Fault lubrication during earthquake propagation in thermally unstable rocks

Lead Research Organisation: Durham University


Three thermally activated mechanisms are considered to be of particular relevance during slip in thermally unstable rocks such as carbonates: 1) flash heating at highly stressed frictional micro-contacts (asperities); 2) thermal pressurization of heated fluids released and/or trapped in the slip zone; and 3) the lubrication effects of nanoparticles produced by thermally-induced chemical decomposition reactions (decarbonation). In order to investigate whether such chemical and physical reactions in carbonate fault zones can make faults extremely weak and favour the continued propagation of earthquake ruptures, we propose here a multidisciplinary research program where mechanical, mineralogical, microstructural, fluid flow properties and modelling data, obtained from both field and laboratory studies are integrated. Fieldwork studies will be carried out in carbonate rocks from the Italian Apennines to reconstruct the natural fault zone geometries, identify the different structural domains and their associated fault rock assemblages. The integration of field observations and microstructural/mineralogical analyses will provide important geological constraints in the analysis and interpretation of the dominant deformation processes observed in experimentally deformed samples. These results will be used to produce a new classification scheme for seismic fault rocks in carbonates, based on the identification and description of diagnostic associations of fault rocks and microstructures which are indicators of earthquake slip events. This classification will aid in the recognition of fossil earthquakes along exposed fault segments and, therefore, can be used to interpret records of palaeo-seismic faulting in other parts of the world, aiding in risk/hazard assessment. High velocity friction experiments will be performed on solid and granular carbonate rocks, sheared at speeds similar to that seen in large earthquakes (1.3m/s), in order to assess the likely dynamic frictional strength Tf of fault rock materials collected from active fault zones in the study areas. Synthetic nano-powders obtained by thermal decomposition of carbonates in a furnace will also be tested. The integration of laboratory friction test results and microstructural studies from both experimental and natural faults should allow the identification of the dominant weakening mechanisms and constrain their operational conditions in natural environments. The permeability of granular materials is controlled by grain size distribution, grain shape, solid volume fraction and pore connectivity. All of these geometric parameters vary across a fault zone. Permeability laboratory measurements will be performed on field samples collected along transects oriented orthogonal and parallel to principal slip surfaces in the fault zones. These data can provide useful 'snapshot' information on the evolution of permeability of slip zones under known/controlled conditions (friction, displacement, timing of fluid emissions), which can be used to calibrate/test fluid flow modelling results. We will use a state-of-the-art numerical model (name) to determine the permeability tensor for the range of geometric parameters obtained from quantitative microstructaral analyses. This numerical approach will allow us to explore systematic permeability variations in a way that cannot be achieved through laboratory experiments alone. The rate of dissipation of the fluids generated by thermal decomposition of the carbonate during slip will be quantified, allowing the role they play in fault zone lubrication to be determined.


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Description The main findings arising from our research, including those outcomes that relate to work currently submitted and in preparation for submission, are:
1) A distinct and measurable geochemical signature, associated with high temperature decarbonation processes, has been observed by the integration of microstructural/mineralogical observations and geochemical data from experimental faults, deformed at seismic conditions. We adopted a simple modelling approach to show that, during earthquake propagation in natural carbonate fault zones, the operation of the same processes observed in the laboratory can: a) release significant amounts of CO2, which are comparable to those released daily by deeper sources (e.g. mantle degassing); b) produce groundwater post-seismic geochemical signatures which can potentially be measured and monitored, depending on the volume and geochemical nature of the aquifers. Our approach and findings can be applied to develop monitoring strategies of spring waters in seismically active areas.
2) We addressed the unsolved paradox of seismic slip episodically occurring along shallow creeping faults in poorly lithified sediments, by investigating the mechanics of creeping faults and producing new documented geological evidence showing how coseismic rupturing overprints creep in near-surface conditions. Field observations from fault zones developed in shallow, poorly lithified sediments show that foliated cataclasites (creeping behaviour) are locally overprinted by sharp slip surfaces decorated by thin black gouge layers. Compared to foliated cataclasites, black gouges have much lower grain size, porosity, and permeability. Moreover, they are characterized by distinct mineralogical assemblages compatible with high temperatures due to frictional heating produced during seismic slip. Foliated cataclasites were also produced
by laboratory experiments performed on host sediments at subseismic slip rates (=0.1 m/s), as well as black gouges produced only during experiments performed at seismic (1 m/s) slip rates. Our results show that black gouges represent a potential diagnostic marker for seismic faulting in shallow creeping faults. These findings can help understanding the time-space partitioning between aseismic and seismic behaviour of faults at shallow crustal levels, including tsunamogenic ones.
3) Superplasticity has long been postulated and recently observed for a range of metals, ceramics and nano-phase alloys deforming at high temperatures and range of strain rates. It has been inferred to occur at lower strain rates and high temperatures in geological materials typical of shear zones in the mid-lower crust and upper mantle. However, it has never been associated with earthquakes propagating in the upper crust, nor has it ever been recognized in the fault rocks of active, seismic faults. Our research shows new microstructural observations from experimental and natural carbonate rocks showing that nanoscale superplastic behaviour in geological materials is triggered in ultrafine grained, frictionally heated fault gouges during earthquake slip. We show that modelled flow stress values, obtained using superplasticity constitutive laws for carbonates at our experimental conditions, match those values we measured in the laboratory. Our findings show that nanoscale superplastic behavior may represent a new mechanism to explain the self-lubrication of faults during earthquake propagation in nature. This is a completely new discovery.
Exploitation Route Our findings are summarised in our publications and can be used by a broad range of scientists, including geologists, seismologists, geophysicists, experimentalists and material scientists, to improve our understanding of earthquake propagation processes. They may have obvious long term implications in terms of hazard and risk issues associated with such destructive, but still poorly understood phenomena. audience .
Sectors Aerospace, Defence and Marine,Education,Energy,Other

