Kinematics and Fault Interaction of the Marmara Segment of the North Anatolian Fault Zone from Fault-Plane Solutions Based on a Refined High Precision Hypocenter Catalogue

Abstract:

The North Anatolian Fault Zone (NAFZ) is separating the Eurasian and Anatolian plates representing a right-lateral transform plate boundary accommodating 20-30 mm annual slip. During the last seismic cycle the NAFZ has produced a series of large earthquakes that started in 1939 in Eastern Anatolia and has propagated westward towards the Istanbul-Marmara region. Here an up to 150 km long segment below the Sea of Marmara remains the only NAFZ segment that was not activated since 1766 representing a seismic gap hosting the potential for a magnitude up to 7.5 earthquake.

Here we present a hypocenter catalogue for the Marmara section of the NAFZ which is a challenge since the fault is located offshore permitting no long-term on- or near fault stations. Using the Akaike Information Criterion applied on a characteristic function derived from higher order statistics as well as autoregressive forward prediction to automatically pick P- and S-onset times, we consistently analyze extensive waveform data provided by permanent seismic broadband stations of a combined regional seismic network with unprecedented station distribution.

The quality of automatically determined travel times is carefully examined by comparing them to manual reference picks which were determined with a scheme emphasizing highest possible consistency and precision. The high accuracy obtained for the travel times results in an improved hypocenter catalog with fewer but well-located events that allow to image the major fault branches of the NAFZ below the Sea of Marmara.

The large network aperture with lacking stations immediately above the seismicity along the fault and insufficient azimuthal station density prevents inversion for focal mechanisms of most single events. Therefore we form spatial seismicity clusters and calculate composite fault plane solutions. Resolving fault-zone geometry and kinematics allow to identify the currently active fault branches and to determine the currently ongoing processes along this key segment of the NAFZ.