Teleseismic interpretation of the 1968 Dasht‐e Bayaz, NE Iran, Earthquake

Abstract

The 1968 Dasht‐e Bayaz earthquake is the oldest destructive earthquake in north‐east Iran recorded by the WWSSN network at teleseismic distances. These records are well distributed in azimuth and allow a detailed study of the rupture process of the main shock. We invert the WWSSN long‐period body waves of the Dasht‐e Bayaz earthquake and its principal aftershock, which occurred about 20 hours later, to their sources to study the complexity of the sources. The results of our analysis suggest that the main shock consists of three major subevents while the principal aftershock is a single event. Mechanisms of the subevents of the main shock are mainly strike‐slip and consistent with the observed fault movement. The principal aftershock has a dip‐slip mechanism. The sum of the seismic moments of the main shock is ∑M0 = 4.5×1026 dyn cm. The moment of the largest subevent of the main shock is M0 = 2.4×1026 dyn cm and its stress drop is about 200 bar. This shows that the main shock has a high stress drop nature. The largest subevent with shallow depth and large lateral displacement mostly caused the great destruction during the source process of the main shock. The moment of the principal aftershock is M0 = 1.9×1025 dyn cm and its stress drop is about 40 bar. Mechanism of the earthquakes suggest that there is a shortening in north‐east Iran mostly due to the north‐east compressional stress in the Iranian plateau.