Earthquakes and fault zone structure

The characterization of fault zone structure and its evolution is essential for understanding earthquake mechanics and rupture evolution. Most of our knowledge about fault structure is derived from field studies of ancient faults. By using earthquake locations, we reconstruct the complex structure of a normal fault at a resolution directly comparable with field geological investigations. At the surface conjugate sets of faults are connected with the main fault plane, which with depth shows bending and dilational jogs. Parallel slipping planes occur at the base of the seismogenic volume, and minor synthetic and antithetic structures are widespread. Fault zone thickness ranges from 0.5 to 1.5 km, while the damage density decays exponentially away from the fault plane, with values comparable to those observed on fault outcrops. The strong similarities between seismological and geological images of fault structure indicate that earthquakes have a key role in the evolution of fault architecture.