Signatures of brittle deformation in a shallow fault in the Hikurangi subduction margin

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Author(s): Savage, Heather M.; Coffey, Genevieve L.; Shreedharan, Srisharan; Polissar, Pratigya J.; Fagereng, Ake; Meneghini, Francesca; Morgan, Julia; Wang Maomao; Hashimoto, Yoshitaka; Wallace, Laura M.; Saffer, Demian M.; Barnes, Philip; Pecher, Ingo Andreas; Petronotis, Katerina E.; LeVay, Leah J.
International Ocean Discovery Program (IODP), Expedition 372 Scientists
Author Affiliation(s): Primary:
Columbia University of New York, Palisades, NY, United States
University of Otago, New Zealand
Pennsylvania State University, United States
Lamont-Doherty Earth Observatory, United States
University of Cape Town, South Africa
University of Pisa, Italy
Rice University, United States
Nanjing University, China
University of Kochi, Japan
University of Texas at Austin, United States
National Institute of Water & Atmospheric Research, New Zealand
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) Expedition 375 cored a shallow subduction splay fault near the deformation front at the northern Hikurangi margin, a region that is known to host both shallow slow slip and tsunamigenic earthquakes. At the drill site (Site U1518), structures within the fault show a mix of brittle and ductile deformation, including fracturing, brecciation and flow banding. Here we use two different techniques to characterize the brittle behavior of the fault. First, we explore whether there is any evidence of earthquake slip within the core. Because earthquakes produce frictional heat over short time periods, earthquake slip leaves indelible evidence of temperature rise. For instance, the molecular composition of organic matter is systematically altered when exposed to an increase in temperature. We compare thermal maturity of organic matter within the fault to the surrounding damage zone, as well as to protoliths for the fault rocks that were sampled by drilling on the subducting plate at IODP Site U1520. Areas of localized thermal maturity indicate where earthquakes (rapid slip) may have propagated along the fault. Second, we quantify the fracture density within the fault and surrounding damage zone through linear fracture counting on digital images of the cores. The deformation is asymmetric, with the hanging wall dominated by fracturing and the footwall behaving more ductilely. The decrease in fracture density away from faults can commonly be described by a power law decay. The splay fault at Hikurangi shows a similar pattern, although the decay in fracture density occurs more rapidly in the footwall than the hanging wall, which could reflect differences in material properties. Together, these observations provide insight into the distribution of possible dynamic slip and associated damage along the fault.
Year of Publication: 2018
Research Program: IODP2 International Ocean Discovery Program
Key Words: 18 Geophysics, Solid-Earth; Brittleness; Crust; Deformation; Expedition 375; Fault zones; Faults; Hikurangi Margin; International Ocean Discovery Program; Lithosphere; Oceanic crust; Oceanic lithosphere; Pacific Ocean; Plate tectonics; South Pacific; Southwest Pacific; Subduction; Subduction zones; Tectonics; West Pacific
Coordinates: S390300 S384100 E1791600 E1783500
Record ID: 2019050434
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