Description Yes, the main research outcomes of this research have been published and these papers are now well cited by other researchers.
First Year Of Impact 2016
Sector Education,Other
Impact Types Cultural

Description Expert Panel in Seismic Hazard and Climate Change appointment
Geographic Reach National 
Policy Influence Type Participation in a guidance/advisory committee
Description NERC Knowledge Exchange Advisory Board appointment (Co-I Prof. Robert Holdsworth)
Geographic Reach National 
Policy Influence Type Participation in a guidance/advisory committee
Title Friction experiments data 
Description About 400 friction experiments have been performed during this project in the Rock Mechanics Laboratory, using a low to high velocity rotary shear apparatus. The experimental database produced is made of raw data from the mechanic experiments as well as processed and interpreted data from each experiment. 
Type Of Material Database/Collection of data 
Provided To Others? No  
Impact The mechanical database produced has the potential to improve our understanding of frictional properties of fault when sliding at seismic and sub-seismic conditions (academic impact), as well as serving as a teaching tool (education impact). We are already using some of these databases to inform our teaching at undergraduate level, following Durham University research led teaching strategy. A web-catalogue of available experimental data and conditions is currently under construction. 
Title Seismic fault rocks collection 
Description Following fieldwork in Italy, when active seismic fault zones were studied and sampled, we have produced in Durham a dataset comprising a collection of: 1) Field samples of active fault zones; 2) Thin sections of fault zones to be used for microscopy analyses; 3) Digital images of micro- and nano-scale structures acquired using optical microscope, SEM and TEM facilities. 
Type Of Material Database/Collection of data 
Provided To Others? No  
Impact This database has the potential to improve our understanding of seismic fault structures (academic impact) as well as serving as a teaching tool (education impact). We are already using some of these databases to inform our teaching at undergraduate level, following Durham University research led teaching strategy. An open-access digital database website is currently under construction. 
Description Grain size analyses of seismic faults 
Organisation University of Parma
Country Italy 
Sector Academic/University 
PI Contribution The Durham Research Team provided access to: 1) Experimental facilities in the Rock Mechanics Laboratory, Earth Sciences Department, Durham University (UK), and 2) Microscopy facilities in the G.J. Russell Microscopy Facility, Department of Physics, Durham University (UK).
Collaborator Contribution The research partners provided the Durham Research Team with: 1) fault rock materials to be tested in the laboratory; 2) available field datasets from seismic faults; 3) available grain size datasets on natural, seismic faults. The Research Partners assisted during fieldwork in Italy, where they guided the Durham Research Team to key outcrops of seismic faults, and took part in the collection of rock samples, to be used for laboratory experiments and micro structural analyses, and structural datasets. Furthermore, the Research Partners provided the human resources to assist during the rock mechanics experiments in the Rock Mechanics Laboratory at Durham University. Research Partners also performed new grain size analyses on experimental and natural fault rock samples, at the University of Parma.
Impact The collaboration with researchers at the University of Parma produced the following publication: F. Balsamo, L. Aldega, N. De Paola, I. Faoro, and F. Storti, The signature and mechanics of earthquake ruptures along shallow creeping faults in poorly lithified sediments. Geology 42; 435-438 (2014). (doi:10.1130/G35272.1). The results arising from collaboration with the Research Team at Parma University were presented at EGU2014 Conference held in Vienna: "Field and experimental evidence for coseismic ruptures along shallow creeping faults in forearc sediments of the Crotone Basin, South Italy" by Fabrizio Balsamo, Luca Aldega, Nicola De Paola, Igor Faoro, and Fabrizio Storti.
Start Year 2012
Description BBC Radio4 media interview (L'Aquila earthquake) 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact Co-I Prof. Bob Holdsworth was interviewed during a BBC Radio 4 programme to comment on the news that "Seven members of a panel convened by Italy's Civil Protection Department in the days prior to the L'Aquila earthquake of 2009 have this week been sentenced to six years each in prison."

Not applicable.
Year(s) Of Engagement Activity 2012
URL http://www.bbc.co.uk/programmes/b01ngnwg
Description Media interest Channel 4 news (Tohoku earthquake, Japan) 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Media (as a channel to the public)
Results and Impact Co-I Prof. Bob Holdsworth was interviewed for a Channel 4 news article following the devastating Tohoku earthquake in japan. He commented on the general aspects of earthquake of such size and the implication that their released energy can cause.

Not applicable.
Year(s) Of Engagement Activity 2011
URL http://www.channel4.com/news/tsunami-hits-japan-after-8-9-magnitude-pacific-quake