Fingerprints and energy budget of the earthquake cycle in shallow sediments

Abstract

Earthquake cycle consists of alternating transient coseismic slip and long-lasting interseismic periods, covering a wide range of slip rates. Unveiling the deformational signature of earthquake cycles in major seismogenic fault systems is an essential component of seismic hazard evaluation. Here, we present a study combining field and microstructural data acquired from an extensional fault zone with ∼100 m displacement, developed in poorly lithified siliciclastic sediments of the Crotone Basin, South Italy. The maximum burial depth of faulted sediments did not exceed 500 m. Within the fault core a dense network of mutually cross-cutting dark gouges and deformation bands is hosted. Dark gouges and deformation bands display striking distinctive features (i.e., geometric arrangement, grain size distribution, displacement, fractal dimension and clast preferential orientation), suggesting their genesis occurred under different slip rates. Based on grain size distribution data, total surface energies required for dark gouge and deformation band development are in the order of 106 and 104 J/m2, respectively. These values are in accordance with literature fault scaling laws regarding moment magnitude-surface energy relationship. Our results support the genesis of deformation bands during inter-seismic, creeping fault activity periods, while dark gouges were produced during coseismic slip events.