Iran Earthquake of 1990
Earthquakes in Iran have killed thousands of people
since the first was recorded about AD 700. There have been fifty-four significant
earthquakes in Iran in the past thirty years alone. Theseearthquakes occur
as Iran is compressed by Africa and the Arabian Peninsula which is moving
towards Eurasia at about sixteen millimeters per year. The epicenter of
the June 1990 earthquake was located in the collision zone between the
Arabian plate and the Eurasian plate. This area-the Northern Seismic Zone-runs
east and west along the southern shore of the Caspian Sea. This highly
seismic region has reportedly experienced fourteen earthquakes with magnitudes
between 6.0 and 7.7 within the last 1200 years. In 1962 an earthquake of
similar magnitude in the area killed 12,000.
The June 1990 earthquake caused widespread damage
in areas within a one hundred kilometer radius of the epicenter near the
City of Rasht and about two hundred kilometers northwest ofTehran. The
cities of Rudbar, Manjil, and Lushan and 700 villages were destroyed, and
at least three hundred more villages were slightly damaged. There was $7,000,000
in damage in Gilan and Zanjan provinces southwest of the Caspian Sea. One
hundred thousand adobe houses sustained major damage or collapsed resulting
in forty thousand fatalities, and sixty thousand injured. Five hundred
thousand people were left homeless.
Rescue operations were hampered by the fact that
the earthquake occurred in the middle of the night, by adverse weather
conditions, and by the rugged terrain of the mountain villages. Roads and
highways were blocked by extensive landslides further hampering rescue
operations.
About one hundred thousand buildings collapsed or incurred major damage.
Factors contributing to this extreme damage include:
Construction materials: the use of brittle construction materials,
brick, block, adobe, wooden timbers, and modern materials inappropriate
for use in traditional structures.
Construction techniques, and workmanship: the use of unreinforced
masonry, and unreinforced sheer walls, poor welding of connections in steel
frames, failure to tie steel support beams together, and the use of heavy
masonry without adequate support in flooring, ceilings, and roofs.
Inadequate design and detailing: Some modern structures lacked
the symmetry of earlier traditional structures. Earthquake resistant designs
were not used. Building codes were inconsistent or unenforced.
Large differential settlement due to liquefaction. The building
to the left sank relative to the small (lighter) attached structure. The
structures probably do not share a joined foundation.
Liquefaction and failure of the soils: This was especially prominent
on the shores of the Caspian Sea. Pressure from the earthquake forced ground
water droplets between the grains of sand. The soil temporarily lost strength
and behaved as a viscous liquid. With no firm support, structures sank
or were spread apart by the liquefied soil. The unconsolidated soils may
also have amplified the seismic vibrations.
Often several factors contributed to the failure of a single structure.
The single most important factor in building failures was the use of unreinforced
masonry walls. Application of the information gained from the study of
this event will result in the saving of lives when the next earthquake
strikes in this highly seismic region.
Source: http://www.ngdc.noaa.gov/cgi-bin/seg/m2h?seg/haz_volume2.men+MAIN+MENU
Last edited 11/30/98
by Thuy Trinh and Andrew Beavers