QUIN 2.0 - new release of the QUaternary fault strain INdicators database from the Southern Apennines of Italy.

QUIN database integrates and organizes structural-geological information from published and unpublished sources to constrain deformation in seismotectonic studies. The initial release, QUIN1.0, comprised 3,339 Fault Striation Pairs, mapped on 445 sites exposed along the Quaternary faults of central Italy. The present Data Descriptor introduces the QUIN 2.0 release, which includes 4,297 Fault Striation Pairs on 738 Structural Sites from southern Italy. The newly investigated faults span ~500 km along the Apennines chain, with strikes transitioning from ~SE to ~SW and comprehensively details Fault Striation Pairs' location, attitude, kinematics, and deformation axes. Additionally, it offers a shapefile of the fault traces hosting the data. The QUIN 2.0 release offers a significant geographic extension to the QUIN 1.0, with comprehensive description of local geometric-kinematic complexities of the regional pattern. The QUIN data may be especially relevant for constraining intra-Apennine potential seismogenic deformation patterns, where earthquake data only offer scattered or incomplete information. QUIN's data will support studies aimed at enhancing geological understanding, hazard assessment and comprehension of fault rupture propagation and barriers.

Surface faulting earthquake clustering controlled by fault and shear-zone interactions.

Surface faulting earthquakes are known to cluster in time from historical and palaeoseismic studies, but the mechanism(s) responsible for clustering, such as fault interaction, strain-storage, and evolving dynamic topography, are poorly quantified, and hence not well understood. We present a quantified replication of observed earthquake clustering in central Italy. Six active normal faults are studied using 36Cl cosmogenic dating, revealing out-of-phase periods of high or low surface slip-rate on neighboring structures that we interpret as earthquake clusters and anticlusters. Our calculations link stress transfer caused by slip averaged over clusters and anti-clusters on coupled fault/shear-zone structures to viscous flow laws. We show that (1) differential stress fluctuates during fault/shear-zone interactions, and (2) these fluctuations are of sufficient magnitude to produce changes in strain-rate on viscous shear zones that explain slip-rate changes on their overlying brittle faults. These results suggest that fault/shear-zone interactions are a plausible explanation for clustering, opening the path towards process-led seismic hazard assessments.

Stress loading history of earthquake faults influenced by fault/shear zone geometry and Coulomb pre-stress.

Whether the stress-loading of faults to failure in earthquakes appears to be random or to an extent explainable, given constraints on fault/shear-zone interaction and the build-up and release of stress over many earthquake cycles, is a key question for seismic hazard assessment. Here we investigate earthquake recurrence for a system of 25 active normal faults arranged predominantly along strike from each other, allowing us to isolate the effects of stress-loading due to regional strain versus across- and along-strike fault interaction. We calculate stress changes over 6 centuries due to interseismic loading and 25 > Mw 5.5 earthquakes. Where only one fault exists across strike, stress-loading is dominated by the regional tectonics through slip on underlying shear zones and fault planes have spatially smooth stress with predominantly time-dependent stress increase. Conversely, where faults are stress-loaded by across-strike fault interactions, fault planes have more irregular stress patterns and interaction-influenced stress loading histories. Stress-loading to failure in earthquakes is not the same for all faults and is dependent on the geometry of the fault/shear-zone system.