## 5 Palaeoseismic Trenching along the Doroud Fault  
Previous studies related to the analysis of the seismic activity of the Doroud Fault have been carried out to investigate the pre-shocks and aftershocks of the two major earthquakes in 1909 (Ms 7.4) and 2006 (Ms 6.1) using Coulomb stress and InSAR data [49]. Investigating the fault ruptures and seismic gaps in the northern part of the fault [32] indicates the fault has the ability to have a magnitude 7.1 earthquake. Therefore, the Doroud plain \begin{table}
\begin{tabular}{l l l l l l} \hline \hline
**Number** & **H (m)** & **V\({}_{\mathrm{max}}\) (m)** & **V\({}_{\mathrm{f}}\) (m)** & **R (Radian)** & **NS (m)** \\ \hline
1 & 21.59 & 6.82 & 6.48 & 17 & 22.58 \\
2 & 13.94 & 14.34 & 13.48 & 44 & 19.40 \\
3 & 10.05 & 5.92 & 5.57 & 29 & 11.49 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The mean of the displacements obtained in the gully area due to Doroud Fault activity. H(m) = cumulative horizontal displacement; Vmax (m) = cumulative displacement of the slope on the ground; Vf (m) = displacement of the slope collapse on the fault surface; R (Radian) = rake angle; NS (m) = cumulative displacement fault slip (net slip). Figure 8: A schematic model of the measured horizontal and vertical offsets along the Doroud Fault. (or Silakhor plain) is considered to be highly active in the duration of tectonic activity, according to seismic catalog data [59; 60; 61]. To retrieve the chronology of surface-rupturing paleoearthquakes, we conducted the first paleoseismological study along the Doroud Fault at a site called Darbe-Astaneh (Figures 4 and 9). This site was selected based on geomorphological observations performed from a 3-D model obtained from the GPS (RTK) surveying and field surveys (Figure 9). The trench was excavated perpendicular to the general trend of the fault (Figure 9a,b), where our DEM map and topography profile show a fault scarp (Figure 9c-e). Figure 9: The location of the trench in the middle part of the Doroud Fault. Red triangles show the fault trace. The red triangles indicate fault trace. The red lines indicate the position of the cross-sections. (**a**) SASPlanet image of the fault trace and the excavated trench location for the paleoseismology studies. (**b**) Field photograph of the fault trace and the excavated trench location. (**c**) The 3-D model obtained of the GPS (RTK) surveying of the trench-digging area. (**d**) Topography map based on GPS measurements of the fault trace and excavated trench location (red line). (**e**) Note the component of apparent vertical movement (30.5 cm) -4.5 m fault scarp obtained from the detailed topographical profiles. (**f**) Field photograph looking west along the fault, at the same time with excavation within the pond (red arrow), the fault trace marked by well-developed vegetation. The Darbe-Astaneh trench was excavated across the fault within the wet pond (Figure 9). The sag pond's best depositional environments for preserving paleoearthquake evidence are relatively low-energy environments where sediments accumulate episodically in thin strata, separated by weathering profiles, organic soils, or peats. The stratigraphy in the sag pond is dominated by the continuous quiet-water deposition of finely laminated clayey silt with some interbeds of well-sorted sand. The depositional environment and the general absence of bioturbation because of the high groundwater conditions permit the cm-scale resolution of individual units [5]. The trench strikes N40\({}^{\circ}\) E and has a length of 30 m, a depth of 4.5-5 m, and a width of around 1.5 m. Once the trench was excavated, the walls were cleaned to remove trench smears and gauges created by the backhoe, and field photographs were shown at the same time as the excavation of the trench (Figure 9,g). The excavation exposes a succession of fine-grained, well-bedded layers interbedded with a few gravelly units. The almost fine-grained deposits are primarily horizontal and composed of laminated silts, sands, and gravel.