The missing sinks: Slip localization in faults, damage zones, and the seismic energy budget

Abstract

The majority of work done during an earthquake may be consumed by dissipative processes that occur within geometrically and mechanically complex fault zones, rather than radiated as seismic waves. Many processes are likely to act as dissipative energy sinks in a three-dimensional faulted volume: slip along the principal slip zone is likely to be accompanied by deformation in the surrounding damage zone volume. Examination of exhumed fault zones in granite, which are meters to tens of kilometers long, shows thin principal slip zones developing on the smallest faults. As slip is accumulated on progressively larger faults, the principal slip zones remain less than 10 cm wide, but there is increasing complexity in the damage zone of the larger faults. By considering the amount of energy required to crush fine-grained gouge in the principal slip zone, and the grain size of gouge reported from other (seismogenic) faults, we conclude that principal slip zones must remain relatively thin for all sizes of rupture. Any energy consumed by dissipative processes in the damage zone will therefore tend to make the principal slip zone thinner, and will reduce the energy available to propagate the rupture.