The structure of the oceanic Moho discontinuity on the Northeast Hawaiian Arch imaged by Pre-Stack Depth Migration of active-source seismic data

The Northeast Hawaiian Arch off O'ahu, formed by the flexure of the Pacific Plate under the load of the Hawaiian volcanic island chain, is one of the regions under consideration for IODP drilling through the oceanic crust to the Mohorovičić discontinuity (Moho). To image the oceanic crustal structure and determine whether the region is affected by the flexural bending or associated young volcanism, the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) carried out an active source 2-D seismic reflection survey along the Hawaiian Arch using R/V Kairei in August and September 2017. One 750-km-long ENE-WSW reflection profile, shot perpendicular to abyssal hill (spreading) fabric passes over five ocean bottom seismometers (OBS) with 150-km interval; three shorter NNW-SSE profiles were shot perpendicular to the long line at OBS locations. Shots from a 7,800 cu.in tuned airgun array were received by 6-km-long streamer cable. The bathymetry is low relief with some small seamounts. Post-stack time migrations (Ohira et al., 2018) showed that the crustal thickness was typical for oceanic crust of Cretaceous age, but the Moho reflection was discontinuous. We conducted pre-stack depth migration (PSDM) in an attempt to better image the Moho reflection. The PSDM images confirm that the crustal thickness is 6 km illustrate that thickness of Moho is approximately 6 km below the basement reflection with local depth variations. Moho reflectivity is still discontinuous and diffuse along the profiles, but the PSDM images are somewhat sharper. Southward-dipping mid-crustal reflectors are also in the N-S lines. The trend of Moho depth is parallel to seafloor and we find no evidence to support magmatic underplating has influence on the Moho along NE Hawaiian Arch.