عنوان مقاله [English]
In the current study earthquakes occurred in the northwest Iran in the past 20 years were relocated using JHD algorithm. A dense seismic network is usually required to produce a stable and precise earthquake location i.e. improved quantitative and qualitative of earthquake data are achieved due to various parameters including less amount of azimuthal gaps. Combining data from different seismic networks in the study area can be effective and useful for this purpose to improve earthquake locations. Thus a list of earthquakes in the northwest region of Iran was developed using data available from different seismic networks. In order to do this, first the recorded earthquakes data by the seismic network stations of domestic and neighboring countries, were collected and a complete data set of earthquakes in the region were prepared. Information from 30,000 recorded and reported earthquakes in the studied area were thus compiled. This information includes more than 400,000 seismic phases which were taken from International Seismological Center (ISC), Iranian Seismological Center (IRSC), Broadband Iranian National Seismic Network Center and National Seismic Network of Turkey (DDA) databases. Then the above dataset was sorted and the outliers were taken off based on analyzing the travel-time residuals. In the next step, the recorded phases from an earthquake from different stations were combined and a homogeneous catalog was then established. This catalog is more complete than the original catalog, e.g. the azimuthal gap of earthquakes has also decreased due to increase number of phases. In the next step, after the preparation of the data, the hypocenter relocation was done using VELEST computer program using both single event and also the JHD algorithms. Comparison of RMS values of earthquakes, indicates a decrease in the RMS amount due to re-location process. So the average value of RMS for the entire earthquakes decrease from 0.69 s to 0.41 s at the final stage, and this is a sign of a closer focus of events to their real places. In the final stage, the RMS value for more than 90% of earthquakes is less than one second. As a result, a homogeneous catalog of earthquakes in the region was prepared. The obtained results were evaluated and the information obtained were compared with the initial information. Finally, the seismicity patterns in the region were investigated by drawing the hypocenter depths sections in the active seismic areas. Based on the results obtained in many sections, the removal of unrealistic structures due to systematic errors in the location of earthquakes has been evident, and in some sections, while reducing the scattering of the earthquake hypocenter locations, the existing structures are enhanced.