CESS seminar series: Fluid effects in frictional faulting
Abstract
The main effect of fluids on frictional faulting is typically expressed through an effective normal stress equal to the fault-normal stress minus the pore fluid pressure. The fault frictional resistance is then given by the product of the effective normal stress and fault friction coefficient. Within this framework, several processes can spontaneously evolve the pore fluid pressure, including thermal pressurization of fluids induced by rapid shear heating, inelastic dilatancy/compaction of the shearing layer, and poroelastic effects that couple pore fluid pressure with bulk deformation. We will focus on two examples illustrating the potential dominance of these effects in earthquake source processes. First, we will show that dynamic weakening due to thermal pressurization may explain the low-heat, low-stress operation of mature continental plate-boundary faults, with the corresponding models reproducing observations of radiated energy and relative paucity of small earthquake events on such faults. Second, we will discuss how the combined effects of poroelasticity and dilatancy significantly affect the response of a fault to fluid injection. Finally, we will show some recent experimental evidence that faults with the same effective stress display different patterns of slip, with stabilizing effects of higher pore fluid pressure. Modeling one of these experiments indicates that the stabilizing effect is not due to dilatancy, for example, but is likely due to changes in friction properties, raising a possibility that the effective stress concept may not be universally applicable. These examples highlight the need to consider fluid effects in modeling fault slip as well as the importance of determining realistic thermo-hydro-mechanical properties of fault zones.
Bio
Nadia Lapusta received her undergraduate degree in Mechanics and Applied Mathematics from Taras Shevchenko National University of Kyiv in Ukraine. She continued her education at Harvard University, receiving her S.M. and Ph.D. degrees in Engineering Sciences in 1996 and 2001, respectively. Since 2002, she has been a faculty at the California Institute of Technology, most recently as Hanson Professor of Mechanical Engineering and Geophysics. She is a co-Director of the NSF I-UCRC Center on Geomechanics and Mitigation of Geohazards (GMG) at Caltech, a co-Leader of the Fault and Rock Mechanics at the Southern California Earthquake Center (SCEC), and an AGU Fellow. Professor Lapusta's interdisciplinary research group works in the areas of computational mechanics of geomaterials, earthquake source processes, fundamentals of friction and fracture, and solid-fluid interactions.
The main effect of fluids on frictional faulting is typically expressed through an effective normal stress equal to the fault-normal stress minus the pore fluid pressure. The fault frictional resistance is then given by the product of the effective normal stress and fault friction coefficient. Within this framework, several processes can spontaneously evolve the pore fluid pressure, including thermal pressurization of fluids induced by rapid shear heating, inelastic dilatancy/compaction of the shearing layer, and poroelastic effects that couple pore fluid pressure with bulk deformation. We will focus on two examples illustrating the potential dominance of these effects in earthquake source processes. First, we will show that dynamic weakening due to thermal pressurization may explain the low-heat, low-stress operation of mature continental plate-boundary faults, with the corresponding models reproducing observations of radiated energy and relative paucity of small earthquake events on such faults. Second, we will discuss how the combined effects of poroelasticity and dilatancy significantly affect the response of a fault to fluid injection. Finally, we will show some recent experimental evidence that faults with the same effective stress display different patterns of slip, with stabilizing effects of higher pore fluid pressure. Modeling one of these experiments indicates that the stabilizing effect is not due to dilatancy, for example, but is likely due to changes in friction properties, raising a possibility that the effective stress concept may not be universally applicable. These examples highlight the need to consider fluid effects in modeling fault slip as well as the importance of determining realistic thermo-hydro-mechanical properties of fault zones.
Bio
Nadia Lapusta received her undergraduate degree in Mechanics and Applied Mathematics from Taras Shevchenko National University of Kyiv in Ukraine. She continued her education at Harvard University, receiving her S.M. and Ph.D. degrees in Engineering Sciences in 1996 and 2001, respectively. Since 2002, she has been a faculty at the California Institute of Technology, most recently as Hanson Professor of Mechanical Engineering and Geophysics. She is a co-Director of the NSF I-UCRC Center on Geomechanics and Mitigation of Geohazards (GMG) at Caltech, a co-Leader of the Fault and Rock Mechanics at the Southern California Earthquake Center (SCEC), and an AGU Fellow. Professor Lapusta's interdisciplinary research group works in the areas of computational mechanics of geomaterials, earthquake source processes, fundamentals of friction and fracture, and solid-fluid interactions.
Practical information
- Informed public
- Free
Organizer
- Prof. Olga Fink (IMOS-EPFL), Prof. Alexandre Elahi (VITA-EPFL), Prof. Dusan Licina (HOBEL-EPFL), Prof. Alain Nussbaumer (RESSLab-EPFL)
Contact
- Federica Paglialunga (LEMR-EPFL)