| Timestamp: | 1958-08-16 19:13:48 |
| Isc-Event: | 884953 |
| Anss-Url: | iscgem884953 |
| Local-Time: | 22:43:48 |
| Magnitude: | 6.7 |
| Depth: | 150NaN0 |
| Location: | 34.29°N 47.867°W |
| Affected: | Iran |
| Foreshocks: | Yes |
| Aftershocks: | Yes |
| Casualties: | 132 killed, 948 injured |
The 1958 Firuzabad earthquake was the second destructive earthquake to strike Hamadan province, Iran, in nine months. The 6.7 earthquake occurred at a depth of on 16 August at 22:43 local time. It caused severe damage to over 170 villages in the province. Due to several strong foreshocks, most of the population fled their homes and the death toll only stood at 132 and another 948 were injured. A destructive aftershock on 21 September killed another 16 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 Main Recent Fault delineates the northeastern boundary of the seismically active 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]
Aftershock activity associated with the 13 December 1957 Farsinaj earthquake continued until mid-February 1958. On 14 August, at 14:00 local time, earthquake activity resumed with a magnitude 5.7 event that was felt strongly in Asadabad, Nahavand and Tuyserkan and scared residents. A magnitude 5.5 earthquake occurred at 19:30; described as violent, it damaged several nearby villages around the three aforementioned cities. These foreshocks had their own sequences of aftershocks with the largest measuring 4.7 and the mainshock on 16 August was preceded by a magnitude 4.5 shock two hours prior. These earthquakes caused panic among the populations and some were damaging. Tourists of Hamadan fled the city following these foreshocks. The last felt foreshock also caused minor damage to villages.[4]
The mainshock was followed by three large aftershocks exceeding magnitude 5.0 while another 30 had magnitudes between 4.0 and 4.9. On 17 August an aftershock damaged several homes in Kangavar and two more in Karkhaneh. Several people died in Asadabad and Akbarabad when homes crumbled during an aftershock in the early morning of 19 August. The most destructive aftershock occurred in Dinavar District on 21 September, devastating a region northwest of the 1957 meizoseismal area. Preceded by a damaging sequence of earthquakes several hours earlier, this magnitude 5.2 shock killed 16 people and devastated Karkasar, Karaj, Balajub, Gamshah, and Kolehjub. Fifty-seven injuries were reported in the villages of Karkasar and Karaj. Homes in Karaj sustained damage including fractured walls and one home was destroyed in the prior earthquake sequence.
The mainshock and its aftershocks occurred southeast of the 1957 earthquake epicenter. Both earthquakes occurred along different segments of the Main Recent Fault. Three sets of surface rupture occurred; all trending northwest–southeast on segments of the Main Recent Fault exhibited vertical offsets. One of these ran between Givaki and Cheshmeh Mahi produced up to of vertical offset. The rupture extended across the Garrin segment to the southeast and Sahneh segment to the northwest. The Nahavand segment was associated with another surface rupture that extended form Barreh Farakh to Laylan. The third surface rupture zone ran for and coincided with the southeastern part of the Sahneh segment.