1. Spatiotemporal Evolution of Slow Slip Events at the Offshore Hikurangi Subduction Zone in 2019 Using GNSS, InSAR, and Seafloor Geodetic Data.
- Author
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Woods, K., Wallace, L. M., Williams, C. A., Hamling, I. J., Webb, S. C., Ito, Y., Palmer, N., Hino, R., Suzuki, S., Savage, M. K., Warren‐Smith, E., and Mochizuki, K.
- Subjects
SLOW earthquakes ,GLOBAL Positioning System ,SUBDUCTION ,SYNTHETIC aperture radar ,PLATE tectonics - 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 accounts 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 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. Plain Language Summary: Subduction zones, where one tectonic plate dives beneath another, generate the planet's largest earthquakes. They also host an important mode of fault slip called "slow slip events (SSEs)," which are essentially earthquakes in slow motion. The Hikurangi subduction zone, where the Pacific Plate subducts beneath New Zealand hosts large and frequent SSEs near the trench, where the plate boundary emerges at the seabed, requiring seafloor instrumentation to investigate them. Seafloor pressure measurements can track centimeter‐level up or down movement of the seafloor during slow slip, and reveal offshore displacement during a large 2019 SSE at the Hikurangi subduction zone. The 2019 event involved substantial migration, beginning at ∼15 km depth, and expanding to the trench over a period of several weeks. We also show that the same areas which have ruptured in previous seismic earthquakes (that involved faster slip) can also rupture slowly, in SSEs. This raises the possibility that regions where we currently observe SSEs could also produce seismic events. This result also demands that more work must be done to understand the physical processes that enable the same part of a fault to rupture both fast and slow at different times. Key Points: Central Hikurangi slow slip events (SSEs) propagate up‐dip over a period of weeks to monthsSeafloor geodetic data reveal that shallow SSEs may last longer than onshore Global Navigation Satellite System data suggestThe same portions of a shallow megathrust can host both large seismic and aseismic rupture [ABSTRACT FROM AUTHOR]
- Published
- 2024
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