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Report from the Field




























                         HT-RESIST

                         Hikurangi Trench Regional


                         Ectromagnetic Survey to


                         Image the Subduction Thrust





                         Christine Chesley with Samer Naif and Kerry Key
                         LDEO, Columbia University










                               ecause New Zealand’s north island lies at the juncture between the converging
                               Pacific and Indo-Australian plates, it is not surprising that the area experiences
                         Bearthquakes. A unique feature of the Hikurangi margin, the name of New
                         Zealand’s subduction zone, is that its earthquake slip behavior varies from north to south
                         along strike. The northern Hikurangi margin is characterized by shallow slow slip events
                         (SSEs) and weak seismic coupling while the southern margin exhibits deeper SSEs and
                         stronger coupling. The host of other properties that change along this subduction zone
                         have motivated the question, “What controls the along-strike variation in megathrust
                         behavior at the Hikurangi margin?”

                         One key element of this question lies in quantifying the porosity and fluid budget along
                         the margin. Marine electromagnetic (EM) methods are well-suited for imaging fluids
                         and fluid pathways within the lithosphere. Of course, a major caveat to any geophysical
                         survey of convergent margins is the challenge of collecting good data on the seafloor
                         beneath a deep ocean. So that is what we set out to do on 16 December 2018.
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