Elastic moduli and physical properties of fault rock and protolith associated with SSEs at the Northern Hikurangi margin, NZ

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http://abstractsearch.agu.org/meetings/2018/FM/T54C-04.html
Author(s): Saffer, Demian M.; Bell, Rebecca E.; Barnes, Philip; Wallace, Laura M.; Kitajima, Hiroko; Moore, Gregory F.; Han, Shuoshuo; Pecher, Ingo Andreas; Petronotis, Katerina E.; LeVay, Leah J.
International Ocean Discovery Program (IODP), Expedition 372 Scientists
Author Affiliation(s): Primary:
Pennsylvania State University, Department of Geosciences, University Park, PA, United States
Other:
Imperial College London, United Kingdom
National Institute of Water & Atmospheric Research, New Zealand
University of Texas at Austin, United States
Texas A&M University, United States
University of Hawaii at Manoa, United States
Columbia University, United States
University of Auckland, New Zealand
International Ocean Discovery Program, United States
Volume Title: AGU 2018 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2018; American Geophysical Union 2018 fall meeting, Washington, DC, Dec. 10-14, 2018. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: International Ocean Discovery Program (IODP) Expeditions 372 and 375 focused on investigating recurring shallow (<2-15 km) slow slip events (SSE) at the N. Hikurangi subduction margin through ocean drilling. The two expeditions conducted a coordinated program of logging while drilling, coring, and borehole observatory installation along a transect of drill sites. These include a borehole that crosses an active thrust splay fault that has accommodated km of displacement and lies in the region where SSEs may propagate near to the seafloor (Site U1518); and two sites that sampled the incoming sedimentary succession. The "inputs" sites include a borehole (Site U1520) in the Hikurangi Trough that sampled a Cretaceous to Pliocene sequence of volcaniclastic sediments and pelagic carbonates overlain by a Quaternary trench wedge; and a site (U1526) on Turanganui Knoll seamount that sampled a volcaniclastic sequence overlain by a thin pelagic sediment cover. Here, we report on the rock physical properties measured by logging and on core samples, focusing on trends spanning the fault and within the pelagic and volcaniclastic portions of the sedimentary sequence, which comprise the protolith for the fault zone in the deeper SSE source region We find that the thrust splay fault zone is more compliant than the surrounding sediment, and characterized by a tens of m-wide zone of decreased elastic moduli and density. The low fault stiffness, in tandem with fault frictional properties, may play a role in driving an otherwise creeping fault toward transitional slip behavior and conditional stability that could promote SSE. We also find that the incoming sediments exhibit a wide range of shear and bulk moduli, density, and porosity. In particular, the volcaniclastic sequence exhibits large variations in properties (P-wave velocities ranging from ∼2 to ∼6 km/s and porosity from <20% to >40%) over length scales less than 1 m, likely related to variations in cementation. This variation is consistent with the observed high-amplitude seismic reflectivity of incoming and subducted sediments. The extreme heterogeneity in physical properties, particularly over such short length scales, should lead to a plate interface and surrounding deformation zone characterized by highly variable rheologies that would promote emergent slow slip.
Year of Publication: 2018
Research Program: IODP Integrated Ocean Drilling Program
IODP2 International Ocean Discovery Program
Key Words: 18 Geophysics, Solid-Earth; Australasia; Crust; Elastic constants; Expedition 375; Fault zones; Faults; Hikurangi Margin; Hikurangi Trough; IODP Site U1518; IODP Site U1520; IODP Site U1526; International Ocean Discovery Program; Lithosphere; New Zealand; Oceanic crust; Oceanic lithosphere; Pacific Ocean; Physical properties; Seismicity; Seismotectonics; South Pacific; Southwest Pacific; Tectonics; West Pacific
Coordinates: S385133 S385133 E1785346 E1785346
S385810 S385810 E1790756 E1790756
S390119 S390119 E1791445 E1791445
Record ID: 2019050447
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