Imaging the shallow subsurface structure of the North Hikurangi subduction zone, New Zealand, using 2-D full-waveform inversion

The northern Hikurangi plate boundary fault hosts a range of seismic behaviors, of which the physical mechanisms controlling seismicity are poorly understood, but often related to high pore fluid pressures and conditionally stable frictional conditions. Using 2D marine seismic streamer data, we employ full-waveform inversion (FWI) to obtain a high-resolution 2D P-wave velocity model across the Hikurangi margin down to depths of ~2 km. The validity of the FWI velocity model is investigated through comparison with the pre-stack depth migrated seismic reflection image, sonic well data, and the match between observed and synthetic waveforms. Our model reveals the shallow structure of the overriding plate, including the fault plumbing system above the zone of SSEs to theoretical resolution of a half seismic wavelength. We find that the hanging walls of thrust faults often have substantially higher velocities than footwalls, consistent with higher compaction. In some cases, intra-wedge faults identified from reflection data are associated with low-velocity anomalies, which may suggest they are high-porosity zones acting as conduits for fluid flow. The continuity of velocity structure away from IODP drill site U1520 suggests that lithological variations in the incoming sedimentary stratigraphy observed at this site continue to the deformation front and are likely important in controlling seismic behavior. This investigation provides a high-resolution insight into the shallow parts of subduction zones, which shows promise for the extension of modeling to 3D using a recently-acquired, longer-offset, seismic dataset

Late Miocene thorugh Pliocene diatoms from Integrated Ocean Drilling Program Site U1361 off Wilkes Land, East Antarctica

第3回極域科学シンポジウム　横断セッション「海・陸・氷床から探る後期新生代の南極寒冷圏環境変動」11月26日（月）、27日（火） ２階ラウン

IODP Expedition 317: Exploring the Record of Sea-Level Change Off New Zealand

Expedition 317 investigated the record of global sea-level change (eustasy) within continental margin sedimentary to produce preserved sedimentary architectures. The Canterbury Basin, on the eastern margin of the South Island because of high rates of Neogene sediment supply from the uplifting Southern Alps. This sediment input results in a high-frequency (~0.1–0.5 My periods) record of depositional cyclicity that is modulated by the presence of strong ocean currents. The expedition recovered sediments as old as Eocene but focused on the sequence stratigraphy of the late Miocene to Recent, when global sea-level change was dominated by glacioeustasy. A transect of three sites was drilled on the continental shelf (Sites U1353, U1354, and U1351), plus one on the continental slope (Site U1352). The transect samples the shallow-water environment most directly affected by relative sea-level change. Lithologic boundaries, provisionally correlative with seismic sequence boundaries, have been identified in cores from each site. Continental slope Site U1352 provides a record of ocean circulation and fronts during the last ~35 My. The early Oligocene (~30 Ma) Marshall Paraconformity was the deepest target of Expedition 317 and is hypothesized to represent intensified current erosion or non-deposition associated with the initiation of thermohaline circulation in the region. Expedition 317 involved operational challenges for JOIDES Resolution, including shallow-water, continental-shelf drilling and deep penetrations. Despite these challenges, Expedition 317 set a number of records for scientific ocean drilling penetration and water-depth.ArticleScientific Drilling. 12:4-14 (2011)journal articl

Drilling Challenger Mound (Porcupine Basin,W of Ireland): a contribution to European research on the microbial mediation in carbonate formation at low temperatures?

In his monumental master work ‘The Face of the Earth’, the eminent Vienna geologist Eduard Suess has formulated visionary thoughts on fundamental topics ranging from the tectonic nature of Europe’s margins to the role of the ‘Biosphere’, a word that he had coined in 1875. This word turned into a concept of Life as a Geological Force through the vision of Vladimir I. Vernadksy (Biosfera, 1920). Recent studies (Vasconselos et al. 1995) have unveiled the possible role of microbial mediation in the formation of natural dolomite, a mineral named after Déodat de Dolomieu (1750-1801).But some of the most spectacular geological bodies, built by Life as a Geological Force, are the carbonate mounds. Carbonate mounds from the fossil record provide evidence of microbial mediation in the mound build-up and stabilization (Henriet et al. 2002). The study of carbonate mounds and associated cold-water coral reefs forms one of the first priorities of IOC/UNESCO’s new programme “Geosphere-Biosphere Coupling Processes” (GBCP).IODP Expedition 307 (Modern Carbonate Mounds: Porcupine Drilling) sets sail end of April, 2005 to the Porcupine Seabight, West of Ireland, to investigate the possible role of geofluids, microbial consortia and cold-water corals in the genesis and growth of Challenger mound, a giant carbonate mound towering over 170m above an enigmatic erosional surface, in water depths close to 1000m

