Estimate earthquake risk to the Takht e Jamshid historical site (ne Shiraz, Fars, Iran)

Taheri F., Zamani A.

Department of Earth Sciences, College of Sciences, Shiraz University, Shiraz, Iran

ttectonis@yahoo.com

Geohazards and natural phenomena such as earthquakes, tsunami, and landslides are mainly caused by processes in the earth which are going on for a long time. Recently scientists used earthquake catalog and geodetic measurements for evaluating active tectonics. But the time span for these data doesn’t cover the whole cycle of deformation. To overcome this difficulty in the study of neotectonics, morphotectonic analysis of landforms is useful because they recorded history of deformation in about one million years.

Slip and creep behavior of Faults may lead to uplift or subsidence and changes attitude of the geological structure and related geological hazards will be accrued. Detecting state of active tectonic and relative activity in structures is the first step to identify any possible geological hazards that related to tectonic. Geological hazards threaten human life and also their structures. Some of these structures are important because of the historical and cultural concepts such as archeological sites.

Iran is one of the high seismic active countries in the world. The occurrence of big and destructive earthquake in this country resulted in the destruction of buildings and economic institutions, cultural and historical sites. The major damage of. Arg e Bam one of the UNESCO’s world heritage sites in Iran. This is destructed in December 26, 2003 by Bam earthquake. During the history, many of Iranian archeological sites are destroyed or damaged by geological hazards the attention of government officials and experts. Many of these sites placed in Fars province. One of the most important sites is Persepolis (Takht e Jamsid).

The Study area is bounded between East longitude 52 ^o 50' and 53 ^o 10' and North latitude 29 ^o 45' to 29 ^o 55.' This is situated in 70 Km northeast of Shiraz in Rahmat anticline. This area registered as a UNESCO’s world heritage site in 1979. On the other hand, this site is located in simple fold zagros (Zagros orogenic belt, one of the active tectonic regions in the world). This incline included faults with combined reverse and strike–slip movements.

In this research in order to study active structures, morphotectonic analysis using geomorphic indices of mountain fronts and related fluvial systems such as mountain front sinuosity index, hypsometric integral, stream, Valley floor width – height ratio and Drainage Basin Shape Index. These indices have been measured with digital elevation model (DEM) with the use of GIS environment.

1- Mountain front sinuosity index: The Smf index reflects a balance between the tendency of stream and slope processes to produce an irregular (sinuous) mountain front and vertical active tectonics to produce a prominent straight front. The Lmf is the length of mountain front along the mountain–piedmont junction and Ls is the straight-linelength of the front [1, 2].

2- Valley floor width – height ratio and Drainage: This study transverse valley profiles were located 0·5km upstream from the mountain front in smaller drainage basins, Vfw is the width of valley floor, Eld and Erd are the respective elevations of the left and right valley divides and Esc is the elevation of the valley floor.

3- Drainage Basin Shape Index: Bl is the length of the basin. The Bw is the width of the basin. The typical basin of a tectonically active mountain range is elongate, and basin shapes become progressively more circular with time after cessation of mountain uplift.

4- Hypsometric integral: In this study Hmin, Hmax, Hmean were defined elevation sub basin [3].

Result:

Results indicate that Rahmat fault zone which is in southeast of study area has a higher level of activity Naghshe Rostam and Takhte Jamshid are located close to this fault. In order to prevent serious damage to these historical sites evaluation of the seismic risk in the study area plays an important role in mitigation of earthquake damages.

References:

1. Keller, E.A., (1986), Investigation of active tectonics: use of surficial Earth processes, In Wallace (ed.), Active Tectonics, Studies in Geophysics, National Academy Press, Washington, DC, p 136–147.

2. Maria Teresa Ramirez-Herrera (1997) Geomorphic assessment of active tectonics in the acambey graben, Mexican volcanic belt P 317-332

3. Strahler, A.N. (1952)”Hypsometric (area-altitude) analysis of,” erosionaltopography Geological Society of America Bulletin 63p 1117–1142.