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Information - MPRG15 The role of fluids in faults and fracture zones - mechanical aspects
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Event Information |
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Fluid infiltration and pore pressure changes are of major importance in the dynamics and rheology of fractured zones. A number of mechanisms and processes can lead to pore pressure changes during rock fracture. It is well-known experimental fact that opening of cracks in brittle rock causes dilatancy, which can lead to local decrease of pore pressure, resulting in temporal hardening of undersaturated area, delaying the onset of instability. Conversely, it is also well-known that, for instance, porosity reduction leads to increase of pore pressure, which can cause triggering of fracture. So, pore-pressure driven aftershocks, pore pressure induced aseismic creep events, earthquake triggering at long distance in geothermal areas and by magmatic pressure in volcanic areas have all emphasized the role fluids play in the redistributions of normal stresses.
Due to the difficulties in monitoring in-situ pore pressures and permeabilities in natural fault zones, little is known quantitatively on the exact role played by varying fluid pressures in the field. Usually in the field pore pressures are inferred primarily from seismic-wave propagation characteristics such as Vp and Vs velocities, their attenuation and reflectivity contacts. Numerous models have been proposed for the temporal variation of seismic velocities expected to occur prior to an earthquake and many of these models (e.g. dilatancy-diffusion model) are based on the observation that brittle failure of rock involves opening of cracks and volumetric change, leading to an undersaturation of the nucleation zone followed by resaturation due to the influx of water from the surrounding rock. However, field observations show that seismic velocities variation have not occurred consistently before earthquakes and have not proven to be reliable prediction tools. Recent advances, however, have now started to shed light on the role fluids play in the process of fracture using complimentary laboratory, field and numerical methods.
In the proposed session, we invite papers that investigate and analyze the process of solid-fluid coupling / interaction in fractured rock at all scales, and their affect on mechanical properties of the rock, ultrasonic characteristics of the rock and seismic signal generation. We particularly welcome contributions that utilize new and novel instrumentation and laboratory techniques, and papers that introduce present observations of natural seismicity and seismic velocities variations both in tectonic and volcanic areas as well as field and laboratory experiments designed to investigate the role fluids play in the process of rock fracture.
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