectonic deformation is modeled with a block–like structure that includes rotations and internal strain rates as well as inter-seismic strain rates estimated for locking on the faults bounding the blocks. The secular velocities are used to constrain the steady block model and then a full inversion is performed where the steady and transient parameters are adjusted to fit all the data. The result provides a predicted time history of deformation anywhere in the model domain that includes both transient and steady changes. Based on the predicted time histories of strain, we estimate time-dependent Coulomb stress changes along the major faults, in particular the Alpine fault. The goal is to understand better what features of the active deformation in the South Island drive faults toward failure and feed into an updated model of seismic hazard for this part of New Zealand.

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