Page 18 - GeoPRISMS_Newsletter_Spring2018_Neat

Slow slip

NW North Tuaheni Frontal accretionary SE
0 U1519 Basin wedge Tūranganui Knoll
2 U1518 Hikurangi Trough U1520 U1526
Depth (km) 4 6

8 interplate thrust
1947 tsunami
10 earthquake
10 km VE = 2
Figure 3. Seismic reflection profile crossing the HIkurangi drilling transect showing locations of IODP sites. Red lines highlight recently active thrust
faults. Black lines highlight older, inactive faults. Interpretation is simplified from Pecher et al. (2018). See Figure 1 for position of trackline.

The RAB data also document borehole breakouts, providing information about the
orientations of maximum and minimum horizontal stresses. Those data will be used, in
combination with rock strength measurements, to estimate horizontal stress magnitudes
(e.g., Chang et al., 2010; Huffman & Saffer, 2016).
Cores from Site U1520 on the subducting Pacific Plate will reveal the rock properties,
composition, and lithologic and structural character of sedimentary and volcanic
materials that are eventually subducted down-dip into the SSE source region. Those tests
Photo by Tim Fulton, IODP-TAMU heating within and beneath the accretionary prism. Samples of the inputs will also be used
will pinpoint the “initial conditions” for key lithologies prior to progressive loading and
for laboratory experiments to inform numerical models that predict evolving physical
and chemical properties. Samples will be measured for elastic and physical properties.
Analyses of pore-fluid chemistry will help identify the source regions of fluids and
assess whether fluids from greater depths are flowing upward and discharging through
the fractured hanging wall (e.g., Hensen et al., 2004; Ranero et al., 2008). Downhole
temperature measurements will constrain thermal models and help elucidate potential
connections among fault slip behavior, fluid production, and diagenetic/metamorphic
dehydration reactions (e.g., Saffer et al., 2008).
The two observatories will monitor volumetric strain (using pore pressure as a proxy),
as well as the evolution of physical, hydrological, and chemical properties throughout
multiple SSE cycles.

Shipboard activities during IODP
Expedition 375. Scientists carefully
examining a split core from the
main fault zone at Site U1518; IODP
personnel working on one of the
CORK heads at the moon-pool level of
JOIDES Resolution. JOIDES Resolution
Photo by D. Saffer prior to departure.
at the dock in Timura, New Zealand,

Photo by Tim Fulton, IODP-TAMU

18 • GeoPRISMS Newsletter Issue No. 40 Spring 2018