Moment tensor and stress inversion for an active fault system in west part of Lut-Block, Iran

Abstract

Iran is one of the most tectonically active regions on the Alpine-Himalayan earthquake belt. Eastern Iran, nowadays, is one of the most active regions of the country. The occurrence of several destructive earthquakes during the past 50 years provides the evidence for the seismic activity in this region. The earthquakes are mostly concentrated around the Lut-block. There are strike-slip fault systems with nearly north-south strike, east and west of the Lut-block. The fault system located in the west part of the Lut-block includes Tabas, Nayband, Lakarkuh, Gowk and Sabzevaran faults. This system is of great importance since it has generated destructive earthquakes such as Dasht-e-Bayaz. Since understanding the focal mechanism of the fault responsible for earthquake is one of the most important parameters, the accuracy to calculate the focal mechanism is extremely vital. Therefore, we have calculated focal mechanisms of the 34 recent earthquakes happened on this system using full moment tensor inversion. The waveform data from 8 broad-band stations, operated by International Institute of Earthquake Engineering and Seismology (IIEES), was used in this study. Appling ISOLated Asperities (ISOLA) package for the full moment tensor inversion using the local and regional data enables us to achieve a higher accuracy in determined focal mechanisms, in comparison with other methods which use teleseismic data. As the magnitude of these events are all smaller than 5.5 (the biggest one equals 5.2), it was not possible to obtain the focal mechanism of almost all of these events through CMT solutions using teleseismic data. The obtained focal mechanisms show that the main mechanism of the Nayband-Gowk-Sabzevaran system is right-lateral strike-slip with a reverse component. The trends of the three main stress axes were also calculated using the 32 focal mechanisms and the stress inversion technique. The results show that the second stress axis (σ2) is nearly vertical, which is one of the characteristics of the strike-slip regimes.