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NOFEAR Report Summary

Project ID: 614705
Funded under: FP7-IDEAS-ERC
Country: United Kingdom

Periodic Report Summary 3 - NOFEAR (New Outlook on seismic faults: From EARthquake nucleation to arrest)

Earthquakes or abrupt ground motions that we feel at the Earth's surface are the result of ruptures propagating in the crust (usually at 7-25 km depth for destructive earthquakes) along geological structures called faults (the “earthquake engine”). The NOFEAR (or "New Outlook on seismic Faults: from EARthquake nucleation to arrest") project funded by the European Research Council aims at understanding the intimate nature of earthquakes by investigating the basic ingredients of the earthquake engine: the elastic strain energy stored in the wall rocks (the fuel), the fault and its mechanical properties (the engine and its performance). The project exploits a multidisciplinary approach to study earthquake physics by integrating (1) field studies of seismic faults (or by lifting the bonnet to look inside the earthquake engine), (2) experiments that reproduce the extreme deformation conditions typical of earthquakes (or by measuring the earthquake engine performances) and (3) numerical models that by integrating the geological complexity of natural faults with the mechanical properties measured in the laboratory, produce simulated earthquakes to be compared with natural ones (or make the earthquake engine work).
The NOFEAR project involves a group of fifteen scientists with different background (geologists, physicists, engineers, seismologists) which produced 21 scientific publications and delivered about 100 contributions to international meetings plus 18 seminars also for popular dissemination purposes. Some of the scientific results include the first quantitative description at the kilometric scale of fault exhumed from seismogenic depths and similar to those responsible of the recent Italian 2016 earthquakes (299 casualties). Importantly, the experimental studies and careful investigation of natural fault products, suggest that the formation of nano-particles (< 20 nm in size) due to intense comminution and other poorly understood physico-chemical processes along faults triggers grain-size and temperature-dependent fault weakening processes which sustain rupture nucleation and propagation during earthquakes. These findings shake our knowledge of earthquake mechanics: rather than the expression of the "brittle" behaviour of the Earth's crust as presented in text-books, earthquakes, at least in some cases like those of the recent Italian seismic sequences, could be the result of ductile crystal-plastic processes in the shallow crust.
A second relevant result is that geologically- and experimentally-based numerical simulations of earthquakes matched quite in detail the general features of natural earthquakes (e.g., rupture duration) estimated from the analysis of seismic waves. However, as expected, when we modelled the Mw 9.0 Tohoku earthquake that generated the large tsunami wave that hit Japan in March 2011, slight variations in the initial and boundary conditions of the model (poorly constrained at the state-of-the-art) resulted in a gamut of earthquake types (megathrust earthquakes, tsunami earthquakes and normal-type thrust earthquakes). These findings suggest that, though our understanding of earthquake physics has made large advancements in the last years, unfortunately a robust physically-based short term (days to weeks) probabilistic earthquake forecasting approach remains a huge challenge for Earth's scientists.
Lastly, we investigated the causes of seismicity induced by human activities, especially those related to the injection of CO2 in deep basaltic reservoirs. The aim of these engineering projects is to dissolve the basalt by interaction with carbonated water (CO2 + H2O) and fix the CO2 gas into a mineral, such as calcite or dolomite (mineral carbonation). Mineral carbonation could be a very efficient technique for long-term storage of CO2 to decrease its concentration in the atmosphere and possibly buffer global warming. Unfortunately, experimental evidence, given the low solubility of CO2 in water at the operating conditions expected at injection sites, suggest that the storing of significant volumes of CO2 will require the injection of extremely large volumes of water which will likely trigger earthquakes. It is clear that the safe exploitation of these reservoirs cannot be performed without a sound knowledge of earthquake physics.

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United Kingdom
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