Fault interactions and Coulomb stress triggering in complex fault networks - A model of the Western Anatolian Extensional Province

Coseismic Coulomb Stress Transfer (CST) from normal faulting earthquakes generally promotes failure of along-strike faults or segments, whereas it reduces stress on across-strike faults. Nevertheless, large earthquakes occur on across-strike faults despite receiving repeated negative coseismic CST. This study explores the triggering mechanisms of large earthquakes in the rapidly deforming, geometrically complex normal fault network of SW Türkiye. We model 400 years of cumulative coseismic CST from 26 M≥6.0 earthquakes plus interseismic CST based on fault slip rates. Subsequently, uncertainties in slip rates (therefore interseismic loading) and locations of historical earthquakes are explored. We find that interseismic loading is the dominant triggering process, (over-)compensating negative coseismic CST. Even CST from repeated large earthquakes on across-strike fault zones will only delay failure but is insufficient to completely suppress large earthquakes. Relatively quiescent faults in such settings should therefore not be disregarded as hazardous seismogenic sources. Nevertheless, in geometrically complex settings, heterogeneous coseismic CST might form stress barriers, reducing rupture extent and magnitude of subsequent earthquakes. Incorporating interseismic loading into Coulomb stress models is vital for robust interpretations of fault interactions, even if fault slip rates used to model interseismic loading contain major uncertainties, as accuracy of fault slip rates used is of secondary importance. Finally, the model allows interpretations of the current stress state of the regional fault network, though interpretations regarding seismic hazard should consider the described model limitations. We emphasize the need to assess uncertainties in Coulomb stress modelling studies, especially when using the historical earthquake record.