Fault damage zones: character and physical properties from field and laboratory studies
| Cosa | seminari |
|---|---|
| Quando | 01/04/2008 da 15:00 al 23:55 |
| Dove | sala conferenza dell'INGV di Roma |
| Persona di riferimento | Sergio Vinciguerra |
| Indirizzo e-mail per contatti | |
| Aggiungi l'evento al calendario |  vCal (Windows, Linux) iCal (Mac OS X) |
1 aprile 2008, ore 15.00| Dr. Daniel Faulkner, dell’University of Liverpool, UK | Sala Conferenze Roma | Sede Centrale |
Fault zones consist of two major components. These are the high strain fault core and the zone of fractured rock surrounding the fault core. The damage zone has received relatively little attention in previous work and as such its physical dimensions and properties are poorly characterized. Here data are presented from field studies and laboratory investigations that quantify the scale, elastic properties and fluid flow properties of the fault damage zone. We concentrate on two important aspects of the properties of fault damage zones: elastic properties and fluid flow properties.
Field data collected from the Atacama fault system in northern Chile where faults cut through a low porosity crystalline rock (granodiorite) indicate that the damage zone consists of microscopic and macroscopic fracturing that decreases in intensity with distance from the fault core. For large displacement faults the width of the damage zone is on the order of 150m wide.
Laboratory measurements of initially intact low porosity crystalline rock show that during uniaxial cyclic loading, microfracture densities increase and this is accompanied by a decease in Young’s modulus and increase in Poisson’s ratio. Modelling of these data suggest that the elastic property changes surrounding fault zones can result in significant modification of the stress field.
Field, seismological and geophysical observations suggest that faults act as significant fluid conduits, and hence the damage zone must act as a high permeability pathway. In order to quantify the contribution of microscopic damage to the fluid flow properties, we measured the porosity and permeability evolution of initially low porosity crystalline rocks under simulated crustal conditions during progressive deformation to failure. The data show permeability enhancement from initial values of ~10-21 to ~10-17 m2 immediately prior to failure. However, these values and the size of damage zones typically seen in the field are not sufficient to explain inferred fluid flow rates and imply that the macroscopic fracture network must play a significant role in fluid transport.