HR: 1340h
AN: S53A-1089    [Abstracts]
TI: Monitoring Fault Growth In a Laser-Equipped Analog Experiment
AU: * SCHLAGENHAUF, A
EM: aloeschlagenhauf@free.fr
AF: Univ. Montpellier II, Place Eugene Bataillon, Montpellier Cedex 5, 34095 France
AU: * SCHLAGENHAUF, A
EM: aloeschlagenhauf@free.fr
AF: LGIT, BP 53, Grenoble Cedex 9, 38041 France
AU: MANIGHETTI, I
EM: Isabelle.Manighetti@obs.ujf-grenoble.fr
AF: LGIT, BP 53, Grenoble Cedex 9, 38041 France
AU: MALAVIEILLE, J
EM: Jacques.Malavieille@dstu.univ-montp2.fr
AF: Univ. Montpellier II, Place Eugene Bataillon, Montpellier Cedex 5, 34095 France
AU: Dominguez, S
EM: Stephane.Dominguez@dstu.univ-montp2.fr
AF: Univ. Montpellier II, Place Eugene Bataillon, Montpellier Cedex 5, 34095 France
AB: Faults grow through the repetition of earthquakes (and possibly creep). Yet, the way they accumulate slip and lengthen during that growth process is not well understood, for it cannot be directly observed. We address that problem with an analog modeling approach. We develop a new experiment that allows producing a homogeneous extensional stress regime, under which networks of normal faults form and grow. An interferometric laser system is combined to the experiment, so that the fault growth process can be continuously monitored. This allows measuring the displacements accumulated at the surface at incremental successive stages of the fault network development. The results show the following points. Faults initiate from dilatance zones in the brittle sand, then start accumulating vertical slip at the surface, i.e., forming escarpments. The very first formed-escarpments show a slip distribution that is roughly triangular and symmetric. Once these first escarpments are formed, faults start propagating bi-laterally at 'fast' rates while accumulating little vertical slip. During that lengthening phase, their slip distributions remain triangular in shape, yet evolving towards an asymmetric triangular shape. The increments of vertical slip and lengthening remain roughly proportional. The long linear slants of the slip profiles point in the direction of the fault propagation. The development of a strong slip gradient at one fault tip coincides with that fault tip meeting another neighboring fault. In most cases, at the end of that first phase of dominant lengthening, both fault tips have encountered another neighboring fault. From that time on, faults stop propagating any further, and continue growing merely by accumulating vertical slip. That second phase is longer than the previous one and is generally not achieved by the end of the experiment. Rates of slip accumulation are 'faster' than before; yet, they seem to decrease in the latest stages of fault growth. During the whole phase, the slip distributions remain globally triangular and commonly asymmetric. Some become more rounded however at the end of the experiment. Finally, for most faults and systems, the transition from the phase of dominant lengthening to that of dominant slip accumulation occurs at a specific, common value of the maximum displacement-length ratio, here equal to about 4.10-3. Some of our results are similar to observations made on real faults. In any case, they give a frame to understand how faults grow through the repetition of earthquakes. During the phase of dominant slip accumulation, faults do not increase in length so that they may produce characteristic earthquakes. By contrast, during the phase of dominant lengthening, it is unlikely that successive earthquakes may be similar.
DE: 8004 Dynamics and mechanics of faulting (8118)
DE: 8010 Fractures and faults
DE: 8020 Mechanics, theory, and modeling
SC: Seismology [S]
MN: Fall Meeting 2005