Fluid pressurisation and earthquake propagation in the Hikurangi subduction zone

S Aretusini,C W Harbord,E Spagnuolo,F Meneghini,G Di Toro

doi:10.1038/s41467-021-22805-w

S Aretusini, C W Harbord + Show 3 more

Open Access

https://doi.org/10.1038/s41467-021-22805-w

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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.

Highlights

In subduction zones, seismic slip at shallow crustal depths can lead to the generation of tsunamis
We show that Pāpaku thrust materials sustain high shear stress at the onset of slip, which dynamically weakens to low shear stress as a direct result of pore fluid pressure changes
The Pāpaku thrust is a shallow branch of the plate boundary fault, which has hosted historic tsunami earthquakes and more recently shallow slow slip events (SSEs) (Fig. 1a, b)

Summary

Introduction

Seismic slip at shallow crustal depths can lead to the generation of tsunamis. By exploiting a new experimental set-up, we shear Pāpaku thrust clay-rich fault materials at seismic slip velocities under fluid-pressurised conditions.

Results

Conclusion