Based on the existing data, Tehran has so far been hit by over 1000 small and big earthquakes within the 100 kilometers of the around of Tehran. The earthquakes registered measured between 0 and 5 on the Richter scale. The most frequent earthquakes have been those measuring over 3.5. Based on this data, micro seismic activities have basically happened in the following areas: Southeast of Tehran, south of Tehran, near south and north Rey faults, east end of Tehran, along Mosha-Fesham fault.

Prediction hazards of earthquakes in Tehran
Fortunately, Tehran has not been hit by a severe earthquake in the last 150 years. According to the catalog of historical earthquakes and the existing documents, many earthquakes have hit the regions around Tehran, which might have affected Tehran. The biggest earthquake of all hit the region (50 kilometers off Tehran) in 958. It measured 7.7 on the Richter scale. The earthquake was due to the activity of the western part of Mosha fault. The fault of the north of Tehran is situated between the western part of Mosha fault and the city of Tehran. If the north fault becomes active, the damages from the earthquakes will be more severe than those from the earthquake in 958. The north fault is situated between the urban areas and the northern mountain. It is more than 90 kilometers long, but its northwest part is far from Tehran. Thus, its eastern part can potentially be the center of a future earthquake.
The fault in the south of Rey, too, can be dangerous. This fault extends along the southern side of Rey subsidence and almost parallel to the fault in the north of Rey and along the northern side of the subsidence. The distance between these two faults is only 3 to 5 kilometers. It seems that both faults are branches of the same fault. It is possible that there are hidden faults under the sediment layers of Tehran. If that is the case, it is very difficult to determine their exact positions, and any part of the city will be equally probability to earthquake. What is certain is that Tehran is liable to earthquakes. This is evidenced by the history of the city and the mechanism of the faults of the region. But the urban management has time to adopt appropriate policies to lessen the possible damages.

Flooding and immersion of streets in Tehran
Tehran has expanded on the slopes of Albourz Mountains, where there is great precipitation. Several rivers take the water to the lower desert. The total drainage area of the north, the northeast and the East mountains is more than 600 square kilometers. The direction of rivers is mainly toward the city. As a result, when there is a shower, the streets of Tehran are immersed and in the case of heavy showers, there is the possibility of flood.
Yet within Tehran urban limits, there are many rivers and drainages, which carry the water from the basins lands and the water from the rain. In some parts of the city, where the land value if very high, the river banks and flood plains have been encroached and their borders have been shrunk. This can affect the natural regime of rivers and bottom lands, resulting in irreparable damage in cases of heavy showers.

Tehran’s drainage network can be divided into three main parts:
  • Northwest and north drainages, which cover Kan, Vask, Farahzad and Darakeh rivers as well as Shahin and Tapeh Neyzar canals. The water of these drainages, after passing the mountain basin and a part of the urban limits, is carried to the Kan river through the levee located in the west of the city. The total drainage basin of these drainages is 415 square kilometers.

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  • The north, northeast and east drainages, expanding from Velenjak in the north to Sorkheh Hesar in the east, include Velenjak, Darband, Golab Darreh, Kashanak, Jamshidiyeh, Dar Abad and Sohanak Rivers and Tehran Pars flood plains and canals. The main canal, situated along the west, Manouchehri and Abouzar canals, joints Sorkheh Hesar canal and leads to Barout Kobi bottom land in the southeast. It is to be noted that Hefdah Shahrivar tunnel, Shahrdari and Shahrzad canals are all part of this system, covering the east urban region of Tehran. These drainages cover an area of 520 km¬2.
  • The drainages in the central districts of Tehran are mainly in the form of tunnels. They collect the surface water of most of Tehran urban limits. Khayyam and Navab tunnels and Firouzabad canal are the most important drainages of the central area of the city. The above-mentioned routes carry the water out of Tehran, overflowing their banks in case of heavy floods.
Considering the characteristics of water transfer routes and the precipitation rate within the basins under study, the areas where floods could affect are shown in the related map. Mass movement in metropolis Tehran limits: Mass movement is a process in which parts of geomaterials move toward the slopes.
This movement often occurs in steep surfaces by a force or the disruption of balance or stability of earth, inflicting heavy damages. There are many factors responsible for this instability, including: topography conditions, humidity and precipitation, natural rivers and drainages, seismicity and also structural geology. Tehran and especially the north of province have great potential for landslides. The famous Tar Lake near Damavand is caused by the slide of a great mountain near Mosha-Fasham fault. The landslides occurring in certain regions are caused by the passage of great faults and the crushed plains resulting from the passage of these faults, existence of unconsolidated rocks, and sufficient precipitation.
The slopes on the right side Beach of Latiyan Lake also have the potential for landslide. Other potential areas include the areas along the river leading to Loshan, Shemshak Skiing Track and the surrounding areas including Aftab piste, Zagoon and Lalon villages, Adran village in the eastern slopes of the Karaj drainage basin, and Khor and Chenaran villages. Some cases of landslides have occurred in Karaj dam upstream area, Taleghan countryside, Javestan road, Gelird village, Orouzan, Dizan, Mehran and Artoon, Khodkavand, Minavand, Gerab, Gateh Deh villages, Nareyan and Khachireh and so many other areas. These slides present potential threat to Tehran.

Solifluction
Liquefaction is a process usually experienced at the time of an earthquake; it happens when soil, turning into liquid, can no longer bear weight and starts to move, destructing all the installations and buildings made on it. Some parts of the greater Tehran have the potential for solifluction. These parts include the mountainous areas due to their caprock, and most dune-bedded areas due to thin earth and lack of subterranean water (except for the valleys and river beds). The northern areas of Eshteharad plain have little potential for liquefaction since the level of the subterranean water is high and the ground is swampy and salty. The southern side of Jaroo Mountain has a high potential for solifluction . In certain areas in the middle of the Hashtgerd plain, due to the high level of subterranean water and the nature of the subsurface earth, there is little potential for solifluction; in the Kordan river bed and its minor branches moderate solifluction can be expected. In Lavasanat region in the northern side of Lathiyan dam, where the level of subterranean water is high, little potential for solifluction is estimated. In the alluvial riverbeds, an average potential for solifluction is expected and in the regions around Boomehen and Abali, the potential for solifluction is low.
In Firouzkooh region, except for an area in the east where there is little possibility of liquefaction, the potential for solifluction is average in the riverbeds of the districts especially in the wide Firouzkooh Savachi riverbeds. Hablehrood riverbed in Mazdaran district has the same condition. Except for some limited areas, there is no potential for solifluction in Tehran and Karaj and the areas outside the cities. In the riverbed of Shoor and Karaj rivers in Robat Karim and Varamin districts in the south of Tehran, and in the Geloo riverbed in Varamin plain, there is an average potential for solifluction.

Flood area with a centennial torrential return period

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حق انتشار اطلاعات براى شهردارى تهران محفوظ است 1396 - 1385
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