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Investigation of Phase-Converted Seismic Waves at the Hikurangi Plate Interface, New Zealand
  • Mel Zhang,
  • Anne Sheehan,
  • Jefferson Yarce
Mel Zhang
University of Colorado Boulder

Corresponding Author:[email protected]

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Anne Sheehan
University of Colorado at Boulder
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Jefferson Yarce
University of Colorado at Boulder
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In the northern Hikurangi margin, aseismic slip events known as slow slip events (SSEs) occur approximately every 18-24 months with a long duration (weeks to months), and have been shown to cause 1 to 3 cm of horizontal surface displacement onshore and 1.5 to 5.4 cm of vertical displacement (uplift) offshore. The discovery of SSEs has expanded our scientific understanding of slip behavior at subduction zones to encompass behaviors beyond earthquake-producing (fast) slip events. Using converted phase seismic signals from local earthquakes in addition to direct P and S arrivals allows us to further analyze the properties of the plate interface along the subduction zone, including its composition, ­topography and heterogeneity. It has been hypothesized that these properties play a role in the process of slow slip, therefore our investigation of converted waves focuses on the area offshore the east coast of the North Island of New Zealand, where dozens of SSEs have been observed in the past twenty years. We examine an earthquake catalog comprised of local slab earthquakes occurring recorded on ocean-bottom seismometers (OBSs) from the one-year-long Hikurangi Ocean Bottom Investigation of Tremor and Slow Slip (HOBITSS) experiment as well as New Zealand’s permanent GeoNet on-land seismic network. Preliminary findings indicate strong secondary arrivals on the vertical component of the land stations which are likely Sp conversions from the plate interface. We aim to identify conversions from the plate interface on the OBSs from the HOBITSS experiment, as these data will help us resolve a part of the plate interface that was not investigated in previous converted wave studies. We will conduct a systematic search for phase-converted arrivals from the plate interface, initially focusing primarily on Sp conversions by examining the vertical component seismograms.