Document Type : Original Research Paper
Authors
1 M.Sc., Engineering Department, Kayson Company, Tehran, Iran
2 Assistant Professor, Department of Geology, Islamic Azad University, North Tehran Branch, Tehran, Iran
3 M.Sc., Atomic Energy Organization, Tehran, Iran.
4 M.Sc., Ahwaz Urban Railway Project, Kayson Company, Ahwaz, Iran.
Abstract
Ahwaz city, the center of the Khuzestan province, is located in southwest of Iran. The four main geological phenomena of this area are Ahwaz Fault, Ahwaz Anticline, Aghajari Formation, and Quaternary Alluvium and Eluvium Deposits. The Ahwaz Urban Railway Project and its related comprehensive geological and geotechnical studies were started in 2006 and the first phase of the project consisted of 24 Km parallel twins tunnel & 24 stations. The project level is -17.5m beneath the ground surface, except for the crossing with the KarounRiver. The twin tunnels cross under the KarounRiver in lower elevation. The most important part of the project is crossing safely under the KarounRiver. Therefore, this area, which is located in the southern vicinity of the Ahwaz Fault, was studied precisely by surface and under-ground methods. The Ahwaz Fault divides AhwazCity into two sections. The north, north-east section (hanging wall), which depth of the bed rock is 8-12m and is covered by young quaternary sediments, and south, south-west section (foot wall), which its bed rock is settled down totally and cannot be reached by geotechnical drilling. The Karoun River has meander form in the Khouzestan Province (also north and south of Ahwaz City), but in center of the city (especially in crossing with the Ahwaz Fault) this form changes into straight shape, so it means that the Karoun River channel in center of Ahwaz is young and affected by the Ahwaz Fault. The logs of geotechnical drilling in river bed and river banks were studied vertically and horizontally in order to find out the stratigraphic changes of the KarounRiver sediments. These studies show that stratigraphic sections of the Karoun River reveres from west to east horizontally and also vertically in recent thousands years in crossing area with the Ahwaz Fault. These evidences support the hypothesis of affection of the Ahwaz Fault activity on the KarounRiver movement. Therefore, the age of river bed deposits was measured by thermal luminescence method in order to realize the age of one the main Ahwaz Fault activities, which change the river channel. The results of age dating show that the old river channel has changed to the recent one about 4000 years ago. In other words, the KarounRiver channel changed after an earthquake struck this area. In addition, two new faults were discovered in the Foroodgah square and the Mosala stations during the excavation in north-northeast of the Ahwaz Fault. An inferred fault was discovered in the CulturalCenter station as well.
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