Manjil Earthquake of June 20, 1990, The Lessons Learned

Abstract

The June 20, 1990, Manjil Earthquake in northwest Iran was the most damaging event to date in the country. That produced the worst earthquake disaster in the history of Iran after the Tabas-e-Golshan earthquake of September 16, 1978, of similar magnitude and intensity in the narrow epicentral area. Considering the damaging effects of one of the most devastating earthquakes in Iran, Manjil–Rudbar Earthquake, with magnitude Ms = 7.4 and estimated epicentral intensity of IX -X degrees of MM Scale, caused 13,911 deaths, 36,693 people treated for injuries, and over 8000 people badly injured taken for hospitalization in Tehran. Damage and losses to the built environment were extremely high, estimated at 4.77 billion dollars in the densely populated region of the provinces of Gilan, Zanjan, and Eastern Azerbaijan, located in the western part of Alborz imbricated mountain belt of northwestern Iran. The real acceleration lines (which are based on a real earthquake in the region) or hypothetical (which are based on a probable earthquake scenario) show the degree of risk and vulnerability of different areas. These maps will be the basis of design and planning decisions in the seismic-prone regions. So the accuracy and precision of these maps will guarantee on the quality and reliability of the design decisions. The June 20, 1990, Manjil Earthquake was strongly felt over an area of 600,000 square kilometers, including Tehran, Tabriz, and several other major cities in Iran. Area of damaging effects in the provinces of Gilan, Zanjan, and Eastern Azerbaijan, with ground acceleration larger than 10% g, was estimated to 49,574 square kilometers affecting 3152 villages and 45 towns and cities in 24 districts with 98 rural districts in the province of Gilan as well as 16 districts with 90 rural districts in the province of Zanjan. More than 214,000 residential units, 1329 school buildings, over 300 health units as well as 82 medical centers and hospitals, a large number of agricultural land and facilities, religious and administrative units, service centers including 68 factories were destroyed or heavily damaged. Over 500,000 families were left homeless, and 178 village locations were abandoned due to landslides and other ground instabilities. In the epicentral region with ground acceleration larger than 30% g with an area of about 8000 square kilometers, 383 villages and the towns of Manjil, Rudbar, Loshan, Jirandeh, and Abbar, most of the buildings were destroyed or damaged beyond repair. More than 67 landslides and many rockfalls were triggered in the wider epicentral region, causing destruction and damages to the transportation systems, water supply, electricity, and other lifelines of regional and urban infrastructure. One of the most dramatic landslides triggered by Manjil Earthquake was the Fatalak landslide, where a huge mass of about one million cubic meters slide down the slope suddenly and all houses of the Fatalak Village were buried with 137 habitants. Lessons learned from this experience and a set of guidelines formulated on its basis will be presented at the end of this chapter.