Slow slip source characterized by lithological and geometric heterogeneity

Slow slip events (SSEs) accommodate a significant proportion of tectonic plate motion at subduction zones, yet little is known about the faults that actually host them. The shallow depth (<2 km) of well-documented SSEs at the Hikurangi subduction zone offshore New Zealand offers a unique opportunity to link geophysical imaging of the subduction zone with direct access to incoming material that represents the megathrust fault rocks hosting slow slip. Two recent International Ocean Discovery Program Expeditions sampled this incoming material before it is entrained immediately down-dip along the shallow plate interface. Drilling results, tied to regional seismic reflection images, reveal heterogeneous lithologies with highly variable physical properties entering the SSE source region. These observations suggest that SSEs and associated slow earthquake phenomena are promoted by lithological, mechanical, and frictional heterogeneity within the fault zone, enhanced by geometric complexity associated with subduction of rough crust

International ocean discovery program expedition 372 preliminary report creeping gas hydrate slides and Hikurangi LWD

International Ocean Discovery Program (IODP) Expedition 372 combined two research topics, slow slip events (SSEs) on subduction faults (IODP Proposal 781A-Full) and actively deforming gas hydrate-bearing landslides (IODP Proposal 841-APL). Our study area on the Hikurangi margin, east of the coast of New Zealand, provided unique locations for addressing both research topics.SSEs at subduction zones are an enigmatic form of creeping fault behavior. They typically occur on subduction zones at depths beyond the capabilities of ocean floor drilling. However, at the northern Hikurangi subduction margin they are among the best-documented and shallowest on Earth. Here, SSEs may extend close to the trench, where clastic and pelagic sediments about 1.0-1.5 km thick overlie the subducting, seamount-studded Hikurangi Plateau. Geodetic data show that these SSEs recur about every 2 years and are associated with measurable seafloor displacement. The northern Hikurangi subduction margin thus provides an excellent setting to use IODP capabilities to discern the mechanisms behind slow slip fault behaviour

Physical properties and gas hydrate at a near‐seafloor thrust fault, hikurangi margin, New Zealand

The Pāpaku Fault Zone, drilled at International Ocean Discovery Program (IODP) Site U1518, is an active splay fault in the frontal accretionary wedge of the Hikurangi Margin. In logging‐while‐drilling data, the 33‐m‐thick fault zone exhibits mixed modes of deformation associated with a trend of downward decreasing density, P‐wave velocity, and resistivity. Methane hydrate is observed from ~30 to 585 m below seafloor (mbsf), including within and surrounding the fault zone. Hydrate accumulations are vertically discontinuous and occur throughout the entire logged section at low to moderate saturation in silty and sandy centimeter‐thick layers. We argue that the hydrate distribution implies that the methane is not sourced from fluid flow along the fault but instead by local diffusion. This, combined with geophysical observations and geochemical measurements from Site U1518, suggests that the fault is not a focused migration pathway for deeply sourced fluids and that the near‐seafloor Pāpaku Fault Zone has little to no active fluid flow

Direct measurement of in situ methane quantities in a large gas-hydrate reservoir

Certain gases can combine with water to form solids-gas hydrates-that are stable at high pressures and low temperatures(1,2), Conditions appropriate for gas-hydrate formation exist in many marine sediments where there is a supply of methane, Seismic reflection profiles across continental margins indicate the frequent occurrence of gas hydrate within the upper few hundred metres of sea-floor sediments, overlying deeper zones containing bubbles of free gas(3-9), If large volumes of methane are stored in these reservoirs, outgassing may play an important role during climate change(10-12), Gas hydrates in oceanic sediments may in fact comprise the Earth's largest fossil-fuel reservoir(2,13). But the amount of methane stored in gas-hydrate and free-gas zones is poorly constrained(2-9,13-18). Here we report the direct measurement of in situ methane abundances stored as gas hydrate and free gas in a sediment sequence from the Blake ridge, western Atlantic Ocean, Our results indicate the presence of substantial quantities of methane (similar to 15 GT of carbon) stored as solid gas hydrate, with an equivalent or greater amount occurring as bubbles of free gas in the sediments below the hydrate zone.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62828/1/385426a0.pd

Technology in Marine Geosciences

This chapter describes the most commonly used technologies and instruments for observing and sampling in the field of marine geosciences and refers to a number of special papers within this encyclopedia and beyond. This chapter is meant as an introduction showing the variability and broad scale of intruments being used. Since technology is a vast and rapidly changing field, numerous specific instruments used throughout marine geoscience are undouptfully missing in this compilation