Evolution of hierarchical self-similar geometry of experimental fault zones: Implications for seismic nucleation and earthquake size

The geometry of fault zones and its evolutionary trend were experimentally investigated for samples of calcareous siltstone nodule through a repetitive procedure of axial loading to grow faults a little, close‐up photographing of faults that appeared on the side surface of the samples, and axial loading again. Irrespective of their size, fault zones are composed of three or four fault segments and compression‐type fault jogs. Smaller segment‐jog structures are nested in larger segments, forming a hierarchical fault zone structure as a whole, and they show self‐similarities. Fault zones grow keeping this self‐similar hierarchical structure. On the basis of this fault zone geometry, we successfully derived the Gutenberg‐Richter's law as well as the previously known relationship of seismic nucleation sizes to seismic moments. These results suggest that fundamentally any seismic rupture nucleates at a smaller jog (asperity) of a lower hierarchical rank and terminates eventually at a larger jog (barrier) of a higher rank, mimicking the hierarchical fault zone geometry.