Characteristics of active deformation, fault interaction, and earthquake triggering in a rapidly-deforming complex normal fault network (south-west Türkiye)

Abstract

Despite often being overshadowed by disastrous earthquakes on subduction zones and continental transform faults, normal faulting earthquakes frequently cause severe destruction and casualties. Understanding earthquake occurrence and determining those faults most at risk of rupturing in destructive earthquakes is crucial to prevent disasters. A key approach to understanding earthquake occurrence is to understand how stress and strain develop through a fault system over the earthquake cycle. In this thesis, Coulomb stress modelling, SAR interferometry, and field work are combined with a comprehensive literature review to study active deformation, fault interactions, and earthquake triggering mechanisms in complex normal fault networks, with the Western Anatolian Extensional Province (SW Türkiye) serving as a case study. Coulomb stress models of earthquake sequences aim to determine the stress state of faults, including the effects of interseismic stress accumulation, and coseismic stress release and transfer. These models rely on accurate determination of model parameters, most importantly a complete and reliable earthquake record, including knowledge of source faults. Herein, a novel approach is presented to constrain the source faults of historical earthquake sequences, applicable to other study regions to provide additional information on insufficiently documented earthquakes. The main objective of Coulomb stress modelling is to study earthquake triggering on across-strike normal faults, which experience stress release due to ruptures on neighbouring faults. After evaluation of uncertainties, interseismic loading is interpreted to be the driving factor for seismicity in across-strike normal fault networks, compensating negative coseismic stress transfers. Large earthquakes in such settings are delayed, possibly leading to the false impression of seismic inactivity based on historical records. Model results also highlight the necessity to evaluate parameter uncertainties, and the importance of accurately modelled fault geometry. Results from SAR Interferometry show that northsouth deformation could potentially be derived from inversion of line-of-sight velocities and required possible improvements to this approach are outlined. Additionally, the use of vertical deformation fields is highlighted as a useful dataset to study active deformation of normal faults.