Laboratoire de Géologie
Ecole Normale Supérieure
24 rue Lhomond
75231 Paris Cedex 0,
France
Email:
madariag@geologie.ens.fr
poster/oral: oral
| Thanks to an increasing number of near field observations, friction experiments and theory earthquake source dynamics has made significant progress in the last decade. I will review a few simple global results and discuss what I think are the most important theoretical issues. (1) It was recognized by Heaton (1990) -- confirmed by observations and experimental results -- that ruptures tend to propagate in a self-healing mode as opposed to a Kostrov-like crack. With Nielsen we found that self-healing behavior is just a higher mode of Kostrov's model. This mode appears spontaneously for heterogeneous initial conditions without invoking special friction properties. (2) A number of independent observations have shown that friction laws have an intrinsic lengh scale that regularizes friction and insures finite energy release on the fault. The scaling length is a subject of controversy, some authors proposing to use the length scales of laboratory experiments (of the order of microns); others propose length scales of the order of cm to m. Some experimental and field information indicates that the length scale increases with the size of the gouge zone involved in the rupture so that the discussion may have to be reframed. (3) Modeling techniques and computer speeds have improved so that it is now possible to invert low frequency near field ground motion for fault stresses and friction. Peyrat et al have shown that this problem is intrinsically ill posed, but they also found that seismic observations can be inverted for certain products stresses and lengths (energies). For instance, energy relase rates are of the order of MJ/m**2 for earthquakes of M>7. (4) Fault interaction has been extensively studied in the static limit using Coulomb stresses. During dynamic rupture faults interact not only through quasi static effects, but also through the dynamic stress concentration near to the rupture front. After testing many models we found with Aochi and Fukuyama that interaction is much more sensitive to shear stress concentrations than to normal stresses. |