Abiz Fault Segmentation Based on Morphotectonic Indices

Iran has been extensively studied over the last decades because its territory offers the rare opportunity to observe and quantify how the convergence between two plates Arabia and Eurasia has been accommodated from its onset to its present-day continuation, i.e., continental collision within Iran. Additionally, Iran is the site of frequent devastating earthquakes, and it is thus of critical importance to understand how those earthquakes emerge from the overall tectonics that affects the Iranian territory. All principal seismogenic faults in eastern Iran are known and their recent to current activity is not in dispute. Abiz fault is one of most active fault in Iran. It is plausible that at present the region is experiencing a temporal clustering of large magnitude earthquakes, just as the Dasht-e-Bayaz and the Abiz faults in northern and northeastern Lut Block. The earthquake took place on the right-lateral Abiz fault. The surface trace on the ground was measured at 125km for a horizontal displacement of 2.3m and a vertical one of 0.9 so a total one of 3m. The rupture length can be considered as the greatest one in the entire earthquake database done here. Nevertheless, the magnitude and the displacements are not the greatest one. The magnitude was reported as 7.3. Previous earthquakes in 1936 and 1979 occurred on the fault but did not break more than 2 segments each time. One of the major challenges in assessing potential seismic hazards is to reliably identify regions of preferred upper crustal deformation. Landform morphometrics and the respective tectonomorphic indices can be used as basic reconnaissance tools of tectonic activity which can indicate areas at risk. The qualitative and quantitative descriptions of landform development are used to identify areas dominated by rapid tectonic deformation or erosion on a local scale. In this paper, the relative active tectonic of the Abiz fault has been discussed according to the geomorphic indices using ArcGIS software. Measured indices are stream length-gradient index (SL), ratio of valley floor width to valley height ratio (Vf), Asymmetry factor (AF), index of drainage basin shape (Bs), Hypsometric curve (HC), Hypsometric integral (Hi), River sinuosity index (S), index of mountain front sinuosity (Smf). The fast evolution of digital elevation models (DEM) provides an ideal base for remotely sensed morphotectonic studies of large areas using Geographical Information Systems (GIS). However, a manual extraction of the above mentioned morphologic parameters may be tedious and very time consuming. Moreover, basic GIS software suites do not provide the necessary built-in functions. Therefore, we present a newly developed, Python based, ESRI ArcGIS compatible tool and stand-alone script, the Morpho Tool. This tool facilitates an automated extraction of the Vf-ratio and the Hc-factor data for large regions. Other factors was calculated manually. Using a digital elevation raster and watershed polygon files as input, the tool provides output in the form of several ArcGIS data tables and shape files, ideal for further data manipulation and computation. This coding enables an easy application among the ArcGIS user community and code conversion to earlier ArcGIS versions. As basic data set we use a freely available 90 m resolution Shuttle Radar Topography Mission (SRTM) DEM of a 800 x 300 km large area of the study area. Using this DEM, we perform several preprocessing tasks using ArcGIS (ESRI), including the ArcHydro extension. These preprocessing tasks include the detection and removal of cells with undefined drainage values (sink cells). Next, watershed areas are delineated by stream flow analysis, along selected mountain fronts, and stored as a polygon shape file. To enable proper distance measurements, all initial files, the watershed shape file and DEM of the study area, are converted to the projected coordinate system WGS 1984 Zone 40S. Using the result of indices, index of relative active tectonic (IRAT) calculated as well. The results show that the Abiz fault relative tectonic activity index falls into three group. From Southeast to the Northwest: they are a) the areas between North of Zeidan to South West of Ahangaran, b) West of Hajiabad to South Nodeh and c) East of Esfad to East of Fandokht. The lowest IRAT values are located in Ardekul and Kalshur. Because of flat topography in Kalshir area, it’s not possible to sense some of morphotectonical indices, so the numeric values are low.