1958 Firuzabad earthquake
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   Tehran | |
| UTC time | 1958-08-16 19:13:48 |
|---|---|
| ISC event | 884953 |
| USGS-ANSS | ComCat |
| Local date | August 16, 1958 |
| Local time | 22:43:48 |
| Magnitude | 6.7 Mw[1] |
| Depth | 15 km (9 mi)[1] |
| Epicenter | 34°17′24″N 47°52′01″E / 34.290°N 47.867°E[1] |
| Areas affected | Iran |
| Max. intensity | MMI IX (Violent) |
| Foreshocks | Yes |
| Aftershocks | Yes |
| Casualties | 132 killed, 948 injured[2] |
The 1958 Firuzabad earthquake affected Hamadan province, Iran, on 16 August at 22:43. The Mw 6.7 earthquake occurred at a depth of 15 km (9.3 mi), nine months after another severe earthquake struck the same area. It caused severe damage to over 170 villages in the province. Because of several strong foreshocks, most of the population had fled their homes: the death toll thus only reached 132, with 948 injured. A destructive aftershock on 21 September killed another 16 people.
The geological region where the earthquake occurred, the Zagros Mountains, is seismically active due to ongoing tectonic convergence. As a result, the mountains hosts active faults and a fold and thrust belt to accommodate the convergence. One of these active faults is the Main Recent Fault, a right-lateral strike-slip fault. The earthquake occurred along part of this fault and surface ruptures were reported on four segments.
The Zagros Mountains, stretching for 1,500 km (930 mi) from Turkey, through Iran and Iraq, to the Gulf of Oman, 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 epochs. 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 the major thrust faults of the mountains is the Main Recent Fault, an active right-lateral strike-slip fault.[3] Convergence between the Arabian plate and Iran occurs obliquely along the Zagros Mountains, and approximately 30–50 percent of the ~25 cm (9.8 in) per year convergence between the two plates is accommodated along the range.[4]
The Main Recent Fault delineates the northeastern boundary of the seismically active Zagros Mountains, having formed about five million years ago. It runs parallel to the Main Zagros Reverse Fault, a suture zone separating the metamorphic rocks of the Sanandaj-Sirjan Zone from the fold and thrust belt. The fault comprises several segments with lengths of more than 100 km (62 mi). 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 end in a zone of north–northwest trending strike-slip faults that offset the series of mountainous features. 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.[5]