Abstract
Slow slip events (SSEs) at the northern Hikurangi subduction
margin, New Zealand, are among the best-documented shallow
SSEs on Earth. International Ocean Discovery Program Expedition
375 was undertaken to investigate the processes and in situ conditions that underlie subduction zone SSEs at the northern Hikurangi
Trough by (1) coring at four sites, including an active fault near the
deformation front, the upper plate above the high-slip SSE source
region, and the incoming sedimentary succession in the Hikurangi
Trough and atop the Tūranganui Knoll Seamount, and (2) installing
borehole observatories in an active thrust near the deformation
front and in the upper plate overlying the slow slip source region.
Logging-while-drilling (LWD) data for this project were acquired as
part of Expedition 372 (26 November 2017–4 January 2018; see the
Expedition 372 Preliminary Report for further details on the LWD
acquisition program).
Northern Hikurangi subduction margin SSEs recur every 1–2
years and thus provide an ideal opportunity to monitor deformation
and associated changes in chemical and physical properties
throughout the slow slip cycle. Sampling of material from the sedimentary section and oceanic basement of the subducting plate reveals the rock properties, composition, lithology, and structural
character of material that is transported downdip into the SSE
source region. A recent seafloor geodetic experiment raises the possibility that SSEs at northern Hikurangi may propagate all the way
to the trench, indicating that the shallow thrust fault zone targeted
during Expedition 375 may also lie in the SSE rupture area. Hence,
sampling at this location provides insights into the composition,
physical properties, and architecture of a shallow fault that may host
slow slip.
Expedition 375 (together with the Hikurangi subduction LWD
component of Expedition 372) was designed to address three fundamental scientific objectives: (1) characterize the state and composition of the incoming plate and shallow plate boundary fault near the
trench, which comprise the protolith and initial conditions for fault
zone rock at greater depth and which may itself host shallow slow
slip; (2) characterize material properties, thermal regime, and stress
conditions in the upper plate above the core of the SSE source region; and (3) install observatories at an active thrust near the deformation front and in the upper plate above the SSE source to
measure temporal variations in deformation, temperature, and fluid
flow. The observatories will monitor volumetric strain (via pore
pressure as a proxy) and the evolution of physical, hydrological, and
chemical properties throughout the SSE cycle. Together, the coring,
logging, and observatory data will test a suite of hypotheses about
the fundamental mechanics and behavior of SSEs and their relationship to great earthquakes along the subduction interface.
margin, New Zealand, are among the best-documented shallow
SSEs on Earth. International Ocean Discovery Program Expedition
375 was undertaken to investigate the processes and in situ conditions that underlie subduction zone SSEs at the northern Hikurangi
Trough by (1) coring at four sites, including an active fault near the
deformation front, the upper plate above the high-slip SSE source
region, and the incoming sedimentary succession in the Hikurangi
Trough and atop the Tūranganui Knoll Seamount, and (2) installing
borehole observatories in an active thrust near the deformation
front and in the upper plate overlying the slow slip source region.
Logging-while-drilling (LWD) data for this project were acquired as
part of Expedition 372 (26 November 2017–4 January 2018; see the
Expedition 372 Preliminary Report for further details on the LWD
acquisition program).
Northern Hikurangi subduction margin SSEs recur every 1–2
years and thus provide an ideal opportunity to monitor deformation
and associated changes in chemical and physical properties
throughout the slow slip cycle. Sampling of material from the sedimentary section and oceanic basement of the subducting plate reveals the rock properties, composition, lithology, and structural
character of material that is transported downdip into the SSE
source region. A recent seafloor geodetic experiment raises the possibility that SSEs at northern Hikurangi may propagate all the way
to the trench, indicating that the shallow thrust fault zone targeted
during Expedition 375 may also lie in the SSE rupture area. Hence,
sampling at this location provides insights into the composition,
physical properties, and architecture of a shallow fault that may host
slow slip.
Expedition 375 (together with the Hikurangi subduction LWD
component of Expedition 372) was designed to address three fundamental scientific objectives: (1) characterize the state and composition of the incoming plate and shallow plate boundary fault near the
trench, which comprise the protolith and initial conditions for fault
zone rock at greater depth and which may itself host shallow slow
slip; (2) characterize material properties, thermal regime, and stress
conditions in the upper plate above the core of the SSE source region; and (3) install observatories at an active thrust near the deformation front and in the upper plate above the SSE source to
measure temporal variations in deformation, temperature, and fluid
flow. The observatories will monitor volumetric strain (via pore
pressure as a proxy) and the evolution of physical, hydrological, and
chemical properties throughout the SSE cycle. Together, the coring,
logging, and observatory data will test a suite of hypotheses about
the fundamental mechanics and behavior of SSEs and their relationship to great earthquakes along the subduction interface.
Original language | English |
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Publisher | International Ocean Discovery Program (IODP) |
Number of pages | 38 |
ISBN (Electronic) | 2372-9562 |
DOIs | |
Publication status | Published - 2019 |