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We use teleseismic recordings from a dense array of seismometers straddling both strands of the North Anatolian Fault Zone to determine crustal thickness, P/S velocity ratio and sedimentary layer thickness. To do this, we implement a new grid search inversion scheme based on the use of transfer functions, removing the need for deconvolution for source normalization and therefore eliminating common problems associated with crustal‐scale receiver function analysis. We achieve a good fit to the data except at several stations located in Quaternary sedimentary basins, where our two‐layer crustal model is likely to be inaccurate. We find two zones of thick sedimentary material: one north of the northern fault branch, and one straddling the southern branch. The crustal thickness increases sharply north of the northern strand of the North Anatolian Fault Zone (NAFZ), where the fault nearly coincides with the trace of the Intra‐Pontide Suture; the velocity ratio changes across the southern fault strand, indicating a change in basement composition. We interpret these changes to indicate that both strands of the NAFZ follow preexisting geological boundaries rather than being ideally aligned with the stress field. The thick crust north of the northern NAFZ strand is associated with low topography and so is inconsistent with simple models of isostatic equilibrium, requiring a contribution from mantle density variations, such as possible loading from underthrust Black Sea oceanic lithosphere.

SUMMARY The 1999 November 12 Düzce earthquake (Mw= 7.1) was apparently the eastward extension of the August 17, İzmit earthquake (Mw= 7.4). The Düzce event caused heavy damage and fatalities in the cities of Düzce and Bolu. Here a finite‐fault inversion method with five discrete time windows is applied to derive the co‐seismic slip distribution of the Düzce earthquake. The fault plane is best modelled as a 40 × 20 km2 plane, with a strike of 262° and a dip of 65° to the north, and that the majority of slip occurred in two distinct patches on either side of the hypocentre, implying bilateral rupture. The possible triggering of this event by the İzmit earthquake is investigated using Coulomb stress modelling of all large events since 1943 with the inclusion of secular loading. The results show that although the Düzce rupture plane was in a stress shadow prior to the İzmit earthquake, that event caused a significant Coulomb stress load, taking the Düzce fault out of the stress shadow, which probably precipitated failure. A comparison of the mapped Coulomb stress change with the inferred slip shows no correlation between the two. Finally, the stress modelling indicates that the northern branch of the North Anatolian fault zone, beneath the Sea of Marmara towards the city of İstanbul, is presently the most highly loaded segment of the North Anatolian Fault Zone.