Fluid pressurisation and earthquake propagation in the Hikurangi subduction zone

Stefano Aretusini,Christopher Harbord,Giulio Di Toro,Francesca Meneghini,Elena Spagnuolo

doi:10.5194/egusphere-egu21-8241

Stefano Aretusini, Christopher Harbord + Show 3 more

Open Access

https://doi.org/10.5194/egusphere-egu21-8241

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Abstract

&lt;p&gt;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 of 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 P&amp;#257;paku thrust (Hikurangi subduction zone, New Zealand). Here we show that seismic slip is characterized by an initial decrease followed by an increase of pore pressure. The initial pore pressure decrease is indicative of dilatant behavior. The following pore pressure increase, enhanced by the low permeability of the fault, reduces the energy required to propagate earthquake rupture. We suggest that thermal and mechanical pressurisation of fluids facilitates seismic slip in the Hikurangi subduction zone, which was tsunamigenic about 70 years ago. 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.&lt;/p&gt;

Highlights

In subduction zones, seismic slip at shallow crustal depths can lead to the generation of tsunamis
Laboratory experiments designed to test theoretical models of coseismic fluid pressurisation have been limited by the technical challenge of imposing realistic normal stress and pore fluid pressure on nonlithified fault materials sheared at seismic deformation conditions
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

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