Estimating the Extent of Low-temperature Ductile Deformation in the Lithosphere Using Seismic Anisotropy Measurements Around the Alpine Fault
Description:
How strong is the lithosphere? This simply posed question is central to our understanding of active tectonics, but the answer is not at all simple. Laboratory experiments extrapolated to geologic conditions typically indicate that at temperatures below ~600°C, the lithosphere is strong and deforms in the brittle regime. However, recent novel experiments and dislocation mobility models have suggested that the lithosphere can undergo ductile deformation at relatively low temperatures (<600-800°C). Reconciling these experimental results with geodynamic models indicating that the generation and maintenance of plate boundaries requires a strong lithosphere remains a fundamental challenge for plate tectonic theory. Here, I present preliminary results using seismic anisotropy as a proxy for viscous strain to investigate how the lithosphere deforms at low temperatures around the Alpine Fault in South Island, New Zealand. Previous studies in this region have shown that viscous strain associated with relative motion across the Australia-Pacific plate boundary is accommodated in a zone up to 200 km wide, but have not been able to determine whether that deformation is occurring in the lithosphere or in the warmer asthenosphere due to limited spatial and/or depth resolution. I use existing data from GeoNet stations and a temporary ocean bottom seismometer deployment to calculate receiver functions with harmonic-percussive separation and dereverberation filters to mitigate high noise levels, and apply harmonic decomposition to constrain azimuthal anisotropy in the lithosphere-asthenosphere system across and around the South Island. Receiver functions provide information on local structure beneath each instrument, making it possible to map spatial variations in anisotropy attributed to viscous deformation around the Alpine Fault.
Session: Seismology in the Oceans: Pacific Hemisphere and Beyond - I
Type: Oral
Date: 5/2/2024
Presentation Time: 08:45 AM (local time)
Presenting Author: Hannah
Student Presenter: No
Invited Presentation:
Authors
Hannah Mark Presenting Author Corresponding Author hmark@whoi.edu Woods Hole Oceanographic Institution |
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Estimating the Extent of Low-temperature Ductile Deformation in the Lithosphere Using Seismic Anisotropy Measurements Around the Alpine Fault
Category
Seismology in the Oceans: Pacific Hemisphere and Beyond