Khurgu (north Bandar Abbas, Iran) earthquake of March 21, 1977: A preliminary field report and a seismotectonic discussion

Abstract

Abstract The Khurgu earthquake of magnitude M s = 7.0 occurred on March 21, 1977, in the mountains about 40 km north of Bandar Abbas, South Iran. It killed 152 people, injured 556, and caused destruction over an area of 550 km 2 . The shock damaged 1,500 houses beyond repair and killed 1.3 per cent of livestock in the area. The maximum intensity of the main shock just exceeded VIII (MM). The earthquake was not associated with any fresh surface faulting, nor with reactivation of existing faults or movements of salt domes at the surface. Small and large landslides and rockfalls occurred on steep slopes. A huge rockfall destroyed a village in the eastern part of the epicentral region. Water changed in springs and in one well, water became more salty. Very intense vibration was noticed at the top of narrow and elongated high Quaternary alluvial terraces where stones were found displaced and upturned. A foreshock, which occurred approximately 10 sec before the main destructive shock, gave an early warning and enough time for many people to run out of doors thus saving their lives. This seems the reason for the relatively low number of casualties. The earthquake hit the epicentral areas of two recent events: the 1975 ( m b = 5.8 − 6.1) and the 1977 ( M s = 5.2) earthquakes. However, past damage did not affect the new macroseismic pattern. The only pronounced distortion on the main shock macroseismic pattern was produced by an aftershock, 12 hr later. The Khurgu earthquake is another “Subsedimentary Zagros-type earthquake” case in the Zagros Active Folded Belt, indicating that the adjustment of the metamorphosed Precambrian Basement at depth, caused no tectonic deformation (surface faulting) at the top of the sedimentary cover. The earthquake is of major engineering significance since it provided evidence of the ground motion characteristics of a rare large event in the Zagros.