Imaging of the 1912 Ganos Earthquake Rupture Zone using Fault Zone Head Waves

The Ganos fault (GF) that is located in the westernmost segment of the North Anatolian Fault Zone (NAFZ) was ruptured by the Ganos earthquake with the magnitude (M) of 7.4 in 1912. The GF is a first order linear and right lateral strike-slip fault with locking depth of 8-17 km. A 40-station seismic network was deployed in September 2017 along GF to investigate the fault zone characteristics at depth. It is possible to analyze the physical properties of the Ganos earthquake rupture zone from the data obtained by the Monitoring of Ganos Network (MONGAN). Fault Zone Head Waves (FZHW) are the best diagnostic signal to examine the characteristics of the low velocity zones and two material (bimaterial) interfaces. A fault consisting of a sharp material contrast between different lithologies is expected to generate FZHW. They spend a large portion of their propagation paths refracting along the bimaterial interfaces. FZHW propagate with the velocity and motion polarity of the faster block, and are radiated from the fault to the slower velocity block where they are characterized by an emergent waveform with opposite motion polarity to that of the direct body waves. The FZHW are the first arriving phases at locations on the slower block with normal distance to the fault less than a critical distance. The high station coverage for MONGAN across the GF allows us to observe micro-earthquake activity and FZHW close to the seismically active region. We have an opportunity to study the rupture process of small magnitude events close to the earthquake source region in unprecedented detail. According to analyzed data from MONGAN (first 6 months), we detect and observe FZHW along the Ganos fault. This observation indicates that variations in seismograms of stations, including significant reflections are identified. These detections are useful in identification of the properties of the 1912 Ganos earthquake rupture zone. Our results also include imaging the velocity contrast across the GF in accordance with the slow side of the fault. This helps to identify damage asymmetry and physical properties of 1912 Ganos earthquake rupture along the GF segment.