1-Introduction
Geology refers to tectonic processes that create changes in the earth's crust during a time scale. Most transformations are important for human societies. Studying the geology of an area is very important in assessing the risk for that area, especially in areas where the amount of tectonic activity during the Holocene and Upper Pleistocene is high, these studies will be important. Although tectonics is the gradual breaking of the earth's crust, which may damage human-made structures, but most of the processes that cause sudden events are important. Based on this, knowledge of the terrain-structure in a region can reduce the risks of sudden events (such as earthquakes) (Keller & Pinter, 2002).
The surface rupture zone of an earthquake fault is defined as the distance from the fault where all structures and facilities face the direct risk of structural rupture, regardless of their vulnerability. Based on this, any type of facility and structure, with any degree of retrofitting, will not be able to deal with surface cracking, and there is no option other than changing the location of the structure for the safety of the structure (CDC, 2002).
The purpose of this research is to investigate the evidence of active tectonics and activity of the Kundaj fault in the Quaternary, which will be done through field observations of trenches in the alluviums and alluvial cones of the investigated area, and it will be tried to clarify the location of the Kundaj fault in alluvial areas.

2-Materials and methods
The investigated area covers the distance between the city of Abek and Qazvin, and in this area, the evidence of the activity of the Quaternary Kundaj fault has been examined. The location of the Kundaj fault is shown on the geological maps in Figure No. (1). As can be seen in the map the Kundaj fault has been identified in a small area and its approximate length is 4 km, and in the 1:100,000 map, the approximate length is 30 km. This fault has been taken into account, and about 9 km of it has been determined, and the rest of the length of the fault, which passes through the Quaternary alluvial zone, is a dashed line, and its exact location is not known. In this research, the location of the fault has been identified and verified.
The research method in the current study is based on library studies and field observations. In this regard, the information related to the geological and geo-structural situation is examined in a library form, and then the evidence of faulting in Quaternes alluviums is discussed in relation to the field investigations. After completing the geological information, evidence of faults and studies of Quaternary alluviums and location of evidence of fault activity, data analysis has been done. Finally, by analyzing the results of the comparison of investigations and evidences of fault and Quaternary activity, the position of Kondaj fault and its Quaternary activity are evaluated.

3-Results and discussion
On the geological maps with a scale of 1:250,000 and 1:100,000, in most parts, it was displayed with a dashed line or it was hidden under the alluvium. This fault has cut Quaternary alluvium in many parts of its length. To determine the location of the fault in the alluvium, it is necessary to dig a trench and prove displacement in the Quaternary alluvium. Therefore, in this research, due to the impossibility of digging a trench due to its high costs, field visits were made to all the north-south waterways located along the fault. More than 50 large and small north-south watercourses cut the fault line, among which there are larger watercourses that have been dug in the bottom of the watercourse due to the high volume of water and intact walls of the watercourse trench where different layers of alluvium can be seen. They were selected for the field visit, the number of which was 8 waterways. Among these waterways, some of them have no evidence of faults and it was not possible to pick up the traces of fault activity in them. Only in three cases of waterway trenches, evidence of faulting and its activity was observed, which will be explained below.
As a result of the investigations, the traces and evidences of fault activity were investigated in three cases of waterway trenches, including the waterways of Behjat Abad, Jezmeh and Falizan villages, and evidence of fault activity, including cutting of alluvial layers and their displacement, was observed in 11 points, and the slope of the fault plane was measured. Various values were measured from 27 degrees to 56 degrees to the north, according to the location of the investigated locations, the average slope of the Kondaj fault plane was about 48 to 55 degrees to the north, and the measured slope of the fault plane was about He attributed 27 to 36 degrees to the branch of the fault. In the south of Behjat Abad village, a case of a fault spring was also observed, which is a proof of the fault zone in the mentioned area.
4- Conclusion
According to the field observations, the location of the fault in the Quaternary alluviums of about 11 km in the south of the villages of Behjat Abad, Tashe Abad and Jezmeh was corrected according to the geological maps, which is shown in Figure No. (19). In the 1:100,000 geological map of Qazvin, the Kundaj fault is located on the border between the Eap6 and Eab6 units with alluvium, and the location of the fault within the Quaternary alluvium was verified by field observations. In the rest, the length of the fault is 3.5 km from Dar al-Soror village to the east and 9.5 km from Khazinabad village to the vicinity of Anjilaq village. The results of the investigations are consistent with the position determined for Kundaj fault in the geological map. In the field investigations, the average horizontal and vertical displacement of the fault was measured as 22 ± 5 and 32 ± 5 cm, respectively.