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Spatiotemporal Evolution of Slow Slip Events at the Offshore Hikurangi Subduction Zone in 2019 using GNSS, InSAR, and seafloor geodetic data
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  • Katherine Woods,
  • Laura Wallace,
  • Charles A. Williams,
  • Ian James Hamling,
  • Spahr C Webb,
  • Yoshihiro Ito,
  • Neville Palmer,
  • Ryota Hino,
  • Syuichi Suzuki,
  • Martha Kane Savage,
  • Emily Warren-Smith,
  • Kimihiro Mochizuki
Katherine Woods
Victoria University of Wellington
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Laura Wallace
GEOMAR & Kiel University

Corresponding Author:lwallace@utexas.edu

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Charles A. Williams
GNS Science
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Ian James Hamling
GNS Science
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Spahr C Webb
Lamont Doherty Earth Observatory
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Yoshihiro Ito
Kyoto University
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Neville Palmer
GNS Science
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Ryota Hino
Tohoku University
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Syuichi Suzuki
Tohoku University
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Martha Kane Savage
Victoria University of Wellington
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Emily Warren-Smith
GNS Science
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Kimihiro Mochizuki
University of Tokyo
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Abstract

Detecting crustal deformation during transient deformation events at offshore subduction zones remains challenging. The spatiotemporal evolution of slow slip events (SSEs) on the offshore Hikurangi subduction zone, New Zealand, during February–July 2019, is revealed through a time-dependent inversion of onshore and offshore geodetic data that also account for spatially varying elastic crustal properties. Our model is constrained by seafloor pressure time series (as a proxy for vertical seafloor deformation), onshore continuous Global Navigation Satellite System (GNSS) data, and Interferometric Synthetic Aperture Radar (InSAR) displacements. Large GNSS displacements onshore and uplift of the seafloor (10-33 mm) require peak slip during the event of 150 to >200 mm at 6-12 km depth offshore Hawkes Bay and Gisborne, comparable to maximum slip observed during previous seafloor pressure deployments at north Hikurangi. The onshore and offshore data reveal a complex evolution of the SSE, over a period of months. Seafloor pressure data indicates the slow slip may have persisted longer near the trench than suggested by onshore GNSS stations in both the Gisborne and Hawkes Bay regions. Seafloor pressure data also reveal up-dip migration of SSE slip beneath Hawke Bay occurred over a period of a few weeks. The SSE source region appears to coincide with locations of the March 1947 Mw 7.0–7.1 tsunami earthquake offshore Gisborne and estimated Great earthquake rupture sources from paleoseismic investigations offshore Hawkes Bay, suggesting that the shallow megathrust at north and central Hikurangi is capable of both seismic and aseismic rupture.