Crustal and Upper Mantle Deformation Beneath Northwestern part of North Anatolian Fault Zone from Harmonic Decomposition of Receiver Functions

A proper understanding of crustal seismic anisotropy beneath the tectonically complex northwestern part of the North Anatolian Fault Zone (NAFZ) will shed light into the depth extent of deformation zones. To investigate the seismic anisotropy in the crustal part of the NAFZ, we applied the harmonic decomposition technique on receiver functions from teleseismic earthquakes (with epicentral distances between 30° and 90°) recorded at the Dense Array for North Anatolia (DANA) seismic network. Harmonic coefficients, k=0, k=1, and k=2 were obtained by applying the harmonic decomposition method to the depth migrated receiver functions. Results from k=0 harmonics suggest south to north (e.g. from Sakarya Zone to Istanbul Zone) increase in crustal thickness. The depth variations of energy associated with k=1 and k=2 harmonic components imply significant lateral variation. For instance, the energy calculated for k=1 harmonics in the north (Istanbul Zone) indicates that seismic anisotropy is likely concentrated in the upper crust (within the first 15 km). However, further south, the signature of anisotropy in Armutlu-Almacik and Sakarya Zones becomes more significant in close proximity to the fault zone and dominates at greater (15-30 km and 30-60 km). Furthermore, k=2 harmonic energy maps exhibit relatively high intensities nearby the fault for all depth ranges.