North Anatolian Fault Passive Seismic Experiment: Receiver Functions Along a Major Strike-Slip Fault

A major question in continental strike-slip fault zones concerns the deformation style in the lower crust and mantle. In this respect, the North Anatolian Fault (NAF) is an excellent example and gives us an opportunity to study a snapshot of lithospheric deformation along an evolving continental transform plate boundary. In this study, we analyzed seismic data recorded by 5 broadband stations deployed near the central segment of NAF in the summer of 2005 as a part of the North Anatolian Fault Passive Seismic Experiment. Teleseismic receiver functions are computed at each station and a grid search scheme is applied for crustal thickness and Vp/Vs using arrival times of the Moho pulse and its multiples. According to our results, crust in the vicinity of the NAF is 35 km thick with a flat Moho and has a relatively high Vp/Vs ratio (>1.8) supporting the presence of partial melt in the crust. Specifically, receiver functions recorded at station ALIC which is located on the main strand of the NAF samples adjacent blocks across the fault and show a sharp change in upper crustal structure (0-20 km) but no Moho offset. These observations may suggest that the NAF becomes a broad shear zone in the lower crust rather than extending into mantle as a vertical fault. Stations that sample adjacent blocks also exist for other major continental strike-slip fault zones such as the San Andreas, East Anatolian Fault, Alpine Fault, etc. By using a similar approach, we can obtain more conclusive evidence regarding the depth extent of these faults and tectonic significance of the absence or presence of Moho offsets.