| 1957 Farsinaj earthquake | |
| Timestamp: | 1957-12-13 01:45:04 |
| Isc-Event: | 887684 |
| Anss-Url: | iscgem887684 |
| Local-Time: | 05:15:04 |
| Magnitude: | 6.5 |
| Depth: | 150NaN0 |
| Location: | 34.388°N 47.748°W |
| Affected: | Iran |
| Casualties: | 1,130 killed |
The 1957 Farsinaj earthquake struck Hamadan province, Iran on 13 December at 05:15 local time. The moment magnitude 6.5 earthquake struck at a depth of . The epicenter of the earthquake was located in the seismically active Zagros Mountains. The mountain range was also the location for several historic earthquakes. The earthquake occurred near two segments of the active strike-slip Main Recent Fault. At least 1,130 people died, including over 700 in the village of Farsinaj. Additional deaths also occurred in Dehasiyab, Sarab, and other villages. The earthquake left an estimated 15,000 homeless; poor weather conditions including a winter storm on 21 December killed another 20 people. Several deadly and damaging aftershocks in that month killed a total of 38 people.
See main article: Zagros fold and thrust belt.
The Zagros Mountains stretching from Turkey to the Gulf of Oman, through Iran and Iraq for formed from continental collision involving the Arabian plate and Central Iran. Its formation occurred during the late-Triassic, late-Jurassic, late-Cretaceous, Oligocene and Pliocene. During its early formation, some extensional tectonics may have occurred. The mountain range is still accommodating deformation, evident from present-day seismicity. Deformation is accommodated by thrust and strike-slip faulting within the range. Parallel to major thrust faults of the mountains is the Main Recent Fault, an active right-lateral strike-slip fault.[1] Convergence between the Arabian plate and Iran occurs obliquely along the Zagros Mountains, and approximately 30–50 percent of the ~ per year convergence between the two plates is accommodated along the range.[2]
The Zagros Mountains is seismically active while in the Iranian plateau, to the northeast, seismicity is nearly absent. The Main Recent Fault delineates the northeastern boundary of the Zagros Mountains, forming between 3 and 5 million years ago. It runs parallel to the Main Zagros Reverse Fault, a suture zone separating the Sanandaj-Sirjan Zone from the fold and thrust belt. The fault comprises several segments with lengths of more than . Southwest of the Main Recent Fault lies the continental margin of Arabia while the rocks to the northeast are of metamorphic and volcanic origin. Its southeastern segments ends in a zone of north–northwest trending strike-slip faults. The strike-slip component of this oblique convergence is accommodated along the Main Recent Fault. The southeastern segments are more seismically active in contrast to the northwestern segments.[3]
Three historical earthquakes were documented near the Main Recent Fault. Two earthquakes in May 912 and April 1008 occurred near the former settlement of Dinavar while a third occurred to the southeast of Dorud before 1889. The first two earthquakes brought heavy damage and casualties in Dinawar. During an earthquake in 912, a "mountain split open" and water ejected from the fissure, sinking many settlements. Ground cracks, possibly associated with tectonic origins was documented during a 1008 earthquake. The Main Recent Fault was also associated with a 7.4 earthquake in 1909 that produced over of surface rupture. Seismicity along the Main Recent Fault was nearly absent since 1909. In December 1955, an earthquake near Razan caused rockfalls and three deaths.
One foreshock was felt 26 hours before the mainshock and 32 aftershocks occurred within a month later. Its epicenters were instrumentally recorded and located, revealing a northeast—southwest trend intersecting the Main Recent Fault. Ground deformations including rockfalls and fractures occurred.[4] There were six reports of ground fractures all trending northeast. Some of these fractures were due to landslides and rockfalls and others extended for kilometers. Villagers reported a vertical rupture located along the Main Recent Fault resulting in the northeastern side subsiding by .