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Adjoint Tomography of the Hikurangi Subduction Zone and New Zealand's North Island

Session: Imaging Incipient and Fossil Subduction Zones

Type: Oral

Date: 4/22/2021

Presentation Time: 10:15 AM Pacific

Description: 

We undertake the first application of adjoint tomography in New Zealand to improve an existing 3D tomography model. We have developed an automated, open-source workflow for full-waveform inversion using spectral-element and adjoint methods (Chow et al., 2020). As a study area we focus on the North Island of New Zealand, which encompasses the Hikurangi subduction zone and associated tectonic features. The chosen domain offers a unique opportunity for imaging material properties near an active subduction zone, due to the availability of well-recorded earthquakes in close proximity to the plate interface. We performed realistic synthetic inversions using New Zealand source and receiver distributions to determine a set of parameters usable in real-data inversions. We have then undertaken an iterative inversion using 2000 unique source-receiver pairs to fit waveforms up to 2.5 s period, relating to a minimum spatial resolution of roughly 5 km. Velocity changes are resolved at shallow crustal depths in tectonically active areas, such as the Taupō Volcanic Zone, regions of geodetically detected slow slip, and in the vicinity of the locked-to-creeping transition within the subduction zone. Data-synthetic misfit is reduced considerably at the periods of interest. We present an accurate, high-resolution tomographic model of the North Island of New Zealand, alongside post-hoc validation of model accuracy, and interpretations of enigmatic tectonic processes related to an active subduction zone.

Presenting Author: Bryant Chow

Student Presenter: Yes

Authors