The role of fluid pressure in induced vs. triggered seismicity: insights from rock deformation experiments on carbonates.

Marco M Scuderi,Cristiano Collettini

doi:10.1038/srep24852

Marco M Scuderi, Cristiano Collettini

Open Access

https://doi.org/10.1038/srep24852

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Abstract

Fluid overpressure is one of the primary mechanisms for tectonic fault slip, because fluids lubricate the fault and fluid pressure reduces the effective normal stress that holds the fault in place. However, current models of earthquake nucleation, based on rate- and state- friction laws, imply that stable sliding is favoured by the increase of pore fluid pressure. Despite this controversy, currently, there are only a few studies on the role of fluid pressure under controlled, laboratory conditions. Here, we use laboratory experiments, to show that the rate- and state- friction parameters do change with increasing fluid pressure. We tested carbonate gouges from sub hydrostatic to near lithostatic fluid pressure conditions, and show that the friction rate parameter (a − b) evolves from velocity strengthening to velocity neutral behaviour. Furthermore, the critical slip distance, Dc, decreases from about 90 to 10 μm. Our data suggest that fluid overpressure plays an important role in controlling the mode of fault slip. Since fault rheology and fault stability parameters change with fluid pressure, we suggest that a comprehensive characterization of these parameters is fundamental for better assessing the role of fluid pressure in natural and human induced earthquakes.

Highlights

Fluid overpressure is one of the primary mechanisms for tectonic fault slip, because fluids lubricate the fault and fluid pressure reduces the effective normal stress that holds the fault in place
In the seminal paper by Hubbert and Rubey (1959)[1], it is proposed that fluid pressure, Pf, reduces the effective normal stress, (σ n − Pf), that clamps the fault in place, facilitating fault slip
Building on Hubbert and Rubey’s work, numerous scientific contributions have emphasized the role of fluid pressure in fault reactivation and earthquake triggering[2,3,4,5]

Summary

Introduction

Fluid overpressure is one of the primary mechanisms for tectonic fault slip, because fluids lubricate the fault and fluid pressure reduces the effective normal stress that holds the fault in place. Current models of earthquake nucleation, based on rate- and state- friction laws, imply that stable sliding is favoured by the increase of pore fluid pressure Despite this controversy, currently, there are only a few studies on the role of fluid pressure under controlled, laboratory conditions. The role of fluid pressure, in facilitating fault reactivation or promoting stable sliding, in frictional stability analysis creates an apparent contradiction in the mechanics of earthquakes. On the other hand, building on frictional stability analysis[9,11], several works have proposed that pressurized fault portions, imaged as high Vp/Vs domains, are characterized by aseismic slip[15,16] This apparent contradiction of the role of fluid pressure in fault stability poses a serious problem in our understanding of earthquake physics with numerous implications, including a better assessment of the risk www.nature.com/scientificreports/. These studies do not systematically analyse the potential role of fluid pressure in the evolution of rate- and state- friction parameters

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