Sgambato, Claudia; (2022) Variations in fault parameters and seismic hazard in the Central and Southern Italian Apennines. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The role of fault geometry, fault interaction through Coulomb stress transfer and variations in slip-rates through time are here investigated to determine changes in seismic hazard attributable to geometry of individual faults and to the geometry of the fault system. Detailed measurements of the fault geometry and of the slip-rates across an individual fault in the Southern Apennines are used to determine what spatial resolution of field measurements is needed to calculate a representative strain-rate, and to investigate the uncertainty introduced in the calculated strain-rate if variations in fault geometry are not measured in the field. Variations of post Last Glacial Maximum throw along the strike of the fault produce different values for the strain-rate, hence different results in expected seismicity rates. The Coulomb stress changes occurring during the historical earthquake sequences that characterised the Southern Apennines and Calabria, Italy, are analysed, to investigate the importance of Coulomb stress transfer and fault/shear-zone system geometry in earthquake recurrence. A novel aspect of fault interaction has been identified and shows that there is a geometry-specific behaviour in the way faults accumulate stress through time, with isolated faults dominated by regional tectonic rather than coseismic interaction. Thus, some aspects of the stress-loading to failure in earthquakes appear not be random, since stress-loading is not the same for all faults and is dependent on the geometry of the fault/shear-zone system. Dating of active normal fault scarps through measurement of the concentrations of cosmogenic 36-chlorine provided essential information on the palaeoseismic history of faults in the Southern Apennines. It is shown that earthquakes on these faults occur in a clustered manner, with an alternance of periods of rapid slip and periods of quiescence, suggesting that these faults accommodate the regional tectonic extension at different times. The results presented concern the identification of seismogenic structures and their geometric and kinematics features, long-term deformation rates and their spatial variability, temporal distribution of past events, as well as fault interaction and earthquake triggering. These represent the first steps of any seismic hazard assessment; thus, they could have a significant impact on seismic hazard estimation.

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