1962 Bou'in-Zahra Earthquake - Geology

Geology

Iran is a seismically active zone, lying between the converging Eurasian and Arabian Plates. Because it has both strike-slip and reverse faults, earthquakes often proceed so that if one fault is overwhelmed by movement, the movement will branch off to another fault, creating a separate earthquake.

Buin Zahra county lies within a zone of active thrust faults, complemented by folds, that extends south from the Alborz mountains. Despite the presence of faults, Qazvin Province does not regularly experience earthquakes. However, the space between earthquakes allows pressure to build up on faults, increasing the power – and magnitude – of the earthquakes.

Specifically, the 1962 event originated on the Ipak Fault of northern Iran, along which it and aftershocks cut roughly 64 miles (103 km) of west-northwest trending surface faulting.. A feature that extends for 64 miles (103 km) with its connected, smaller faults, the fault runs from the village of Ipak to Takhrijin. Iranian geologist Manuel Berberian's research indicates that the Ipak Fault is at least as old as the Carboniferous period, and has probably been reactivated several times since its formation. On the fault's south side, Carboniferous material is visible; this debris is not evident on the north side, which suggests that the fault was acting as a "dividing fault" while the area around it underwent sedimentation. Berberian could find no trace of Upper Guadalopian or Julfian sediments north of the fault. Another possible reason for this anomaly could be erosion; uplift could have exposed the northern portion of the fault but not the south.