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Objavljeno v: Gradbeni vestnik - 11 - 1968

Avtorji

Sergej Bubnov, dipl. inž.

Potres v Khorassanu

UDK: 624.042

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EARTHQUAKE OF KHORASSAN

EARTHQUAKE OF KHORASSAN Synopsis
The main shock on 31st of August 1968 at 14t7 local time (1047 GMT) destructed the settlements situated in the area of Dasht-I-Piaz and the town of Kakhk. According to informations of USIS the magnitude was 7,8, Richter scale. Duration of motion 3—4 seconds, epicenter near Dasht-I-Piaz. An other severe chock occured on 1th 0f September 1968 at 1057 local time (727 GMT). The magnitude as reported by USIS was 65, duration of motion 2—3 seconds, epicenter near Ferdaus. This shock destructed the major part of Ferdaus and neighbouring settlements. In the period of 15 days there were many earthquakes having the epicenters west and east of the main shock, along the main tectonic fissure in a length of 70 to 80 kilometers and direction WNW—ESE.
The earthquake of Khorassan had many epicenters in the region between 58° 00', and 59° 20' longitude east and 35° 50' and 34® 10' latitude north.
The hypocenters were in the depth of 10 to 25 kilometers.
The intensity of the main shock in the epicenter was according the scale of Medvedev-Sponheuer-Kar-nik between IX and X degree. The destruction effect of the earthquake (isoseist of VII degree) encompassed an area of approximately 5000 sq. km. The entire region showing the destruction effects of all earthquake shocks encompassed an area of nearly 7000 sq. km.
The casualties were the following: 7000—75C0 dead an approximately 2500 blessed.
The geomorphology and geology of the area essentially affected to the resistance of buildings to the earthquake loads. The settlements situated in the narrow mountain clefts 5 to 10 kilometers west of the destructed Khakh showed no damage.
The dwellings on the earthquake area are constructed of clay and unbaked bricks. The cupola chaped roofs with a square ground plan are constructed of the same material. The heavy cupolas could not resist a short but severe earthquake shock and a great number of people were struck during their afternoon rest. Some settlements were totally destructed.
A smal number of ground floor buildings constructed of baked bricks (public buildings) in the zone of VIIIth degree (at Khakh) showed relatively good earthquake resistance.
Some rare high buildings with a long period of vibration (factory chimney at Ferdaus, water tower at Bidokht) remaind undamaged.
Some massive mosques with a short period of vibration were partially destructed, while the cupolas with a circular ground plan in the middle of the building remained undamaged.
The earthquake of Khorassan permits the following conclusions, important for the further development of eartquake engineering:
Geomorphology and particularly the geology of the earthquake region essentially affect the intensity and character of the seismic loads.
Buildings founded on the rocks even with a short period of vibration showed a better resistance to the seismic loads than the buildings founded on a softer geological structures. This fact justifies en elaboration of a microseismic zoning of the earthquake regions, particularly in the towns.
Resistance of the buildings to the seismic loads essentially depends on their capacity to absorb the earthquake energy. As a consequence, the existing method of static and dynamic analysis of structures based on the theory of elasticity (linear deformations) should be replaced by the analysis based on the theory of plasticity (non linear deformations) and the energy theory. Consequently, the materials with a high grade of ductility should be used.
On the earthquake region of Khorassan as well as on other earthquake regions of Iran, the cupola shaped roofs of dwellings constructed of non baked bricks, should be replaced by the light roofs (Siporex, light concrete, light ceramics, timber).
On the ceiling levels of brick buildings the bearing walls should be provided with wreaths (reinforced concrete or steel). Heavy floor structures of solid bricks should be replaced by lighter ones.

Synopsis

The main shock on 31st of August 1968 at 14t7 local time (1047 GMT) destructed the settlements situated in the area of Dasht-I-Piaz and the town of Kakhk. According to informations of USIS the magnitude was 7,8, Richter scale. Duration of motion 3—4 seconds, epicenter near Dasht-I-Piaz. An other severe chock occured on 1th 0f September 1968 at 1057 local time (727 GMT). The magnitude as reported by USIS was 65, duration of motion 2—3 seconds, epicenter near Ferdaus. This shock destructed the major part of Ferdaus and neighbouring settlements. In the period of 15 days there were many earthquakes having the epicenters west and east of the main shock, along the main tectonic fissure in a length of 70 to 80 kilometers and direction WNW—ESE.

The earthquake of Khorassan had many epicenters in the region between 58° 00', and 59° 20' longitude east and 35° 50' and 34® 10' latitude north.

The hypocenters were in the depth of 10 to 25 kilometers.

The intensity of the main shock in the epicenter was according the scale of Medvedev-Sponheuer-Kar-nik between IX and X degree. The destruction effect of the earthquake (isoseist of VII degree) encompassed an area of approximately 5000 sq. km. The entire region showing the destruction effects of all earthquake shocks encompassed an area of nearly 7000 sq. km.

The casualties were the following: 7000—75C0 dead an approximately 2500 blessed.

The geomorphology and geology of the area essentially affected to the resistance of buildings to the earthquake loads. The settlements situated in the narrow mountain clefts 5 to 10 kilometers west of the destructed Khakh showed no damage.

The dwellings on the earthquake area are constructed of clay and unbaked bricks. The cupola chaped roofs with a square ground plan are constructed of the same material. The heavy cupolas could not resist a short but severe earthquake shock and a great number of people were struck during their afternoon rest. Some settlements were totally destructed.

A smal number of ground floor buildings constructed of baked bricks (public buildings) in the zone of VIIIth degree (at Khakh) showed relatively good earthquake resistance.

Some rare high buildings with a long period of vibration (factory chimney at Ferdaus, water tower at Bidokht) remaind undamaged.

Some massive mosques with a short period of vibration were partially destructed, while the cupolas with a circular ground plan in the middle of the building remained undamaged.

The earthquake of Khorassan permits the following conclusions, important for the further development of eartquake engineering:

Geomorphology and particularly the geology of the earthquake region essentially affect the intensity and character of the seismic loads.

Buildings founded on the rocks even with a short period of vibration showed a better resistance to the seismic loads than the buildings founded on a softer geological structures. This fact justifies en elaboration of a microseismic zoning of the earthquake regions, particularly in the towns.

Resistance of the buildings to the seismic loads essentially depends on their capacity to absorb the earthquake energy. As a consequence, the existing method of static and dynamic analysis of structures based on the theory of elasticity (linear deformations) should be replaced by the analysis based on the theory of plasticity (non linear deformations) and the energy theory. Consequently, the materials with a high grade of ductility should be used.

On the earthquake region of Khorassan as well as on other earthquake regions of Iran, the cupola shaped roofs of dwellings constructed of non baked bricks, should be replaced by the light roofs (Siporex, light concrete, light ceramics, timber).

On the ceiling levels of brick buildings the bearing walls should be provided with wreaths (reinforced concrete or steel). Heavy floor structures of solid bricks should be replaced by lighter ones.

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