## 4 Geomorphology and Slip Rate of the Doroud Fault  
The use of morphological offsets to determine the long-term slip rate on an active fault requires datable morphologic features, which were first displaced by the fault motions and then preserved over the observable displacement [54; 55; 56]. We used the satellite image of the satellite interpretations of the digital elevation model (DEM) at 10 m, SASPlanet satellite images ([[http://www.sasgis.ru](http://www.sasgis.ru)]([http://www.sasgis.ru](http://www.sasgis.ru))), and the field observations by reconstructing the satellite image and measuring in the field; we came to the conclusion that the Doroud Fault has caused the maximum cumulative horizontal (dextral) offsets in the Pliocene-Quaternary units of the rivers by \(\sim\)775 m and \(\sim\)30 m (Figures 5 and 6). The observed displacements are associated with the southeastern and middle segments of the Doroud Fault, which ruptured during the 1909 Silakhor earthquake [16; 18; 32; 48]. Geomorphic evidence, such as dextral surface ruptures including beheaded gulles (Figure 6c) and shutter ridges (Figure 6d), is visible within the mezoseismal area of the 1909 earthquake, which demonstrates the fault zone in this region (Figures 6 and 7) and its relationship to the late Pleistocene-Holocene activity of the Doroud Fault. However, the surface expression of the strike-slip fault is poorly exposed in the study area, with only a few possible nominations. These offsets, ranging from several meters to a kilometer, are observed from southeast to northwest. Figure 5: Offset reconstruction and morpho-structural interpretation: (**a**) The 3D perspective diagram (vertical exaggeration = 2) of the SE area (see Figure 2 for the location). Digital elevation model extracted from Aster 15 m. In this area, the Doroud Fault trace located between Quaternary alluvial and Pliocene piedmont deposits. (**b**) The present-day situation with three drainages and fault. The red box indicates the location of the (**c**). (**c**) Google Earth image of the right-lateral horizontal offsets of three rivers. The blue and red arrows indicate the rivers and right-lateral fault mechanism, respectively. (**d**) Reconstruction of the rivers to their initial position after back-slip the fault on the SASPlanet image of \(\sim\)775 m of the rivers (1 and 2) offsets along the fault trace. Figure 6: The Doroud Fault trace with offset reconstruction for drainages in the Quaternary sediments. The blue line and red arrows show rivers and fault traces, respectively. The red and blue arrows indicate fault trace and rivers, respectively. The dark box indicate the location of the (**b–d**). (**a**) The topographic map of the central part of the area. Black lines delineate a topographic crest for calculating the ratio of vertical and horizontal displacement across the fault. (**b**) Field photograph of three offset rivers with fault trace within young alluvial. Offsets from left to right are 13 \(\pm\) 2 m, 20 \(\pm\) 3 m, and 23 \(\pm\) 2 m, respectively. (**c**) SASPlanet image view of the reconstruction of the drainage to its initial position after back-slip (30 \(\pm\) 2 m) along the fault trace. (**d**) Another field photograph of several offset drainage with fault traces. Slip rate studies are landform-based paleoseismic studies, the aim of which is to calculate a long-term fault slip rate from landforms offset by multiple events. They are usually reconnaissance studies on poorly known faults and precede trending studies. Slip rate studies can be performed at widely varying spatial and temporal scales [5]. These different sizes of offset features propose an excellent opportunity to better document the seismic behavior and the occurrence of past large earthquakes on the Doroud Fault. Several displaced guillies close to the TC trench site (Figure 4) afford an opportunity to establish the fault slip rate.