Physical-social pathology of Tehran historical fabric viewed from a resilience approach

Introduction
Historical fabric generally refers to the part of a city in which most of the structure remain but the elements, components and spaces have changed. In Iranian cities, historical fabric refer to the part of urban fabric that have been formed before 1920s.  Preserving these areas plays an important role in societies' awareness of the past and cultural values, and can evoke national pride, a sense of identity and a sense of belonging in citizens. This precious human heritage has been exposed to various damages over time and many of them have been destroyed. Although the emergence of Tehran as a city in Iran does not take long, but during these two and a half centuries, many precious buildings have emerged under the influence of the ancient culture of Iran and the glory of Islamic-Iranian architecture and urban planning. Due to the irrationality of irrational urban plans, lack of protection and maintenance against events and renovations and buildings renovation or due to inappropriate interventions and restorations, an important part of Tehran heritages has been deteriorated. This paper aimed to investigate the factors threatened Tehran historical fabric
Materials and methods
This is a descriptive-analytical research. The data are in three categories. The first category of data taken from documentary sources such as GIS data set of 2016 Iranian Public Census of Population and Housing, Tehran’s land use, and Tehran worn-our fabric. The second category including survey data from the research project of Neighborhood Sustainable Development Document of Tehran, and the third is the evaluation was conducted by 15 experts.  In order to describe and compare the data, survey data were converted to percentage scale. The first and third category data were also were matched with the second category data according to the expert’s opinion. Then resilience map of the neighborhoods has been drawn and analyzed using GIS tools.  The study area is the historical fabric of Tehran, which is known as the Nasiri fence area. It has an area of about 1,500 hectares and was once enclosed in an octagonal wall was built in 1905. This area currently includes 21 neighborhoods.
Results and discussion
One of the risk factors for the Tehran historical fabric is the high probability of occurring devastating earthquakes. In the earthquake risk zoning maps, it lies in a high-risk zone. Tehran has suffered from devastating earthquakes in the years 300 BC, 743, 851, 855, 958, 1177, 1384, 1830 and 1930 AD. Subsidence is also an emerging risk. Digging underground tunnels for city trains, subsidence of old aqueduct canals that have passed through historical sites in particular, extraction of groundwater and the fall of aquifers, the collapse of old sewage absorption wells is among the factors for the occurrence of this phenomenon in the city. The worned-out buildings which cover a relatively vast surface area indicate high vulnerability of the study area. In more than one third of the neighborhoods, more than half of the buildings area is considered as worn- out and in the neighborhoods of Agahi, Harandi, Rah Ahan and Foroozesh, more than 80% of the area is defined as worn -out fabric. Overcrowding can cause more vulnerability. In the neighborhoods of Pamanar, Ferdowsi, Sirus, Baharestan and Sheikh Hadi, the population density is lower than 100 and even in Pamanar neighborhood is 16.7 people per hectare. However, according to unofficial estimates, the daily population of these neighborhoods is even up to 10 times namely more than 1000 people per hectare. High proportion of tenants usually indicates greater vulnerability. In the historical fabric, in general, the proportion of tenants is high. In Darvazeh Shemiran and Harandi neighborhoods, only 23.4% and 32.4% of households live in their own homes, respectively. In two-thirds of neighborhoods, the proportion of tenants is more than 50%. Awareness and appreciation of cultural heritage can be an important factor in enabling public participation in the preservation and protection of heritage. While in the Ferdowsi neighborhood, more than 85% appreciated their neighborhood's cultural heritage, in some neighborhoods, such as Agahi and Rah Ahan, this was close to zero, indicating a lack of awareness. This is normal for Ferdowsi neighborhood due to its location near the three most important universities of Iran. The figure of 2.7 indicates the average vulnerability of the historical fabric. Meanwhile, four neighborhoods of Pamanar, Baharestan, Ferdowsi and Emamzadeh Yahya, which have more important historical monuments, have higher vulnerability. Central neighborhoods in the study area are more vulnerable than peripheral neighborhoods.
Conclusion
Urban historical fabric is a legacy of the past and a link among people and their ancestors. If the cultural heritage disappears from the cities, the link with the past will be disconnected which leads to cities’ loss of identity. Therefore, protecting this heritage from destruction and damage is considered to be a very important and vital task. It is worthwhile for trade and political-administrative functions of the historical fabric to be adjusted and organized, and also for its residential function to be revived and strengthened. Paying attention to cultural heritage requires a holistic approach that encompasses complex concepts as social, cultural, historical, artistic and architectural, economic, urban planning, and sustainable development. However, cultural heritage protection should not only include the capacity to withstand wear and tear over time without losing credibility and usability, but should also pay attention to the capacity of heritage resistant to natural hazards. In the meantime, preventive protection to maintain the historical fabric should be a priority.