IODP Expedition 323—Pliocene and Pleistocene Paleoceanographic Changes in the Bering Sea

High-resolution paleoceanography of the Plio-Pleistocene is important in understanding climate forcing mechanisms and the associated environmental changes. This is particularly true in high-latitude marginal seas such as the Bering Sea, which has been very sensitive to changes in global climate during interglacial and glacial or Milankovitch time scales. This is due to significant changes in water circulation, land-ocean interaction, and sea-ice formation. With theaim to reveal the climate and oceanographic history of the Bering Sea over the past 5 Ma, Integrated Ocean Drilling Program (IODP) Expedition 323 cored a total of 5741 meters of sediment (97.4% recovery) at seven sites covering three different areas: Umnak Plateau, Bowers Ridge, and the Bering slope region. Four deep holes range from 600 m to 745 m spanning in age from 1.9 Ma to 5 Ma. The water depths (819 m to 3173 m) allow characterization of past verticalwater mass distribution such as the oxygen minimum zone (OMZ). The results highlight three key points. (1) The first is an understanding of long-term evolution of surface-water mass distribution during the past 5 Ma including past sea-ice distribution and warm and less eutrophic subarctic Pacific water mass entry into the Bering Sea. (2) We characterized relatively stagnant intermediate water mass distribution imprinted as laminated sediment intervals that have beenubiquitously encountered. Today, the OMZ impinges upon the sediments at ~700–1600 m water depths. In the past, the OMZ appears to have occurred mainly during interglacial periods. Changes in low oxygen-tolerant benthic foraminiferal faunas clearly concur with this observation. (3) We also characterized significant changes between glacial episode of terrigenous sedimentary supply and interglacialepisode of diatom flux

IODP Expedition 333: Return to Nankai Trough Subduction Inputs Sites and Coring of Mass Transport Deposits

Integrated Ocean Drilling Program (IODP) Expedition 333 returned to two sites drilled during IODP Expedition 322 on the ocean side of the Nankai Trough to pursue the characterization of the inputs to the Nankai subduction and seismogenic zone, as part of the Nankai Trough Seismogenic Experiment (NanTroSEIZE) multi-expedition project. SiteC0011 is located at the seaward edge of the trench and Site C0012 on a basement high, Kashinozaki Knoll (Fig. 1). The main objectives of drilling again at these sites were to fill coring gaps in the upper part (<350 m) of the sedimentary sequence, to measure heat flow, and to core the oceanic basement to a greater depth on the Knoll. New results include the observation of a diagenetic boundary within the Shikoku Basin sediments that may be compared to one documented further west by ODP Legs 131, 190 and 196 but occurs here at a lower temperature. Borehole heat flow measurements confirm spatial variations in the Shikoku Basin that were indicated by short probe surveys. Heat flow variations between topographic highs and lows may be related to fluid convection within the basement. This expedition also included the objectives of the Nankai Trough Submarine LandSLIDEhistory (NanTroSLIDE) Ancillary Project Letter (APL) and cored at Site C0018 a pile of mass transport deposits on the footwall of the megasplay fault, a major out of sequence thrust that presumably slips coseismically during large subduction earthquakes. This brought newinsight on the timing of these mass wasting events and on the deformation within the sliding slope sediments

Rhizon Sampling of Pore Waters on Scientific Drilling Expeditions: An Example from the IODP Expedition 302, Arctic Coring Expedition (ACEX)

No abstract available. doi:10.2204/iodp.sd.4.08.2007</a