Fluid pressurisation and earthquake propagation in the Hikurangi subduction zone

Abstract

In subduction zones, seismic slip at shallow crustal depths can lead to the generation of tsunamis. Large slip displacements during tsunamogenic earthquakes are attributed to the low coseismic shear strength of the fluid-saturated and non-lithified clay-rich fault rocks. However, because of experimental challenges in confining these materials, the physical processes responsible for the coseismic reduction in fault shear strength are poorly understood. Using a novel experimental setup, we measured pore fluid pressure during simulated seismic slip in clay-rich materials sampled from the deep oceanic drilling of the Pāpaku thrust (Hikurangi subduction zone, New Zealand). Here, we show that at seismic velocity, shear-induced dilatancy is followed by pressurisation of fluids. The thermal and mechanical pressurisation of fluids, enhanced by the low permeability of the fault, reduces the energy required to propagate earthquake rupture. We suggest that fluid-saturated clay-rich sediments, occurring at shallow depth in subduction zones, can promote earthquake rupture propagation and slip because of their low permeability and tendency to pressurise when sheared at seismic slip velocities.

Evidence of Seismic Slip on a Large Splay Fault in the Hikurangi Subduction Zone

“…Because friction evolves with sliding over some thermal weakening distance, we calculate the average friction as a function of displacement. To do this, we calculate friction at each point ( n = 1,000) during an event's total displacement using peak and steady‐state friction values derived from experiments on samples from the turbidite sequences surrounding the Pāpaku fault (Aretusini et al., 2021; Di Toro et al., 2011; Seyler et al., 2020). Larger displacements are associated with lower average friction as these events spend more time sliding at a lower, dynamically weakened friction (see Methods in the supporting information).…”

GEOLOGY WITHOUT BORDERS - 90° Congresso della Società Geologica Italiana

“…In 1997, Tsutsumi & Shimamoto reported the first data of dynamic fault strength in cohesive rocks at seismic slip rates: this study opened a new era in experimental rock deformation. Several fault dynamic weakening mechanisms first proposed theoretically (i.e., frictional melting lubrication and, more recently, fluid thermo-mechanical pressurization and elastohydrodynamic lubrication), were eventually reproduced in the laboratory (e.g., Aretusini et al, 2021). These experiments allowed us also to explore new dynamic fault weakening mechanisms and other will be probably discovered in the future.…”

“…This allow us to hypothesize how earthquake propagation could be easier in a lithology under a specific hydration state (Vannucchi et al, 2017). Moreover, the experiments constrain the physical processes controlling fault weakening thanks to direct measurements of temperature, pressure and shear stress (Aretusini et al, 2021). Finally, these experiments provide a parametric basis for modelling the earthquake propagation during megathrust earthquakes (Murphy et al, 2018).…”

“…In this scenario, although the mechanisms controlling the nature of slip as well as the relationships between rock physical properties, fault zone composition and fault slip behavior remain undiscovered, several Authors (e.g. Aretusini et al, 2021) suggest that in the shallow part of the subduction zone a key role can be played by the frictional properties of the clay and therefore by the clay content.…”

Deep submarine infiltration of altered geothermal groundwater on the south Chilean Margin

“…Locally, our depth estimates for the Aysén geothermal reservoir may be of particular interest for efforts to harness geothermal energy for societal consumption. Globally, freshening in over pressurized accreted sediments on active margins can influence the mechanics of shallow-slip tectonism and potentially contribute to mega-thrust earthquakes that are commonly experienced in Chile and elsewhere 45 . Indeed, similar links between meteoric freshening and tectonism may operate on the Cascadia, Nankai, and Okhotsk margins, where meteorically altered geothermal groundwaters 46,47 and pore water trends similar to J1003 48,49 have been reported.…”