Is the Northern Hikurangi Plateau Well Hydrated? Insights from 2D Streamer Tomography and Reflection Imaging
Jackie Harris, University of Washington
Andrew Gase, Boise State University
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Abstract
Elevated pore fluid pressure resulting from the underthrusting of fluid-rich sediments and volcanic basement is commonly cited as a cause of recurring shallow slow-slip at the northern Hikurangi Margin. Although high fluid content in subducting volcaniclastics has been confirmed through drilling, 3D seismic surveying, and electromagnetic surveying on a small portion of the margin, additional analyses are required to generalize this finding to a broader segment of the subduction margin and the Hikurangi Plateau. I perform seismic travel-time tomography on a >100 km-long seismic profile using multi-channel seismic and ocean-bottom seismic data to test whether the northern Hikurangi Plateau has uniformly high hydration. Additionally, I process a reflection image for this seismic line to compare the structure of the plateau to that of ``normal'' oceanic crust. These data show that the upper $\sim$2 km of the Hikurangi Plateau basement have P-wave velocities between 3.0 and 4.5 km/s, which is significantly slower than that of oceanic crust in other subduction zone settings (4.0-6.5 km/s). These slow velocities suggest that the crust of the Hikurangi Plateau is a km-scale fluid reservoir and a dominant source of subducted fluids at the northern Hikurangi Margin. I also find that the basement of the northern Hikurangi Plateau has many bright, laterally continuous reflectors and poor evidence for persistent normal faulting, implying that the high water content of the plateau is related to its formation.