Examination of reasons of variance in earthquake damage rates in earthen buildings of the historic village of Esfahak post Tabas earthquake

Earthen building materials have been in common use as cheap, available, and practical construction materials in hot and dry areas for a long time. Earthen buildings exist in Iran, especially in villages, because of the large and numerous areas that have the same climate. Given that Iran is highly earthquake prone and the importance of paying attention to the possible vulnerability of all the indigenous buildings, endeavours for identifying the possible weak points of the earthen village buildings in an earthquake situation become doubly important. Especially to save human life. On the other hand traditional building methods and life patterns related to village earthen buildings are an important part of the Iranian architectural history in using local building materials that need conservation. One of the collections of earthen buildings that has been damaged and has suffered various degradation during the Tabas earthquake of 1979 is the village of Esfahak located 38 kilometres south-east of the Tabas county, which has also been inscribed in the National Heritage List of Iran. After the aforementioned earthquake and the damage and destruction of the earthen houses in this region, the survivors left these buildings and started constructing buildings using new materials and building styles that clashed with their old architecture just a short distance away. But currently, with the focus on indigenous heritage and the development of the indigenous tourism sector, the residents in this area are asking for the repair and restoration of these buildings. In this respect and before any action is taken on strengthening the above-mentioned buildings, it is essential to study the earthquake damage in these buildings. A remarkable point related to the earthen buildings, is the different rates of damage in these buildings during the earthquake. Some of the buildings have suffered serious damage while other others have only minor damage or are completely unharmed. The existence of possible difference in the architectural template and the implementation method for these buildings is a possible factor in the variance in the rate of damage in the buildings and better performance of some of these structures during the earthquake. Examining the validity of this matter and a study on the existence of other factors influencing the difference in performance of some of these earthen structures have been done in this research. In this research, a field study of the different rates of damage in the earthen structures has been used as a basis to perform diagnostic studies in attaining the reasons for the structural failures of the earthen buildings in this village. Apart from endeavouring to reach a correct understanding of the seismic behaviour and the damage in these structures form the earthquake, such research is a precursor for any type of seismic improvement of these structures. This research is descriptive-analytical and the required information has been gathered using academic and field studies. The results of this research show that the passing of the Qanat underneath some of the homes has resulted in the increase in the damages. Also the different building patterns used for the structures (troglodytic, strata, moulded mud brick), has a direct impact on the seismic performance of these structures. The low implementation quality, and not using the appropriate structural strengthening methods to increase the seismic resistance of these buildings by the builders is another reason for the different rates of damage in these buildings.