Stress State Study of Siah Cheshmeh-Khoy Fault Zone (NW-Iran) and Using Stress Separation Method in Separation of Neotectonic Stresses from Paleostresses

In the present study, the state of stress in SiahCheshme-Khoy fault zone area in the North-West of Iran has been analyzed based on the systematic inversion of focal mechanisms of earthquakes, and fault slip data, to characterise the stress regime controlling of most faults and earthquakes in this area. The calculated average stress regime in this area indicates major NW-SE trending compression which dominates stress regime in strike slip mode with an intermediate stress axis, σ2, close to vertical. Reconstructed stress has shown that average seismotectonic stress and average stress obtained from fault slip data do not have consistency due to of the multi stress regimesin this fault zone. Nonetheless stress separation analysis results for fault slip data and earthquake data have good consistency and their first and second analyzed stress regimes have the same trend. Also comparison between the results of the stress separation analysis between fault slip data and earthquake data, has shown that the second andthird stress regime of this analysis are neotectonic stresses that controlling this fault zone movements. The forth stress regime also is a neostress regime that has been shown in seismotectonic stress separation analysis also, but it seems related to the deep faults. The first stress regime that have resulted from stress separation analysis of both field and earthquake data, it seems a paleostress regime which is not shown in seismic data analysis. Also reconstructed stresses in this study, have good consistency with the latest studies in this area especially with geodetic studies.