تحليل زمين لرزه سال 1990 فورك (داراب ) در جنوب ايران

Analysis of the 1990 Fork (Darab), southern Iran, earthquake sequence

The Fork earthquake occurred in Zagros mountains at a distance about 120 km from Darab city in Fars province, producing extensive destruction but relatively low rate of human loss. Field investigation and the distribution of aftershocks suggest an east-west trend faulting with a reverse mechanism having a small strike-slip component. The locally recorded aftershock activity was extended to a length of about 40 km and a depth of about 30 km. The majority of aftershocks took place at a depth range 10-20 km and was scattered indicating a complex mode of faulting. The result of waveform inversion indicated that the mainshock had mainly reverse mechanism and the source process included two main fault slip. The total seismic moment was calculated to be M()= 3.1 x 10^ dyne cm. The calculated maximum dislocation was about 50 cm and the obtained moment magnitude was Mw = 6.2. The average stress drop was estimated to be 25 bar and the average dislocation was 25 cm. The Fork earthquake is one of the rare events that has occurred in Zagros suture zone with magnitude greater than 6. Therefore, the ground-motion characteristics during the mainshock should be considered for the high safety design of structures in the damaged area.