4.7 Article

Near Trench 3D Seismic Attenuation Offshore Northern Hikurangi Subduction Margin, North Island, New Zealand

Journal

Publisher

AMER GEOPHYSICAL UNION
DOI: 10.1029/2020JB020810

Keywords

fluids; seismic attenuation; subduction zone

Funding

  1. NSF GRF, CIRES Research Award
  2. Ford Foundation Dissertation Fellowship
  3. CU Boulder Geological Sciences Thompson Fund Research Award
  4. NSF [EAR-PF 1725753, OCE 1551922, 1551758, 1333311, 1333025, 1332875, 1334654]
  5. National Science Foundation [NSF]
  6. EQC
  7. GNS Science
  8. LINZ
  9. Directorate For Geosciences [1332875] Funding Source: National Science Foundation
  10. Directorate For Geosciences
  11. Division Of Ocean Sciences [1334654, 1333025, 1333311] Funding Source: National Science Foundation
  12. Division Of Ocean Sciences [1332875] Funding Source: National Science Foundation
  13. Division Of Ocean Sciences
  14. Directorate For Geosciences [1551758] Funding Source: National Science Foundation

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Using seismometers on the ocean floor and on land, seismic attenuation near the Hikurangi trench offshore New Zealand was investigated. The study revealed high attenuation above a recurring shallow slow-slip event and within the subducting Hikurangi Plateau. The presence of high temperatures, melt, fluids, and fractures in the region was inferred through the analysis of seismic attenuation.
We image seismic attenuation near the Hikurangi trench offshore New Zealand, using ocean bottom and land-based seismometers, revealing high attenuation above a recurring shallow slow-slip event and within the subducting Hikurangi Plateau. The Hikurangi subduction margin east of the North Island, New Zealand is the site of frequent shallow slow slip events. Overpressured fluids are hypothesized to lead to slow slip at shallow depths close to the oceanic trench. Seismic attenuation, energy loss of seismic waves, can be used to detect high temperatures, melt, the presence of fluids, and fractures. We use local earthquake P- and S-waves from 180 earthquakes to invert for t*, and subsequently invert for Qp and Qs, offshore the North Island directly above the area of slow slip. We image Qp and Qs to similar to 25 km depth, increasing resolution of previously identified coastal low Q (100-300), and finding a new region of even higher attenuation (Qp and Qs < 50-100) directly above the shallow slow slip event of 2014-2015, beneath the offshore seismic array. This highest attenuation is downdip of a subducting seamount, and is spatially correlated with a high seismic reflectivity zone and Vp/Vs > 1.85, all of which provide evidence for the presence of fluids. The Qp and Qs is low at the trench (<50-100) and in the subducting plate (100-200), suggesting that seismic wave scattering due to faults, fractures, and the inherent heterogeneous composition of the Hikurangi Plateau, a large igneous province, plays a role in seismic attenuation.

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